# DIY dumb fast charger 100 amps - ideas?



## dimitri (May 16, 2008)

I have been pondering what it would take to build a fast dumb charger for LiFePo4 pack? My Zivan NG3 dumps 22 amps and takes few hours to charge, depending on how deep the pack is discharged. Since we now almost exclusively drive our EV ( last month we did not buy any gas at all, woohoo ) sometimes I wish I had 100 amp charger to quickly boost the battery pack for the next trip.

I'm not talking about smart CC/CV charger with low current end phase, blah blah.... I am talking simple rectified AC dumped straight to the pack. What would it take? Typical house has 120V and 240V single phase AC line capable of 200 amps. I need 100-200 amp capable diodes or perhaps there is an integrated bridge already produced for such purpose?

My TS 160AH cells can safely absorb 160Amp charging current, or even more. 

I looked on Ebay for big enough variac, but didn't see anything more than 40-50 amps. I believe variac is required to control the voltage level if I don't want to deal with PWM and high power IGBTs, right?

If not variac, what can be used to control voltage at 100 amp current levels? It has to be cheap and simple as I am not looking to invest $$$$.

I have 40 cell pack, so I will need 40 * 3.6V = 144V DC from the charger to the battery. At this voltage I don't have to worry about balancing or overcharge, I would just do regular finishing charge with Zivan overnight to keep the pack balanced. 

Any feedback? Ideas?

Thanks


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## TheAtomicAss (Feb 19, 2009)

I would think that 8 of these would probably do the trick nicely as far as rectification went.

As for the transformer, perhaps look into a fixed transformer that can handle the amperage, and has an open circuit voltage of 144V? I can't point you towards any manufacturers, I'm afraid.

It doesn't sound like a bad plan, but then again I'm not sure what would happen to the transformer if your batteries are at say, 120V, (IOW pretty much dead) and you just suddenly spank the transformer with all that draw.

You would also be subject to voltage variances, which would affect the output voltage of the transformer. My voltage at home will vary anywhere from 115V to 125V throughout the day.


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## dimitri (May 16, 2008)

Just thinking outloud, hypothetically, if I rectify 120V mains with full bridge I will have about 170V RMS half sine wave output. No sense using capacitors here since load current is huge and any reasonable capacitor will not smooth the ripple anyway, right?

Say for example my battery is at 130V resting. What happens when I connect it to this hypothetical circuit? As voltage is rising on each half sine wave from 0 to 130V there will be no current because battery voltage is higher than input voltage. Then as it passes 130V current will rise and flow into the battery. How can I calculate how much current will rise? How much voltage will drop and what component if any will ovrheat and blow up in my face ? 

Are there any simple solutions to limit the current in this circuit without generating too much heat as a waste? I'd like to be able to limit the current between 50 and 100 amps, so I don't trip my main breaker.

I know its all dangerous stuff and I will not attempt it unless I fully understand expected outcome.

I also don't know if there is any harm to LiFePo4 cells in being charged with 60hz pulses, although we discharge them in PWM pulses , so I guess reverse should be OK as well.

I wonder if anyone with proper training and experience with high power levels can comment on this crazy idea.

Thanks


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## CroDriver (Jan 8, 2009)

Interesting idea... Wait for Tesseract to see this thread. He mentioned today that his next project will be a EV charger+BMS.


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## xp_lynx (Aug 17, 2009)

I'd urge you strongly to contact a fellow member here in NZ with the user ID:  samborambo, he's an EE Engineer and works in a Power utility company and should have the answer for this. If not, he'll know how and where to get it. Best of luck, let me know about it as i'm in the same mindset to. Rgds!


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## Tesseract (Sep 27, 2008)

Yeah, yeah... wait for Tesseract... 



dimitri said:


> Just thinking outloud, hypothetically, if I rectify 120V mains with full bridge I will have about 170V RMS half sine wave output. No sense using capacitors here since load current is huge and any reasonable capacitor will not smooth the ripple anyway, right?


Correct... there is no need for filter capacitance and the 120Hz ripple probably has no effect (there are some that argue it does reduce the lifespan of lead-acid batteries, but I'm not convinced).

You don't want to try this with a single 120V branch circuit because it severely imbalances the transformer on the pole. Instead, use a full wave rectifier with the neutral - which is the transformer's center tap - as the negative. These will have to be very large rectifiers btw. 




dimitri said:


> Say for example my battery is at 130V resting. What happens when I connect it to this hypothetical circuit?
> ...
> Are there any simple solutions to limit the current in this circuit without generating too much heat as a waste?


Divide (peak voltage - pack voltage) by the total internal resistance of the pack to see what the maximum current will be. Add some form or resistance (wasteful) or reactance (impractically large, I'm guessing) to limit the current to the desired 50-100A.

FOR EXAMPLE (not actual data!) - each cell is ~6 milliohms and there are 40 cells in series. At full discharge the pack voltage will be ~100V so...

(170-100)/(40 * 0.006) = 291A without any additional impedance.

Let's see how much additional impedance it would take to limit that to 50A:

50/(170 - 100)= 0.714 ohms
0.714 - (40 * 0.006) = 0.474 ohms additional impedance needed

That could, of course, be a resistor. A very large oil or distilled-water cooled resistor.

It could also be a capacitor... a whole lot of motor run oil-filled capacitors in parallel, to be precise, because:

Xc = 1/(2 * pi * f * C)
C = 1/(6.28 * 120 * 0.474)
= 2800uF

Hmmm... that's not _too_ bad.


This brute force method of charging, though, is likely to be unpleasantly spectacular every time you use it.


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## EVComponents (Apr 20, 2009)

dimitri said:


> Since we now almost exclusively drive our EV ( last month we did not buy any gas at all, woohoo ) sometimes I wish I had 100 amp charger to quickly boost the battery pack for the next trip.


Manzanita Micro has a PFC 75...

Rich Rudman told me that he is getting a ton of orders for these things.



> Fully assembled and tested with full REGBUS interface. The PFC-75 is the same size footprint as the PFC-50 but includes a panel mounted line current meter. The inside is completely revamped including extra heavy duty wiring and components designed for running at 75 amps continuously.
> This charger is designed for...
> 75 amps in to 75 amps out
> The PFC75 weighs 42 pounds and resides in a box that is 19.5 x 10.5 x 6.5 inches.


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## xp_lynx (Aug 17, 2009)

EVComponents said:


> Manzanita Micro has a PFC 75...
> 
> Rich Rudman told me that he is getting a ton of orders for these things.


Price tag my dear EVComp is the deterrent to the majority of us. Although the DIY approach is a hectic, time consuming, and painful process but for HV applications (in my humble opinion) it is a hardcore easily DIY matter, not requiring very sophisticated LV and component level management of electronics. 

I'd urge dimitri to continue in this path, its not utterly impossible and i will share results and thoughts as well, besides it a 'dumb' charger we are after in the end so should be sweat


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## xp_lynx (Aug 17, 2009)

Don't know what you have in mind exactly dimitri in terms of a charger (on-board or not) but i personally presume strictly at home due to the size of and power ratings hence on that grounds, i think it pays to see what the high end forklift battery chargers constitute (from a component and circuitry perspective). 

