# Variable Voltage Battery Charger



## JRoque (Mar 9, 2010)

Nice "poor man's" charger there Gator. To add to your warnings so it's not also a "dead man's" charger is that no transformer, no isolation. Touching (or grounding) either lead, whether charging or not isn't a good idea. A classic example would be trying to charge a car's 12V battery while the battery is connected to the car. The car's frame will likely be at >55V or so potential. 

JR


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## Gatorman (Aug 22, 2010)

I haven't had enough time to experiment as much as I'd like to with this circuit, so thanks for the warning! There is however a way to limit the voltage as well to give the unit a "Float charge", I'll post that circuit later today.


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## Gatorman (Aug 22, 2010)

This is the version that acts like an inductive battery charger.
I haven't spent the time with this setup to know the exact ratios of capacitors, but I do know that the second capacitor has to have a greater capacitance than the first. I'm under the impression that the second capacitor needs to have around 10 times the microfarad rating of the first capacitor.
If any of you experiment with this circuit, please share your results.


I'm sure some of you will make use of this equation for finding the right values.

CT= (C1 x C2)
(C1 + C2)


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## Gatorman (Aug 22, 2010)

I'm wondering about the possibility of just plugging this charger into a 110 to 220 step up transformer so that it will charge up to a 220 volt battery pack.


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## rmay635703 (Oct 23, 2008)

Gatorman said:


> I'm wondering about the possibility of just plugging this charger into a 110 to 220 step up transformer so that it will charge up to a 220 volt battery pack.


Actually a 110v outlet is up to 180v on the top of RMS on the swing

You can charge up to approx 144v at a reduced rate

From knowledge though these aren't real efficient, never bothered to calculate it but I doubt its much better than a resistive charger.


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## Roy Von Rogers (Mar 21, 2009)

rmay635703 said:


> Actually a 110v outlet is up to 180v on the top of RMS on the swing
> 
> You can charge up to approx 144v at a reduced rate
> 
> From knowledge though these aren't real efficient, never bothered to calculate it but I doubt its much better than a resistive charger.


 
Actually it is x 1.414.....155.54


Roy


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## JRoque (Mar 9, 2010)

> Actually it is x 1.414.....155.54


Ok one more: Actually... in the US, "110V" is 120V and actually closer to 125V these days to cope with the heavy modern loads. But 1.414 is correct so 125 * 1.414 = 176VDC give or take a few for losses.

JR


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## Tesseract (Sep 27, 2008)

rmay635703 said:


> From knowledge though these aren't real efficient, never bothered to calculate it but I doubt its much better than a resistive charger.


Depends how you define efficiency... if you take power factor into account then it's awful; if you are only interested in real power consumed vs. delivered, then it's extremely good. This is because the AC reactance of the capacitor is used to limit the current so the only major losses come from the capacitor's ESR (major reason you shouldn't use electrolytics here).

The reactance of a capacitor = 1/(2*pi*f*C) 

Where C is farads and f is in Hz.

So a 22uF capacitor will have a reactance of 121 ohms at 60Hz. Just like a resistor, the amount of current passed will depend on the load - ie, the short-circuit current here will be ~1A and anything less than a short-circuit will draw less. Trying to charge a 120V battery pack with this setup will prove disappointing as a result because the difference in voltage between the charger and the pack will be so low.

That said, it does limit current effectively without dissipating a lot of heat. Empirical testing is needed, but the closer your battery pack is to ~150V fully charged the less effective this technique will be (unless you use a 240V line, that is). Count on needing a lot more capacitance than you expected, regardless.

Motor run capacitors are perfect for this job, btw. I would be very wary of substituting anything else unless you have a deep understanding of capacitor dielectrics.


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## Newbiee (Feb 16, 2011)

Has anyone built this chargers and tested it? I want to try and build one even though i have no experience. Does anyone have a picture of this charger completed? My local electronics store had some 470VAC 100 microfarad capacitors but they were axial so i did not get them. Why is the motor run capacitor ideal for this charger? Radio shack has only an 8amp rectifier according to their website. This charger may look very simple, but just to be safe what is the step by step guide for building this charger? lol


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## alvin (Jul 26, 2008)

Here is a link to the Bonn charger. It does work.

http://www.evdl.org/docs/bonn_charger.pdf


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## Newbiee (Feb 16, 2011)

Hmm this seems like a perfect charger for my EV! thanks Alvin. Do you have any tips on where to get all the parts necessary to make it? even from old random stuff laying around lol? I'll try for the 96v version.


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## alvin (Jul 26, 2008)

I think Digi-Key or Mouser have the electronic parts. The timer , GFCI and breaker came from Lowes. The inductor core and fan came from microwave. The wire for winding the inductor came from motor shop. They usually have wire left over on spool(they gave it to me for free). The amp gauge came from Tractor Supply Store. The toggle switches came from Harbor Freight. Fuse holders and lights came from Radio Shack.

An old battery charger transformer core and the gauge from it will work.

Alvin


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## Gatorman (Aug 22, 2010)

Oh wow, I never got any updates from this thread until now. Sorry Newbiee. I can still send you a scematic if you want. But it's just a capacitor in series with a bridge rectifier. Every 22 uf the capacitor is rated for is an amp. So 100uf is roughly 4 amps for example. You use an AC Run capacitor because it will not blow up like an electrolytic (+-) capacitor, and is already designed to handle AC current. 


I bought a 110-220volt step up transformer to increase the maximum charging voltage, but I never got around to testing it.


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## Newbiee (Feb 16, 2011)

haha nice to see you're still checking the forums gator thanks! i have not built anything like this before and am learning what each component is still...You're schematic could help thanks, the more the better lol.

If i understand, then upping the components to turn it into a bonn charger will make it isolated and i wouldn't need to disconnect the battery pack from the rest of the EV right? Also when using the Bonn charger model is it still necessary to use the motor run capacitors MFD value to determine the charging current? or is their some other piece that determines that?

I have an old sears 12v battery charger, im wondering how many parts i can use from it to make the bonn charger? I really do not have an idea on how to make my own inductor core


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## alvin (Jul 26, 2008)

Newbiee

The Bonn charger is not isolated. The ground fault breaker is there to disconnect power if it goes to ground. That is some measure of safety. The capacitor is a motor run cap. The 12 volt charger core should work. 

The link has pretty good instructions with it. This is voltage that can kill you. If you are not sure about it maybe buy a charger. 

I turn the power off from my battery pack to the controller what ever charger I use.

Alvin


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## Russco (Dec 23, 2008)

Gatorman said:


> Try it out for yourselves. Open circuit voltage will read as 110 wall voltage. But after being connected to a battery (or batteries), the voltage will drop to whatever voltage is necessary to push the selected current through the circuit. So if it's a 12 volt battery, you would read approx. 13 volts on a voltmeter. If the batteries are sulfated, the internal resistance of the batteries will be higher, so the charging voltage will rise to accommodate this, and decrease the required voltage over time as a result of the desulfation. Yes, this charger is also a desulfator. Because it is rectified AC, it is 120 hertz pulsed DC on the charger leads.
> 
> So charging any combination of batteries is possible, as long as the total of the battery voltages in series is less than 110 volts, as this is the maximum voltage that the charger can reach due to the Mains voltage. However, in Europe the Mains voltage is 220, so the charger can go as high as 220, and the desulfation frequency will be 100 Hertz, as they have 50 Hertz Mains.
> 
> ...


Oh Boy! The old John Wayland ammo box capacitor charger. 

Ever heard of power factor?

A full wave bridge single phase AC to DC charger has a poor power factor.

An SCR phase control charger has a poorer power factor.

A series capacitor charger has a horrific power factor.

What does power factor mean for you?

A 100% or unity 1.0 pf means the current and voltage are in phase and the ratio of rms to peak current is 1.414.

As the power factor gets worse, the ratio of rms to peak current increases. The higher peak current will heat the wires and components, aka the old K & W battery charger extension cord burner upper.

The above series capacitor charger is as bad as it gets. Oh, don't forget the GFCI, output fusing, automatic current and voltage regulators, automatic shut off, etc.

As always, you get what you pay for. 

Russ Kaufmann

RUSSCO Engineering

14 years manufacturing "high power factor" chargers.


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## Gatorman (Aug 22, 2010)

Newbiee, if you still want to try it out, I made a short video of wiring one up. It's dead easy. 

http://www.youtube.com/watch?v=eDDO5BzGBHw


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## JRoque (Mar 9, 2010)

Gatorman said:


> It's dead easy.


Yikes. Can we call it anything else?  

Seriously, no transformer, no isolation. Your "ground" wire will be at ~55V potential. Do not connect that to your car chassis or neg wire of 12V system if you are charging batteries in a car.

JR


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## Gatorman (Aug 22, 2010)

I thought about making a pun about that when I said it, lol read the first reply to my original post. You posted it in fact!

You have to add a quick blow fuse or something in case the cap shorts out or you grab both leads while it's hot. But even then, it's still pretty bad.


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## Newbiee (Feb 16, 2011)

wow awesome thanks Gator so much for taking the time to make that video for me, really appreciate it! I guess im one of those visual learners lol. 
I just bought the rectifier from radio shack today actually! its really small and doesn't come with a heatsink on it, if i just put some thermal paste on it and stick it to an old computer cpu heatsink i have laying around will that be ok? Im definitely building this, i want to build another one too after i get to play around with this one and get more experience. Maybe soon i can take on the bonn charger style one.


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## Gatorman (Aug 22, 2010)

Whatever suites your fancy, lol. I personally use this circuit with the 3 uF capacitor and a radioshack rectifier to make colloidal silver. I got the plans for this charger from Eagle Research and some other site (http://poormanguides.blogspot.com/2009/06/homemade-diy-battery-desulfator-charger.html), but I never really tested it on any decent batteries. You should test it out on some used batteries if you can.


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## Newbiee (Feb 16, 2011)

I wonder if this capacitive charger can de-sulphate SLA batteries? or will not being able to add water to an SLA battery be a problem? I have an old 36v SLA battery that someone gave me, it wont hold a charge and i was hoping this charger could bring it back to life lol. After some research it seems quite a lot of people use this charger to de-sulphate batteries. Any thoughts?


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## Gatorman (Aug 22, 2010)

Every time I tried adding water to a SLA battery (7AH) it just blew the caps off and bubbled back out when I tried to charge it. But if your battery is already kaput, it can't hurt to try it, lol


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## Gatorman (Aug 22, 2010)

I also saw this same charger on another website where they're trying to sell it for $145. http://www.e-volks.com/capacith_charger.html
I can't imagine it not working if it's all around the net like this.


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## rmay635703 (Oct 23, 2008)

Duh, of coarse they work but they are
1. Inefficient
2. Dangerous
3. Overcharge the crap out of your battery if not watched like a hawk.

That said I build a battery charger out of a diode, 2 battery clamps, a burnt up electric cord and a 60 watt lightbuild.

These things have their uses but really aren't worth more than $5, mine cost $1.65 which was about right.


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## Newbiee (Feb 16, 2011)

Nice find Gator, i wonder why they don't mention any safety precautions for it? whats the difference between the capacitor charger and the bonn charger? i know the bonn has an inductor, but how does it help?


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## Guest (Jul 9, 2011)

Steer clear of that charger.


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## 9852 (Jan 17, 2010)

newbee,I built and use this charger in my neon, and will use it again in my triumph conversion,it works good, dont let any one tell you different, i built a monitoring circuit to turn it off when the pack reaches full charge, but a 120v wall plug in timer from home depot will do the same thing, the first time you charge, you will need to monitor it closely, so you dont over charge the pack, i would also only use it on FLAs. mine out puts 20 amps of current and i hide the caps in the car, so all you see is the box that i have my monitoring circuit and bridge rectifier in. you can see in the picture that i dont have all the leads hooked up yet but that is because im waiting for batteries.


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## rmay635703 (Oct 23, 2008)

billhac said:


> It works good, dont let any one tell you different, i built a monitoring circuit to turn it off when the pack reaches full charge,
> The first time you charge, you will need to monitor it closely, so you dont over charge the pack, i would also only use it on FLAs. mine out puts 20 amps of current and i hide the caps in the car, so all you see is the box that i have my monitoring circuit and bridge rectifier in.


A+ would you mind posting your monitoring circuit schematic?

I generally don't recommend newbys use these types of chargers because they don't shut off on their own.

I would build battery chargers myself for my EVs (not just experiments) if I could effectively get the things to turn off once charged, but I haven't used cap chargers but your circuit still would be usable in my variations I would think.

Using a Killowat meter how many KW's go in and out of your batteries using a cap charger?

I am mainly interested in comparing its cost at the wall versus a more standard charger with a transformer.

I have shy'd away from them because of the power factor issues but am uncertain how that affects the cost at the wall.

I am moving toward monitoring how many Ahr move out of my batteries so I can more effectively determine how long to set my spring wound timer for (my current charger has the wrong profile for gel and I am too cheap to change it)

How does your circuit work? Is it a simple timer or is it more advanced?

Thank You
Ryan


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## Gatorman (Aug 22, 2010)

I would like to see the schematic as well. That was the biggest drawback to making a homemade charger.
Although, you can limit the maximum charging voltage on this cap charger so that the current drops off when it gets close to the cutoff voltage.


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## 9852 (Jan 17, 2010)

rmay635703 said:


> A+ would you mind posting your monitoring circuit schematic?
> 
> I generally don't recommend newbys use these types of chargers because they don't shut off on their own.
> 
> ...


its a bit more advanced. but not much
first, i did use a kill a watt meter when i first used the charger and at the wall wasent much, i dont remember how many kws it was using but i did figure it costs me 1.00 a day to charge. i can do it again in a few weeks, i no longer have the neon, but i will be using the same charger for my triumph spitfire conversion, the pic that i posted in this thread is the charger installed in my triumph. now the circuit, sure i can post it here, just let me convert it to something that i can post here with.
the circuit itself is a 12v battery monitoring circuit, i added a 120v 10 amp ice cube relay with a 12v coil to turn the 120v wall power off and on, it needs a 12v input to monitor, but basically it monitors the voltage of the battery it is wired to and when that battery reaches full charge it turns the relay off, turnning off the 120v power to the charger, the turn off voltage can be set to any voltage from 12.5 to 15v so i set it for my batteries to turn off at 14v for my FLAs, i wire it to the weekest battery to insure that all the batteries in the pack get charged completely.


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## 9852 (Jan 17, 2010)

here is the circuit that i use to disconnect the charger with.


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## Roy Von Rogers (Mar 21, 2009)

I'm not going to make a comment about this charger pro or con, each need to determine this stuff on their own, as long one understands the issues involved.

I keep hearing about this power factor issue, and I like to know whats that got to do with anything.

As far as I know in a domestic home the power meter can only read watts, not VA.

Roy


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## coryrc (Aug 5, 2008)

Roy Von Rogers said:


> I'm not going to make a comment about this charger pro or con, each need to determine this stuff on their own, as long one understands the issues involved.
> 
> I keep hearing about this power factor issue, and I like to know whats that got to do with anything.
> 
> ...


If the power factor is low, you can't draw as much real power from the outlet.


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## Newbiee (Feb 16, 2011)

Well i am currently charging that 36v sla battery with my finished cap charger hehe, i kept getting jipped off by drillspot.com ordering run capacitors and then 3 days later getting a message that they want me to purchase a more expensive one because they ran out of the one i ordered?? So i purchased a different MFD value capacitor and 3 days later i get the same message! Never buying from them again thats for sure!
I ended up finding a very good deal though on some motor run capacitors, here is the link if anyone needs some too:

http://stores.directhvacsupply.com/StoreFront.bok

this company sells the capacitors on ebay, however i found that if you go direct to their website to make the purchase and forget ebay then the prices become even cheaper. However i don't have the device for testing if the capacitor is good, i will look into a method for testing if they are good and post later. 

Now lets see if i can bring a bunch old batteries back to life! muahahaha thanks again guys!


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## Newbiee (Feb 16, 2011)

holymoly lol the charger is really trying to bring the 36v battery back to life! Before i started charging, it read 23.6v with the multimeter, measuring the voltage while its charging its reading 106.2 volts! must be a lot of resistance in that thing.


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## Gatorman (Aug 22, 2010)

What uF value were the caps you ended up getting? And how are the batteries doing now?


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## Newbiee (Feb 16, 2011)

i got 2 of the 80 mfd caps for something like 7.2 amps, i'm only using 1 right now though, didn't want to blow them both to smithereens if something went wrong, i would still have 1 left. 
Im charging the sla battery very slowly turning it off and letting it cool down before charging again since i cant add water to it, so it will be a while i think before i know if its going to work.


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## Gatorman (Aug 22, 2010)

If you put the caps in series, it'll be like a 1.5 amp charge instead of 3. So wire them -----◙-◙----


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## Newbiee (Feb 16, 2011)

huh? i don't get it lol.. if wired in parallel it would be 7+amps charging current right? and in series it becomes 1.5amps? how does that work?
also can i lay the caps down or do they need to always stand up? should i add a GFCI to the circuit also?


