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BrianG · 12:49 PM

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"...

	(#3)
BrianG RC-Monster Admin Offline Posts: 14,609 Join Date: Nov 2005 Location: Des Moines, IA	04.30.2008, 12:07 PM 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 120F or 30F 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 130F (or 40F 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 120F temperature. This pack is rated for 30C burst with no less than 3.2v (for 90% of the cycle) @ no higher than 130F 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"... Last edited by BrianG; 04.30.2008 at 12:49 PM.