Results will be the very similar for the application here if not the same, see this charger rated at 125VDC/75Amps and yes EVComp at 11% the PFC75 price. I understand PFC's portable ultra feather light and provide opportunistic charge, but at a healthy premium.


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## dimitri (May 16, 2008)

EVComponents said:


> Manzanita Micro has a PFC 75...
> 
> Rich Rudman told me that he is getting a ton of orders for these things.


The hell will freeze over before I will spend over 4K on a charger.... 

I don't know how this thread could have been more clear that I am pondering inexpensive DIY solution, not an overpriced toy.

Thanks


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## neanderthal (Jul 24, 2008)

http://cgi.ebay.com/2-48-Volt-C-D-F...in_0?hash=item27ab896e43&_trksid=p3286.c0.m14I think that possibly 2 big used forklift chargers could work out well. 2 big 72v chargers maybe. Or 3 http://cgi.ebay.com/2-48-Volt-C-D-F...in_0?hash=item27ab896e43&_trksid=p3286.c0.m14 chargers like these maybe. They could work in series. One to charge one half of the pack, the other can charge the other half. Used, mega sized dumb forklift chargers seem to be inexpensive and fairly easy to find, but the voltage is never high enough for us. So 2 could work out well, I think, since you have the zivan to do an overnight balance charge.

I know it isn't a diy solution like you had in mind, but its an option, and way cheaper than $4000 ha ha


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## xp_lynx (Aug 17, 2009)

LOL.....

I knew i had the answer tucked under my bed  well actually to be more accurate in my garage somewhere.... Bloody hell, couldn't get to sleep, its 3:30am NZ time, you owe me one dimitri , i froze my bums off looking this stuff up at this time of day.

BTW, Screw DIY approach, will probably end up costing you more. Here's the solution:

1- I bought myself 3 of these those the other day here locally for something around 200NZD or 142USD, lol beat that, lets see the PFC beat that in the next millennia

Thus at:

Input 208-240vac, 50-60Hz, 10amps. 

Output 54v DC peak (i think) and 48V nom DC, 28 amps, whatever the efficiency maybe (in my case probably round the 72% mark) so hook up 3 of those babies and you've got : 

48V x3 = 144V 
28A x3 = 84 amps

ehmmmm.... ehmmm.... guess what, that's not all !!!! These toys weigh 5.5 Kgs each totaling 16.5Kgs    so on-board even if you like  and very compact and space efficient.

In contrast, you've got a 42lbs (ehhmmmm 19kgs) PFC for the $4k+, heavier/pricer

2- I've seen even more efficient models in the range of 90% or so.. oh by the way, before i forget, you get them best from telecom company sites as they are primarily used for charging the cell tower's backup battery packs  and the cool thing is that the telecoms usually replace their old stock (although maybe not that frequently), but a quick search on Ebay gave me those many options for you to think about:

opt1-

opt2-

opt3-

Let me know if you seriosly consider this as an option (especially that of option 3), i'll share with you the cost of the lot. See what you need probably 5 units and i'll take the other 5 

Bet u'll sleep well tonight
Cheers!


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## dimitri (May 16, 2008)

My guess is these big forklift chargers are nothing more than big ass transformers coupled with big ass bridge rectifiers, which is pretty much what I had in mind for DIY project.

In my case, however, I may just be able to get away without transformer based on my pack voltage being in the general area of mains voltage.

Tesseract,

thanks for the info, this is exactly what I was looking for. So, assuming that I would start the charger when my pack is at 130V, then my expected current would be about 160Amps (170-130)/(40 * 0.006) = 166A , which is incidentally the 1C rate for my cells 

What do you mean by "unpleasantly spectacular" ? Are you referring to arcing on the circuit breaker? 

Provided I use large enough connectors like Anderson SB175 and large enough wires ( 1 AWG I guess ) and large enough circuit breaker, what kind of troubles can I get into?

Also, I can't figure out how to make full wave bridge using 120-0-120 AC input and get 0-120 ( 170 RMS ) DC output, using both halfs of mains input as you suggested for transformer balancing. Can you post a napkin drawing? Would I just parallel outputs of 2 bridges together? I'm afraid to short something out....

I found 80Amp bridges on Ebay for $10, can I parallel 2-3 of them?

xp_lynx, thanks for your input. Yes, this is meant for home use only, not onboard. I would mount everything on the wall next to my power panel and just run cable with Anderson connector to the car.

All this is just theory, I may or may not have balls to actually try this for real


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## dimitri (May 16, 2008)

xp_lynx said:


> Output 54v DC peak (i think) and 48V nom DC, 28 amps, whatever the efficiency maybe (in my case probably round the 72% mark) so hook up 3 of those babies and you've got :
> 
> 48V x3 = 144V
> 28A x3 = 84 amps


I don't think 3 would do it, if you add volts AND amps, you'd need 9 of those babies. I will account this mistake to your lack of sleep


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## xp_lynx (Aug 17, 2009)

With the compact, safe, solution i recommend above, all you need is 3 wires from your power outlet (<12-13 Amps input at 240VAC each for each of these units 36-39 Amps Power IN in total) and these telecom units do the rest for you (no cooling needed i forgot to mention required at all, although i'd say chuck in a couple of old PC fans won't harm) and u've got nothing to fear man. Don't fiddle around with rectifiers, transformers, cicuit breakers unless you have the know-how and balls, which apparently u don't LOL... just teasing, no hard feelings!

Grow some balls bro!!! Big ones too  and let the magic happen in front of u, see opt 3 above!


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## major (Apr 4, 2008)

xp_lynx said:


> Output 54v DC peak (i think) and 48V nom DC, 28 amps, whatever the efficiency maybe (in my case probably round the 72% mark) so hook up 3 of those babies and you've got :
> 
> 48V x3 = 144V
> 28A x3 = 84 amps


Hi xp_,

You can't have in both ways at once. Either 144V, 28A for 3 in series or 48V, 84A for 3 in parallel.

Good idea using telecon equipment. I've done some of it myself. Is why I like 48V systems, or multiples of 48.

major


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## xp_lynx (Aug 17, 2009)

You are right u guys!!! Let me go sleep better. Sorry for the dumb dumb mistake ... since we are speaking of dumb chargers  makes me + No Sleep = Super dumb dumb .. Good night


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## DavidDymaxion (Dec 1, 2008)

Do a Google on:

EV +"Dump Pack"

With a dump pack you'd slowly charge a bank of cheap floodies all day, then quickly charge at 100 (or 200, or 300) Amps.


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## dimitri (May 16, 2008)

DavidDymaxion said:


> Do a Google on:
> 
> EV +"Dump Pack"
> 
> With a dump pack you'd slowly charge a bank of cheap floodies all day, then quickly charge at 100 (or 200, or 300) Amps.


