Ah, you need path-sensitive analysis to parse Weber's sentence. There is a predicate "if you don't know the internal temperature of the cell at the time". It is possible for this predicate to be false, i.e. you know (something about) the internal temperature. So then the predicated statement "A voltage-sag or internal resistance figure is utterly meaningless" doesn't apply in paths where the predicate is false. So it's not always a contradiction.Nevilleh wrote:weber wrote:
1. A voltage-sag or internal resistance figure is utterly meaningless if you don't know the internal temperature of the cell at the time. The figures can almost halve with a temperature increase of only about 10 degrees Celsius....
Self-contradictory! How can it be "utterly meaningless" in one sentence and "almost halve" in the next?
To summarise the above (sorry, couldn't help injecting some terminology from work ), if you measure the temperature, voltage-sag and internal resistance measurements are no longer meaningless.
...there is NOT a lot of rapid heating in the cell at 3C.
Neville, I suppose it depends on what you mean by a lot. We've found temperature rises of about 30°C after full 3C tests; the temperature only stops rising some 10-20 minutes after the test has ended. (With the fan on, it rises maybe 20°C and starts falling perhaps a little before the 10 minute mark.) A 20°C rise from about 20°C only brings the cell to blood temperature, and a 30°C rise brings it to warm but not hot. But the voltage sag seems to be very dependent on cell temperature, so these moderate temperature rises are important.
See for example this thread: Current Limiting on Curtis and TS cells thread (probably posted to the wrong forum, sorry). It's with a big fan blowing on the cell, but it compares with previous data that was not using the fan.