john61ct wrote: ↑
Mar 15 2020 8:39pm
Nope, same thing.
C-rate is just **a unit** of measurement.
The acceptable "peak output" might be 5C, while highest continuous is 1.5C.
Of course the **vendor ratings** are pure fiction.
And you may not agree with what one forum tester accepts as OK, it really is a judgment call how much you prioritize longevity, adjust the maximum temperature rise effect or the voltage sag effect to below what **you** consider abusive in your use case.
How long do you define "a brief peak" session of very high discharge rate?
Same with charging, if I'm not in a big hurry, I consider anything over 0.4C too high a rate.
While others are fine with routinely going to 2C or even higher!
Depends on the weather too of course. . .
Essentially what I was alluding in my subsequent post.
Just for discussions sake, if we can agree that a single Samsung 25R has a maximum continuous discharge rating of 20 amps (because attempting to continuously discharge at over that rate would allow the cell temperature to reach more than 80 Celsius where cell damage is presumed to occur) then adding a second 25R in parallel would allow you to discharge at a maximum of 40amps while maintaining the same temperature as a single cell at 20 amps. The 40amp load would be spread between the two cells. Double cells, double the continuous discharge rating of the group. You were absolutely right though, the c rate would remain unchanged. (I was clearly wrong initially.)
Of course attempting to use those cells continuously at their mutually accepted maximum would negatively effect cycle life. It would not however be unsafe in the sense of risking thermal runaway.
That said, if the highest load ever put on that pair of cells was 40 amps and the duration of that 40 amp load were only a few seconds at most before dropping to say 5 amps continuous, I wouldn't expect to see much reduction in cycle life as the cell would never get the chance to accumulate any real amount of heat. Of course if we had 2 more cells in parallel bringing the CDR of the group to 80a, and were only asking 40a for a few seconds here and there it would be all the better. The more the merrier to share the load.
As you noted though, vendor ratings are fiction and some manufacturer ratings aren't necessarily much more accurate. Combine that with the fact that finding 2 people with the same opinion or standard is neigh impossible and there's no wonder a consensus is difficult to reach.
Fwiw, I outright ignore any sort of pulse or burst rating thrown around by sellers as there is no standard that I'm aware of which defines the duration of a pulse or burst. Could be 5ms, could be 5 min. Pure marketing malarkey without qualification.