Thanks for the idea, but its not what I am looking for. If I want to quickly dump 50-100ah worth of charge into my LiFePo4 pack, then "cheap floodies" won't cut it, since they will not stand a chance of sustaining 100amp current for an hour. Considering Peukert effect, those "cheap floodies" would have to be about 200ah in size and I will waste almost half of my power in Puekert loss. That is not acceptable....


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## 280z1975 (Oct 2, 2008)

dimitri said:


> snip ... Since we now almost exclusively drive our EV ( last month we did not buy any gas at all, woohoo ) ... snip


I would LOVE to get to that point ... just wanted to say congrats.


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## Tesseract (Sep 27, 2008)

dimitri said:


> ... What do you mean by "unpleasantly spectacular" ? Are you referring to arcing on the circuit breaker?


Yep, or whatever you use to interrupt the current. Incidentally, most circuit breakers are not rated for "switch" duty, which basically means they are not meant to be turned on and off more than a dozen times in their _life_. 

If you use capacitors to limit the current (they must be large oil-filled "motor run", not electrolytic or "motor start", capacitors) you can start with 1/5th the total amount (e.g. - 560uF) then add more in parallel with switches or contactors to bring the current up in steps, rather than all at once.




dimitri said:


> Also, I can't figure out how to make full wave bridge using 120-0-120 AC input and get 0-120 ( 170 RMS ) DC output, using both halfs of mains input as you suggested for transformer balancing.


This is nothing more complicated than a center tapped full wave rectifier. See, for example: 

http://www.electronics-tutorials.ws/diode/diode_6.html

You will two large (probably stud mount) rectifiers or you could use a three phase bridge from a VFD (or two). Essentially, you tie all the cathodes together (the band) for your positive output, and the neutral from the pole becomes your negative. Put your current limiting impedance in between the cathodes and the battery pack. Ideally, put a double pole contactor/breaker on the anode (AC) side, or use the above idea to ramp the current up in increments.

Finally, even though this does not use a transformer, unless you get all of the components used they will be pricey.

For example, you would need (80) of these capacitors to get 2800uF total (for an estimated 50A of charging current):

http://www.eemotors.net/catalog/product_info.php?cPath=216_217_220&products_id=1095

Do not be tempted to use the motor start capacitors - they are electrolytics and cannot carry high currents for very long... usually only for a few seconds at most.

Good luck, and don't forget your safety glasses with this one


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## dimitri (May 16, 2008)

So, this is what would happen if I charge the pack which is at 130V with rectified AC from 120V line. 

Correction on my previous post about RMS. 120V is the RMS value, not 170V. 170V is the amplitude of the sine wave, which equals 120V RMS value.









Red areas represent time during which current will flow into the pack. This is basically a poor man's PWM, which looks about 40% duty cycle. 

So, charging current will only peak at 160amps ( according to formulas in above posts ) at the center of each half wave, but average will be somewhere in 40-50 amp ( considering RMS value of the top portion of the wave and duty cycle ).

Did I get it right?

NOTE: this example is for my particular pack of 40 LFP cells, your pack may differ and may not be used in this manner.


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## CroDriver (Jan 8, 2009)

Tesseract said:


> Yeah, yeah... wait for Tesseract...


You´re our EV batman


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## dimitri (May 16, 2008)

Tesseract said:


> This is nothing more complicated than a center tapped full wave rectifier. See, for example:
> 
> http://www.electronics-tutorials.ws/diode/diode_6.html
> 
> ...


That link was brilliant! Thanks a million for that! The whole site is a good reading to refresh lost and forgotten EE knowledge 

Now, if my previous post with the graph is not totally off base, then I believe I may not need any current limiting at all. In fact, I may be getting less overall charging current than I expected.

So, I will get 2 appropriate size diodes, connect them as shown to take advantage of both halfs of 240V wave and maybe give it a shot 

Hopefully the breaker will pop before batteries do, if I made any miscalculations


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## Tesseract (Sep 27, 2008)

CroDriver - that was hilarious!



dimitri said:


> That link was brilliant! Thanks a million for that!


Your welcome 

Sure I can't interest you in buying a $4k charger instead? No? Maybe after this next bit you'll see why PFC is useful, though. Maybe not $4k useful, but useful all the same.




dimitri said:


> Now, if my previous post with the graph is not totally off base, then I believe I may not need any current limiting at all. In fact, I may be getting less overall charging current than I expected.


Not so fast, buster.

You are correct in noting that current will only flow when the haversine (the technical name for a rectified sine wave) voltage exceeds the pack voltage, but the peak current will still be based on the peak of the haversine, or somewhere around 150-170V (depending on line impedance), and the total internal resistance of the pack, the resistance of the wiring and connections, etc., of course. Thus, the current pulses are narrower versions of the voltage waveform, and this makes the power factor crappy, leading to breakers tripping far earlier than the _rms_ amperage would suggest.

Which is why I REALLY REALLY suggest inserting some form of impedance to limit the current. For example, you could put several 3500W/120V water heater elements in parallel (must be in water, of course) after the rectifier, and you could start off with just one in series with the battery pack then switch the other ones in in succession to bring the amperage up... this is about the minimum level of stupidity I would accept in a charger, btw, and you'll still have to watch it like a hawk!

Oh, and you absolutely need a true RMS AC and DC clamp ammeter for this sort of stuff. It doesn't need to be be a pricey Fluke, just something that will let you know what's going on.


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## dimitri (May 16, 2008)

This is yet another time when I wish I had 45 cells in my pack. Resting voltage of 145V would have been easier for this dumb charger, less current limiting would be needed.



> the peak current will still be based on the peak of the haversine, or somewhere around 150-170V (depending on line impedance)


This statement contradicts previous formula of I=( Vm - Vb )/R , can you please elaborate? What am I missing?

Thanks for all your insight, its been very helpful.


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## Tesseract (Sep 27, 2008)

No contradiction at all... I was simply referring to the peak voltage of the rectified sine wave as being between 150 and 170V. The actual RMS current, which is what you would use to calculate the charging time, will be lower than the peak value.

One other thing I've been thinking about it that I am skeptical you can pull a full 100A from even a 200A residential service for 1 hour. You may want to check with your electric utility (TECO? Progress Energy?) to see what the "KVA" rating of the distribution transformer is and how many residences it serves. Pole mounted distribution transformers serving a single house are almost always less than 25kva, while pad mounted transformers rarely serve a single house but are usually rated for more than 25kva (that is, you could "steal" some of the unused capacity from your neighbors).


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## azdeltawye (Dec 30, 2008)

Tesseract said:


> ...
> One other thing I've been thinking about it that I am skeptical you can pull a full 100A from even a 200A residential service for 1 hour. You may want to check with your electric utility (TECO? Progress Energy?) to see what the "KVA" rating of the distribution transformer is and how many residences it serves. Pole mounted distribution transformers serving a single house are almost always less than 25kva, while pad mounted transformers rarely serve a single house but are usually rated for more than 25kva (that is, you could "steal" some of the unused capacity from your neighbors).


I wouldn't worry about over stressing the distribution transformer that feeds your house. Those things are pretty stout. If its a pole mounted unit you can periodically look for a red light on the top of the can while your charging to see if it is above the thermal alarm limit. Otherwise I wouldn't worry about it. 

