# DIY Chargers?



## SimonRafferty (Apr 13, 2009)

There's loads of stuff on the web about DIY controllers - and even motors - but almost nothing about simple, low cost charging solutions.

Commercial chargers seem to cost as much as controllers, motors or batteries - so seem an obvious target for doing it yourself.

I wondered about just rectifying mains with a big bridge rectifier (out of a welder for example) then using an IGBT to vary the current with PWM. Control the whole thing with a simple microcontroller and it should be possible to build for very little.

Are there any links to charge profiles, particularly in my case for AGM / Gel batteries?

If I can get a good profile - and code it - I'll post the design and code here.

Si


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## ga2500ev (Apr 20, 2008)

You don't want to try to PWM that level of current. If you were going to do it, do it on the high side of the rectifier.

The best design is probably the Bonn Bad Boy charger. You can find it here:

http://www.evalbum.com/tech/bonn_charger.html

Good luck. I need a charger so I'll be watching this thread.

ga2500ev


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## ngrimm (Oct 19, 2007)

I've wondered about that too. Seems like the problem would be filtering the rectified current enough to be able to control it via pwm without spending a fortune on large caps etc. On the other hand, I have powered a small pwm driving a hydroxy cell with a battery charger and unless I also connected a battery in parallel to the charger, the pwm didn't seem to produce as much power. It was hard to get my scope to trigger on the pwm pulse due to the presence of 60 hz. Maybe all you would only loose is some efficiency but I don't see why it wouldn't work tho. I would be interested in what others have to say as well.


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## rmay635703 (Oct 23, 2008)

ngrimm said:


> I've wondered about that too. Seems like the problem would be filtering the rectified current enough to be able to control it via pwm without spending a fortune on large caps etc. On the other hand, I have powered a small pwm driving a hydroxy cell with a battery charger and unless I also connected a battery in parallel to the charger, the pwm didn't seem to produce as much power. It was hard to get my scope to trigger on the pwm pulse due to the presence of 60 hz. Maybe all you would only loose is some efficiency but I don't see why it wouldn't work tho. I would be interested in what others have to say as well.


There is the $3 inefficient charger
http://www.alpharubicon.com/elect/3dollarbattggn.htm
it can be made slightly more efficient by using a bridge (4 diodes) instead of 1. I use it for small spot charges for odd voltage batteries and to desulphate and charge bad batteries (or test them) It also works as a trickle and float. That said it could be used for PWM with a small load if your pack voltage is near the mains voltage (spell very bad boy charger)

There is also the cap charger which could be PWM'd but god only knows inefficiency.
http://www.otherpower.com/images/scimages/231/pulsecrg.GIF
http://www.thefuelman.com/blog/index.php?tag=capacitive-battery-charger
Though I have often wondered how workable the capacitor only voltage transformer would be.

There is a nice thread on a DIY charger here
http://ecomodder.com/forum/showthread.php/diy-open-source-ev-charger-6795.html

Generally from what I've gathered PWM in terms of AC works best if the voltage is matched fairly closely to the battery OR if you use a sizable inductive load of some type before or after the PWM circuitry to slow the current inrush as wall AC is theoretically an unlimited amp source.

Generally it all comes back to if you want efficiency you will probably end up with a transformer of some type and add PWM if you want or end up with a triac both of which start getting your cost near the commercial varieties unless you "find" a transformer out of something else.

The most promising potential DIY I've come across is the buck regulator / transformer method (which works as well as PWM and is controllable) A DIY in that direction would probably work out fine and the cost would be acceptable.

http://www.edaboard.com/topic314125.html interesting stuff there.

Hope this is clearer than mud, inevitably we all end up back on the charger issue somehow.


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## SimonRafferty (Apr 13, 2009)

Thanks for the info - Like the $3 Light bulb solution ;-) - but not quite what I'm hoping for!

A couple of other options! I bought a 'managed' battery charger (12v) from a local motor spares store for ~£15. With the casing removed, it's just a switch mode supply that weighs about 300g and charges at up to 5A

The output is fully floating - so it did occur to me just to string 20 of these in series (connecting one to each battery individually). this should provide a degree of equalization and even though 5A isn't a lot, it will give a top-up charge over night - at only £300 and 6kg weight. That's not bad compared to £2500 for an 8A 'grown-up' charger! Is there a pitfall to doing it like this?

It looks a bit like this (found on the web) There are some on eBay at the moment too









Yesterday, I was also given a 24v 'computerized' fork-lift charger rated at 50A. Initially I thought about just souping up the control to handle 240v DC instead of 24v.