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## 9852 (Jan 17, 2010)

you can lay them down, here are some pics for reference,wireing in parallel, just makes one big cap(sort of) it gives you greater current, just like paralling batteries will increase the capacity of the battery, so will paralleling the caps


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## Newbiee (Feb 16, 2011)

Well for whatever this is worth i can vouch for this variable voltage charger lol!
Here's the story, i purchased a cruddy $50 scooter 36v charger a while back to charge a scooter that my dad bought which had an unknown battery state. Charged up the scooters 36v 10ah battery for almost a day until the chargers green light finally surfaced meaning full SOC. I then flipped on the scooter and bam it moved about 2 inches and that was it. So my dad went out and bought 3 new small 12v 5ah batteries for around $55 and i wired them up in series, voila working electric scooter.
Now i made the variable voltage charger for my EV, however i decided to test it on the old 36v scooter SLA battery that i left in the garage still waiting for someone to go recycle it. The charger started off with a 1oo volt charging power, and upon flipping the on switch the battery made crackle noises the first couple of times (i assumed or hoped this was the crystals breaking up lol) but i really have no idea. The next day 60volts under charge, and the next day 50 volts and then in the 40's, it was a slow process because i turned the charger off whenever the battery started feeling hot to the touch, which did not take very long! I didn't want too much pressure to build up, and it did take very long times for it to cool down completely. Starting from 23 volt multimeter readings of the 36v battery, today i got it to 38.6 holding that number over night, so i felt it was ready to test it out! Dropped it in the scooter and vroom vroom drove it around as far as my street would go. Now of course its not going to perform like a brand new battery but hey it works good enough for me, when i got back home it still measured as fully charged. A saved $100 battery originally destined for trash. And now i can use the 3, 12v batteries to build an electric bicycle with! Thanks to you guys! I love this charger here are some pics of mine!

The on and off switch and circuit breaker i took from a broken saw table someone left out in the street. The battery clamps were found on the street also lol one clamp had a broken handle, but i only needed on side of the clamps anyway!
Question: I notice the little 13a circuit breaker has no resistance and makes no click when depressed, i wonder if thats normal? it can only be depressed if triggered ?


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## alvin (Jul 26, 2008)

If the GFI is tripped it would not have resistance. The reset button might not work without power to it.
Alvin


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## Gatorman (Aug 22, 2010)

Any updates on either of your projects?


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## jackbauer (Jan 12, 2008)

I do love the simplicity of this device. As a suggestion you could use much larger value dc electrolytic caps with steering diodes. Might make it smaller / more powerfull.


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## Newbiee (Feb 16, 2011)

I didn't install a GFI in my charger yet, i am still looking for one, not sure if i should get one that comes in a portable plug or one that is made for the bathroom wall. So i guess that means my 13amp circuit breaker is broken since it cannot be switched on and off? 
I really don't know if this means anything but also using the charger with a p3killawatt meter shows that it draws around 117 volts and 7 amps from the wall when charging with 2x 80mfd capacitors.


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## Dennis (Feb 25, 2008)

> I'm not going to make a comment about this charger pro or con, each need to determine this stuff on their own, as long one understands the issues involved.
> 
> I keep hearing about this power factor issue, and I like to know whats that got to do with anything.
> 
> ...


In simple terms some of the energy will go to work (becomes apparent power when doing work) charging a battery and some will go to work being stored in the capacitor (reactive power). This energy is returned to the source that is stored up in the capacitor, but a portion of the energy from the source is actually used by the load to do work (becomes real power) and is not returned. So in effect you are drawing lots of current, but only a small portion of it will go towards charging the battery and the rest will be going toward the charging the capacitor. This is a ratio of real power to apparent power and is called power factor.


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## Roy Von Rogers (Mar 21, 2009)

Dennis said:


> In simple terms some of the energy will go to work (becomes apparent power when doing work) charging a battery and some will go to work being stored in the capacitor (reactive power). This energy is returned to the source that is stored up in the capacitor, but a portion of the energy from the source is actually used by the load to do work (becomes real power) and is not returned. So in effect you are drawing lots of current, but only a small portion of it will go towards charging the battery and the rest will be going toward the charging the capacitor. This is a ratio of real power to apparent power and is called power factor.


 
I know what power factor is, it was a tongue in cheek comment of why should I care.

Roy


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## Dennis (Feb 25, 2008)

Roy Von Rogers said:


> I know what power factor is, it was a tongue in cheek comment of why should I care.
> 
> Roy



You should care because you have to size the wire for the current that will go towards charging the capacitor up plus what the load needs. Although the energy is returned, it must pass through the wires to do so which results in I^2R losses. Power factrors close to one will not need near as big of conductors since the majority of the energy is going towards the load.


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## 9852 (Jan 17, 2010)

Gatorman said:


> Any updates on either of your projects?


yes, mine is working in my triumph now, i put an amp meter on it at the battery connections it is charging at 24 amps, i need to go buy a kill a watt meter to get some cost estimates but here is one thing, my 120v circuit is drawing about 11 amps and is on a 20 amp breaker, now you only get 80% of the rating of the breaker safely before running the risk of over current an tripping the breaker, so when the charger is on my amp meter says 16 amps from my 120v outlet, so that tells me my charger is pulling around 5 amps and outputting 24 and some change, not bad if you ask me and i paid less than 50 bucks for it.


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## rumleyfips (Oct 15, 2008)

I don't have a bad boy, but my old Lester 36 volt is a bit uncivilized: no on/off, no timer. We get along fine. Connect the alligators before plugging in and watch the time and it charges my lawn tractor fine. 

The potential for shocks ( from a guy that will test for live by touching a wire if in a hurry) seems manageable. Don't run the traction pack to chassis ground, use relays to isolate key switch, contactor, accessories etc. plug in to a GFI ( maybe the only thing I do right) and unplug first.

Using Anderson connectors seems a good idea, hard to grab a live wire here, but I see other sites saying that the battery leads should be shorted for stroage. Any comments here? 

Would a couple of chunky diodes help isolate from the mains?

Thanks:
John McManus


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## jackbauer (Jan 12, 2008)

I did a few experiments yesterday with this system. Have to say for simplicity vs performance its hard to beat.

I'm thinking that it wouldn't be much extra work to include a 2 stage function. For lead acid you want to dump in as much energy as possible during the cc phase then drop the current to a trickle for absorbtion. So a voltage detector or timer rigged to a contactor that switches out some of the caps should , in theory , perfrom that function. Lifepo4 is a bit more tricky but could still use the same basic principle. 

http://www.youtube.com/watch?v=FSDmzDuJ7HI


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## 9852 (Jan 17, 2010)

jackbauer said:


> I did a few experiments yesterday with this system. Have to say for simplicity vs performance its hard to beat.
> 
> I'm thinking that it wouldn't be much extra work to include a 2 stage function. For lead acid you want to dump in as much energy as possible during the cc phase then drop the current to a trickle for absorbtion. So a voltage detector or timer rigged to a contactor that switches out some of the caps should , in theory , perfrom that function. Lifepo4 is a bit more tricky but could still use the same basic principle.
> 
> http://www.youtube.com/watch?v=FSDmzDuJ7HI


thats a good idea jack, the circuit that i posted on this thread could be used to do just that. you would simply hook the output to the relay coil and then hook the caps to the relay switch, the way i was using it was to disconnect the power completely at 14.8v for lead acid batteries, but your idea could work too. and if you put this charger in a car, you can orient the caps so they cant be seen, if looks are an issue that is.


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## Rocketmaker10000 (Dec 7, 2008)

What will this type of charging do to a Lithium Battery? I'm very curious on this and thanks for posting the video. Just watched it and it was very interesting to say the least.


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## Rocketmaker10000 (Dec 7, 2008)

Would this capacitor work? 

This looks like a fun project.

[URL]


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## jackbauer (Jan 12, 2008)

Today I effectively charged my lifepo4 pack with the cap charger.
http://www.youtube.com/watch?v=kBzzOlKwE5s

I think this system warrants some further investigation regards control etc but it works great


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## Gatorman (Aug 22, 2010)

@Rocketmaker10000, 

Sure thing!


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## Rocketmaker10000 (Dec 7, 2008)

jackbauer said:


> Today I effectively charged my lifepo4 pack with the cap charger.
> http://www.youtube.com/watch?v=kBzzOlKwE5s
> 
> I think this system warrants some further investigation regards control etc but it works great



JackB, since you are in Ireland, your wall voltage is 240v AC on one 1 wire and 1 ground (earth). Here in the US, our 240v AC is carried on 2 120v AC wires. Since I would ultimately like to have this car I'm doing now charge at a public chargers supply, do I parallel the two 120v wires after they go through two independent Bridge Rectifiers? Would that bring the "Capacitive Charger" voltage up to the 240v? I'm aiming for 20 to 30 amps of charge current. 

Also, those little Bridge Recifiers tend to not last long in my opinion, have you had your working for a long period or did you just start doing this? Thanks for the videos.


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## jackbauer (Jan 12, 2008)

As far as I know you can just take the two 240v legs and run them to the charger. This gives you 240 2 phase but the circuit wont care. You would only see 120v between either leg and ground. Be sure to ground the vehicle frame and use a gfci as its not an isolated charger.

The rectifier is only a 35amp model i had lying around. I have some nice 75amp 1200v 3 phase rectifiers that will be much better. I ran it for two hours today and like i said on the video it was only the rectifier that got hot. I can only surmise that people who have had extension leads burn up when using this type of charger must have been using inadequate cable. Even the 2.5mm sq flex I used today was barely warm. 

Not that i'm hugely concerned about the power factor issue but i am thinking that perhaps a little inductance might help. Maybe a large metal halide lamp ballast .........


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## 9852 (Jan 17, 2010)

jackbauer said:


> As far as I know you can just take the two 240v legs and run them to the charger. This gives you 240 2 phase but the circuit wont care. You would only see 120v between either leg and ground. Be sure to ground the vehicle frame and use a gfci as its not an isolated charger.
> 
> The rectifier is only a 35amp model i had lying around. I have some nice 75amp 1200v 3 phase rectifiers that will be much better. I ran it for two hours today and like i said on the video it was only the rectifier that got hot. I can only surmise that people who have had extension leads burn up when using this type of charger must have been using inadequate cable. Even the 2.5mm sq flex I used today was barely warm.
> 
> Not that i'm hugely concerned about the power factor issue but i am thinking that perhaps a little inductance might help. Maybe a large metal halide lamp ballast .........


that is correct, now ive used this charger for a year with a 50 amp rectifier at 30 amps of current and the rectifier does get hot, so i put it on a heat sink, and put a fan in just for the hell of it, the rectifier has never gone out, although it might if i did not have it on a heat sink.


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## Rocketmaker10000 (Dec 7, 2008)

I ran my first Bad Boy charger for a year and cooked two Rectifiers. They were the weak link in my Lead Acid pack charger. Worked really well except for those. I always had used lead acid batteries so I wasn't too concerned with a little "overcharging"....helped them balance...HEHEHE...

Anyway, with the Lithium Pack, I'm working with a friend to create an Ardiuno chip that will monitor for a Preset High Voltage Cutoff so we won't cook the lithium cells. Secondly, I have a BMS hooked up already to balance the cells so all I think I will need with this is the High Voltage Cutoff. The Controller has a Low Voltage Cutoff so now, High Voltage cutoff is the only thing missing and I can use this set up. So one thing I want to make sure I understand is that for each 25 farads equals 1 amp of current for the capacitive charge. So if I want a 188v, 100AH battery pack (nominal) to charge at 30 amps I would need 750 farads of capacitor bank right? If I used the 80 Farad capacitors I linked to earlier that would be 9 or 10 Capacitors in series? Do I have this right? Thanks in advance.


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## Gatorman (Aug 22, 2010)

For 110 volt ac, it's roughly 1 amp per 25 mfd. For 220, it's 2 amps. For 30 amps at 110v ac, it's around 10 of those caps in parallel, not series. Or it's 5 or so at 220v ac. But at $5 a pop, I'd just get a bunch and add them one at a time until the amperage is where you want it, if you watched jack's video, then you saw the charging amperage was less then expected, so just play around with it.


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## 9852 (Jan 17, 2010)

Rocketmaker10000 said:


> I ran my first Bad Boy charger for a year and cooked two Rectifiers. They were the weak link in my Lead Acid pack charger. Worked really well except for those. I always had used lead acid batteries so I wasn't too concerned with a little "overcharging"....helped them balance...HEHEHE...
> 
> Anyway, with the Lithium Pack, I'm working with a friend to create an Ardiuno chip that will monitor for a Preset High Voltage Cutoff so we won't cook the lithium cells. Secondly, I have a BMS hooked up already to balance the cells so all I think I will need with this is the High Voltage Cutoff. The Controller has a Low Voltage Cutoff so now, High Voltage cutoff is the only thing missing and I can use this set up. So one thing I want to make sure I understand is that for each 25 farads equals 1 amp of current for the capacitive charge. So if I want a 188v, 100AH battery pack (nominal) to charge at 30 amps I would need 750 farads of capacitor bank right? If I used the 80 Farad capacitors I linked to earlier that would be 9 or 10 Capacitors in series? Do I have this right? Thanks in advance.


i posted a circuit for high voltage cutoff, its for a lead pack but it can be modified for a lifepo4 cell with a little work.


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## jackbauer (Jan 12, 2008)

The required capacitance for a given current can be calculated by using the difference in the rectified mains voltage to the pack fully charged voltage and then calculating the required reactance to limit the current to the desired value. 

As an example in my car :

Rectified mains approx 340vdc
pack fully charged voltage 164v
difference = 176v
say i want 10amps
R=V/I
R=176/10
R=17.6 ohms
So use the calculator on this page:
http://www.sengpielaudio.com/calculator-RC.htm
to pick a capacitor whose reactance is as close to the 17.6 ohms required.

Or just forget all that and find the required values by trial and error. Remember that the caps will have LESS reactance at 60hz than at 50hz. You guys in the US get more bang for your microfarad


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## Rocketmaker10000 (Dec 7, 2008)

billhac said:


> i posted a circuit for high voltage cutoff, its for a lead pack but it can be modified for a lifepo4 cell with a little work.


Bill, the circuit is on this thread right and not someplace else? Just checking. Thanks again. When I get this done in a few days I will post a video or some photos. Whichever I get around to. Thanks again.


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## Rocketmaker10000 (Dec 7, 2008)

jackbauer said:


> As an example in my car :
> 
> Rectified mains approx 340vdc
> pack fully charged voltage 164v
> ...


Wow! 340vdc from the mains! I doubt I can do that here on my end. However, thanks for the formula. I will figure this out and make one. I will try and post when it is done.


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## Rocketmaker10000 (Dec 7, 2008)

JB, one more quick question: When you use that calculator for the capacitive resistance, if I have the 80 micro farad capacitor it comes out to 33 ohms resistance. So that would be one capacitor. If I put two together in series that would bring the capacitance up to 160 micro farads and then the hz stays the same and the resistance goes down to 16 ohms. Am I calculating this right so far? 

So lets say I have 59 3.2v 100Ah cells in my conversion (I'm trying to add in more but thats what I have in there now). So nominal is 188.8v (3.2 per cell) and charge voltage brings that up to 224.2. My 120v AC line used to produce around 98 vdc through the rectifier. So if I am at 240v and I tie the two AC legs together my total mains vdc would be 196v. Not sure I can do this since my pack voltage charged is higher than the mains dc output. Am a doing this right?


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## Roy Von Rogers (Mar 21, 2009)

Rocketmaker10000 said:


> Wow! 340vdc from the mains! I doubt I can do that here on my end. However, thanks for the formula. I will figure this out and make one. I will try and post when it is done.


 
The common voltage in the US is 240 single phase, if you use a bridge rectifier you take that voltage of 240ac and multiply it by 1.414, and thats your recified dc voltage mentioned in his formula.

240 X 1.414 is 340dc.

And dont forget when you experiment with those caps, make sure you check they are not hot when you handle them...(discharge).

Roy


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## jackbauer (Jan 12, 2008)

Recitifed 120vac typically comes in about 150vdc if i'm not mistaken. 340vdc from 240vac is actually a bit on the high side. Its actually nearer 300v in practice. You could just about charge a 59 cell pack with 240vac but the current would probably be quite low.


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## jackbauer (Jan 12, 2008)

Good Point Roy. Those caps will hold 300vdc for weeks! Wire a 100k 10w resistor across the cap as a bleed.


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## 9852 (Jan 17, 2010)

Rocketmaker10000 said:


> Bill, the circuit is on this thread right and not someplace else? Just checking. Thanks again. When I get this done in a few days I will post a video or some photos. Whichever I get around to. Thanks again.


yep,second page i think


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## Rocketmaker10000 (Dec 7, 2008)

You stated the a 120v AC line will deliver 150vdc? I haven't ran a bridge rectifier in some time but I'm trying to recall what my bad boy was pulling back then. I'm pretty sure the output DC voltage was around 98 just above my 96 volt battery pack that I had back then. 

So let me assume your calculations are correct and I can get 150vdc out of the mains. With two legs I would be up at 300vdc. Since my current 59 cell pack would be charged up to 3.8v per cell that would take pack voltage up to 224.2 vdc. Now using that formula you stated before, 300vdc - 224.2vdc = 75.8

So if I want 24 amp charging, I take 75.8/24 and I get 3.15 ohms. That means I would need 10 or 11, 80 Micro Farads in order to charge up the pack as currently configured. Am I still thinking clearly?


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## Rocketmaker10000 (Dec 7, 2008)

jackbauer said:


> Good Point Roy. Those caps will hold 300vdc for weeks! Wire a 100k 10w resistor across the cap as a bleed.


Jack....wiring this up do you have to use that size resistors? I have lots of 1.3k resistors laying around from other projects. Will that work or draw too much during charging?

Learning alot from this thread. Thanks for your contribution.


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## Citystromer (May 2, 2009)

The way I built mine wassimilar, only that I did use a bulky transformer befor the rectifier. The value of the secondary voltage calculates by dividing the target voltage by the root of 2. so to charge a 100V battery I aimed at a open circuit voltage of 120V and came up with some 85V for the secondary side of the transformer. It`s just a little saver to touch. 
I`m still looking for an elementary simple and failsafe way to shut off the charger, I do use a circuit using a 8051 and a ADC to activate a relay upon reaching 108V. The cutoff is rather inacurate because of the voltage varying with net inacuraccies. 
Anyone has a better way to determine charge end?