Also as mentioned previously, the RMS current supplied to your pack will be less than 0.707*I peak because of the reduce area under the haversine waveform. A better approximation would be closer to 0.5*I peak, which is the RMS equivalent of a half wave rectified sinusoid. So for the numbers stated previously; V peak = 170V, V pack = 130V, R pack = 0.24 ohm, the approximate RMS battery current would be 0.5*((170-130)/0.24) = 83.33A


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## dimitri (May 16, 2008)

My neighborhood has ground pad mounted transformers serving 4-5 houses, from TECO.

What do you guys think of these 3ph bridges?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250490369578

I would use 2 bridges, each bridge serving as a single diode, essentially using 6 internal diodes in 2S3P configuration. This should triple 80amp rate and double voltage rate although voltage rate is not important since its already much over what I need.

The reason for picking these bridges is low cost, high power, easy mounting on a heat sink, etc.

I am thinking of using water heating element or element from electric range oven as a current limiting resistor.

I would use 1 AWG cables and SB175 connectors and mount the whole thing few feet away from my distribution panel to minimize cable runs.

I would use 100amp circuit breaker, its the largest I can find that fits into my distribution panel. In case of emergency I can always flip main 200amp breaker and then I would build larger separate panel, but I doubt my pack will pull so much current to require this additional expense.

Main variable in this whole project is battery resistance. The numbers posted were theoretical, real numbers could vary somewhat.

I am also looking on Ebay for clamp current meter that supports DC current. Most of common meters only do AC, not DC. Some are misleading, listing DC, but after closer research turns out to only measure AC current. I know Fluke is the best, but I can't afford another $300 toy at this moment. I can always get cheaper AC only meter and use it on wires prior to the diodes, but I was hoping to get universal meter which can also help measuring DC currents inside the car if I ever need to.

During charge I would closely monitor pack voltage and turn it off when voltage climbs to 148V ( 3.7V x 40 cells ) , which is the safe point before it starts climbing fast. I would watch it like a hawk entire time since there is no automatic cutoff.

If I had a 45 cell pack, this setup would be much easier and safer, although not as powerful, since I could just leave it until pack voltage rises to match mains peak at 170V , which is equal to 3.78V per cell in 45 cell pack. Charging current would taper down to zero on its own, making it safer solution.

I can't believe I didn't get extra 5 cells, I really regret this decision now. If this dumb charger works, maybe I will sell Zivan and buy extra 5 cells at some point down the road.

Please comment on my ideas here, hope I didn't make any major mistakes


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## major (Apr 4, 2008)

dimitri said:


> I am also looking on Ebay for clamp current meter that supports DC current. Most of common meters only do AC, not DC. Some are misleading, listing DC, but after closer research turns out to only measure AC current. I know Fluke is the best, but I can't afford another $300 toy at this moment. I can always get cheaper AC only meter and use it on wires prior to the diodes, but I was hoping to get universal meter which can also help measuring DC currents inside the car if I ever need to.


Hey dimitri,

You might consider one of these. I bought the 1000 amp model last year and have not regretted it. 

http://www.mcmelectronics.com/product/TENMA-72-7226-/72-7226 

major


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## xp_lynx (Aug 17, 2009)

*Hi all, 

First of all, thanks Dimitri for bringing this thread up. Not only was it fruitful and beneficial, but i hope it starts a revolution in "chargers" by a DIY approach through fellow EVers that would drive those crazy priced commercial chargers down to at least half of what they currently are at. In response to comments:* 



dimitri said:


> I am thinking of using water heating element or element from electric range oven as a current limiting resistor.


I think its a great idea here too, for i have the same approach already setup in another project using those as current limiters these two components, namely 2x 4kW heater tank elements and 4x (variable Watts) oven elements. Of course, i've done the resistance calcs and all for the connections at the time. I even have them immersed in water with an air-cooled condenser to feedback evaporating water



dimitri said:


> I would use 1 AWG cables and SB175 connectors and mount the whole thing few feet away from my distribution panel to minimize cable runs.


Thanks for bringing that up, helps narrow it done to particulars directly.



dimitri said:


> During charge I would closely monitor pack voltage and turn it off when voltage climbs to 148V ( 3.7V x 40 cells ) , which is the safe point before it starts climbing fast. I would watch it like a hawk entire time since there is no automatic cutoff.


Great idea and a must , for a start, but can u imagine having to do this every single night to charge? A better approach would be to automate this (later on that is):

Cheap, easy straight-forward: using an alarm mechanism with a simple timer.

(or even if you want it more sophisticated further in future possibly)

using something similar 'along the same lines' as this. In short a circuitry for voltage sensing and a relay (in the kW range obviously at least double/triple that of your charging V & A) as an auto-shutoff mechanism, possibly can even give u trickle charge mechanism this way through voltage sensing, if voltage in your battery bank slightly drops overnight or so). 

But get it working with the 'basics' first and see how it goes. For a start, log some data on an excel sheet for say 10 days. 

(well obviously a lot of speculation and inaccuracy will be there as you will definitely not be charging from a completely depleted bank nor will you have the same consistent consumption (bank SOC before charging) all the time, but just as an average, to get a feel and know). 

Measure data like:

- initial bank's SOC
- Time taken to reach target voltage (in your case 148V)
- Current rate form charger to bank (and if its hugely variable or relatively stable)

That way you can work out the simple electronic timer/buzzer scenario to know when to cutoff power.



neanderthal said:


> I think that possibly 2 big used forklift chargers could work out well. 2 big 72v chargers maybe. Or 3 chargers like these maybe. They could work in series. One to charge one half of the pack, the other can charge the other half. Used, mega sized dumb forklift chargers seem to be inexpensive and fairly easy to find, but the voltage is never high enough for us. So 2 could work out well, I think, since you have the zivan to do an overnight balance charge.


Thanks for the encouragement neanderthal. Do you an dimitri wanna know what i did  i went insane and bought me some more of these very lovely telecom toys  I just adore these telecom equipments, 

*Dimitri you are gonna truly love this;* check this out. I'd rather spend this amount ($650) than $4000. I know you might say well it's not cheap and so forth, but given the amount of time and headache i'd have to cope up with having to rig my own ICs and components, shipping, PCB or soldering, time, things blowing  lol or going wrong at high voltages (DC) etc... i'll take the easy way out (in this case only  not always though) anyday.

So let me try and not do more stupid calculation mistakes (its 2:10am again, boy why do i insist on working at 0% charge....lol)

Basically, here's the specs:

Its a 12,000 Watts Out charger that i got (2 of those 6000W rack beauties) and their specs are as follows (specs are for each module because there are 3 separate modules of 2000W in each of those 6000W rack) :

Rack: 6000W like in the link above / Module 2000W each (x3)

Module Specs (at 70% efficiency):
208-240V AC IN 48-56V DC OUT
11.6A IN 2000W max (so current varies 41.667-35.71A)

So basically (let me be careful not to screw up my math again )...

if i connect a rack (all 3 of the modules) in *series (3S)*, i have: 48-56V x 3 = *144-168V *(at 35.71-41.667A)

and then if i connect the two racks together in *parallel (2P)*, i'll have:
= (144-168V) at *71.42A-83.334*

Do any of guys forsee any problem with this approach (calculations especially dimitri, major, neanderthal, anyone?)

