# High current battery testing. How to...?



## CroDriver (Jan 8, 2009)

I'm building a high performance EV and I need every Amp I can squeeze out of my battery pack. There are some TS tests but no one tested them above 3C. I have a few brand new ThunderSky 100Ah cells that I don't need. I would make a 5C, 10C, 15C and 20C test. What equipment do I need to make those tests?

If it's impossible for me to make such a test I will donate a cell or two to someone who will guarantee that he'll make those tests and share the results.


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## DavidDymaxion (Dec 1, 2008)

I don't know that you can get this where you live, but I have been happy with this battery tester, so far:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91129

One would do the 5C test, and you could hook 2 in parallel and get a 10C test.

I thought TS weren't spec'd for beyond 10C?

Also, theoretically when you push a battery to 1/2 voltage, it's at max power. There's no sense trying to draw it down as far as possible.

Another trick I have heard, but not tried, is a coat hanger in a bucket of water.

I have a clamp on ammeter that goes to 600 Amps, that has been handy.



CroDriver said:


> I'm building a high performance EV and I need every Amp I can squeeze out of my battery pack. There are some TS tests but no one tested them above 3C. I have a few brand new ThunderSky 100Ah cells that I don't need. I would make a 5C, 10C, 15C and 20C test. What equipment do I need to make those tests?
> 
> If it's impossible for me to make such a test I will donate a cell or two to someone who will guarantee that he'll make those tests and share the results.


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## major (Apr 4, 2008)

CroDriver said:


> I'm building a high performance EV and I need every Amp I can squeeze out of my battery pack. There are some TS tests but no one tested them above 3C. I have a few brand new ThunderSky 100Ah cells that I don't need. I would make a 5C, 10C, 15C and 20C test. What equipment do I need to make those tests?
> 
> If it's impossible for me to make such a test I will donate a cell or two to someone who will guarantee that he'll make those tests and share the results.


Hi Cro,

Here is something like what I use. See photo. A bank of locomotive braking resistors. Got an extra bank of these all mounted up with fan. Can give you a good price. But shipping would be a bitch 

Regards,

major


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## major (Apr 4, 2008)

DavidDymaxion said:


> I don't know that you can get this where you live, but I have been happy with this battery tester, so far:
> 
> http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91129


Hi David,

Yeah those carbon pile load test resistors are good for high current checks on car starting batteries. And would work for a quick test for Cro. But they won't dissipate the power for an "energy" test, if that is what he is after. Those testers can give you a decent "power" test, up to its limit.

Regards,

major


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## frodus (Apr 12, 2008)

Both of those loads don't keep current constant. As voltage drops, so do amps. It wouldn't give a consistant C-rating.

It'd work for a quick test, but it wouldn't be a very "accurate" test.


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## DavidDymaxion (Dec 1, 2008)

I should have clarified a bit. Mine is the one in the link I posted. I put it on its back and blow a fan at the base. I have pulled 400 Amps for 40 seconds a bunch of times (you are supposed to do <= 500 amps only for 15 seconds or less). It was cheap enough I was willing to take a chance on pushing it past spec. The cables get warm, and I would definitely give it alot of cooling time between tests. It's very handy it comes with built-in volt and amp meters. They are adjustable, after adjustment agree well with my expensive volt meter.

So agreed it's not the best tool for an extended high power energy test, but for drag racing / autocross / drifting time scales it's good (I believe Cro is a drift racer). I'm planning to buy a 2nd one so I can push up to about 800 Amps for 40 seconds (which is beyond an Optima's spec).

Caveat: You would be going beyond spec! You might ruin it!


major said:


> Hi David,
> 
> Yeah those carbon pile load test resistors are good for high current checks on car starting batteries. And would work for a quick test for Cro. But they won't dissipate the power for an "energy" test, if that is what he is after. Those testers can give you a decent "power" test, up to its limit.
> 
> ...


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## DavidDymaxion (Dec 1, 2008)

For a quick, 40 second racing kind of test I have been doing, I keep twisting the load knob to keep the current constant (you could also keep voltage constant, or if you are quick with the math or have a table, you could even keep the power constant ). So it is not automated, but for a quick once-in-a-while kind of test that's OK.


frodus said:


> Both of those loads don't keep current constant. As voltage drops, so do amps. It wouldn't give a consistant C-rating.
> 
> It'd work for a quick test, but it wouldn't be a very "accurate" test.