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## Rocketmaker10000 (Dec 7, 2008)

OK guys and gals, I went to the local electronics store today and purchased the Bridge and a couple of capacitors for this project. In order to test I had an old Trojan T1275 sitting in the garage and it wasn't that discharged but figured I would try one 12v on the following setup. 1) Bridge, 2) 270uf 250VAC capacitor 3) 120v AC supply line via an Extension cord for the test.

Well, I tested the 12v first and it seemed to work really well. Then I decided to do a second test on an absolutely useless Lithium Cell 3.2v Mottcell 40Ah battery. Well, I started to charge it up and it started dumping in more amps than it did into the 12v. 12amps and jumped the battery voltage up to 1.9v from 0.05v initially. I will try and upload a video of this experience with both the 12v and the 3.2v lithium and get some feedback. 

Only issue was the Capacitor got really HOT! The top near the connections around the rim I started to notice a small bubble and then immediately unplugged the unit so no more current was available. That is when I noticed the Capacitor was HOT. No evidence before that. Now the capacitor is rated at 250vac and it was on the AC side of the bridge so I don't understand why it would do that but I have no experience with large caps before so I look forward to some feedback. I will see if I can upload the video. No video of the bubbles. I hit the wrong button on the cell phone and it is history. Happy EVing!


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## jackbauer (Jan 12, 2008)

I would hazard a guess that it is an ac electrolytic motor START capacitor. Not suitable for this application. You need either a motor RUN cap or a power factor correction cap.


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## Rocketmaker10000 (Dec 7, 2008)

Jack, seems like I made a mistake as I went down to the Electronics store and forgot which capacitor I was supposed to get. I looked at the Farad ratings and took a guess. Guessed wrong. Oh well. No harm done as the owner said he would take them back if I was wrong. Which it turns out I was. I made a video of it anyway so I will post it and then order ones online since my Electronics store only had 30uf Motor Run caps. Stay tuned. I will test again as soon as I get a new set of motor run caps!


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## 9852 (Jan 17, 2010)

Rocketmaker10000 said:


> Jack, seems like I made a mistake as I went down to the Electronics store and forgot which capacitor I was supposed to get. I looked at the Farad ratings and took a guess. Guessed wrong. Oh well. No harm done as the owner said he would take them back if I was wrong. Which it turns out I was. I made a video of it anyway so I will post it and then order ones online since my Electronics store only had 30uf Motor Run caps. Stay tuned. I will test again as soon as I get a new set of motor run caps!


try ebay, you can get 80 or 100 mf motor run caps for about 10 bucks each.


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## Rocketmaker10000 (Dec 7, 2008)

billhac said:


> try ebay, you can get 80 or 100 mf motor run caps for about 10 bucks each.


I looked there yesterday and didn't see any with those farad ratings. Do you have any links you could post. I will order them tonight if you do. thanks. Having trouble uploading the video as Youtube seems to be SLOWTUBE these days!


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## Rocketmaker10000 (Dec 7, 2008)

found some on EBay. Never mind.


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## 9852 (Jan 17, 2010)

Rocketmaker10000 said:


> I looked there yesterday and didn't see any with those farad ratings. Do you have any links you could post. I will order them tonight if you do. thanks. Having trouble uploading the video as Youtube seems to be SLOWTUBE these days!


i think so i will check to see if they are still vailed. update in a while.


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## 9852 (Jan 17, 2010)

here is the first one i found
80mf motor run cap
http://cgi.ebay.com/PRCF80-Round-80...aultDomain_0&hash=item2566609435#ht_744wt_698


100uf motor run cap and the ones that i use, but i got them a little cheaper on ebay.
http://cgi.ebay.com/PRC100-Round-10...aultDomain_0&hash=item2566c62be9#ht_744wt_698


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## 9852 (Jan 17, 2010)

Rocketmaker10000 said:


> found some on EBay. Never mind.


me to just read your post


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## Rocketmaker10000 (Dec 7, 2008)

Hey Bill,

I just found this one. It looks like the one I purchased today but ended up being a motor start cap. Is it possible this is just miss labeled? I like the Farad rating as I think I need close to 800 Micro Farads to charge up my 58 cell Lithium pack which is 3.2v per cell brings the total voltage up to 185.6v. The charging voltage is 3.7v per cell so that will be 214.6v. That is the High Voltage Cutoff! I hope to have a High Voltage Cutoff Circuit done by this weekend. Can't wait to put up a video but my internet has been messed up all day. Upload speeds are almost zero at the moment.

http://cgi.ebay.com/MARS-11051-MOTO...ltDomain_0&hash=item519a7f38e9#ht_1562wt_1037


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## Gatorman (Aug 22, 2010)

Is 250 vac a high enough rating? And that looks awful small to be a 190 mfd run cap. I think it might be a start capacitor and they posted wrong. My 60 mfd caps on my charger are about 10 inches tall. Here's the link to them. 
https://www.surpluscenter.com/item.asp?item=22-1296&catname=electric

They're longer then the one shown in the photo. Good luck with your project!


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## 9852 (Jan 17, 2010)

Gatorman said:


> Is 250 vac a high enough rating? And that looks awful small to be a 190 mfd run cap. I think it might be a start capacitor and they posted wrong. My 60 mfd caps on my charger are about 10 inches tall. Here's the link to them.
> https://www.surpluscenter.com/item.asp?item=22-1296&catname=electric
> 
> They're longer then the one shown in the photo. Good luck with your project!


yea, gatorman is right, they posted that wrong, the caps i got from ebay are 100mfd and 370v but which should be ok for you, are you building the cut off circuit that i posted in this thread or something else? if its mine it will need some tweeking to work with the 3.7v cells but its just changing a resistor value, so its not complicated.


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## Rocketmaker10000 (Dec 7, 2008)

billhac said:


> yea, gatorman is right, they posted that wrong, the caps i got from ebay are 100mfd and 370v but which should be ok for you, are you building the cut off circuit that i posted in this thread or something else? if its mine it will need some tweeking to work with the 3.7v cells but its just changing a resistor value, so its not complicated.


I noticed it will need tweaking so I'm going to be using an Arduino chip and a programming loop. My friend has the Arduino and said he knows how to do it. I haven't programmed anything since my freshman year of college so I won't be doing the programming. Once I have that working I will let you know. Your circuit looks like it would work but my pack voltage is higher. I'm running 58 3.2v cells in series so I'm up at 185 nominal voltage. Charge high voltage cutoff will be 214v. 

Just a follow up on the results of this test (since I can't upload the video because our internet is down around here because of all the rain most likely).

The little 3.2v Lithium 40Ah cell that read 0.05v when I started this test, is still reading 2.9v today. It is holding the charge from yesterday! It wouldn't do that before. I was impressed that i could dump in 12amps into that cell with this set up. Nice way to charge. I'm going to get some Motor Run Caps and do some more tests prior to setting it up in the car. I'm going to permanently mount it with a J1772 inlet and communications so it will be able to use public infrastructure EVSEs.


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## Rocketmaker10000 (Dec 7, 2008)

billhac said:


> yea, gatorman is right, they posted that wrong, the caps i got from ebay are 100mfd and 370v but which should be ok for you, are you building the cut off circuit that i posted in this thread or something else? if its mine it will need some tweeking to work with the 3.7v cells but its just changing a resistor value, so its not complicated.


Another thought, If I use your circuit instead of using my friends arduino chip, what resistor values would i need to change in your circuit? Maybe I will try both and test them. This is such a cool project!


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## MN Driver (Sep 29, 2009)

You can get them from Grainger at a decent price too which would cut the shipping cost if you have a branch near you. I have a business account with them as they are business to business, which anyone can setup, just tell them the name of the business(or make one up) and an address to put it under and they'll sell to you. I think a large sum of their business is HVAC stuff and these capacitors would be used with HVAC.

A quick search and just picked 80mfd(don't know what you guys really need) 370v and they've got this one on clearance for $11.89 plus tax. You could find different voltage and mfd levels depending on what you need. I'm pretty sure they don't take returns on caps so be sure you are buying what you need.
http://www.grainger.com/Grainger/DAYTON-Motor-Run-Capacitor-2GE91?Pid=search


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## 9852 (Jan 17, 2010)

Rocketmaker10000 said:


> Another thought, If I use your circuit instead of using my friends arduino chip, what resistor values would i need to change in your circuit? Maybe I will try both and test them. This is such a cool project!


well my circuit monitors the voltage in one individual cell and disconnects at the cells full charge voltage, you could use a 100 ohm resistor in place of the 330 ohm hysteresis resistor, that will change the disconnect voltage to around 4-5 volts and trim it to the exact voltage with the pot. but the circuit was designed to work for lead which is a bit tougher with over voltage than lithium is so it would need some tweaking to make it work, but changing the hysteresis resistor would be a good start, i have not tried to use it for lithium but i could do some tests with my small lithium pack to get it right, i never thought anyone would charge lithiums with it so i never tried either.


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## 9852 (Jan 17, 2010)

Rocketmaker10000 said:


> Another thought, If I use your circuit instead of using my friends arduino chip, what resistor values would i need to change in your circuit? Maybe I will try both and test them. This is such a cool project!


i think if i could use an ardunio i would do that instead, but i cant program them, so i went with what i could do.


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## Rocketmaker10000 (Dec 7, 2008)

billhac said:


> i think if i could use an ardunio i would do that instead, but i cant program them, so i went with what i could do.


Thanks for your help Bill. I haven't tried programming in years so I will probably leave it up to my friend. 

I picked up some used Caps today. I will try and upload pictures of them in a little bit as I just watched a movie with my kids. I got them from an old UPS setup. Really nice caps. Do you know how you can test if a cap is good or not? I don't have any experience with Caps at all.

Look for my next post with the description of what I have. Lots and Lots of caps!


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## Rocketmaker10000 (Dec 7, 2008)

OK, here is the awesome deal I got today. A whole lot of Capacitors! Outstanding variety and the best price "FREE"! Got them out of an old UPS! 

Now the question is, how do you test them to see if they are good? I don't feel like welding any screwdrivers to the tops of them so does anyone have a way to effectively test these caps. The big BLUE ONES are 8500uf 350WDC and +85C and Max surge 450vdc. Check out the variety! Not a bad deal today I think. Please comment as I am very new to capacitors other than I know that I should respect them very much! My Internet Service provider has been having some problems the last few days. Download speeds are pretty normal but uploads are a pathetic 19kbs. I think it will take a week to upload all the pictures at this rate. I have the following numbers of each:

Corneil Dubilier (Blue) 11 Referenced above:
Aerovox Inc. (White Label) 27 46uf 580v
Max Torque (Silver Oval) 12 13mf 1000Vp
Mallory (Silver) 03 25mf 370Vac
Total 53

Still couldn't upload any material because it times out so my ISP is having problems still. Maybe I can upload the pictures tomorrow.


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## jackbauer (Jan 12, 2008)

First off you can only use a cap that has an AC rating. DC caps are no use and will explode if used in this system. Simplest way to test a cap is to use an analog multimeter. First , short the cap out to make sure its discharged then put the meter on resistance (say 10k) and put the probs on the cap. The needle should flick over the scale and then settle back to zero.

If you dont have a suitable meter you can use a torch bulb and a small 6v battery. wire em up in series. The buld should glow for a second or two then fade out.


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## bruceme (Dec 10, 2008)

This is really just an unrefined "bad boy" charger right? It doesn't even attempt to step down the voltage any with a variac and it's totally uncontrolled and can easily wipe out your battery if left unattended on an under.

ie... an interesting idea, fun project, but not a practical charging solution.

-Bruce


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## Rocketmaker10000 (Dec 7, 2008)

jackbauer said:


> First off you can only use a cap that has an AC rating. DC caps are no use and will explode if used in this system. Simplest way to test a cap is to use an analog multimeter. First , short the cap out to make sure its discharged then put the meter on resistance (say 10k) and put the probs on the cap. The needle should flick over the scale and then settle back to zero.
> 
> If you dont have a suitable meter you can use a torch bulb and a small 6v battery. wire em up in series. The buld should glow for a second or two then fade out.


Jack, I have an analog meter so I will use that method. Secondly, why will the DC caps explode? Are they good for anything? As you see I have a lot of them.

Also the two 120v lines: Can I attach them together at the capacitor or should I have two sets of capacitors and then connect the two legs together after the bridge on the DC side of this to charge up the big pack? Please advise. Thanks as always.


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## Rocketmaker10000 (Dec 7, 2008)

bruceme said:


> This is really just an unrefined "bad boy" charger right? It doesn't even attempt to step down the voltage any with a variac and it's totally uncontrolled and can easily wipe out your battery if left unattended on an under.
> 
> ie... an interesting idea, fun project, but not a practical charging solution.
> 
> -Bruce


Bruce, if you read the whole thread this is practical when you add in a High Voltage Cutoff circuit. This is the key to making this a reality. Also tying it into a BMS makes this very practical. Step down Voltage isn't considered on this thread. There is another 10Kw charger discussion thread you should probably read to understand all the details in making an open source controller.

You can find it here: http://www.diyelectriccar.com/forums/showthread.php/10kw-60a-diy-charger-open-source-59210.html


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## Gatorman (Aug 22, 2010)

DC caps are polarized so that they can only charge with dc current. If you hook them up backwards, the coating inside breaks down and electrolysis occurs. Then once enough hydrogen gas builds up, they explode. AC current changes to the wrong direction 30 out of 60 times a second and ruins DC caps.

I think it's 1 120vac leg to the capacitor, the other side of the capacitor goes to the bridge rectifier. And the other 120 vac leg goes straight to the rectifier.

You could use the 350 volt DC caps on the battery side to improve the power factor, but you have to touch the charging leads together after you unhook them from the batteries to discharge the dc capacitors, or you run the risk of a big nasty (probably fatal) shock.


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## Rocketmaker10000 (Dec 7, 2008)

Gatorman said:


> DC caps are polarized so that they can only charge with dc current. If you hook them up backwards, the coating inside breaks down and electrolysis occurs. Then once enough hydrogen gas builds up, they explode. AC current changes to the wrong direction 30 out of 60 times a second and ruins DC caps.
> 
> I think it's 1 120vac leg to the capacitor, the other side of the capacitor goes to the bridge rectifier. And the other 120 vac leg goes straight to the rectifier.
> 
> You could use the 350 volt DC caps on the battery side to improve the power factor, but you have to touch the charging leads together after you unhook them from the batteries to discharge the dc capacitors, or you run the risk of a big nasty (probably fatal) shock.



Mr. Gatorman, thanks for the description. I wasn't going to use the DC caps on the AC side. I know the difference. Now on the DC side, if I run a big enough resistor across the DC caps, won't this slowly remove the capacitive charge sitting inside the cap? 

Also, I repeated the bench test with a 3.2v 40Ah lithium cell and with 3 of the 46uf Vac Caps on the AC side (parallel). The AC side is delivering a nice smooth 6.1 amps into the Bridge and the battery voltage was at 2.45vdc when I started and it is up to 3.35vdc now so the charge is working very well! Now I am setting up to start building the bigger set up for the 240v 28amp system I am going to use for the EV. Thus, since each cap was equaling about 2 amps I figured I would use 8 caps on each leg of the 240v setup thus delivering 14amps for each leg (120v = one leg). Each leg will then go through a Bridge Rectifier (50amp 1000v). Thus, after the two bridges, I can then tie them together to then have 240vdc + and 240vdc - which would then go to 185v battery + and 185v battery -. Does this sound right to you? It is making sense in my head but since I am working alone, I appreciate running this by someone else prior to actually connecting electricity to it. No DC caps are used at present. I may add one in on the DC side like you said after this test proves effective. Once I get this part setup I will attempt to work on the High Voltage Cutoff switch to then power down the Charger.


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## jackbauer (Jan 12, 2008)

I've attached an image of 4 possible connection schemes for this charger. Two for Europe and two for the US. For clarity I have ommitted fuses , switches and earth leakeage protection (GFCI). These are a must. I have not tried the 3 phase setup as yet so its theory only. Hope to give it a test this weekend.


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## Rocketmaker10000 (Dec 7, 2008)

JB, Gator, Bill, and everyone,

Here are the results of my test on the cars battery pack and the build out which I did today.

I wired up two legs of 120v capacitor banks (parallel) with 7 capacitors in each. After the caps, I wired them directly to two independent Bridge Rectifiers. After the bridge rectifiers I took the DC output from the bridge rectifiers and combined them to a positive post and negative post. From that post I wired up an Andersen Connector and then connected it to the battery. The pack was partially charged up to 191v with Peak Voltage cutoff pegged at 214v. 

I plugged the charger into the AC mains via a Welding plug in my garage thus giving it life! I checked the current flowing into the cells, which was at 11.2 amps on each leg (22.4 amps total), and the battery pack voltage went up to 193 very quickly thus showing that it was functioning. I didn't want to charge that pack, as it is partially charged so the test is finished for today! 

Overall rating for this test.....YEAH! It worked!  240v charger for a big pack is well on its way to being totally functional. Still can't upload any pictures but I have to say with this many wires and caps, it is one UGLY contraption. I will definitely have to build a cover for it.


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## 9852 (Jan 17, 2010)

Rocketmaker10000 said:


> JB, Gator, Bill, and everyone,
> 
> Here are the results of my test on the cars battery pack and the build out which I did today.
> 
> ...


glad to see you had good results, i would like to see it after you build the covering for it. this charger works well for both my conversions so i did not see a need to spend hundreds or even thousands of dollars for a charger with the same charging current. granted those chargers have better current control, but nothing that cant be done cheap with discrete components from radio shack.