Best of all, if this worked, the racks are like those server station modules they use in network rooms so i can grab one of those mini-lightweight server cabinets and have it all nicely wired up and hey it would be under 80lbs for those racks and say another 20lbs for the server rack so under 100lbs for the charger ... hehehe... 

now i'm getting greedy and may mount onboard the EV a rack and keep one at home, the onboard one for opportunistic charging at 6kW and the one at home (coupled with the onboard one when charging from home at total of 12kW for quick charging)... 



major said:


> Hi xp_,
> You can't have in both ways at once. Either 144V, 28A for 3 in series or 48V, 84A for 3 in parallel.
> Good idea using telecon equipment. I've done some of it myself. Is why I like 48V systems, or multiples of 48.
> major


Major, jump in above if i messed up again up there 



dimitri said:


> Please comment on my ideas here, hope I didn't make any major mistakes


 Hope i didn't blabber a lot...

You guys, give me some feedback and let me know if this will work? Would be real sweet, wouldn't it: a 12kW charger ([email protected]~83A). I could probably get your 23kW bank Dimitri charged in just about 2 hours at C/2.
SWEEEEET.

Cheers all!!!


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## jwriter (Apr 26, 2009)

Just thinking out loud. If you need to adjust charging voltage, how about a low voltage, high current transformer working in buck or boost mode? If you are running off the 110 Volt line you would need one output winding; for the 220 Volt line in FW rectifier mode, you would need two output windings.

The advantage of this is that you would have a simple sort of voltage control without passing the entire 15 KW or so through a single transformer. What I visualize is a 220 V primary and a pair of 10 V secondaries at 80-100 Amps. You use contactors to configure three arrangements: 1) buck mode, 2) direct mode with no adjusting transformer, and 3) boost mode. 

Then, you have a simple circuit that senses your battery voltage and cycles through the appropriate modes as the batteries charge. Again, this is just brainstorming, but then you are not dependent on one line voltage and you can maintain a more or less regular charging current.

Since you are transferring only about 1-2 KVA, you can use either a 110 or 220 Volt primary, without worrying about imbalancing the line. Hope this helps.


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## dimitri (May 16, 2008)

Major, thanks a lot for the link, I bought it, seems like a nice tool at fraction of the Fluke's cost. Should have it in my hands in a few days.

xp_lynx, thanks for your support. The only issue I have with these telecom rectifiers is that you step down too much in volts, so you have to use multiple units to step back up again, seems like a waste. Also, those Ebay deals are one time thing, not repeatable and still come out to pretty high price if you buy multiple units and have to ship them. I guess its an option if you can get them cheap and local. My goal is most simple and least expensive, dumbest charger possible. Its meant for occasional quick battery boost between the trips during the day, not a replacement of the smart charger, which is still in the car and used on regular basis overnight.

Its also meant as a learning experiment and an excuse to buy nice clamp meter ( thanks to major  ).

Jwriter, what you said makes sense, but in my specific example mains voltage is just right for my pack, so I don't need a boost.

UPDATE:

I got 2 bridges today from Ebay and the RMS meter is ordered, so I guess I am doing this thing, there is no turning back now 

Those bridges are pretty impressive, the Ebay picture doesn't do them justice. Again, I will use one bridge as a single diode, 2 bridges will form full wave rectifier as shown in link Tesseract posted above.

Tomorrow I will buy 1 AWG soft cable from local welder shop and order SB175 connectors. Hopefully in a few days I will put it all together and test it. I will post pics and maybe even a video if I survive the experiment


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## azdeltawye (Dec 30, 2008)

dimitri said:


> ...
> UPDATE:
> 
> I got 2 bridges today from Ebay and the RMS meter is ordered, so I guess I am doing this thing, there is no turning back now
> ...


Just remember that if things start going south and you end up killing power to your section of the neighborhood make sure to remove all evidence of your science project before the utility troubleman comes by to investigate the outage.


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## dimitri (May 16, 2008)

Well, I got all the parts and put it together last night. Initial test with heating element acting as current limiter produced very low charging current, less than 20 Amps I get from my Zivan, so that wasn't very exciting. Despite all warnings from Tesseract I decided to try direct circuit without any current limiting  , I knew that breaker would trip if current got too high, so I wasn't worried much. Unfortunately largest breaker I could find in local hardware store that fits my panel was 60 amps, so that was my limiting factor. My goal is 80-100 amps, but I had to use what was available, so here we go.

I wired SB175 connector into the car such that circuit goes thru my main contactor, this was done on purpose, so I have to use ignition key to start this fast charging process and have ability to interrupt "high" current without using circuit breaker on the panel every time, to prolong its life.

I used my new toy, DC clamp meter to see how much current flows into the battery. 

Drum roll.........switch the key on.......no bang...no fire....no explosion...
meter is reading 98 Amps, woohoo 

After about 30 seconds my 60 amp breaker trips, which was expected, so all is good for now. Also, bridges rated for 80 Amps got pretty warm, but I didn't have any additional heat sinks on them, so that is expected as well.









Next steps, figure out a simple and cheap way to limit current at 70-80 amps, maybe a coil of wire submerged in water... get 100amp breaker... put bridges on large heat sink.... that should do it. My goal is to sustain 70-80 amps for an hour, if I can do that, I am all set.


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## neanderthal (Jul 24, 2008)

Wow That is sweet. I am surprised it came together so quickly, that's awesome. 80 plus amps of charge current and you didn't spend $5000!


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## SimonRafferty (Apr 13, 2009)

Dimitri - That's very naughty!

I got thoroughly flamed for suggesting this on a more conservative forum! Well done for having a go!

Si


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## dimitri (May 16, 2008)

SimonRafferty said:


> Dimitri - That's very naughty!
> 
> I got thoroughly flamed for suggesting this on a more conservative forum! Well done for having a go!
> 
> Si


Si, thanks  , I really like your project for intelligent charger, I'm following with interest. I know that my toying with high power circuits is not conventional and many people would consider it dangerous, but I keep stating limitations and risks of this approach, so hopefully no one will attempt it without undrstanding risks involved. Afterall, this is what DIY community is all about, trials and errors 

I could care less about being flamed, if you don't like it, don't read it


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## adamj12b (May 4, 2009)

dimitri said:


> I could care less about being flamed, if you don't like it, don't read it


LOL. Thats a great attitude. 

Did you happen to measure the rectified voltage you were using to charge the batteries? 

I know I saw it before, but forgot, what do you have for batteries? 

how big was the heating element? 

-Adam


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## dimitri (May 16, 2008)

adamj12b said:


> LOL. Thats a great attitude.
> 
> Did you happen to measure the rectified voltage you were using to charge the batteries?
> 
> ...


I have 40 cells pack of TS 160AH LFP cells.