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## Sunking (Aug 10, 2009)

Well there are professional computer controlled load banks that do exactly what you want manufactured by companies like Alber, but it is very expensive and meets IEEE 455 standards.

However there is a POOR MAN's JAMES BOND method of simply using car headlights assembled in a combination of series and parallel configurations to get the voltage and load requirements you need. Or the same can be done with wire wound power resistors and a switch box.


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## CroDriver (Jan 8, 2009)

Thank you all for your replies.



DavidDymaxion said:


> I don't know that you can get this where you live, but I have been happy with this battery tester, so far:
> 
> http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91129


I've been searching a bit and found this:

http://www.americastoolwarehouse.com/automotive-tools/AOE-6036B-24-p-AOE02.html

And this:

http://www.absolutebattery.com/testers_bva2000.htm

The first one looks good. So if I connect two of them in series with the battery I could measure the double load?


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## major (Apr 4, 2008)

frodus said:


> Both of those loads don't keep current constant. As voltage drops, so do amps. It wouldn't give a consistant C-rating.
> 
> It'd work for a quick test, but it wouldn't be a very "accurate" test.


Yeah frodus,

You are correct. It is a constant load resistance load test. But unless you have a power converter controlled discharge test stand, this is pretty good. You can take the data and integrate it in a spread sheet and come out with an average current and amp-hour figure. See attached plot. 

I have used both these resistive loads and an ABC-150. The ABC-150 was real nice  Like 500V, 500A, charge/discharge, programmable. But $100,000  I got to borrow one. Aside from that, I use the resistors. Link to ABC-150 http://www.avinc.com/ev_test/dc/abc-150 

And I did make a converter for one of those resistor banks. For testing high voltage battery sets, like 200V. And up to 400 amps. I didn't think contactors would last at that current and voltage. Got that working pretty well with a couple of giant IGBTs. But never got a current control circuit implemented. Just manual adjustment.

Now Cro's talking about some very high current on some very low voltage cells. Single cell at 2000 amps and like what, 2 or 3 volts. In my book that is a length of double 4/0 cable. I've done up to 500 amps. And would give 1000 a go. What the H, I'll try 2000. I think I got a shunt for it. I know I have 1000 amp shunts.

Regards,

major


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## frodus (Apr 12, 2008)

> You are correct. It is a constant load resistance load test. But unless you have a power converter controlled discharge test stand, this is pretty good.


The funny thing is that most of us have "controllers".... just can't run them off 3.2V..... but some will run off 12V or higher. I did this curve off my Synkromotive controller and a little data logger:

Set current limit to 50A, go full throttle, measure voltage. Could just as easily been 400A




But yeah, much harder to do with 100Ah cells at a 10C rate


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## DavidDymaxion (Dec 1, 2008)

You'd want to connect them in parallel. You'd also have to carefully ramp up both current knobs to keep currents equal, so one doesn't take all the load. Are you sure those cells can deliver 1000+ Amps? You might want to rent or buy just one tester and see if another is justified. 



CroDriver said:


> Thank you all for your replies.
> 
> I've been searching a bit and found this:
> 
> ...


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## major (Apr 4, 2008)

CroDriver said:


> I've been searching a bit and found this:
> 
> http://www.americastoolwarehouse.com/automotive-tools/AOE-6036B-24-p-AOE02.html


Yeah, that looks like a nice battery tester. Again, for short burst tests. It just has #2 ga leads. And the 1000 amp load is likely for a 12 volt battery. On a 3 volt cell, figure 1/3 that. I guess you could test 3 or 4 cells in series.

Regards,

major


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## CroDriver (Jan 8, 2009)

DavidDymaxion said:


> You'd want to connect them in parallel. You'd also have to carefully ramp up both current knobs to keep currents equal, so one doesn't take all the load. Are you sure those cells can deliver 1000+ Amps? You might want to rent or buy just one tester and see if another is justified.


If I know that I would not make those tests... ThunderSky claims 3C continuous, 10C peak. But they don't say for how long they can take the 10C. In some new specs. sheets they even claim 20C! But again, no time limit...