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## Rocketmaker10000 (Dec 7, 2008)

billhac said:


> glad to see you had good results, i would like to see it after you build the covering for it. this charger works well for both my conversions so i did not see a need to spend hundreds or even thousands of dollars for a charger with the same charging current. granted those chargers have better current control, but nothing that cant be done cheap with discrete components from radio shack.


My ISP is still having problems with the Uploads. I can download 1.5Mbs but only get 19ks for uploads and will take so long to upload even 1 picture so I am going to call them tomorrow and find out what the hell is wrong here.

I'll try and see if I can upload a picture of the Charger tonight but I doubt it will upload. Wait and see....


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## Rocketmaker10000 (Dec 7, 2008)

OK, I shrunk the pictures down a whole lot to make sure the upload worked. Now they made it through. Now, I must say the box looks insane but it works so I am going to tidy it up but since I was given the capacitor holder, I used it during my testing today. Also I undid the Andersen Connector and pulled all the 2/0 wire out the back of the Jeep for this test. Now that I know if works, I will work with my business partner to get the High Voltage Cutoff working. Then I will connect it to the J1772 inlet with the communications protocol to turn off the EVSE from the Arduino once that high voltage limit is reached. Then drive it over to the nearest EVSE and plug it in for a test. Watch it charge and then drive back home with a fully charged EV with a charger that was virtually free! 2 $1.95 Bridges, already had the heat sinks, was given the Capacitors and the holder and I had to go out and get some more connectors for these connections but all in all, an outstanding project so far. Once it is done, I am going to try and build one of those 10Kw ones from the other post in this section! YEAH!


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## Rocketmaker10000 (Dec 7, 2008)

Ok, finally waited a 1/2 hour to upload this to Youtube for an 18sec video.....I am going to have some choice words for the ISP tomorrow! Anyway, this was a quick shot of charging up the a 3.2v 40Ah lithium cell. It was started at 2.45v and it was up to 3.3 after I finished the video. This is a nice little charger for any battery really! Just have to sit and watch it as there is no automatic shut off! http://www.youtube.com/watch?v=bGrhO0u1Jmk:)


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## Coulomb (Apr 22, 2009)

jackbauer said:


> I've attached an image of 4 possible connection schemes for this charger. Two for Europe and two for the US.


For the single phase US circuit (lower right corner), surely the input marked "Gnd" should be "N" for Neutral. You should never draw power from the protective earth lead. You will trip GFCIs and raise the voltage of cases of appliances that have their cases connected to protective ground (I hope you can follow that mouthful).

Edit: the exception of course is in a fault condition, when you briefly have to draw a lot of current to throw a breaker or blow a fuse, thus clearing the fault.


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## jackbauer (Jan 12, 2008)

Your correct. My mistake.


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## Rocketmaker10000 (Dec 7, 2008)

The High Voltage Cutoff is coming along so I should be able to test it by this weekend and see how well it works. Thanks everyone for this threads idea. It truly came at a great time and now I'm making lots of inroads on this conversion. Hope to have it done soon as well. I will let you know how it performed on Saturday most likely.


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## rmay635703 (Oct 23, 2008)

billhac said:


> yes, mine is working in my triumph now, i put an amp meter on it at the battery connections it is charging at 24 amps, i need to go buy a kill a watt meter to get some cost estimates but here is one thing, my 120v circuit is drawing about 11 amps and is on a 20 amp breaker, now you only get 80% of the rating of the breaker safely before running the risk of over current an tripping the breaker, so when the charger is on my amp meter says 16 amps from my 120v outlet, so that tells me my charger is pulling around 5 amps and outputting 24 and some change, not bad if you ask me and i paid less than 50 bucks for it.


The above is very confusing, not sure how many amps from the wall you are really using, my KillAWat was $9 no ev enthusiest should be without a means of measuring current use at the wall and into the battery.
_________________
My main question is would this circuit work with a Honeywell 2000i inverter? I would like to drive my fathers EV directly for range extending purposes (and tests) I get 17amps of AC output continuously efficiently and would like to input as much current into the 48v pack as the genset can handle.

I am uncertain how many amps of roughly 50v power I can output from 17amp AC source. My goal is obviously as close to the 1800watts as I can get which would be about 36 amps, the genset should handle 40amps but it would probably not run as efficiently.

Would this circuit work for this purpose? The genset would mount off the rear triailer hitch and is relatively light, it provides a little better than half the power needs of the car and can run the car at low speeds.

I also wonder what bridge and caps are the best and most reliable to use?

Also on an unrelated note, how would I tap the alternator directly in the Honeywell Inverter thus bypassing an inefficient conversion? If I could keep the alternator 3 phase internal output direct connected to a 3 phase version of your circuit it might be a bit more efficient. That would be in the 300 volt area though. 

If I would have to take the DC power I would need a simple square wave chopper circuit to direct run this circuit, I am uncertain how your caps would handle square wave, might need a mighty inductor. This would allow me to accurately dial the current up or down depending on how many HZ ac I make.

Anyone have a cheap simple circuit that can make 1:1 DC-> square wave AC? I may need that if I want to bypass the rather lackluster inverter efficiency of the native HW circuit.

Thank You For any suggestions.


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## 9852 (Jan 17, 2010)

rmay635703 said:


> The above is very confusing, not sure how many amps from the wall you are really using, my KillAWat was $9 no ev enthusiest should be without a means of measuring current use at the wall and into the battery.
> _________________
> My main question is would this circuit work with a Honeywell 2000i inverter? I would like to drive my fathers EV directly for range extending purposes (and tests) I get 17amps of AC output continuously efficiently and would like to input as much current into the 48v pack as the genset can handle.
> 
> ...


what is confusing about it. before the charger is plugged in to the wall out let the circuit is drawing 11 amps of ac power, when the charger is plugged in the total draw on the circuit is 16 amps, and i piont out that at 80% of the breaker rating is where the break will trip, that is around 18 amps so the charger is not drawing enough ac current to trip a breaker that all ready has a load on it. and i did have a kill a watt meter, how do you think i got the first reading i just said i need to get another one and since then i have, hope this explanation helps


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## rmay635703 (Oct 23, 2008)

billhac said:


> what is confusing about it. before the charger is plugged in to the wall out let the circuit is drawing 11 amps of ac power, when the charger is plugged in the total draw on the circuit is 16 amps, and i piont out that at 80% of the breaker rating is where the break will trip, that is around 18 amps so the charger is not drawing enough ac current to trip a breaker that all ready has a load on it. and i did have a kill a watt meter, how do you think i got the first reading i just said i need to get another one and since then i have, hope this explanation helps


I usually use the KW to measure one thing at a time and list it in AMPs and watts.

Anyway I don't think a 2000 watt continuous genset will be able to output 1800 watts of 50v power with this circuit without a failure or breaker going.

What I do not know is what percentage of the 2000watts I can send into the car.

Running through the calcs I need roughly 800mf to get close to my goal current of 36amps (aka around 30amps I think) Since my nominal system voltage under load hovers in the 50v area (150-50)/3.315 = 30amps

Anyone think this would be workable or will I make the genset a big flaming pile of crap?

Due to Peukert cutting my power consumption in half or better actually just about doubles my real range and would be usefull in getting the EV usuable more often in more places so to say (aka I can withstand going without home charging to a local place to charge without a holdover and the amount of genset use would still be relatively limited while getting my range greatly increased and my ability to reach a remote charging location more easily).


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## 9852 (Jan 17, 2010)

rmay635703 said:


> I usually use the KW to measure one thing at a time and list it in AMPs and watts.
> 
> Anyway I don't think a 2000 watt continuous genset will be able to output 1800 watts of 50v power with this circuit without a failure or breaker going.
> 
> ...


im not sure how well it would work for your application, this circuit is still realitivly new to me and i have not conducted any tests to se which caps work best, and i have never tried using a genset, but it is interesting to see if it could work and what kind of power you could get out of it.


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## Rocketmaker10000 (Dec 7, 2008)

rmay635703 said:


> Anyone think this would be workable or will I make the genset a big flaming pile of crap?


Hysterical! I would say that testing with a clamp on meter and getting some actual results might be in order here. With this setup and the pictures I put up before was tested on a 184v pack and a charging voltage of 214v. It was pulling 24 AC amps from the capacitors. I had 7 caps 46uf each in parallel on each 120v leg. 

In your circumstances if you need 50 amps, I think you will need a 240v and a 12kw genset output. You could try it with a smaller genset but please video it as if your genset ends up like the above prediction then I have to see it!


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## Coulomb (Apr 22, 2009)

rmay635703 said:


> Anyone think this would be workable or will I make the genset a big flaming pile of crap?


I think that this sort of charger is not suitable for matching a generator to an EV. Basically, the source (in this case a generator), the capacitor(s), and the load are all in series, and so have the same current. So to get 36 A @ 50 V into the pack, you'll need 36 A @ 240 VAC from the generator, so 80% of the generator's output will be wasted. Most of it won't appear as heat, fortunately; it will just circulate into and out of the capacitors. But it means that you need a generator almost 5x as large as you really need, which is a huge expense, generates too much noise, and wastes a lot of fuel.

These chargers are okay when the source is the mains, so you can handle some extra reactive current without too many problems. But for a generator, I think you need a charger with the best power factor you can get.

[ Edit: I was under the impression that you have to use real engine horsepower to generate the reactive current in the load, but a quick search seems to indicate that I'm wrong on that count. However, a typical generator is sized for a power factor of about 0.8, and so won't be able to output 5x the current required for a unity load. ]


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## rmay635703 (Oct 23, 2008)

Coulomb said:


> So to get 36 A @ 50 V into the pack, you'll need 36 A @ 240 VAC from the generator, so 80% of the generator's output will be wasted. Most of it won't appear as heat, fortunately; it will just circulate into and out of the capacitors. But it means that you need a generator almost 5x as large as you really need, which is a huge expense, generates too much noise, and wastes a lot of fuel.
> 
> These chargers are okay when the source is the mains, so you can handle some extra reactive current without too many problems. But for a generator, I think you need a charger with the best power factor you can get.


This is exactly what I figured, I could not understand how you would/could get any current multiplication.

Also I have a 110vac genset, internally it is about 150v-300v DC depending on load (inverter) If I could build a reliable buck it might work but still probably not that efficient.

Also so does this mean that if I ran off the mains I would have to pay 5x more money to use this charger than one with a very good power factor?
Or is this load not visible to the company meter?


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## Gatorman (Aug 22, 2010)

The utility meter is supposed to read "watts" and not "Va", so it shouldn't cost more then a good power factor charger.


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## rmay635703 (Oct 23, 2008)

Gatorman said:


> The utility meter is supposed to read "watts" and not "Va", so it shouldn't cost more then a good power factor charger.


So it would not place an actual load on the motor for the back and forth? It would just heat wires more.

The genset although 2000watt continous / 17amp cont. actually has wires and components rated (I believe) at about 25-30 amps cont, the wires and other items would handle it, the one that might not is the inverter which I will have to look over.

If a real load of pretty close to my goal actually translates into the same load (what the motor feels) on the genset this may still work but I will be limited to the breaker/wire rating of the system which as stated above is more than 17amps.

In other words the genset can probably handle 25amps continous even though the rated output of the what the motor itself is capable of is only about 17amps if the motor loading is "Efficient".

But also based on this my old Coleman 1875 watter with oversized wires and an undersized motor might actually tolerate as much current flow as the Bigger inverter because of the inverter being the limitiing factor instead of the windings and HP of the motor.

Even 25amps is OK but at that point I might as well use a charger I have laying around because the efficiency is probably similar but lacking the overheating of the genset part.

Thanx
Ryan


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## Coulomb (Apr 22, 2009)

Gatorman said:


> The utility meter is supposed to read "watts" and not "Va", so it shouldn't cost more then a good power factor charger.


Yes. For domestic customers, it's not worth chasing up bad power factor loads. But if you are an industrial customer, you would probably be charged a penalty for poor power factor. I don't know if it's typically proportional to VA or something in between VA and watts.


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## Coulomb (Apr 22, 2009)

rmay635703 said:


> So it would not place an actual load on the motor for the back and forth? It would just heat wires more.


It looks like I was wrong, and it will not in fact place a large load on the diesel engine, at least for a sine wave load that is just not in phase. So I've edited my response above to note this.

With a battery charger, there is also considerable distortion of the sine wave; it will in fact draw no real current for much of the sine wave, then suddenly draw real (in-phase) current for a short part of the sine wave output. It's unclear to me whether this distortion of the load current would place an extra load on the engine.


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## rmay635703 (Oct 23, 2008)

Coulomb said:


> With a battery charger, there is also considerable distortion of the sine wave; it will in fact draw no real current for much of the sine wave, then suddenly draw real (in-phase) current for a short part of the sine wave output. *It's unclear to me whether this distortion of the load current would place an extra load on the engine.*


I know a little more than I let on but in this case I am in the same boat.

The way I figured this actually worked out was that this circuit only places a load on the circuit equal to what is actually needed in watts; in addition to this load is an artificial large amount of "noise" both constructive and destructive which equals itself out thus not making any real load EXCEPT for the resistive load in the wires and cap caused by this large amount of extra current, because the amount of this "noise" is quite large the resistive component is relatively sizable but probably no more than the conversion losses in a "good" charger.

Then again I might be completely wrong which is why I am asking here before I waste 800mf of caps.

I still wonder if this circuit could be modded to survive a square wave AC input?

Also my head is buzzing with a 220v 50amp circuit (to charge my 48v batpack) (my batteries are rated to 63amps) this would be a quick and dirty way to get a 75% quick charge circuit so my EV can be on the road more without the irritating 4 hour charge time and without the costly expense of a true 220v charger.


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## jackbauer (Jan 12, 2008)

I built the charger up for 3 phase. 150uf per phase. Pumped 20amps into my 160v traction pack today no problem. Drawing about 19amps per phase from the mains at 415v. The phase currents were a little unbalanced. I would guess due to the capacitors having a 10% tolerance. All in a success.


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## Coulomb (Apr 22, 2009)

rmay635703 said:


> I still wonder if this circuit could be modded to survive a square wave AC input?


I'd say no. The capacitors would look like a short circuit to the initial part of the square wave; after that, there is no change of voltage to keep the current going. So there would be spikes of current limited only by the resistance of the wires, rectifiers, windings, and internal resistance of the battery, followed by nothing for the rest of the half-cycle. This would be even worse power factor. About the same as that of a bad-boy charger, I guess.


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## rmay635703 (Oct 23, 2008)

Coulomb said:


> I'd say no. The capacitors would look like a short circuit to the initial part of the square wave; after that, there is no change of voltage to keep the current going. So there would be spikes of current limited only by the resistance of the wires, rectifiers, windings, and internal resistance of the battery, followed by nothing for the rest of the half-cycle. This would be even worse power factor. About the same as that of a bad-boy charger, I guess.


Hmmm, even a big inductor wouldn't help? Like a microwave transformer?

If not Ah well, then I am stuck with the 25% eff loss off the top.


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## bruceme (Dec 10, 2008)

jackbauer said:


> I built the charger up for 3 phase. 150uf per phase. Pumped 20amps into my 160v traction pack today no problem. Drawing about 19amps per phase from the mains at 415v. The phase currents were a little unbalanced. I would guess due to the capacitors having a 10% tolerance. All in a success.


Is that 19A * 415v * 3 phases => 23kw?

Seriously WOW?!?!


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## Coulomb (Apr 22, 2009)

rmay635703 said:


> Hmmm, even a big inductor wouldn't help?


An inductor would help. You could possibly just replace the capacitor with an inductor.



> Like a microwave transformer?


Well, a transformer isn't designed to be an inductor, so please be careful.


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## Coulomb (Apr 22, 2009)

bruceme said:


> Is that 19A * 415v * 3 phases => 23kw?


No, it's 19 A * 415 V * sqrt(3) = 14 kVA. Not the same as 14 kW because of the low power factor. I'm thinking that only two phases are conducting at any one time, and all that current goes into the pack. So for 19 A average, there must be about 3/2 x 19 = 28.5 A into the pack. So that's about 160 * 28.5 A = 4.6 kW; still pretty impressive for such a simple circuit.

Since the load is essentially capacitive, it might correct some of the predominantly inductive loads that the electricity supplier usually sees (from induction motors, fluoro ballasts and the like). So they might not even be too upset about the 14 kVA.


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## bruceme (Dec 10, 2008)

Brass tax... 

I have:

- 144 vNom / 160 vMax (end of charge) 100Ah LiFEPo4 pack
- 2-phase 30A 220VAC source

What is the maximum capability of the capacitive charger configuration here?


Thanks!


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## bruceme (Dec 10, 2008)

rmay635703 said:


> this would be a quick and dirty way to get a 75% quick charge circuit so my EV can be on the road more without the irritating 4 hour charge time and without the costly expense of a true 220v charger.


This is exactly where my head is at as well. I already have a Manz PFC20 which is overkill for most of my charging, but nowhere near what I need for quick turn around. 

When I'm shopping and in and out, I want to turn and burn... max out the capacity of a strong 30A/220V line (home and ChargePoint stations).

I wanted to make one minor correction to your post... This is as true a charger as any, it's just not the PFC/buckboost style the community has embraced for day to day charging.


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## Coulomb (Apr 22, 2009)

bruceme said:


> - 144 vNom / 160 vMax (end of charge) 100Ah LiFEPo4 pack
> - 2-phase 30A 220VAC source
> 
> What is the maximum capability of the capacitive charger configuration here?


If you can draw 30 A continuous, you should be able to get 30 A RMS into your pack; slightly less near the end of charge. So that would be something like a 3 hour charge from say 20% to 90% SOC (since 30 A is 0.3C for your cells). I say 30 A RMS since the current will not be smooth, but pulsing, but the RMS value should be the same as the RMS current from the mains.