Heating element was 2kW , it was the only one they had at local Lowes. Clearly it's resistance is way too high for my purposes. In fact any reasonable size/cost heating element would be too much resistance since I only need a fraction of one Ohm to reduce my current from 100 amps to 80 amps. I'm going to drop this idea for now and try to sustain 100 amps if I can keep those rectifiers cool enough. Since I use 6 diode bridge as a single diode, its 80 amp rating should now be 240 amp ( 3 parallel strings of 2 diodes ) , so I just need to keep them from melting .

As for voltage, it depends on where you measure it and how you measure it ( RMS or peak ). I didn't have much time to measure voltages since my breaker was tripping. At the battery, voltage is 135V.

I just ordered 100 amp breaker that would fit into my panel, I'm going to try and sustain 100 Amps current.

Will have more updates once my breaker arrives....


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## jackbauer (Jan 12, 2008)

I built a plasma cutter a few years back from an electric cooker. Just turn on more rings for extra power. Just don't hit the oven!


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## Gavin1977 (Sep 2, 2008)

dimitri said:


> Since I use 6 diode bridge as a single diode, its 80 amp rating should now be 240 amp ( 3 parallel strings of 2 diodes ) , so I just need to keep them from melting .


You may have a slight issue here. As a general rule, diodes do not share current very well when in parallel. The diode which has the smallest forward drop will take most of the current, which will cause it to heat up quicker, which will cause its forward voltage to drop more and take even more current.

If you can, its best to use a single diode rated for the current you need


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## Tesseract (Sep 27, 2008)

Gavin1977 said:


> You may have a slight issue here. As a general rule, diodes do not share current very well when in parallel. The diode which has the smallest forward drop will take most of the current, which will cause it to heat up quicker, which will cause its forward voltage to drop more and take even more current.
> 
> If you can, its best to use a single diode rated for the current you need


Theoretically speaking, you are totally correct in that you can't parallel bipolars, rectifiers or any other semiconductor where minority carriers are used because the diode equation rears its ugly head (essentially, the -2mV/C change in forward voltage). Practically speaking, though, if you thermally couple each diode together well (ie - the dice are attached to the same baseplate) then there won't any problems with sharing current. The hottest diode dumps more heat into the baseplate which soon raises the temp of its neighbors and current is shared more or less equally soon after.

This also relies on the typical happy occurrence that multiples of the same diode (transistor, whatever) will have similar Vf/Vce vs. current, temperature, etc... distributions.

All that said, this is why there is a practical limit to how many devices you can connect in parallel on the same heatsink. Personally, I think that limit is 8. Beyond that it gets too difficult not only to ensure good current sharing, but also to synchronize turn on and turn off of the devices (remember, diodes switch too, you just don't have any say as to when they do so  ).

Smart to point this out, anyway. Has anyone considered how that valuable and expensive lithium pack might respond to being subjected to AC current when/if a rectifier fails in the usual mode of a short circuit?


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## dimitri (May 16, 2008)

Thanks guys, I realize those practical limitations of paralleling components, I would never actually plan to get even close to max currents and max temps. Since I don't plan to allow more than 100 amps thru this circuit, I should be well in the safe zone as fas as current goes. I will also be watching temperature of those diodes and not let them get too hot. 

I can't get datasheets on these bridges, but I guess that I should be safe if I can keep them under 200 F , right? 

I will have them mounted on aluminum plate and have a fan blowing at them. If that doesn't keep them cool enough, then I will consider either different diodes or larger cooling, or reduce the current.


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## TheAtomicAss (Feb 19, 2009)

dimitri said:


> I'm going to drop this idea for now and try to sustain 100 amps if I can keep those rectifiers cool enough. Since I use 6 diode bridge as a single diode, its 80 amp rating should now be 240 amp ( 3 parallel strings of 2 diodes ) , so I just need to keep them from melting .


Diodes, even at the high power ratings you're using, are awfully cheap, relative to the charger you are emulating. Why not add more until they barely warm their thermal block? (I'm assuming you did mount them to some type of thermal block, because if you didn't their rating is less than half)


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## dimitri (May 16, 2008)

TheAtomicAss said:


> Diodes, even at the high power ratings you're using, are awfully cheap, relative to the charger you are emulating. Why not add more until they barely warm their thermal block? (I'm assuming you did mount them to some type of thermal block, because if you didn't their rating is less than half)


Excellent point! Thanks! I just bought 2 more bridges to add to those 2 I have to spread thermal losses. These bridges come integrated in finned aluminum casing, and I mount them on aluminum plates and will have fan blowing at them.

Now here is the question, should I put additional bridges in parallel or in series? Considering that I don't have current limiting resistance in the circuit, diodes become current limiters themselves, right? If I put 2 in parallel, I will increase the current even further, while doubling thermal loss, which is not desired for my needs. If I put them in series, it will reduce the current and spread thermal loss across 2 modules, which is better for me. Did I get it right?


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## Gavin1977 (Sep 2, 2008)

No, the diodes get hot because they have a volt drop across them when conducting (0.6 - 0.7 volts for the currents i play with. Don't know what it is at 100's of amps, >1 volt i guess) Anyway, putting two diodes in series will give you two volt drops and therefore twice the heat. It will reduce your current draw but not significantly.

Putting them in parallel, will spread the thermal load between them (As Tesseract correctly pointed out, they will sort of current share if you keep them at similar temps, ie bond them all to the same chunk of ally.) Paralleling them will increase your current draw, but again, not significantly.

I think ive got that right, though my expertise is in low power electronics, so Tesseract may well correct me somewhere.


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## tj4fa (May 25, 2008)

Tesseract said:


> Smart to point this out, anyway. Has anyone considered how that valuable and expensive lithium pack might respond to being subjected to AC current when/if a rectifier fails in the usual mode of a short circuit?


Could something be installed that if a diode failed it could shut off the output or AC input to the rectifier?


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## SimonRafferty (Apr 13, 2009)

tj4fa said:


> Could something be installed that if a diode failed it could shut off the output or AC input to the rectifier?


The current out of the rectifier should only flow one way. If you connected a relay in series with a diode biased such that the relay does not energise unless the current reverses - you would have something that detects the fault.

I would probably have the relay short out the mains input when energised so it blows the mains fuse.

Si


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## Tesseract (Sep 27, 2008)

SimonRafferty said:


> ...
> I would probably have the relay short out the mains input when energised so it blows the mains fuse.
> 
> Si


This is not "legal" in the US, even if the fuse is inside the equipment. Why not simply interrupt the power, anyway?


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## SimonRafferty (Apr 13, 2009)

Tesseract said:


> This is not "legal" in the US, even if the fuse is inside the equipment. Why not simply interrupt the power, anyway?


It's probably illegal here too these days - but surprisingly common on older kit. Admittedly, it's generally on the low voltage side of a transformer.

So long as the fuse works (and I know that's the question) - it is quite effective.

One of the advantages of using capacitors for isolation. The capacitors only need to conduct the required current at 40Khz or so. At 50 or 60Hz - barely any current will get through (1/000th as much). Hopefully, that will not be enough to cook the batteries. Likewise, if the IGBT fails closed circuit - no DC will get through.

