Lipo Battery Standards, open discussion

[BrianG]

This sounds good to me! It would definitely help substantiate some manufacturers claims and weed out the packs with inflated ratings.

For continuous C rating:

Discharge graphs at 1C, 5C, 10C, 15C, 20C, etc should be done while measuring voltages and pack temperatures taken at 30 second intervals for each C rate.

The voltage drop at a particular current would allow you to graph internal resistance since it's non-linear and is a function of C rate.

The measured temps should then dictate the max discharge C rating the pack is good for. And anything over 120*F or 30*F above ambient (whichever comes first) should be considered non-useable.

Not sure what the minimum allowed voltage should be during the test for the associated C rate to be considered valid. 3.5v would be nice, but is that too optimistic? I think 3.4v would be acceptable.

For burst C rating:

This is a little trickier since I doubt anyone is going to agree what exactly constitutes a burst. Heli burst is probably different than land vehicle burst. And racing has a different burst profile than bashing. And what is the period (frequency) and the "resting" C value between bursts? We know current does not go to 0A in between these bursts, so that has to be taken into account. So, I would suggest using a worst-case test.

Discharge graphs of 15C, 20C, 25C, 30C should be take while measuring voltage and temps. A burst should consist of 2.5 second 10C "rest" period and 0.5 second bursts (~17% duty cycle). Anything over 130*F (or 40*F above ambient) should be considered unusable. That should cover basically anything.

Again. not sure what the minimum allowed voltage should be during the test for the associated C rate to be considered valid. I'm thinking 3.2v would be acceptable.

Results

Using the results from these tests/graphs, manufacturers could then rate batteries using something like:

This pack is rated for 20C continous with no less than 3.4v (for 90% of the cycle) @ no higher than 120*F temperature.
This pack is rated for 30C burst with no less than 3.2v (for 90% of the cycle) @ no higher than 130*F temperature.

Sounds similar to how amplifiers are rated "rated 100 watts RMS X 2 channels into 4ohms from 20Hz-20kHz with no more than 0.05% THD"...