I'd be very nervous about letting LiFe cells get near 90% SOC with an uncontrolled charger. You'd want at least to monitor the total pack voltage, and terminate the charge when a certain voltage is reached.

If you were top balancing, I suppose you could control the current to an extent with how many capacitors you used. Suppose you have 3 in parallel; you could start with all three in circuit, and have a circuit monitor the total pack voltage. When it gets to 160 V, switch out one of the capacitors with a contactor or relay. Now the current has dropped to about 2/3 of maximum, and the cells can charge a bit longer at this reduced current. When they reach 160 V again, drop back to one capacitor. When they reach 160 V again, terminate the charge by dropping out the last capacitor.

Maybe you can simplify the control circuit by staggering the thresholds slightly. So drop out one capacitor at 158 V, the second at 159 V, and the last at 160 V.

If you were bottom balancing, I guess you could just terminate the charge as soon as the highest voltage cell reaches your threshold (3.5 V, 3.65 V, maybe 3.8 V). Again, you could drop back from 3 to 2 to 1 capacitors to make sure you are not undercharging.


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## bruceme (Dec 10, 2008)

Coulomb said:


> I'd be very nervous about letting LiFe cells get near 90% SOC with an uncontrolled charger. You'd want at least to monitor the total pack voltage, and terminate the charge when a certain voltage is reached.


I have a miniBMS which I would hook to a relay that would open on fault. So no, it wouldn't be totally un-monitored. Also I have a 40A/220V timer that I can use to ball park the charge time to avoid over charging.


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## Rocketmaker10000 (Dec 7, 2008)

Power Factor Question:

On this thread way back, there was a bit of a discussion about putting a DC Capacitor after the Bridge Rectifier to improve the Power Factor. On my capacitive charger I built using this design, I didn't put a DC Capacitor in the circuit. Can I add a DC Capacitor in and what size, shape and type should I use in my case. For a refresher, I have a 185v Lithium Pack 100Ah cells. High voltage cutoff is 214v and I have a BMS balancing the cells.

I have 2 120v legs into two separate Bridge Rectifiers and out to the battery pack together. I have 7 46uf AC capacitors on each leg. I have some very large DC Capacitors I could use on the DC side. Like 1000uf type. Would these work?

Thanks in advance.


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## bruceme (Dec 10, 2008)

Rocketmaker10000 said:


> I have 2 120v legs into two separate Bridge Rectifiers and out to the battery pack together.


Sorry, I can't answer the Cap question. I know it's acting as a filter to smooth out the waves left after the bridge chops off the bottom n-volts of the cycle. The exact size would have something to do with the difference between your AC RMS voltage and your typical pack charge voltage. As that is the wave-form you're trying to smooth. If nobody answers I'd google power cap filters. I bet something is better than nothing so long as it's spec'd for the power we're talking about.

Why two recifiers? You can do the job with just one. Ignore neutral and hook L1 / L2 you get the same effect less one bridge.


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## jackbauer (Jan 12, 2008)

I would guess that the dc caps would smooth out the peak currents. This should help the power factor a bit. Be careful as those caps will then hold traction voltage even when the charger is shut off and disconnected. I'd put a 100k 5w resistor across them to bleed off the charge.

As a previous poster pointed out the load is largely capacitive. Most poor power factor loads are inductive so its likely to help and not hinder the overall power factor of a building or area.


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## Rocketmaker10000 (Dec 7, 2008)

bruceme said:


> Why two recifiers? You can do the job with just one. Ignore neutral and hook L1 / L2 you get the same effect less one bridge.



I have had Bridge Rectifiers fail so I put each leg through its own Bridge and with its own Heat Sink. Hopefully this will keep them both cool enough to give them long life! Still not sure if I understand "power factor" enough to worry about this. Just figured since I have all these capacitors lying around, that I might as well try and use them if it makes the charge more efficient.


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## bruceme (Dec 10, 2008)

Rocketmaker10000 said:


> I have had Bridge Rectifiers fail so I put each leg through its own Bridge and with its own Heat Sink. Hopefully this will keep them both cool enough to give them long life! Still not sure if I understand "power factor" enough to worry about this. Just figured since I have all these capacitors lying around, that I might as well try and use them if it makes the charge more efficient.


I googled it... I will try to summarize (to see if I am learning). I am learning this if I am not right... please somebody correct my rambling explanation. 

kw/kva = pf (power factor)

ie... power factor is a unit-less number that describes how effective a circuit is at converting volts and amps into power. Let's say one measures an input 1kw, if you output 0.8kw, your 80% pf. So where did all that energy go? usually heat like all energy losses, but I suspect there are other factors. 

So to be more efficient they make special circuits for "correction" called PFC (power factor correction, go figure). Some are simple, like installing another capacitor, which is what you're doing. Some are much more complex and use control ICs to correct non-predictive cycles (ie... not flat or sinusoidal). That said, I believe most PFC work on the principal that condition the circuit so it makes critical circuit components "more happy" or effective effective at delivering power. In the case of the capacitor, I think it smooths out the source/load interface and makes less current have to flow through the big AC(motor run) cap. (please comment, I'm guessing here)

Why bother? If one's circuits aren't PFC corrected, one would be pulling more amps than they'd strictly have to in order to deliver a set amount of power. The PFC correction lowers your electric bill to charge and allows you to use smaller components.

btw... I'd suspect this is why your bridge's fail, they are likely over-currenting because of PF issues.


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## Gatorman (Aug 22, 2010)

I saw only one thing wrong with that. Correcting the PF does not lower your charge bill, it only lets you use smaller components. That was the whole issue of nobody caring about the power factor for this charger, because we're only charged for the watts of power it uses, and not the Va.

That was the big kick about power factor correction devices is that they saved you no money, lol


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## Rocketmaker10000 (Dec 7, 2008)

Gatorman said:


> I saw only one thing wrong with that. Correcting the PF does not lower your charge bill, it only lets you use smaller components. That was the whole issue of nobody caring about the power factor for this charger, because we're only charged for the watts of power it uses, and not the Va.
> 
> That was the big kick about power factor correction devices is that they saved you no money, lol


Well, if PFC doesn't save money and I already have "big components" I don't quite see what the big bang is about PFC. Does the battery really notice a difference between a PFC current vs a non PFC current?


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## Rocketmaker10000 (Dec 7, 2008)

Come to think of it, what measure is KVa? Kilo Volt Amps? My understanding of electrical measurement is watts = volts x amps. So what is a KiloVoltamp or KVA? I guess I am going to have to do more research to understand KVA as well as PFC and RMS. Any more acronyms I need look up to continue my electric DIY education?

So far, I just met IRENE and she isn't at all like I expected her to be....


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## Gatorman (Aug 22, 2010)

Rocketmaker10000 said:


> Well, if PFC doesn't save money and I already have "big components" I don't quite see what the big bang is about PFC. Does the battery really notice a difference between a PFC current vs a non PFC current?


I guess the only benefit of a dc cap on the output would be it would be slightly increasing the charging current? I don't know if the Va comes down, or if the Wattage goes up when you correct it. All I can say is try it and see what happens, lol.


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## EVfun (Mar 14, 2010)

Let me take a shot at a simplified explanation of power factor.

Let's look at a 60 watt bulb on a 120 vac circuit. Light bulbs are purely resistive loads so they have a power factor of 100. A meter show the bulb draws 0.5 amps at 120 volts. 

AC is not a steady voltage but a sine wave. The actual voltage swings between 0 volts and 170 volts, back and forth. The lamp draws 0 amps when the voltage swings to 0 volts but about 0.71 amps at 170 volts of the peak. This is all happening 120 times a second so we don't see it without a scope. 

A bad power factor is when the current draw doesn't match the voltage curve. One type of bad power factor is current flowing at 0 volts, which can't contribute to power because watts is volts times amps. However, these amps still result in resistive line losses (heating your wiring) and so the breaker is designed to be sensitive to them. 

A simple charger, like the ammo box (capacitor current limited charger) or a bad boy with table manners (variac controlling the voltage to a bridge rectifier) has a bad power factor. The reason is that current only flows for part of each half of the sine wave; it only flows when the line voltage is above the pack voltage. So you might see 10 amps flowing into your pack but what you are actually getting is 40 amps for 25% of the time happening 120 times a second. That is the 25% of the time when the line voltage is greater than the pack voltage. 

The problem with this is resistive losses. Let's model the wiring as a 0.1 ohm resistor since all wire (except superconductors) have resistance. What we see is 10 amps across 0.1 ohms for 1 volt drop, times 10 amps is 10 watts, happening 100% of the time for a total line loss of 10 watts. What we are actually getting is 40 amps across 0.1 ohms for 4 volts, times 40 amps for 160 watts, happening 25% of the time for a total line loss of 40 watts. That is a lot different and explains why breakers blow and bridge rectifiers fail with these simple charging schemes.


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## Rocketmaker10000 (Dec 7, 2008)

EVfun said:


> Let me take a shot at a simplified explanation of power factor.
> 
> Let's look at a 60 watt bulb on a 120 vac circuit. Light bulbs are purely resistive loads so they have a power factor of 100. A meter show the bulb draws 0.5 amps at 120 volts.
> 
> ...


OK, this is becoming clearer. Now, in order to try and minimize the resistive load losses described above, what can be done to make sure we even this out? Thus, put a capacitor on the DC side to try and fix this issue? I am starting to see the problem but since, batteries always only take DC energy from an AC source, how are we going to get everything Power Factor corrected? Is is possible? I have my capacitive charger all set and ready to go and I'm really glad this thread was started. It is a great resource. If we can add in some PFC help this would be one way to truly build an outstanding low cost charger to any size battery pack with minimal problems associated with it. Great job everybody. This has been an outstanding thread to be a part of.


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## Rocketmaker10000 (Dec 7, 2008)

Well folks, I wanted you to see the picture of the Capacitive Charger actually in the Jeep. It is located in a box that I made for the front of the car and everything is in place but not totally wired up yet. Just wanted to get all the components in place. The DC to DC converter, the Potbox, and the Vacuum Canister are all mounted to the top of the Capacitive Charger box. The box is made of wood and bolted to a steel frame that is then bolted to the vehicle frame. I have put some pictures up of the build so you can look at it here:



https://picasaweb.google.com/lh/sre...1sRgCPT0ucWL0_WAGA&invite=CNPFyusH&feat=email


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## Coulomb (Apr 22, 2009)

Rocketmaker10000 said:


> Well, if PFC doesn't save money and I already have "big components" I don't quite see what the big bang is about PFC.


The only real issue is the high currents, especially the high peak currents, from the input (mains).



> Does the battery really notice a difference between a PFC current vs a non PFC current?


There is a difference: the charge current is pulsing at 120 pulses per second; most conventional chargers output pretty much smooth DC. Some batteries actually do better with pulsed charging; for example it is supposed to help with desulfating lead acid batteries. Especially near the knee of the curve, I think I'd prefer to charge LiFe cells with pure DC, not pulses. But it may not make much real difference.

As for the capacitors to smooth the output, I don't think that they'd be worth the space, weight, and hazard. The hazard due to retaining lethal voltage at the output for tens of seconds with a bleed resistor, and for many minutes without such a bleed resistor. The pack is like a giant capacitor to start with. If the Effective Series Resistance (ESR) of the capacitors is comparable or higher than the internal resistance of the pack, then they will do no good. Low ESR capacitors are more expensive and less common than ordinary, high ESR capacitors. The ones you have are unlikely to be low ESR.

Capacitors at the output of the charger will not change the power factor at all. The power factor comes about due to the mismatch between the current and the voltage at the input. Whether the spiky current goes straight into the pack or into an output capacitor and then slowly bleeds into the pack makes very little difference to the shape of the current from the mains.


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## Coulomb (Apr 22, 2009)

Rocketmaker10000 said:


> Thus, put a capacitor on the DC side to try and fix this issue?


As posted above, no it won't.



> ... how are we going to get everything Power Factor corrected? Is is possible?


Yes, it's certainly possible. There are two main ways.

The first is an active power correction stage for the charger (regardless of what happens after that stage). This is a switch mode power supply circuit that draws current from the mains in synchronism and proportional to the input voltage, just as a pure resistor would. So as the mains crosses zero, the current drawn is close to zero; at the peaks of the input sine wave, the current is at its peak, and at half input voltage, the current is close to half the peak current. That means manipulating the pulse width modulation to achieve this. It also means boosting the mains voltage at times, and bucking it at others. Consider a 120 VAC input and a 120 VDC nominal pack. Let's say it's charging at 135 VDC. The mains is sinusiodally varying between zero and +170 V, back to zero, then back to -170 V and back to zero again. The input rectifier will take care of drawing power from the negative half waves, although the voltage drop across the rectifier means that you can never get the power factor right up to 100%; when the mains voltage is at 2 V or less, then the voltage drop of the two diodes (at about 0.7 to 0.8 V each) leaves nothing left to boost to 135 VDC. Typical active power factor circuits provide about a 90 to 95% (occasionally about 98%) power factor. For the part of the waveform below 135 V (perhaps 75% of the time, a little less than 135/170 because of the flatness of the sine wave near the peaks), the PFC stage will be boosting from a low mains voltage to the higher pack voltage. For the other 25% of the time, it will be bucking the higher mains voltage to the lower pack voltage. It turns out that this is inconvenient fro the electronics, so typically they will boost to some highish voltage (say 200 V) then a separate buck stage will regulate the current into the battery based on the charge curve and the current state of charge of the pack.

That's always seemed inefficient to me; there are buck/boost topologies that would be able to do everything in one stage. These would not be isolated, but the variable voltage battery charger that is the subject of this thread isn't isolated either, nor are some commercial chargers such as the Manzanita Micro PFC range. No-one seems to consider using this topology, possibly because of the perceived poor silicon utilization. I happen to not agree with that, but that's an argument for another thread.

The other way, which would be more applicable to the variable voltage charger, is passive power factor correction. With this, various Ls and Cs (inductors and capacitors) are connected to the input to make the input current more sinusoidal and more in phase with the input voltage. Depending on the number and values of the components used and the load, I believe that the power factor that results is in the 70-80% range. So just putting an inductor in series with the capacitors of a variable voltage charger would probably improve its performance. The penalty is the extra bulk and weight of the inductor. It would probably not be a problem for a garage mounted charger.


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## Rocketmaker10000 (Dec 7, 2008)

Coulomb said:


> As for the capacitors to smooth the output, I don't think that they'd be worth the space, weight, and hazard. The hazard due to retaining lethal voltage at the output for tens of seconds with a bleed resistor, and for many minutes without such a bleed resistor..


I have two large resistors on the caps. I also have planned to put diodes on the J1772 plug to keep current going one way. The Battery packs are in their own boxes as is the capacitive charger. Seems like, I really don't need to bother messing with this very much more except add the High Voltage cutoff. Once that is installed this thing will work really well I think. I posted pictures of it via a Picasa link above. It is slowly coming along! Can't wait to see how it works with the Auto Trans! That is what I am worried about.


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## Coulomb (Apr 22, 2009)

EVfun said:


> Let me take a shot at a simplified explanation of power factor.


Good work. Let me have a go too 

There are two effects contributing to poor "power factor" with the variable voltage battery charger. One of these is due to the phase of the current drawn being different to the phase of the voltage of the mains. This is the traditional power factor problem, which has been around since the first induction motors and fluorescent lights.

The other one is the distortion of the current, so that the current is not a sine wave. This one is more of a problem since rectifiers and electronics, and has become a major problem with the advent of the switch mode power supply in computers from the 1980s. Now Europe has mandated that everything that draws more than 75W has to have a power factor better than 80% or so. So these variable voltage battery chargers could not be sold as a commercial product in Europe.

Back to the first contribution, the difference in phase. This contribution dominates where the pack voltage and the mains voltage are significantly different, e.g. 120 VDC pack and 220 VAC mains. See next post.

Suppose we connect an ideal 22uF capacitor across a 120 VAC mains. The capacitive reactance is 1/(2.pi.f.C) = 120 ohms, so one ampere will flow. If we put an AC ammeter in series with the capacitor, it would read one amp. So that's 120 V at one amp, or 120 VA. What is the power that a power meter would read?

In fact, the power meter would read zero. There is actual current flowing into the capacitor, so actual power is coming out of the mains. But there is also power flowing out of the capacitor and into the mains.

Lets consider the first quarter cycle, as the voltage is increasing from zero to maximum and the current is decreasing from maximum to zero. At both ends, the instantaneous power is zero, either the voltage or current is zero. The peak will happen right in the middle, when the current and voltage are at 0.717 of their peak. The voltage and current are both positive, same as with a resistive load, so the power flow is out of the mains into the capacitor. The lights in the house will very slightly dim as power flows into the capacitor.

The next quarter cycle ((just over 4 ms later at 60 Hz), the voltage is decreasing from maximum to zero, and the current is decreasing from zero to the negative peak. Again, power is zero at both ends, and maximum in the middle. The current and voltage are in opposite directions, so power flow is out of the capacitor and into the mains. The house lights get very slightly _brighter_.

Over the next two quarter cycles, the power flow is again towards the capacitor, then back to the mains again. So over a whole cycle, or even a single half cycle, the net power flow is zero, so we say that the power factor is zero. (It has to be an ideal capacitor for the power consumption to go to literally zero; in practice, there will be losses in the capacitor foils and in the house wiring etc).

A mains cycle (at 16.7 ms for 60 Hz, or 20 ms for 50 Hz) is quite short in human terms, so we are much more interested in the average effect than the instantaneous effect. The average effect is that we have a power factor, which means that if a circuit has a power factor of 33.3% (as one of these capacitor input chargers could have), then the total current sloshing around is three times the value that it would be if the circuit could be magically changed to 100% power factor.