Si


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## adamj12b (May 4, 2009)

Si,

What about doing like you said, but use a mechanically held contactor on the line side?? Instead of just shorting the line when it breaks, it would just turn off and stay off. 

-Adam


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## dimitri (May 16, 2008)

Got my 100 amp breaker and 2 more bridges today.

Gavin was absolutely right, series connected bridges got twice as hot, but current was still 100 amps. So I changed them to parallel config, and now they are much cooler, and current is still at 100 amps 

I ran the charge for 15 minutes, checking current and temperature of the rectifiers. Current pretty much hovers at 98-100 amps, pack voltage was 135V while charging and 131V while resting, this was about 60% DoD after 40 miles of driving today.

Heat sinks got quite warm, about 120F after 15 minutes of charging, but I don't know if this is a peak or if its going to keep rising, I need to do longer tests, just didn't have time today.

Here is what the setup looks like, hanging on the wires so far, I will clean it up and put in a box later on.

So basically I charged for 15 minutes at 100 amps, which is equivalent of 75 minutes of charging with Zivan NG3.


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## dimitri (May 16, 2008)

Guys, I think this thing turned out pretty damn good 

This morning I started with full pack, drove 16 miles, came home with battery at 134V, plugged in my "supercharger" ( TM ) 

For 23 minutes I watched current hover from 101 amps to 93 amps, while voltage slowly climbed from 135V to 139V. Diode temp peaked at 132F and did not rise any further, woohoo!

Then, right in front of my eyes voltage climbed from 139V to 148V WITHIN 30 SECONDS !!!! at which point I turned off the contactor. During this 30 seconds current dropped from 90 amps to 20 amps.

This is absolutely perfect and exactly what I expected, 100 amp fast charger for less than $200 ( almost half of which was 1 AWG wire, damn copper is expensive and I should have used 2 AWG anyway, 1 AWG is an overkill ).

Next steps, put the contraption in a box on the wall, clean up wiring, then work on automatic cutoff circuit, which I already have designed in my head  , very simple. I will use existing BMS HVC trigger to shut off main contactor.... so when first cell gets to 3.8V charger will stop.

Still, I never plan to run "supercharger" unattended, just to be safe....


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## Zemmo (Sep 13, 2007)

Wow, this is great! Congrats on your success! Is there a chance you could take more pictures and post them? Some without the fan to see your work. If it would be possible, also draw on one of the pictures of what each of the lines are and where they go. Again, great work!

Most people stop their charge at 3.7 or 3.8 per cell on LFP. Do you think for your little HVC circuit to shut it off a little earlier than 3.8 in case charging up the pack at that speed causes a little more out of balance between the cells? If you have gotten it up to that voltage you are almost at 100% charged. I am just wondering if it would be a little safer if it was shut off a little earlier than 3.8 volts per cell.


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## dimitri (May 16, 2008)

Zemmo said:


> Most people stop their charge at 3.7 or 3.8 per cell on LFP. Do you think for your little HVC circuit to shut it off a little earlier than 3.8 in case charging up the pack at that speed causes a little more out of balance between the cells? If you have gotten it up to that voltage you are almost at 100% charged. I am just wondering if it would be a little safer if it was shut off a little earlier than 3.8 volts per cell.


Most people don't stop charging when FIRST cell gets to 3.7V-3.8V, they start shunting/balancing then and stop charging when ALL cells reach 3.7V-3.8V, see the difference?

My "supercharger" is not intended to balance the pack, so it would stop right when balancing would normally begin.

It will not cause any noticeable imbalance since all cells get exactly same amount of charge. Its still expected that you will use regular charger overnight to balance the pack. This project goal is to quickly boost the pack during the day between multiple trips. I didn't have to let it run all the way to full charge, I only done it to see how it will happen.

I don't want to spend too much time documenting this, the link from Tesseract to full wave rectifier page should explain everything. If you are not comfortable with it, don't mess with it, it can be pretty dangerous.

Remember, this only works because my pack voltage just happens to be in the right area compared to mains voltage. Lower pack voltage will produce way too much current to be safe and higher pack voltage will produce too little current to be effective, so there is a sweet spot which makes it cheap and effective at the same time.


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## dimitri (May 16, 2008)

This pic explains the concept. Transformer on the left is your house transformer, feeding 240V ( A and B ) and neutral ( C ) into your main panel. This forms 2 legs ( A-C and B-C ) of 120V each, which is evenly distributed across the house for 120V service, while 240V service uses A-B.

Since I needed 120V RMS ( 170V peaks ) and wanted to keep my transformer balanced ( thanks Tesseract ) , I used 2 diodes as shown to rectify each leg evenly.

I used 2 3-phase bridge rectifiers in parallel ( total of 4 bridges ) as a single diode. This allows to spread 100 amps across total of 24 diodes ( 6 diodes in each 3ph bridge ).

Neutral line becomes negative and diode's bands (cathodes) become positive. By connecting directly to car's controller terminals I allow the use of main contactor to turn the charge on/off since contactor is between battery and controller in the car wiring.

Hope this makes sense...


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## dimitri (May 16, 2008)

*DISCLAIMER !!!*

This project requires you to open your main panel and install 100 amp breaker and 2 AWG or 1 AWG wires into the panel. It requires entire project to be physically close to the main panel to avoid heat losses and inductance noise and minimize wiring cost.

PLEASE DO NOT ATTEMPT IT unless you understand what the hell you are doing and DO NOT LEAVE IT UNATTENDED while running.

I releave myself of all and any responsibility for the damage this information may cause to you or your posessions.


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## peggus (Feb 18, 2008)

Don't forget to keep a fire extinguisher nearby.


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## tj4fa (May 25, 2008)

Pretty Cool!!

I do have a "what if" question though.



dimitri said:


> Most people don't stop charging when FIRST cell gets to 3.7V-3.8V, they start shunting/balancing then and stop charging when ALL cells reach 3.7V-3.8V, see the difference?
> 
> My "supercharger" is not intended to balance the pack, so it would stop right when balancing would normally begin.
> 
> It will not cause any noticeable imbalance since all cells get exactly same amount of charge. Its still expected that you will use regular charger overnight to balance the pack. This project goal is to quickly boost the pack during the day between multiple trips. I didn't have to let it run all the way to full charge, I only done it to see how it will happen.


Going with the full pack reaching the 3.7~3.8V threshold concept over the first cell to reach 3.7~3.8V, what if there is a bad cell (or cells) in the pack and because of crappy internal resistance they would never come up to full charge.

Would those weak/bad cells overheat or blow up jamming all this power in at this fast rate?

Is that a reason you're going with the "first cell" to reach full voltage shut-off concept?


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## tj4fa (May 25, 2008)

A couple safety things:

-When you put this charger inside a box, I would recommend you ground the box chassis back to your electrical panel ground bar with a green or bare copper grounding conductor.

-I don't know if you have a neutral grounded conductor to the device, but if you do, it should be grounded back to your neutral bar inside your electrical panel.