Then I wondered about just connecting it in series with a 220v DC supply. Since the forklift charger is managing the current delivered to the batteries - it shouldn't care if it's 24v output is floating at 220v? The 220v can be supplied by an isolating transformer so the two transformer outputs can be additive.

Just a thought!

Si


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## major (Apr 4, 2008)

SimonRafferty said:


> Is there a pitfall to doing it like this?


Hi Simon,

This is called modular charging. I use this method on some 48V industrial trucks. With Minn Kota chargers like this. 

http://www.minnkotamotors.com/products/battery_chargers/on_board_chargers/mk440_4bank.aspx 

It basically takes care of equalization of each of the four 12V batteries. And also allows me to tap one of the four for 12V accessories instead of using a DC/DC converter. It works out pretty well.

The only downside that I have heard concerns about is the failure mode where one of the individual chargers does not function and the operator is unaware of it. Then when the string is discharged, the uncharged battery is damaged. So, for modular charging, some checks, or monitoring system would be in order.

Regards,

major


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## MalcolmB (Jun 10, 2008)

Hi Simon
I use similar 4A switch mode chargers to charge each battery independently on my motorbike (60V system). It works very well so far, though I've since read recommendations from Odyssey that to get the best from their AGM batteries they should be charged at a minimum of 0.4C during the bulk charging stage, so ideally 10A upwards for a 25Ah battery.

By the way, I think I may have met you at the Maker Fair in Newcastle a couple of months ago. Was that you with the oversize electric version of a Strida folding bike?


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## Zemmo (Sep 13, 2007)

I don't see much details on how high of a battery pack these chargers can be used on. I have a battery pack that I need to charger, I can't get access to the batteries without a ton of work. So individual charging is out of the question, but it is a high voltage pack. What could I used to be able to charge an equivalent 192 volt battery pack (its a 180 volt NiFe battery pack, thats why I say equivalent 192 which would be regular 6 volt batteries)? Would need it to hit 249 to 255 volts when charging. I am talking to a few charger companies to make a NiFe profile charger, but thats the long run. I need something for the short term. Thanks for the help.


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## rmay635703 (Oct 23, 2008)

SimonRafferty said:


> Then I wondered about just connecting it in series with a 220v DC supply. Since the forklift charger is managing the current delivered to the batteries - it shouldn't care if it's 24v output is floating at 220v? The 220v can be supplied by an isolating transformer so the two transformer outputs can be additive.
> 
> Just a thought!
> 
> Si


Thats only possible if the forklift charger is a dumb charger, if it checks the voltage at all you are sunk as it won't turn on, unless of coarse you wire it up hard.



Zemmo said:


> I don't see much details on how high of a battery pack these chargers can be used on. I have a battery pack that I need to charger, I can't get access to the batteries without a ton of work. So individual charging is out of the question, but it is a high voltage pack. What could I used to be able to charge an equivalent 192 volt battery pack (its a 180 volt NiFe battery pack, thats why I say equivalent 192 which would be regular 6 volt batteries)? Would need it to hit 249 to 255 volts when charging. I am talking to a few charger companies to make a NiFe profile charger, but thats the long run. I need something for the short term. Thanks for the help.


Do the following during an emergency (aka your charger blew) or in times when you are waiting for a definate new charger and have no way to charge.

I have charged "odd" voltage batteries manually a variable hi amperage resistor (like the 500 amp battery discharger I have) and an AC power source that matches voltage closely. (a good size variac helps along with a good analog ammeter and voltmeter)

For the very short term if you have 220v access, string up a proper set of diode(s) (aka bridge) wired directly into the mains, keep the kids and onlookers away, and run the current through an ammeter and a resistor of some type like a 110v hotplate, 110v heater, stove element whatever directly into the batteries. Add or remove resistance to get the charge rate you want up to of coarse the limits of your power line. Its safe so long as you don't attempt to interupt the current while charging. (no touching for you)

Its not very efficient, (in your case maybe 60%) but because 220v peaks match your pack voltage closely it should be doable at 5-20amps using a few 110v hotplates and some hi amp rated diodes (or a bridge), that battery charger I made out of a bad power strip can charge at up to approx 8 amps off a 110v line. And when charging 120v packs I need very little resistance and the efficiency is actually somewhat respectable.

If you want to be "safer" locate a transformer that is wound to match your pack voltage closely and repeat the same procedure I described above to limit your current to a "safe" level, and obviously a variac can do it by default since you can turn up the voltage until you get proper current flow.