So the capacitive load draws maximum instantaneous power as the mains voltage is rising. It turns out that an inductive circuit is similar but opposite: it also draws and returns instantaneous power as the mains voltage crosses zero, but on opposite transitions. So if as it typical you have some inductive loads (fridges, fluorescent lights with inductive ballasts, etc), then just as your capacitor input charger is drawing instantaneous power, the inductors are returning it; just as the capacitive input charger is returning power, the inductive loads are drawing it. So leading power factor devices (like the capacitor input charger, where current leads voltage) tend to cancel out their power factor with lagging power factor loads (such as induction motors, where current lags voltage).

However, the power factor due to distortion of the current waveform will typically not cancel (or will cancel to a rather limited extent), since the sum of a sine wave and a non-sine wave will never be zero.


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## Coulomb (Apr 22, 2009)

Finally, I have sorted out in my mind how this circuit works; hopefully correctly. It's not as I first thought.

Consider the diagram below.










Let's assume that the capacitor starts with zero volts across it, and we consider the positive half cycle first (upper part of the diagram). No current will flow until the 240 V mains gets to 120 V (say it's a 120 V pack that is nearly empty, so its actual terminal voltage is 120 V). Remember that the 240 V mains peaks at 340 V, so 120 V is only 35% of peak voltage.

I've shown voltages for two parts of the cycle, red voltages at the peak of the mains, and blue voltages when the mains is at 100 V.

So current starts to flow at arc sin(0.35) = 20 degrees into the half cycle. That's not too bad; we will see almost sinusoidal current starting at 20/180 * 100% = 11% into the cycle. For unity power factor, it should start at zero percent, but 11% is not too bad.

Unfortunately, the current will go to zero once the voltage across the diode goes negative. That will happen when the current through the capacitor goes to zero, which will be when the voltage across the capacitor starts to fall. That will happen just after the peak of the mains cycle. So while current started at 11% of the cycle, it has dropped to zero at 25% into the cycle. For unity power factor, the current should fall to zero at the 50% point. Ok, well 25-11 = 14%, a little less than a third of the ideal 50%.

But there is more. When the current through the diode and capacitor go to zero, the voltage across the capacitor stays constant. In this case, there will be 220 VDC, with the polarity as shown, until current starts flowing again next half cycle. So now we switch to the bottom part of the diagram. Note that the diodes have swapped positions for clarity.

With the 220 V of the capacitor adding to the mains, the diodes will start conducting _before _the zero crossing of the voltage, in fact when the positive half cycle is still at +100 V. The current at the mains input will suddenly jump negative, and increase for the last 20 degrees of the half cycle, as the slope of the voltage is still increasing (i.e. the voltage is becoming more negative quicker, if you know what I mean ). Once the voltage crosses zero, it becomes more negative slower, so the current through the capacitor and hence pack will decrease towards zero. At the negative peak of the half cycle, the capacitor current has fallen to zero, and the diodes stop conducting. Now the capacitor has 220 V across it, with the opposite polarity to that shown. So the capacitor voltage changes polarity completely over the half cycle.

This is what I think the current waveform before rectification would look like:










As you can see, it is basically a sine wave leading the voltage by 90 degrees, but with some pieces missing where it goes to zero. If these missing pieces were restored, the charger would draw no net power from the mains. (Perpetual motion cranks, here is your opportunity ). The bigger the mismatch between mains and pack voltages, the closer the current waveform is to a sine wave. Conversely, the closer the pack voltage is to the mains peak voltage, the closer the circuit comes to the classic "bad boy" charger, where the current drawn is essentially two spikes at the mains voltage peaks.

So which is worse: sinusoidal current but out of phase, or in-phase but spiky? I suspect the former, which would make this circuit better than the traditional bad-boy charger.

By adding the auto transformer, you would be able to juggle the waveform shape to minimise the peak current. It's not obvious to me at what mains voltage the peak current is minimised at.

[ Edit: I meant to point out that with the first cycle starting with the capacitor at zero volts, the first half cycle of current will be different from the rest, as shown. After that first half cycle, the charger will start drawing current before the zero crossing of the voltage. ]


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## bruceme (Dec 10, 2008)

EVfun said:


> Let me take a shot at a simplified explanation of power factor.


Thank you! That makes much more sense now. So a buck circuit would be higher because when the buck gate is open the coil will take at least some current from any point in the phase.


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## rmay635703 (Oct 23, 2008)

I am starting to wonder if a variation of this circuit could be used to control some beefy transformers that don't match my battery or mains voltage correctly. (AKA they are too high V output but are only 110v in when I want 220)

If I made effectively an RLC circuit (a motor run cap in series with a transformer) that had the cap sized to limit current to the limits of the transformers output (aka the transformer could not get enough current to self destruct) I wonder if I could make a more tame charger that would simply output an appropriate current that I decide on?

I would still need a battery HV shutoff but the power factor might be a little better because the transformer would be outputting earlier than normal because it is wound for a higher voltage than my battery pack. The cap would disallow excessive current draw thus allowing me to protect my circuit breaker and the transformer.

Anyone think this might work?


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## Lee Hart (Oct 16, 2009)

I've been reading this rather long thread with a certain sense of morbid fascination. I'm amazed that people would spend thousands of dollars on controllers and batteries, and then seek out the cheapest possible charger.

You're going to use a non-isolated charger, with no GFCI, no fuses, no shutoff timer, no overtemperature cutout, to charge lithium batteries, with no BMS, in a wooden box? My gawd, Murphy will love it! It's an invitation for disaster.

I wrote the page on the Bonn Charger, mentioned early in this thread (see http://www.evdl.org/docs/bonn_charger.pdf). It describes a "Bad Boy" charger with what I think is the absolute minimum number of safety features. And it is only suitable for lead-acids; not lithiums (because it can overcharge and set the pack on fire).

If you're building your own "bad boy" type minimalist charger, please please *please* read that page, and include the safety features you see there (input and output fuses or circuit breakers, shutoff timer, fan or overtemp cutout, meter, etc.) Otherwise, any small mistake can quickly become a major disaster.

Much of this thread discusses using capacitors as the dropping element. Capacitors are indeed an alternative to inductors. However, they tend to be bigger and more costly than inductors. An inductor the size of your fist can provide 10 amps of charging current -- capacitors for the same current are several times larger and more expensive.

The inductor also smooths the current better. You don't get the sharp discontinuities and huge current peaks that you do with capacitors.

On power factor: Forget about it for el-cheapo chargers. You can improve the power factor, but it adds cost. Spend your money on better charging voltage and current control instead.

If you really want improved power factor with a bad boy, use an inductor instead of a capacitor for the series impedance. Then add capacitance straight across the AC input until you find the value that minimizes the AC input current. The capacitor across the line has no effect on charging current or voltage, but lowers the AC input current by canceling out part of the inductive reactance.

Please take this as constructive criticism. I'm all in favor of experimentation and clever ways to reduce cost. But safety is also important!


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## Salty9 (Jul 13, 2009)

Thanks Lee,

I needed that.

Chuck


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## bruceme (Dec 10, 2008)

Lee Hart said:


> You're going to use a non-isolated charger, with no GFCI, no fuses, no shutoff timer, no overtemperature cutout, to charge lithium batteries, with no BMS, in a wooden box? My gawd, Murphy will love it! It's an invitation for disaster.


What could possibly go wrong... Here's the system I'm building:

- My wall setup has a GFI and a 40A timer. 
- I already run a miniBMS for my 44 x 100Ah TS (144v nom) system. 
- 240V/40A DPDT relay (switched on by miniBMS) 
- I have a pair of 30A/400V fuses in the aluminum charger case. 
- 6 x 60mF motor run caps (targeting 26A)
- 50A / 1000V bridge rectifier

Total cost... $60 sound more reasonable?

It's really just an experiment. My best outcome is that is can do better bulk charging on a 240 line than my Manzi PFC20. It's only pulls about 2kw at 90F ambient. It's a good 3.3kw bellow 60F.


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## Lee Hart (Oct 16, 2009)

bruceme said:


> What could possibly go wrong... Here's the system I'm building:
> 
> - My wall setup has a GFI and a 40A timer.
> - I already run a miniBMS for my 44 x 100Ah TS (144v nom) system.
> ...


OK, good! You're addressing most of my concerns. But just to be sure:

- Does the miniBMS switch off the charger if any cell goes overvoltage?
- Is it fail-safe? (so *lack* of a signal from a miniBMS or a broken wire
etc. will turn the charger *off*).
- Is there a fan and/or overtemperature cutoff device? (in case something
overheats).
- Is it in a fireproof box? (Many motor run caps have *flammable* oil
inside that vents if they fail).
- Are the output side fuses DC rated? (If the bridge fails, they have to
break a DC dead short as the pack tries to dump into a shorted bridge).


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## bruceme (Dec 10, 2008)

Lee Hart said:


> Does the miniBMS switch off the charger if any cell goes overvoltage?


Yup... miniBMS puts a regulator on each cell and runs an issolated "closed=ok" loop terminated at the miniBMS controller. If for any reason that loops opens, the bms will de-energize a line that will go to the relay (it does similarly for the motor controller). So if any cell is in a bad state (opens the safety loop), everything turns off.



Lee Hart said:


> Is it fail-safe? (so *lack* of a signal from a miniBMS or a broken wire


Yup... failure mode is off both for miniBMS and mechanically in the relay. This isn't a mosfet switch which could fail closed.



Lee Hart said:


> Is there a fan and/or overtemperature cutoff device?


I was going to heat sink the caps and bridge and put a 120vac fan on them.



Lee Hart said:


> Is it in a fireproof box?


Aluminum



Lee Hart said:


> Are the output side fuses DC rated?


Hmm, ok will do. Thx


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## 9852 (Jan 17, 2010)

Lee Hart said:


> I've been reading this rather long thread with a certain sense of morbid fascination. I'm amazed that people would spend thousands of dollars on controllers and batteries, and then seek out the cheapest possible charger.
> 
> You're going to use a non-isolated charger, with no GFCI, no fuses, no shutoff timer, no overtemperature cutout, to charge lithium batteries, with no BMS, in a wooden box? My gawd, Murphy will love it! It's an invitation for disaster.
> 
> ...


that is why i said i would only use it for lead, but it seems to be working for lifepos too. you are correct about the safety features, i incorperated them into my charger, it is pluged in to a gfci protected outlet, and does have a timer, but i have a circuit to monitor battery voltage to turn off at full charge.


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## Rocketmaker10000 (Dec 7, 2008)

My setup has BMS units with cutoffs/shunting. The capacitive charger now has a High Voltage Cutoff via an specially designed computer program sensor set up and relay controls. The supply line is GFCI protected, fuses have been added and it is in a wooden box. Now regarding caps exploding and burning then the wooden box isn't good, however if that happens in a metal box, things can still be pretty bad. I heard that the Manzanita chargers aren't isolated an are in a metal box. Have there been many failures to date? I can line the wooden box with thin metal I suppose. What is the failure rate of caps venting and exploding? Really high? No experience with caps exploding. Thanks in advance.


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## Lee Hart (Oct 16, 2009)

Rocketmaker10000 said:


> My setup has BMS units with cutoffs/shunting. The capacitive charger now has a High Voltage Cutoff via an specially designed computer program sensor set up and relay controls. The supply line is GFCI protected, fuses have been added and it is in a wooden box. Now regarding caps exploding and burning then the wooden box isn't good, however if that happens in a metal box, things can still be pretty bad. I heard that the Manzanita chargers aren't isolated an are in a metal box. Have there been many failures to date? I can line the wooden box with thin metal I suppose. What is the failure rate of caps venting and exploding? Really high? No experience with caps exploding. Thanks in advance.


Good work! it sounds like you are well on your way to making it a safe and reliable charger.

Capacitors come in many styles. New UL listed ones have an internal pressure cutoff switch that opens the circuit if it gets too hot or the internal pressure gets too high, preventing venting and fires. But old parts, or non UL listed ones from eBay etc. won't have this.

Electrolytics (AC motor starting capacitors, and DC filter capacitors) won't work in this circuit. They will fail (dramatically!) at high currents. They will get hot, and boil the liquid inside (a caustic water-based solution). While they don't burn, they can burst and throw aluminum foil and hot caustic liquid everywhere.

Older metal can paper/foil AC types (motor run capacitors) will work OK. But they are filled with an oil for insulation and cooling. If they overheat, they vent this oil. In old parts, the oil is a PCB; highly toxic but not very flammable. In newer parts, it's an environmentally safer oil, but highly combustible.

Some AC capacitors are "dry film" types (basically, aluminum foil and plastic). They don't have the venting problem but will burn. They tend to be much larger than the "wet" types, and don't dissipate heat as well.

Capacitors generally fail shorted. That's why it's vital to have fuses. Without a fuse, if a capacitor fails, the current can shoot way up, leading to serious venting or fires!

This is why I would not put capacitors in a wooden box. In general, nothing involving high power should be in a wooden box -- wood is not a good insulator, and burns.

The Manzanita Micro PFC chargers are well made, but also stripped down to include only what is absolutely necessary. If you know what you're doing and don't make mistakes or cut corners, they are great. But failures have occurred from such things as using them without fuses or GFCIs, disconnecting the output while the charger is on, powering them from a generator, mis-adjusting the controls. and other things that better chargers already have internal protection for.


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## bruceme (Dec 10, 2008)

Rocketmaker10000 said:


> Now regarding caps exploding and burning then the wooden box isn't good


Making an aluminum box is really easy. 

From your local hardware store you'll need:

- A sheet of 0.025 (pretty thin) from your local hardware store
- Pop rivets
- Sheet metal screws
- Tin snips

Cut two narrow pieces as wide as you want the box. Using a vice bend them into thirds to make two C-shapes that will conform to one another and make a box. Remember to bend the edges to tabs.. dril a whole for the screws and voila! Aluminum is easier to work than wood, nobody should be intimidated by it.


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## Rocketmaker10000 (Dec 7, 2008)

Lee, I guess I should be clearer about the wooden box. The capacitors sit inside a metal frame custom made to hold them and the caps are screwed down to it. The ones I am using are filled with combustible oil like you said. The only part of the caps that are not enclosed in metal are the tops. So my question is this, when a cap "blows" does the top come off or the bottom come off or does the whole thing become shrapnel like napalm? I trust your experience a great deal and will likely line the top of the capacitor rack with a plate of mild steel if this is true just to make sure. It will be a box within a box at that point. The cap pictured here is what is inside the box. 14 of them give me about 20 amps of charge to the 58 cell lithium pack. 3.2v nominal per cell.







http://www.youtube.com/watch?v=m_gp-PVmkyE&feature=relmfu


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## Rocketmaker10000 (Dec 7, 2008)

the Video above I have two legs going to two bridge rectifiers. I changed that so that only one leg goes through the cap bank. Wasn't getting enough amps the other way. The video has the cover off the box to see the cap bank inside the aluminum holder. I will build a cover for them if Lee or anyone tells me that the failure event of a cap is a napalm type explosion then the caps with be inside the wooden box encased in aluminum. I already have things made up and fixed to the wooden box but I'm not opposed to reinforcing the cap bank in case of failure of one of the caps.


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## Lee Hart (Oct 16, 2009)

Rocketmaker10000 said:


> when a cap "blows", does the top come off or the bottom come off or does the whole thing become shrapnel like napalm?


See the solder blobs on the top of the capacitors? That's the safety vent. When the cap gets hot enough to melt the solder, it vents! The oil will be boiling inside, and sprays out; so whatever is near may get hit with molten solder blobs and/or boiling flammable oil.

How severe the "event" is will depend on how severe the fault is. A modest overcurrent in the capacitors won't do much. The solder just runs off to the side, and a little oil may bubble out the opening. But in a worst-case fault (like the capacitor shorts internally), the failure can be pretty violent! I've seen cases where it literally blew the entire cover off!

One other concern: The capacitors will get warm, or even hot at full rated current when packed as tightly as you have them. You may need to add a fan to keep them cool. Use it to cool the bridge rectifier as well.

Newer capacitors are a lot safer than these older ones. For example, they may have a deliberate dent in the case, or be arranged so the top can bulge up. Inside, there is a switch that opens if this dent is pushed out due to internal heat or pressure. They also have better vents, less flammable oils, and other safety features.


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## Rocketmaker10000 (Dec 7, 2008)

Lee Hart said:


> One other concern: The capacitors will get warm, or even hot at full rated current when packed as tightly as you have them. You may need to add a fan to keep them cool. Use it to cool the bridge rectifier as well.



Lee, thanks. The Bridge is mounted on a Heat Sink. The caps don't even seem to get warm and are mounted in the unit that I got them from. From an old UPS system at a major University. They upgraded their UPS so these were made redundant so to speak. I decided they were perfect for this application since I just started reading this thread. As a result, I built the cap charger. Since you said the top is likely the venting source on these, I am going to fabricate a metal top cover to protect the wood. Also I will mount a fan inside to suck air into the box. I should be all set this way! I love the way the cap charges more than the inductor one I build a few years ago. Also with the High Voltage Cut off program, I can feel confident that the charger will shut off at the high side and the BMS will handle everything else! This is just grand!


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## rumleyfips (Oct 15, 2008)

Thanks Lee:

The capacitors I got on ebay all had dents about 1/4 up from the bottom. I wondered about it but now you have cleared everything up ( I know I should say 'not the type of thing with which I can up put but what the hell').


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## bruceme (Dec 10, 2008)

What does the charge profile look like? You start off at 20Amps, but as the V's pickup, does it drop off?

Thanks


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## Rocketmaker10000 (Dec 7, 2008)

*HVC Cutoff.*










I always seem to have trouble uploading pictures on this site but I'm trying again.

Doug


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## Lee Hart (Oct 16, 2009)

bruceme said:


> What does the charge profile look like? You start off at 20Amps, but as the V's pickup, does it drop off?


