# 400W constant current battery test setup



## frodus (Apr 12, 2008)

Some of you may know what I've been brewing in my evil mad scientist laboratory because you read my blog. For those that don't, here's a quick rundown:

I wanted to build a good test setup for testing various small/medium format batteries. Lots of battery manufactures don't give you many discharge curves if any. I want to know how my batteries are going to perform before I install them, and have the option to match capacity and IR within my pack.

So to do this, I need a constant current load. Just putting a resistor on the output is ok if you're trying to see if the cell can "put out". If you want a truly accurate curve, you need an electronic load that keeps current constant as voltage decreases during discharge. So to do this, I bought a load from Camlight Systems called a CC400. To drive the load, you can use a CBA-II or III or use a device that will output a servo signal. I opted for a servo signal and bought a servo driver that I can adjust very easily. I previously bought a 10-channel analog data analyzer (DI-148U from DataQ) when I discharged my lead acid batteries last year. The logger will be used to log the voltage (and potentially temperature) during the discharge test.






The CC400 has the following specs:

Current: 1A-150A for 2V-60V cells/packs, dropping to 100A max. at 0.9V.
Voltage: 0.5V-60V
Power: 400W continuous at 30C ambient, 500W for 15 seconds. Allows for 100A discharging of a Li cell.
Basic Accuracy: From 1A-20A, +/-35mA, from 21A-150A, +/-1%, typically better than +/-0.6%.
So I’ve got the CC400, a servo driver to adjust the current level and a Data Logger to measure the voltage. Here's a shot of the setup:



The data logger is completely seperate from the discharging setup. I may shorten the clip leads, but the logger gives me the ability to calibrate. I haven't had to, as its good to the thousandths and matches my multimeter. The cables from the discharger to the battery are 4gauge to minimize losses, afterall, I'll be doing up to 150A through them.

I got the final pieces last week, put it together last night, and plan on doing some testing over the next week to get a hang of how the CC400 and servo driver work. The software for the logger allow me full control over the graph, so I should be able to come up with some great discharge curves. I don't know if I can overlay them though, I'll look into that.

For now, I just want to get this set up so I can do some 5-10C discharges on each cell for 30 seconds to verify that they will meet spec. I don't want any weak cells. Its going to take a while, but I think it'l be worth the peace of mind.
I'll update as I do more testing.


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## rillip3 (Jun 19, 2009)

A very neat setup, very good info to have too. It'll be nice to be able to take a battery and run it until it breaks, and know when that breaking point is exactly instead of having to guess. Ought to help improve range/acceleration/life, being able to know where to limit the batteries at. Good luck with your project!


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## frodus (Apr 12, 2008)

So I FINALLY set up the discharger and ran some initial tests. I'm still waiting on a converter for my k-type thermocouple (converts to a linear 0-5V output that can be used with the logger). That way I can log volts and temperatures (current is held constant, no need to measure it).

I hooked up the servo driver to the throttle input of the CC400 and calibrated. I hooked up a battery and turned everything on and set my amps to 10A max and slowly dialed up the current to 1C. I watched the voltage go from 3.3V drop to 3.2V 'ish and continue discharging, but it held that voltage fairly constant. I then dialed it up and down to watch voltage rise/fall. I have a thermocouple on the battery that I monitored, it never heated up at 10A (or 20A and BARELY at 5C). 

I then dialed up to 20A, and the voltage dropped to around 3.05V and held there for quite a while acutally, and never heated up. I did some short bursts of 5C and while it did drop the voltage more, the voltage held fairly well. For what I'm doing with them, I think I might only ever do 2C continuous out of these, the rest will be peaks of 5-8C (550A controller COULD potentially peak at 550A input current, but not likely).

So here's a shot of the setup with the headway in the back:











To do:
- Get the data logger hooked up to the computer
- get the k-type thermocouple hooked up
- secure everything to that board and install some insulation for the battery under test
- install some disconnects for the battery (anderson) so I can quickly disconnect the battery if there is an emergency
- test some more headways. I want to test all of my cells under 5C load and record serial numbers
- test some other brands of batteries (kokam, a123, K2)


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## rwaudio (May 22, 2008)

I really like the setup. When are you going to have some numbers?? Then we can atleast compare them to what headway is giving us and see if we can trust their curves or not. What batch are your cells? I have some "JC29" cells here, just curious what you will be testing.





frodus said:


> So I FINALLY set up the discharger and ran some initial tests. I'm still waiting on a converter for my k-type thermocouple (converts to a linear 0-5V output that can be used with the logger). That way I can log volts and temperatures (current is held constant, no need to measure it).
> 
> I hooked up the servo driver to the throttle input of the CC400 and calibrated. I hooked up a battery and turned everything on and set my amps to 10A max and slowly dialed up the current to 1C. I watched the voltage go from 3.3V drop to 3.2V 'ish and continue discharging, but it held that voltage fairly constant. I then dialed it up and down to watch voltage rise/fall. I have a thermocouple on the battery that I monitored, it never heated up at 10A (or 20A and BARELY at 5C).
> 
> ...


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