BIG cell capacity testing

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Grumplestiltskin

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I have about 10kWh (and growing) of "large" LiPo cells that I really want to classify via capacity testing.

Most cells are 12.5 to 15 Ah, rated at 5C to 10C although I would prefer to test at 1C, which is my planned load.

Has anyone ever done such athing? How did you do it and what setup did you use?


image_avlumj.jpg
 
I do have the icharger 208b and with an external load you can discharge with upto 20A.

I do have two 0,33R resistors in parallel and can discharge my 150Ah packs with 15A which is aceptable to me... you can also set cut-off voltage.

I am quite happy with its versatility...

Regards
Karl
 
Ive used my iCharger with an external load (resistors) but you can always use a shunt of sorts and a load that is constant. CellLog or other items can be used as a LVD or alarm.

Lots of ways beyond the typical 18650 testing meathods to consider but I think a hobby charger is pretty solid route, its just not that volume friendly.
 
I've been using my iCharger 4010 with its regenerative discharge feature where it puts the energy back into the source it's running from. I like that very much because you don't just waste the energy by turning it into heat. I hook it up to lead acid batteries and store the energy this way. You can then recharge the tested cell from the batteries again and you only waste a part of the energy through conversion losses. You are only limited to ~40A per channel (or ~70A in synchoronous mode) and ~60A on the input (which then becomes the output). So testing a 15Ah cell at 1C, 15A, is no problem. You just have to make sure the energy from the cell you are testing will fit into the source.

I've tested my selfmade 80Ah cells that way and it works great.
 
I haven't actually used regenerative discharge yet, but I did notice note in the manual that concerned me a little about accuracy...

"4? Regenerative current limit is not very accurate, which may be 20% difference, max."

If true, its a great feature for not wasting power and moving energy from one pack to another, but I might not be the most accurate method for capacity testing. Not sure how to all sums out in the end with not being able to meter the current limit accurately, but an external load using resistors might be the best option.
 
I don't know the answer which is why I asked/made mention... My concern with that was is the displayed current used to calculate the mAh out.

If its calculated using the displayed value, it could very well have uo to 20% worth of error in the mAh measurement.

If it is metering though a separate shunt then it would not be a problem... Is the displayed value the actual current, which may not always agree with the set limit?

When you read all of the notes, it almost sounds like its not using a synchronous buck/boost to push the power. More like opening a gate.

Again, I dont know the answer, but I think more testing of Regenerative discharging should be done to validate the accuracy of the measurement.

From Manual-
Note:
1? When in Regenerative discharging, chargers power supply needs to be rechargeable. For example,
Pb battery can be used for input power supply, but switch power adapter cannot.
2? The setting of regenerative discharges current and voltage limit should be suit for power supply. For
example, using 12V Pb battery as power supply, the regenerative current and voltage should not be more
than its max charging current and voltage, or it may cause danger.
3? Regenerative discharge max power is the same with chargers setting max charging power, not
discharging power. (Restricted by setting regenerative discharge current and voltage limit, and discharge
current limit.)
4? Regenerative current limit is not very accurate, which may be 20% difference, max.
5? If input power supply voltage is more than setting regenerative limit voltage, charger will not start
regenerative discharge and internal discharge instead.
 
It doesn't affect calculations or measurements. It's just the primary side current limit that might be off.
 
Grumplestiltskin said:
Most cells are 12.5 to 15 Ah, rated at 5C to 10C although I would prefer to test at 1C, which is my planned load.

Has anyone ever done such athing? How did you do it and what setup did you use?
Click to expand...

So 1C means 12.5-15A discharge rate in this case.
I'm using ZKE EBC-A20 in my tests. It can discharge at up to 20A, uses 4-wire connection and is PC-connected so i can control it and build curves under Windows.
 
thunderheart said:
So 1C means 12.5-15A discharge rate in this case.
I'm using ZKE EBC-A20 in my tests. It can discharge at up to 20A, uses 4-wire connection and is PC-connected so i can control it and build curves under Windows.
Click to expand...

Nice! That is what I want!

Here's a nice review...http://budgetlightforum.com/node/56801
 
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