If you're referring to a simple capacitor-bridge rectifier setup, it's known as a taper charger. Other types of taper chargers use a resistor, or inductor, or transformer in place of the capacitor.

Taper chargers are equivalent to a fixed voltage power source and a resistor, charging a battery whose voltage rises as it charges. The charging current is at its maximum into a dead battery, and "tapers" down as the battery charges.

How much it tapers down depends on the difference between the supply voltage and the battery voltage. For example, suppose the supply is 160vdc (the rectified peak of the 120vac line) and the pack voltage is nominally 120v. A "120v" pack actually varies from something like 100v when completely dead to 150v when completely full and under charge. So, the voltage drop across the "resistor" (or capacitor or inductor or transformer) varies from 160v-100v=60v when dead to 160v-150v=10v when full. The charging current tapers proportionately; for instance 6 amps when dead tapering down to 1 amp when full.

Almost all inexpensive chargers are taper chargers. The designer plays with the transformer and/or series element (resistor, capacitor, or inductor) so it "just happens" to taper down to almost zero current when the pack is fully charged.


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## rumleyfips (Oct 15, 2008)

I got my charger finished today ( still waiting for some resistors to bleed the caps and a breaker) and it works fine. I charged a lawn mower batter really quickly , then the 36 volt pack on my lawn tractor. Next is the 96 v bank for my wind turbine.

I used 222.5 uf and only saw 7 amps. I wimped and used a power bar with a breaker. It got hot. I also used a light 75 ft. cord which may be a problem.

The heat sink for the bridge saw 130F and the caps 67F at 80F ambient. Higher amps may need a fan for the heat sink.

Off to ebay for more caps.

Thanks to all the posters who helped me on this project.

John


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## jackbauer (Jan 12, 2008)

Don't have much time these days for projects as work is frantic but i did get a chance today to do a little bit more with the cap charger :
http://www.youtube.com/watch?v=0PdFlpP7jLY

Aim of the game is to make it suitable for use with lifepo4. With 3 or 4 ssr it can throttle itself back at a preset cv point. The control circuit will probably use an atmega128 dev terminal and just monitor pack voltage. No need to monitor current. I'll add a safety timer and a mains side contactor just in case.


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## Lee Hart (Oct 16, 2009)

jackbauer said:


> Don't have much time these days for projects as work is frantic but i did get a chance today to do a little bit more with the cap charger: http://www.youtube.com/watch?v=0PdFlpP7jLY


Looks like you're making progress, Jack! A couple comments:

What are the ratings of those capacitors? They look like electrolytics (motor starting capacitors), rather than paper/oil or film (motor run) capacitors.

Also with your resistive heater load, the current is basically sinusoidal (easy to measure, things won't get hot). But when you are charging a battery, the current will be much "peakier" (is that a word?). Your meter will show the average current, but the true RMS current will be higher. Thie high peak currents will be hard on your solid state relays and bridge rectifier, and watch out for parts or wiring that get hot.


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## bruceme (Dec 10, 2008)

Nice! I'm interested in discussing the high voltage cut-off. I'm building my own with 9-45mf motor runs and a 35A bridge. I was thinking of putting the majority of the capacitors on a TRIAC with a zener/resistor off the gate set to cut-out the circuit at the knee voltage (~155v). I'd then leave one or two on to ballance until my BMS shut the whole works off with a relay. What where you thinking for controlling end of charge?

-Bruce


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## jackbauer (Jan 12, 2008)

They are epcos phicap 440v ac rated. Originally formed a pfc in an emerson 3 phase ups. I'll try to test it on the car today. If the solid states can't handle it i'll switch to mechanical contactors. All wiring is at least 6mm sq per cap "string". Its really just an experiment.

My aim would be to use the same atmega dev board as simon rafferty used on his charger with simpler code that just allows a voltage setpoint to be programmed. Would work like this :

All caps on until setpoint reached then progressevily switch caps out until again setpoint is reached. Then use last cap bank setup for 0.05C on your pack and once setpoint reached again , terminate charge. Will need a backup timer and a hardware overvoltage circuit for safety.


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## jackbauer (Jan 12, 2008)

Did a nice test on the charger today. Ran it at just under 22amps on the dc side and cut back current via the ssr and achieved a 100% controlled charge of the traction battery. Max temps on the bridge rectifier and ssr heatsink was about 40C after 2 hours.
http://www.youtube.com/watch?v=3nLSuwmFf7s


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## bruceme (Dec 10, 2008)

OK... can anyone explain this to me?

At the start of charge, Jack said he was reading 21A on the 240VAC line. Then he went to the DC side and he was pulling 19A on 160V. Quick conversion to power... AC is indicating 5kw, while the DC side is showing 3kw. Did 2kw (2/5ths) go into power factor (0.6 PF)? Is that right? So to charge 40A/DC You'd need 45A on the AC side?

-Bruce


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## Coulomb (Apr 22, 2009)

bruceme said:


> At the start of charge, Jack said he was reading 21A on the 240VAC line. Then he went to the DC side and he was pulling 19A on 160V. Quick conversion to power... AC is indicating 5kw,


No. The AC side is showing 5 kVA. 5 kW would indicate 5 kW of real power, meaning that all of the 2 kW difference is being dissipated as heat. That would be a lot of heat!

Fortunately, most of the 2 kW difference goes into the capacitors, and most of that comes out of them again, back into the mains to power other things in your house, or your neighbour's. All this happens 60 times per second. So there is a lot of power moving about.



> while the DC side is showing 3kw. Did 2kw (2/5ths) go into power factor (0.6 PF)? Is that right?


Yes. When the output power is 0.6 of the input VA, then the power factor is 0.6, by definition.



> So to charge 40A/DC You'd need 45A on the AC side?


For the same conditions (voltage ratio), the current will be proportional, yes. So 40/19 * 21 ~= 44.2 A. That's why it gets a bit scary.


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## bruceme (Dec 10, 2008)

Coulomb said:


> No. The AC side is showing 5 kVA...


Awesome explanation, I totally get it now.


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## brainzel (Jun 15, 2009)

I still didn't got it ... the cap-charger takes f.ex. 25,7A at 240V out of the wall, DC side is 161V 21Amps, thats 6168W (or VA?) to 3381 W (or VA?).
That would be loss of ~45% ... that would be a warm garage after a couple of hours ... 
Please explain it to me ...


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## jackbauer (Jan 12, 2008)

The AC input is volts x amps or VA. Its AC so it is comprised of real power and apparent power. If you just multiply AC current and voltage you get the apparent power. The real power is delivered to the load and the balance is returned to the mains supply. This is where power factor comes into play. If the power factor is one then real power = aparent power and no power is returned to the mains. In this case I think a previous poster calculated the power factor as 0.6. This means that 60% of the aparent power is delivered to the load (ie charges the battery) and the other 40% is returned to the supply. It is not disipated anywhere so nothing gets hot. Its just sent back! 

I'm doing some experiments with this because I believe it has merits. Power factor is not the be all and end all of life as some people choose to believe.


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## Coulomb (Apr 22, 2009)

brainzel said:


> Please explain it to me ...


Think about a capacitor connected straight across the mains. Now there is no output, so the power factor is zero.

As the mains voltage rises, the current increases, so real power flows into the capacitor. As the voltage peaks, the current drops to zero, and in fact starts reversing. So for the next quarter cycle, the current is into the mains, while the voltage is still positive. So energy flows back from the capacitor into the mains. The same thing repeats on the next half cycle, except that the mains voltage is now negative. Some energy flows into the capacitor, and if everything was ideal, it all flow back to the mains again.

Now put a resistor in series with the capacitor. There is current flowing into and out of the capacitor; since they are in series, the resistor and capcitor have the same current, so that current will cause power to be dissipated in the resistor. By choosing the right resistor and capacitor values, you could have whatever fraction of the mains voltage you want appear across the resistor.

Now replace the resistor with a bridge and battery; you have a charger where you can choose the output voltage and current. The voltage that has to be dropped across the capacitor largely charges it and most of it goes back to the mains.

There is no violation of the conservation of energy or anything like that. It's a bit like a transformer, but transformers don't cause as much current to be drawn from the mains.


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## bruceme (Dec 10, 2008)

I think of it this way... 

Imagine you have a compression spring fastened to a brick sitting on a table. With your hand you pulse a force into the spring... the brick moves a little each time you push forward, but each time you retreat, the spring gives you back some of that energy.

The spring is the capacitor, the brick is the battery(load) your hand is the supply.

-Bruce


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## brainzel (Jun 15, 2009)

Thank you all for your posts!
I could imagine, that these hugh reactive power could cause problems with our power/current provider in germany.
How would this "power ping pong" be counted on your wattmeter and how would it be charged on your next bill?


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## Coulomb (Apr 22, 2009)

brainzel said:


> I could imagine, that these hugh reactive power could cause problems with our power/current provider in Germany.


Yes. Or anywhere else.



> How would this "power ping pong" be counted on your wattmeter and how would it be charged on your next bill?


The watt-meter and hence your power bill reflect only real power. So for household consumers, reactive power is free, despite the problems it causes. Basically, it's not worth the utility's time to chase up domestic users.

For industrial users, the story is different. I don't know the details, but I believe that power factor is measured, and penalties apply if it is worse than a certain figure. So it becomes worthwhile for industrial users to correct their power factors, at least up to a certain level, say 0.8 (about what induction motors are, for example).

In Europe, however, there is a directive that says that anything that draws more than a certain amount of power, 75 watts from poor memory, has to have a power factor better than a certain standard, about 0.9 I believe. So computer power supplies now have active PFC stages if they are sold in Europe. This doesn't apply in America, so often power supplies intended for the US market don't have the extra $5 or $10 of parts to do the power factor correction. So in Europe, they attempt to avoid the problem with regulation. As far as I know, a home made charger doesn't have to conform to these regulations, but you could end up in hot water if you attempted to sell low power factor chargers.

BTW, fluorescent lights (not the compact fluorescent ones, the long tubes) use more or less this circuit, but using an inductor instead of a capacitor to drop the voltage with minimal losses. The inductor is called a "ballast". (These days, electronic ballasts are replacing iron cored inductors, but I think that cost prevents their widespread adoption so far). To correct the power factor, such fluoro installations have "power factor correcting" capacitors. Capacitors and inductors store their energy at different parts of the mains cycle, so they have opposite effects to each other. Applying both (having energy slop around between the capacitors and the inductors) partly cancels the bad power factor, making the overall power factor closer to unity. It doesn't do a perfect job, partly because the current waveform isn't sinusoidal. So the next issue after power factor is the distortion of the current wave form, sometimes called "harmonics".

So you could actually partly "correct" the power factor of these chargers by adding an inductor in parallel with the mains. You would put this before your extension cord, so that it wouldn't have to suffer from the extra current. But that would add a lot of weight and bulk to the already rather bulky capacitors.


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## brainzel (Jun 15, 2009)

Thanks a lot!
Space is no problem. I'm so interested in the cap-charger because it seems to give a diy-high current way of charging.
So if I want to charge my 144V/130Ah pack, I could take my Zivan NG3 and push 15A into the pack, or perhaps the self made cap-charger to charge at 40A, if it's possible.


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## Jan (Oct 5, 2009)

Can someone explain why this way of charging doesn't need an inductor?


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## jackbauer (Jan 12, 2008)

Jan , like an inductor a capacitor has impedence when presented with an ac waveform. This impedence is what limits the charge current.

One thing regarding the power factor. Most bad power factor is caused by inductive loads such as large induction motors used in industry. This produces a lagging current. A capacitive load produces a leading current. So ,in theory at least , putting a capacitive load on a distribution system may not be as detrimental as an inductive load.


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## Jan (Oct 5, 2009)

jackbauer said:


> Jan , like an inductor a capacitor has impedence when presented with an ac waveform. This impedence is what limits the charge current.


So, a fast switching IGBT does not really limits the current? Without an inductor the braker will trip, even if the current was only for a few ns to high.


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## jackbauer (Jan 12, 2008)

Essentially correct. In a buck converter the inductor is used both to store / release energy and also to oppose a change in current flow. When the igbt switches on the inductor pushes back against the incomming current.


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## rumleyfips (Oct 15, 2008)

My charger was working , then I tried to make it safer and faster. Now its problematic.

I went from 220 to 420 mfd and fom 7 to 13 amps into 36 volt nominal. I added a 15 ampDC breaker.

Now the breaker tripps after about 3 minutes. Amps are steady at 13 and the voltage rises to about 44.4. The voltage then drops and fluctuates between 44.2 and 39.9. After about 30 seconds of this the breaker tripps. The caps, heat bridge heat sink and cables are all cool to the touch. The GRI in the wall, which is pretty sensitive is OK. The battery pack on my lawn tractor is at 37.4 volts.

I can't figure out what is wrong. I already removed the resistors. No change.

Should I try removing a cap at a time?

Thanks:
John


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## rumleyfips (Oct 15, 2008)

Wtried to include an image they asked me to log in again and wiped out my post.

I have now finished my tantrum and I think a picture should show up.

Thanks:
John


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## jackbauer (Jan 12, 2008)

Is the breaker on the ac side or the dc side? My guess would be that it is rated a bit too close to the steady state current.


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## Gatorman (Aug 22, 2010)

That's one sexy looking charger, lol


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## rumleyfips (Oct 15, 2008)

Gatorman:

Not sexy but it has a good heart. I just improved it until it won't work.

Jack:

The AC side has a GFI in the recepticle box. The breaker in the charger is on an out cable to the battery pack. I think pulling a cap at a time to lower the amperage will tell me if the breaker needs to be 20 amp.

Thanks:
John


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## Coulomb (Apr 22, 2009)

rumleyfips said:


> I went from 220 to 420 mfd and fom 7 to 13 amps into 36 volt nominal. I added a 15 ampDC breaker.
> 
> Now the breaker trips after about 3 minutes. Amps are steady at 13 and the voltage rises to about 44.4. The voltage then drops and fluctuates between 44.2 and 39.9.


That's pretty weird. I think maybe the breaker is on the verge of breaking, and is actually attempting to break the circuit, but not quite getting there.



> After about 30 seconds of this the breaker trips. The caps, heat bridge heat sink and cables are all cool to the touch.
> 
> I can't figure out what is wrong.


I think it's the spiky nature of the current. Your multimeter or whatever is measuring the DC current is responding differently to the spiky current than the breaker is. I'd say the breaker is responding to true RMS, which weights more on the peaks, than the multimeter, which may be reading the average current.

[ Edit: oops. I see you're using an analog meter, not a digital multimeter to measure the current. But I think that they respond to average current, since they have such a small voltage drop, so my guesses still stand. ]

With your battery voltage so low compared to the mains, the current will (from memory) be more spiky than if the voltages weren't so unmatched.



> Should I try removing a cap at a time?


Yes, or use a higher current breaker.


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## rumleyfips (Oct 15, 2008)

Coulomb:

Thanks. I pulled a capacitor out of the circuit and the breaker was stable at 11 amps. I'm used to 15 amp AC breakers carrying a starting load of 19 v and 16volt steadily.

My ammeter may be off, I'll check it against another when I can. I tried 3 different multimeters yeasterday and got 12.3, 12.6 and 12.8. I have no idea which one is right.

Today I charged my lawntractor pack. It charges at 49.7-50 volts. I usually charge up to 45 volts with an old Lester and ~45 with the solar panels. I have been advised to stay under 15 volts per gel battery. Other web advice says no more than 14.6. I don't think I will use this charger for the lawnmower. It's OK though it works and I learned something.

When I get the new slip ring in my wind turbine, I will try the charger on the 96 volt pack. RMS may push voltage high but it may work that close to line voltage (119). There's only one way to find out.

Jack. I appreciate your help.

Thanks:
John


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## ga2500ev (Apr 20, 2008)

After doing some research I have decided to revive this thread. My two agenda items are to share some information and ask a couple of questions.

As a reminder, this technology is dangerous. Lee Hart graciously offered quite a bit of safety advice on page 16 of this thread. Be sure to follow those recommendations if this type of technology interests you.

I found this very good foundational article that describes the power supply and explains the parameters. Just in case the article disappears the name of it is "Step down rectifier makes simple DC power supply." It was written by Sokel, Sum, and Hamill and appeared in the April 9th 1998 edition of EDN magazine. They based it on an academic paper that is also floating around. I'm going to spend a few minutes summarizing what I've learned.

The most important thing to understand is the capacitors function as reactance with AC waveforms. From a conceptual standpoint caps, inductors, and resistors can be functionally treated as resistors on the AC side. Once it is clear that caps can be used as current limiting and voltage dividing elements in AC circuits as resistors are in DC ones, then the design concepts become really simple. The key parameters is reactance formula 1/(2*pi*freq*C) with the frequency in Hz and the capacitance in Farads. This value, called X, can be treated as resistance on the AC side of the circuit.

Now the rectifier bridge and the battery act as a resistance (R) in the circuit. So in the end you get two impedance elements in series that functions as a voltage divider. 

Since the frequency is fixed at 50/60 Hz, the reactance is directly related to the capacitance. Since the reactance acts in the same manner as resistance, the higher the capacitance, the lower the reactance, the more current that is allowed through the circuit. The maximum current happens when the DC side of the bridge is shorted. This current has a value of 4*sqrt(2)*f*C*Vin which is equation (7) in the article. The first 3 terms are fixed and have a value of 339 at 60Hz and 283 at 50Hz. So the max current is a function of only the capacitance and the input voltage. So for example I have 80 mFD motor run caps. At 240V/60Hz the max current of one cap is 339*.00008*240 = 6.5A. Two caps would double the available current to 13A. Of course there's some slop with the bridge voltage drop.