Without ground wires back to the service panel ground bars, if only hot wires off the breaker are going to the charger, you could become the path of least resistance to ground and if you have inadvertant contact with them, you will likely die.

-I would recommend a disconnect switch to cut power off to this super-charger between the electrical panel and the charger so that you can shut the power off to it when not in (supervised) use. Circuit breakers are not meant to to be used as switches and will weaken in constant use. 

You would want this disconnect switch turned off before installing/pulling the plug to your EV as there would likely be an arc produced while mains power is applied).


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## dimitri (May 16, 2008)

tj4fa said:


> Going with the full pack reaching the 3.7~3.8V threshold concept over the first cell to reach 3.7~3.8V, what if there is a bad cell (or cells) in the pack and because of crappy internal resistance they would never come up to full charge.
> 
> Would those weak/bad cells overheat or blow up jamming all this power in at this fast rate?
> 
> Is that a reason you're going with the "first cell" to reach full voltage shut-off concept?


Usually bad cell would reach full voltage sooner since it can't hold as much charge as a good cell, so bad cell would be the first one to trigger shutoff.

Again, this is by definition a dumb charger, so let's not come up with too many "what if's" 

The main reason to shut off on the first HVC trigger is to avoid shunting phase, since this charger immediately overruns any possible shunting capacity with its massive current. 

I bet it will only take about 10 seconds to go from 3.8V to 4.5V at this current levels, so immediate shutoff is required.


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## dimitri (May 16, 2008)

tj4fa said:


> A couple safety things:
> 
> -When you put this charger inside a box, I would recommend you ground the box chassis back to your electrical panel ground bar with a green or bare copper grounding conductor.
> 
> ...


You didn't look at schematic above, did you? Negative wire IS neutral / ground....it's already connected to massive ground terminal inside the panel.

The box will be plastic.....

Good point about separate disconnect switch, I will think about it...but only as means to prolong the breaker's life, however, there is no arc since car's main contactor will always be the one closing the circuit and its designed for much much higher abuse.


Thanks


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## tj4fa (May 25, 2008)

dimitri said:


> You didn't look at schematic above, did you? Negative wire IS neutral / ground....it's already connected to massive ground terminal inside the panel.


Ok missed that from the drawing. 



dimitri said:


> The box will be plastic.....
> 
> Good point about separate disconnect switch, I will think about it...but only as means to prolong the breaker's life, however, there is no arc since car's main contactor will always be the one closing the circuit and its designed for much much higher abuse.


If your circuit breaker is annotated as "SWD" (SWitch-Duty) it is made so you can use it to turn-on/off the circuit.

The location of the arc I was referring to is when pluggin/un-plugging the power cable from the charger into the car's receptacle when the charger is still putting out power while there is a load on it. 

From your response above, it sounds like you have already thought that through using your EV contactor energized only after you plug-in and de-energized before you un-plug your power cable from the charger by using your ignition key-switch circuit to close/open the circuit from the load.

So in this case since there should be no load appled that would be drawing power that would produce an arc-flash immediately while plugging/un-plugging.

But for others who may be following this thread, shutting off the power to the charger before plugging/un-plugging the power cord to the vehicle should be considered as a prudent and fool-proof safeguard to avoid damage and injury in regards to an accidental (~100A) arc-flash.

Hopefully, this little tidbit of information will help "smarten up" the "dumb- side" of the charger.


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## tj4fa (May 25, 2008)

Oh forgot...

The output wire, plugs, receptacles, etc, from the charger to the EV connection points should be sized appropriately to handle the DC current and voltage and be as short as practicable.


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## samborambo (Aug 27, 2008)

Dimitri, what was the voltage at the switchboard prior to testing?

I don't know the electricity regulations in the US but here in NZ, for example, voltage is allowed to be -5% to +10% of the nominal 230V. That's fine as long as the network company is doing their job properly and ensuring the voltage is within these limits. In reality, voltage can vary wildly outside those limits, especially if you're a reasonable distance from the subtation that your neighbourhood is fed from.

Calculate what the current will be when your supply voltage gets to 110%. I think you'll find this will cause some serious damage to your pack if you don't have some form of over voltage protection.


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## dimitri (May 16, 2008)

Sam,

thanks for your comment. Not only I checked the voltage, I also checked the sine wave with the scope, it was exactly at the spec, 168V peaks, 120V RMS.

I don't think I can damage the pack as long as rectifiers hold up, my cells can safely absorb 160 amps ( 1C rate ) and I have not seen more than 100 amps max, usually around 90 amps.

Yesterday , after I put the charger in the box and cleaned up wiring, etc, I used it for almost an hour, which was like 70% of charge in one hour, woohoo 

This allowed me to drive my EV for 90 miles in one day


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## ngrimm (Oct 19, 2007)

This was a great topic so I thought I would open it up again. I was thinking about something like this dumb charger to bulk charge my lead acid batteries. I take full responsibility for any risks incurred. I am getting ready to convert a very light 71 Toyota pickup and I plan to use only 10-12 12 volt 85 ah batteries. On my Ninja I have never had a charger that would charge the batteries individually more than 15 amps at a time so I don't know what the maximum charge rate would be for the LA batteries but I assume it is less than the 100 amps the op uses. Can someone straighten me on this?


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## dimitri (May 16, 2008)

ngrimm said:


> This was a great topic so I thought I would open it up again. I was thinking about something like this dumb charger to bulk charge my lead acid batteries. I take full responsibility for any risks incurred. I am getting ready to convert a very light 71 Toyota pickup and I plan to use only 10-12 12 volt 85 ah batteries. On my Ninja I have never had a charger that would charge the batteries individually more than 15 amps at a time so I don't know what the maximum charge rate would be for the LA batteries but I assume it is less than the 100 amps the op uses. Can someone straighten me on this?


I'm afraid LA batteries can't take such large charge currents, it will boil the hell out of them. I'm not an expert on LA charging, but I think its limited to 1/10C, I might be wrong though, so check your battery specs for max charging rate.


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## ngrimm (Oct 19, 2007)

Hey thanks for the reply. I found this info but not necessarily for my exact batteries: Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps". 

So 85 ah would call for 8.5 amps at C/10 or 10.6 amps at C/8. That seems kind of low but what do I know. Anyway if I needed to maintain 14 volts and for 12 batteries that would be 168 volts at 10 amps. Do you think I would be able to do a half wave setup for that? Thank you. Norm


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## SimonRafferty (Apr 13, 2009)

You really need to find the specific data for the batteries you are going to use. Odyssey PC range of batteries recommend 1/4C bulk charge - and seem to store more charge the closer to that you give them.

My batteries are only 55Ah - so 13.75A is ideal. The down side is I have a 220v string of them and delivering 14A at 220v is more than I can get out of a single phase 13A mains socket.

It's also difficult to find a charger which will spit out that kind of power without it costing thousands. That's why I went down the route of building my own.

I've settled on 10A @ 220v = 2.2kw which seems to give good results all round.

I've tested my (and the forum's) charger design up to 50A - at which it gets quite hot even with forced air cooling - but that is 11kw so not surprising.

Si


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