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## major (Apr 4, 2008)

frodus said:


> The funny thing is that most of us have "controllers".... just can't run them off 3.2V..... but some will run off 12V or higher. I did this curve off my Synkromotive controller and a little data logger:
> 
> Set current limit to 50A, go full throttle, measure voltage.


Hey frodus,

What do you use for the load? Just drive your car around at 4 mph? 

major


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## frodus (Apr 12, 2008)

major said:


> Hey frodus,
> 
> What do you use for the load? Just drive your car around at 4 mph?
> 
> major


Field coil on my motor  It was a static test.... just disconnected the armature and ran the field coil to the controller.

It got a little warm, not bad though.


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## DavidDymaxion (Dec 1, 2008)

I have seen their specs say "20 C Impulse," so the question is how long is an impulse? Since some other battery makers say something like 5 or 10 seconds for a "pulse" it probably isn't very long.

I (and I'm sure many others) will be interested in your results.


CroDriver said:


> If I know that I would not make those tests... ThunderSky claims 3C continuous, 10C peak. But they don't say for how long they can take the 10C. In some new specs. sheets they even claim 20C! But again, no time limit...


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## major (Apr 4, 2008)

frodus said:


> Field coil on my motor  It was a static test.... just disconnected the armature and ran the field coil to the controller.
> 
> It got a little warm, not bad though.


Hi frodus,

Tricky 

But I don't understand something. Current limit is "motor" current, right? So how does this keep a constant current in the battery? And if you set the current limit to get 50 amps from the battery, and it was a 12 volt battery, then that would have been 100's of amps in the motor (or motor field). Seems like you risk a lot using the motor field for a load resistor.

Regards,

major


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## frodus (Apr 12, 2008)

major said:


> Hi frodus,
> 
> Tricky
> 
> ...


Current limit of the controller is set to 50A. Field coil of motor is hooked to output of controller. 12V battery at 50A is what, 600W? Set throttle to 100%. Motor current wasn't much different than battery current at 100% throttle.


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## CroDriver (Jan 8, 2009)

ThunderSky:



> Dear Mate,
> 
> Thanks for your E-mail.My answer to your questions are as follows,
> 
> ...


Not exactly what I expected... 

Looks like A123 are the only way to go for real performance


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## major (Apr 4, 2008)

frodus said:


> Current limit of the controller is set to 50A. Field coil of motor is hooked to output of controller. 12V battery at 50A is what, 600W? Set throttle to 100%. Motor current wasn't much different than battery current at 100% throttle.


Hi frodus,

I don't get it. Sorry. But the typical resistance of a series EV motor field would be on the order of 0.01 Ohm. The current limit of most controllers is the motor current. So, 50 amps times 0.01 Ohm is 0.5 volts across the field. This is the output from the controller.

Let's call the input to the controller 12 volts. Say the controller has a 1 volt drop. Then 11 volts must be reduced or modulated down to 0.5 volts. That would be like a 4 or 5 percent duty cycle. That would put the input current into the controller (battery current) at around 2 or 3 amps.

Now with resistance this low, cables and the like enter into the picture. And at such low duty cycle of modulation on the controller, the current may be discontinuous. All this make the above calculations inaccurate. But the point is that I don't think your method holds a constant current for the battery discharge. And for some other reasons, it would not be a constant power discharge either.

Maybe Tesseract sees this and can provide some insight.

Regards,

major


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## frodus (Apr 12, 2008)

Its been over a year since I did the test....I think you're right. The motor side had to have been higher. I didn't write down the details in my blog on the entire test, just the outcome, not setup/actual test. Appologies.

The battery current WAS kept constant though, I do know that for fact. It was measured with a clamp meter and the controller and regulated via the controller (custom code running on the Synkromotive controller). This isn't "any" controller. It had custom code in it to regulate the battery current. The voltage was measured via a Data-Q. Current was continous.

The cables did get warm, but they were large cables (size of my finger) to the motor.


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## major (Apr 4, 2008)

frodus said:


> (custom code running on the Synkromotive controller).


Ahhhh...O.K. Now we know 

But for those following this, beware trying this with your standard motor controller and motor field.


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## frodus (Apr 12, 2008)

oops, the devil is in the details 

I still think it's a little funny that all you really need is a load, and a controller running code to regulate battery current. Most of us have the equipment, but no ability to control the controller.


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