Obviously you will need to monitor your voltage and amperage manually during the charge, however if you know the rate and the approx capacity used from your batteries you don't need to sit there and watch continous, just figure out how long it will take to dump the proper ahr into your batteries and choose a time a bit ahead of when you need to be there to shut it off, a cheap timer works well for that task of interupting current while you change the charge current rate to "finish" the batteries. Haveing a variable load resistor or a good selection of loads to string up will help keep things under control because a 220v line can peak a little upwards of 300v but the rate you can draw at drops significantly around 270ish volts so it will be critical near the end to watch the voltage carefully as it is possible to overcharge, luckily your NIFE don't really care but its still something to note.

Remember the most intelligent charger in the world is you, its probably also the most expensive but for a one or two time deal for testing purposes what is a few hours of your time and $5 or $10 in parts? I certainly would rather find out after a bit of wasted time that one of my irreplacable NIFE batteries is shot before I build a decent and expensive charger to handle the entire set.

Cheers
Ryan


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## Zemmo (Sep 13, 2007)

My charger did blow for this pack. I haven't been able to fix or replace the charger card which controls the charger. Thats why I am looking for a charger.

Is there any way you could draw out a schematic for this charger? A MS Paint picture works if nothing else. I do better by a visual example. I am not an EE, but if I have a schematic in front of me with the parts list I need, I can easily build it (like my battery desulfators). I do have access to 220v, thats what the van use to plug into, so thats no problem. Finding a transformer to match voltage, probably would be a problem. I am hoping to hit an electronics store this weekend to pick up some meters and a shunt. Maybe they would have something like that.


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## rmay635703 (Oct 23, 2008)

Zemmo said:


> My charger did blow for this pack. I haven't been able to fix or replace the charger card which controls the charger. Thats why I am looking for a charger.


I would strongly recommend asking on this forum and on the EVDL if anyone is willing to look at and attempt a repair of your car, there are some very intellegent people here who may be willing to repair it at a fee, (which is probably less than a new card)



Zemmo said:


> I do have access to 220v, thats what the van use to plug into, so thats no problem. Finding a transformer to match voltage, probably would be a problem. I am hoping to hit an electronics store this weekend to pick up some meters and a shunt. Maybe they would have something like that.


First off remember to be safe during charging, exposed HV will be present so make sure everything is hooked up safely before firing it up since you can't manipulate cables once plugged in.

Anyway 
I will make a complete parts list and get back later today. For a quick list you will need a 

*Proper plugin and cable for your paticular 220v plug that you are willing to cut and splice, I would keep it as cheap as possible.

You need a few HV diodes that are rated at 5 amps or preferably more or a Bridge, I would ask jyanof at ecomodder where he got his $6 600v 40amp bridge from as that is about as good as it gets. You can steal diodes out of broken TVs, CRT monitors and other devices with HV PSUs if you are on the cheap or you have some laying around

http://ecomodder.com/forum/showthread.php/diy-open-source-ev-charger-6795-7.html#post105269

You will need a soldering iron and some wires (preferablly 10guage or better, they can be cut from your sacrificed 220v cable)

You will need a method of easily wiring a load in series with your batteries the easiest way I've found of doing that is to break open a double row power strip since 110v wires and cables are plentifull

I have attached some pictures of my 110v charger the only difference between mine and yours is that you will probably use a full bridge not just a diode and you will need to wire in the two hot wires into the device as opposed to the hot and neutral.

I will be back Later, I don't have much time
Ryan


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## SimonRafferty (Apr 13, 2009)

MalcolmB said:


> Hi Simon
> By the way, I think I may have met you at the Maker Fair in Newcastle a couple of months ago. Was that you with the oversize electric version of a Strida folding bike?


That would be me!
http://www.evalbum.com/609

Si


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## hondo (Mar 30, 2009)

*what about this?*

Hey guys, I just had an idea i wanted to run past you. I just added two more 6v batteries to go from 96 to 108 volts and I bought two 6v 6amp smart chargers to take care of them (I have two 48v 17 amp golf cart chargers for the rest), and I was thinking.... would it be possible to tap into a cheap 12v smart charger and hook it up to a dumb charger (like the Bonn) and have the smart charger monitor two of the 6v batteries to turn the Bonn off when the two 6v batts reached full charge? If this could be done it would save a lot of building time. Also do you think I would need a transformer since I'm at 108 volts and the house is 120?

Hondo


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## rmay635703 (Oct 23, 2008)

A good description of how my charger works is here

http://www.alpharubicon.com/elect/3dollarbattggn.htm

my charger is no different in that it wires a battery in series with a load except that I use a power strip so I can wire in multiple loads or multiple batteries or discharge batteries through a load.