Now the problem is that if the bridge is open, then the open voltage is the root mean square (RMS) of the nominal AC. So if no battery is connected the terminal voltage in that case will be 339V. Ouch.
This problem can be managed by the fact that as impedance elements, a pair of caps in series can be used as a voltage divider. A sample of this is shown in Fig. 5 of the article. The ratio of the top cap to the total capacitance divides the input voltage. So two equal caps will have half the voltage across each cap. The bridge can then be paralleled with the lower cap. At max current, the lower cap is shorted out and it reverts to the original circuit. But when open, the second cap will limit the max voltage across it. So if we had a 240V input and a 48V battery, the input voltage could be limited to 60V across the bridge for example. to get the 1/4 voltage take 3 equal cap in parallel for C2 and tie in series with the single cap for C1. Note the max current is limited to C1. So if we use the 80 mFD again, then the maximum current is 6.5A and the max voltage across the terminals is 60V*sqrt(2)=84V. To double the current we can either use the same number of caps and raise the open voltage, or we can add more caps to both the top and bottom keeping the same ratio and therefore the same max voltage.

That's my summary. Now where all of this gets sticky for me is the power factor concept. I understand the concept. Unimpeded AC, or resistance only AC, keeps the changing current and voltage in phase so that power is always being converted at the load. However reactance does its impedance by shifting the phase of the voltage (in caps) or current (in inductors). In both cases that means that sometimes power is being transmitted from the AC source to the load, and sometimes power is transmitted back from the reactive element back to the source. This power it real in the sense that it travels through elements of the AC circuit. However, it's also phantom because it's not actually consumed. Resistive power (real power) is always consumed. The ratio of the real power to the total power (real and apparent) is the power factor. And circuits such as this one that is overloaded with one type of reactive element (caps) generally do not have good power factors.

Now it gets worse. Both AC voltage and current are varying constantly. Charging only occurs when the input voltage exceeds the battery voltage. So during the AC wave there are parts of the time when no power is being transmitted. However the average current of the circuit is still the values we computed above. So that means there are times when there are very heavy current draws against the source. It's like PWM where a very high voltage is pulsed to generate a new average lower voltage. Very high current when the pulse is on, and no current draw at all when it is off.

This leads to my question. How can you compute the peak power of the circuit. Items such as wires, circuit breakers, diodes in the bridge, etc have to be able to withstand the pulse peak currents of the circuit. However it is unclear how to figure out what that peak current is going to be. Is it the average current divided by the power factor? Can the peak current be computed or measured?

I found out about this when testing with my circuit a while ago. At 120V and a couple of caps, it was very well behaved with a 50A bridge. I tried to push the average current to 20A with a 240V input, and instantly smoked it. There was no problem with PIV rating of the bridge (1000V), or the average current (20A). But it's clear that the peak current was much higher, even though it was pulsed.

I'm about to run my next set of tests and put my newfound knowledge to work. I have a set of 200A 100V diodes that I plan to use for my bridge. I can use the cap voltage divider to get the voltage down, and use enough caps to get the current up. However, without a clear understanding of the max current that will flow through the diodes, I am unclear what is the proper reactance to put on AC side to keep from generating a smoldering mess.

I hope this post will be helpful to someone. And I'd really appreciate if anyone can explain how to figure out what the peak current is going to be.

ga2500ev


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## Gatorman (Aug 22, 2010)

Nice to know someone thought this was worth reviving

I've tried the voltage limiting capacitor in series like the article states before, but I didn't like the electric hum that the C2 capacitor gives off. I also didn't like the idea of the C0 capacitor without having a resistor bridged across it to drain off the voltage after you turn the circuit off. I haven't had any problems with popping rectifiers. The cheapo Radioshack ones do run pretty hot though. Just get one off ebay that is already built into a heatsink like this one http://www.ebay.com/itm/BRIDGE-RECT...262?pt=LH_DefaultDomain_0&hash=item5652de9ca6 
Try to find a cheaper one though. But don't go for something like this one because they're crap.
http://www.ebay.com/itm/10-50A-1000...076&pid=100005&prg=1088&rk=2&sd=370757508262&

I'll be waiting on those results


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## ga2500ev (Apr 20, 2008)

Gatorman said:


> Nice to know someone thought this was worth reviving
> 
> I've tried the voltage limiting capacitor in series like the article states before, but I didn't like the electric hum that the C2 capacitor gives off. I also didn't like the idea of the C0 capacitor without having a resistor bridged across it to drain off the voltage after you turn the circuit off. I haven't had any problems with popping rectifiers. The cheapo Radioshack ones do run pretty hot though. Just get one off ebay that is already built into a heatsink like this one http://www.ebay.com/itm/BRIDGE-RECT...262?pt=LH_DefaultDomain_0&hash=item5652de9ca6
> Try to find a cheaper one though. But don't go for something like this one because they're crap.
> ...


I already have the diodes. Can you give me the parameters of your charger. What is the voltage, frequency, and capacitance that you use? What is the nominal voltage of the battery being charged? What amps are reading during charging?

ga2500ev


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## Coulomb (Apr 22, 2009)

ga2500ev said:


> This leads to my question. How can you compute the peak power of the circuit.


I think you mean the peak current. It's a tricky, non linear problem. Probably the best way is to use a free circuit simulator. I have one at work, but I forget the name of it... PSpice maybe? You will need to model your cable resistance and the resistance of the inductor (if used) explicitly to get meaningful results. Possibly also the Effective Series Resistance (ESR) of the capacitor(s).


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## rmay635703 (Oct 23, 2008)

I have been strongly considering building this into a 144v NiCD trickle charger for my insight.

Due to voltage variation though I am up near the "taper" side of the current and am uncertain what I need to start around .5 amps and taper down to .383 amps during absorbtion.

Any ideas? I am running off 110v so I am going to be hitting the "gray" area between 156-180v that varies from socket to socket hour to hour.

Off first calcs it looks like I need to big of a cap and the variation in current is horrible.

My 2nd option is to voltage double to feed this circuit, that would make the current more continous and reduce the size of the caps needed.

3rd is to just use the lightbulb style charger, which in this case is probably the best option since it would vary the voltage based on current flow with low flow lowering resistance.

Ah well

Thanx
Ryan


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## Coulomb (Apr 22, 2009)

rmay635703 said:


> ... I need to start around .5 amps and taper down to .383 amps during absorbtion.


I don't think you will get much automatic tapering with pack voltage rise; the 10%+ variation in voltage at the wall will nearly swamp the pack voltage rise.

You need to be so careful with hybrid packs; this sort of charger gives very little control. Remember Velma; rest in peace.


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## ElectriCar (Jun 15, 2008)

The charger in post #1 makes for a GREAT emergency charger in the US when your charger is 240V like mine and you only have access to 120V. I made one and put a heat sink on the bridge rectifier to dissipate the heat, and it gets hot at 12A or so. I used the old long extension cord trick to limit the current.

I have ran out of power only once on an ice cold day with lead batteries when I first built mine. You won't get your calculated mileage out of a cold pack!  How quickly we learn... Luckily I had that charger in my truck and used it just long enough to get me back to my office a mile or so away.


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## ElectriCar (Jun 15, 2008)

On limiting the max voltage, you can use a voltage relay to monitor the pack voltage and have it shut down the circuit with the aid of a relay but now you've added about $150-200 to your $10 charger. It still won't give you that constant voltage finish charge you'll want on lithium batteries. For those I would NOT entrust a $10,000 pack to a $10 or $200 charger. Even thinking you'll "keep a close eye on it", the first time you get a phone call or other issue and don't get back to it in time, your pack is done for!


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## ga2500ev (Apr 20, 2008)

ElectriCar said:


> On limiting the max voltage, you can use a voltage relay to monitor the pack voltage and have it shut down the circuit with the aid of a relay but now you've added about $150-200 to your $10 charger. It still won't give you that constant voltage finish charge you'll want on lithium batteries. For those I would NOT entrust a $10,000 pack to a $10 or $200 charger. Even thinking you'll "keep a close eye on it", the first time you get a phone call or other issue and don't get back to it in time, your pack is done for!


A couple of thoughts here:

1) I'm looking at this for SLA only. It's quite a bit more forgiving of overcharge than Lithium.

2) Any charger that doesn't monitor pack voltage is worthless anyway. However, a simple monitoring system, even off the shelf, isn't going to be $150-200. Personally I'm a microcontroller developer, so simple voltage monitoring is going to take a handful of parts DIY to do.

ga2500ev


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## ElectriCar (Jun 15, 2008)

I decided NOT to do this charger last week. However after driving 148 miles today, having to SIT AND CHARGE a couple of hours to be sure I could make it back safely and thus getting home at 9pm, I just have to do this as an adjunct to the main charger. 

I'm wanting to do a 40-50A unit from 208V at the office. I have used this inductor calculator successfully to build 12uh chokes to protect electronics from my Soliton controller. Using a #8 wire with a diameter of .212" on a 3" PVC pipe or conduit of 6-12" in length, one turn should be sufficient per Lee Hart's diagram linked on page 16. But his was for 10A, I want 4-5X that but not sure what size inductor to build. Any ideas???


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## steelneck (Apr 19, 2013)

Have recently read this whole thread, quite interesting.

Two questions. The drawing in the first post have one cap in series with the rectifier, what happens if there also is another cap, with the same value, on the other leg of the AC input?

If i have 240V AC fused to 10A, how may amps could a charger like this push into a 250V (nominal) pack (288V fully charged)? I guess the 10A outlet wont allow many amps due to the low power factor.


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## Siwastaja (Aug 1, 2012)

ga2500ev said:


> 1) I'm looking at this for SLA only. It's quite a bit more forgiving of overcharge than Lithium.


This is an old post, but I nevertheless need to correct this legend. SLA, especially in long series strings, is a very difficult chemistry to charge and is easily damaged by overcharging. Practically, it needs a BMS for good life. Lithium may work actually better even with a quick&dirty charger like this even without a BMS, _if_ the pack voltage matches the charger voltage _and_ the cells are in top balance.

The problem with SLA is that you _need_ to charge them fully to prevent sulfation but they can't withstand much overcharging like flooded LA can. Lithium is fine when undercharged.

Lithium cells also stay in balance, helping prevent overcharge. SLA needs strong balancing and some cells overcharge easily when charged in strings of about 50 cells as in EVs. SLA self-balancing (H2+O2 recombination) works in 12V packs (6 cells), but try putting 10 12V batteries in series and one may have 16 volts over it while some may sulfate at the same time. (This is what happens to many people using SLA and this is why they get only 1-2 years out of their packs.)

So use _flooded_ lead acid if you want to make the charging process easier without battery damage. Then you need to check the water levels.


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## Larry Anthony (Mar 20, 2014)

Hi,
I’m new here so be gentle with me.
I am experiencing this imbalance on my mobility scooter when charging two AGM batteries in series; one reads 15.1v and the other reads 14.5v during the absorption phase. I was hoping they would equalise but it’s not happening.

My question is: would I get more life out of these batteries if I charged them in parallel? Of course I would still have to run them in series.

Thanks



Siwastaja said:


> This is an old post, but I nevertheless need to correct this legend. SLA, especially in long series strings, is a very difficult chemistry to charge and is easily damaged by overcharging. Practically, it needs a BMS for good life. Lithium may work actually better even with a quick&dirty charger like this even without a BMS, _if_ the pack voltage matches the charger voltage _and_ the cells are in top balance.
> 
> The problem with SLA is that you _need_ to charge them fully to prevent sulfation but they can't withstand much overcharging like flooded LA can. Lithium is fine when undercharged.
> 
> ...


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## Larry Anthony (Mar 20, 2014)

Just a thought, someone may be interested in this schematic.


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## Larry Anthony (Mar 20, 2014)

Is it something I said?


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## major (Apr 4, 2008)

Larry Anthony said:


> Is it something I said?


Don't know  Your question (tagged onto a dormant thread) somewhat off topic:


> My question is: would I get more life out of these batteries if I charged them in parallel? Of course I would still have to run them in series.


 Answer is likely as unclear as the question without knowing a bunch more about the products and application. A whole lot a variables enter into it. I pretty much always saw a voltage differential on series pairs of AGMs charged on a 24V charger. Once every few months I'd use a pair of top-of-the-line 12V chargers and float the batteries individually. Parallel charging on a regular basis is a PITA. I'd recommend modular charging if you're bent on a change. The Minn Kota is my choice. http://store.minnkotamotors.com/products/605078/MK_210D_(2_bank) I recently installed one of these on a cart for a friend. It used 2 AGM. I found a good deal at WalMart on-line but the pricks never did give me the promised rebate


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## Larry Anthony (Mar 20, 2014)

major said:


> Don't know  Your question (tagged onto a dormant thread) somewhat off topic: Answer is likely as unclear as the question without knowing a bunch more about the products and application. A whole lot a variables enter into it. I pretty much always saw a voltage differential on series pairs of AGMs charged on a 24V charger. Once every few months I'd use a pair of top-of-the-line 12V chargers and float the batteries individually. Parallel charging on a regular basis is a PITA. I'd recommend modular charging if you're bent on a change. The Minn Kota is my choice. http://store.minnkotamotors.com/products/605078/MK_210D_%282_bank%29 I recently installed one of these on a cart for a friend. It used 2 AGM. I found a good deal at WalMart on-line but the pricks never did give me the promised rebate


 Hi major, your answer is spot on, I have two 12v smart chargers which I have used on these 34 Ah batteries occasionally but there is always this discrepancy when I charge them in series with the 4 stage charger supplied with the scooter. The rested voltage after charging is 13.1v on each battery so I suspect one of the batteries suffers more sulfation than the other. The only thing I don’t understand is what does PITA stand for?

Thanks

Edited to say: I just worked out what PITA means. Please excuse me; I’m getting very old.


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## dcb (Dec 5, 2009)

ekthor said:


> But again the question: any issue on Lithiums? I just got my brand-new LiFePO4 pack!
> 
> Regards,
> 
> ekthor


if you know exactly what you are doing, then it seems not. If you select the capacitors just right so that you hit your charge termination voltage and current, then shut it off at that point, then you are good to go.


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## Coulomb (Apr 22, 2009)

dcb said:


> if you know exactly what you are doing, then it seems not. If you select the capacitors just right so that you hit your charge termination voltage and current, then shut it off at that point, then you are good to go.


Lithiums don't like being overcharged at all. So the caveat "then shut it off at that point", seems critical to me. You might be able to use a timer to prevent the worst effects of this.


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## Moltenmetal (Mar 20, 2014)

I am relying on a BMS to prevent overcharging- one or more cells trip the BMS before I get to my charger shutoff voltage anyway... This charger would do a poor job of equalizing cells at the end of charge but that's a very minor capacity impact after a manual top balance from what I've seen so far with my own pack and charger. Too bad I didn't see or appreciate this before I blew the big bucks on my unnecessarily sophisticated charger... What's the efficiency like? Power factor doesn't matter unless I takes your utility meter read high, but efficiency does, and it would seem that this thing limits current without wasting energy as heat- sounds pretty good!


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## dcb (Dec 5, 2009)

been playing with a voltage doubler version (line peak is 170, and pack CV is 180) and some considerations I see are:

1. it is peaky. A regular bms or pack monitor may trip too early.

2. The battery chemistry responds to average current, not rms. This is good news as real rms can be challenging, where average can be a glorified RC circuit on an ADC.

3. ideally you want to hit 1/10C at your finish voltage, if your current is low when you hit your finish voltage, then you overcharged. Might be some way to compensate based on internal resistance or something, but not there yet.

4. three takes a bit of experimenting with capacitor values. Also make sure your testing looks at average current, not rms (found out I was way low on capacitance because I was looking at 3.3A rms). There is a fake rms that assumes a sine wave and a real rms, and you don't want either.

5. My ssr-20 DA apparently has zero cross detection, also declaring this to be good news as I am thinking that I could oversize the caps and start dropping sinewaves, i.e. only input 9 out of 10 sinewaves when I first hit 180V, eventually reaching 1/10C average current. On a bike it may be tough to find room for lots of capacitance, so I may wind up just making a 1/10C charger and shutting it off when it looks like 180v is reached OR when current drops below 1/10 C.

6. the usual challenges in monitoring pack voltage/current accurately enough (plus pulsing).

7. I also checked to see if maybe electrolytics could be used in a doubler instead of run caps. If your output voltage is NEVER below your peak input voltage, then maybe. Otherwise they will be experiencing reverse polarity.

8. it is peaky, but it is nothing like the current spikes you see with a triac/scr slice, with this mode you start charging at zero voltage, a triac slice on the downslope could be hundreds of amps peak, vs 11ish here for the same average current.

9. it is insanely efficient on paper.

10. the same components seem to work on 240 (340 peak), output current is ~10 amps average, so that would be a situation for testing dropping sine waves algorithm (zero cross ssr is nice for that).


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## dcb (Dec 5, 2009)

I'm glad it works. I wasn't sure if JackBauer had sorted out the microcontroller/display bit, and it occurred to me that with a microcontroller and a single zero cross SSR that it could do the same job as dropping out capacitors with a lot finer resolution and less components, better approximating a CC/CV charge curve, hopefully, skipping whole input sinewaves with a small well timed 5v pulse (every 1/100 or 1/120 of a second), instead of dropping caps out. I was hoping to make it more "intelligent", on the cheap.


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## charlie78 (Jun 23, 2011)

JRoque said:


> Nice "poor man's" charger there Gator. To add to your warnings so it's not also a "dead man's" charger is that no transformer, no isolation. Touching (or grounding) either lead, whether charging or not isn't a good idea. A classic example would be trying to charge a car's 12V battery while the battery is connected to the car. The car's frame will likely be at >55V or so potential.
> 
> JR


A isolation transformer is cheap insurance,safety first


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