Anyway here is the complete parts list (short I know)

600v Diode or Bridge (amperage rating as high as 
possible)

Double Row 15 amp Power strip (check wally world)

Two short 10 guage 110v extension cords (one could be broken or missing an end)

1 220v power plug for your connection type

A pair of wire terminals that match up with the size terminals in your cars existing wire system (they will go on where your HV charger would attach to the full battery pack voltage)

Several 110v lightbults, hot plates, george forman grills what have you to use as a load. An EV speed control Nichrome coil would probably also work if it restricts the current sufficiently.

Kill A Watt Meter to measure amperage or an analog ammeter if you can locate one cheaply.

A standard multimeter to monitor pack voltage and to determine polarity of wires during assembly.


I couldn't find the part number of the diode I used but it isn't important you need something in the range of 600 volts or more and preferably as many amps as possible.

The two schematics above as you probably guessed are missing a few things. They only show the power strip bus bars and how to wire them, once wired you will have a normal looking power strip that has the two rows of power sockets wired in series so the only way to pass current is if there is are two loads, one connected to each side of the power strip. Also I would strongly recommend you wire the power switch on the power strip to the "battery" side hot so you can shut off the power and disconnect the battery voltage from the power plug that goes into the wall when you are disconnecting for safety reasons.

Once you have your power strip wired up, choose which side of the power strip you want to use to charge batteries on. Carefully lable the polarities and don't forget, the charger can discharge if wired backwords. Always double check polarity before making a cable and before attaching to your car.

Next you will want to break the battery disconnect cable or switch on your car (so you don't zap yourself) and located where the full pack voltage ends up, hopefully you can locate terminals to wire to. (you should also remove and check all the batteries if you haven't already)

Get a 10 guage 110v cable and route it from where your full pack voltage is located to a convient location to access. This will be your "Battery Tap" cut the male end of the cable off and crimp terminals and wire up to your battery pack terminals, the female end will provide a safe way of accessing your full battery pack voltage for this little charger or for a future external charger. Make sure you lable and double check the polarity of the cable and its end so there is no oops. If you are feeling fancy there are high voltage DC power plugs but they are not generally standard or cheap.

Now take the male end you cut off the 10 guage 110v cord and 
either 
wire it permanently into your power strip 
or make a double ended male power cord 
to plug into your "charger" 
One end will always stay in the power strip battery "charger".

Once you have everything wired up (simple I know) you will need some way of measuring amperage a 220v Kill A Watt meter is probably easiest (if it exists)

Or plug a standard 110v Kill A Watt meter into the load side of your power strip. The amperage that flows through your load is the same current flowing through your battery.

If you use an analog meter it will need to be wired/soldered through between the bridge and the load side of the meter

Once everything is wired up and assembled follow this procedure to hookup

1. Make sure the power strip is "OFF", 

2. be sure to have your double ended male electric wire plugged in the battery side of your power strip

3. Do not have any "load" plugged into the power strip yet and connect your double ended male extension cord into the battery tap you wired up into your cars battery pack. The charger should now be connected to the car via that cable and you can check the pack voltage with a standard multimeter, just shove its probes into one of the unused plugs on the power strip.

4. Plug the power plug for the power strip battery charger you wired up into the 220v plug. 

5. Your charger is now ready, plug in a load, choose a small one like a 110v lightbulb, if using a killawatt meter plug the bulb into the meter and then into the load side of the power strip battery charger.

6. Turn the power strip "on" and you should be able to read an amperage and the killawatt meter should also show how much voltage you are burning off, generally the less resistance the more efficient this type of charger becomes.

You can then fiddle with different resistive loads to get the amp rate you want, take care to monitor voltage making sure it doesn't overcharge past your goal level. I have also found certain motors will run on pulsed DC as well, I do not recommend doing that but if you have one that you don't care if it lives you can try that route if your hotplates do not allow enough current to pass.

When you are ready to disconnect the charger, always shut off the power strip, unplug & remove the load unplug from the wall then unplug the cable from the car to keep HV hidden from touch.

You will need to monitor pack voltage fairly often during the first charge until you can get a timeframe for your pack. This is obviously something that isn't a long term fix but it will work for testing purposes, just don't leave it unattended. The Battery Tap might come in handy should you decide on an offboard charging solution, it also can be used to run some devices that are compatible with your full pack voltage and comes in handy if your voltmeter or charger blow 

If you have further questions, ask, I know I don't have much of a schematic but this really is as simple as I show it gets just a diode or bridge with a load wired in series with the batteries. Not efficient or controlled but it does work

Good Luck
Ryan


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## alvin (Jul 26, 2008)

Has anyone built the Bonn charger and used it ?
I have the parts but not sure what kind of #12 wire to use .
Solid house type or strand or magnet wire ?
What if you made an isolation transformer and did the secondary
like the bonn inductor? Hope someone is still monortering this thread.
Thanks


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