justaperson76 said:
This all makes sense. You are right, I should have used the full capacity charge rather than nominal. I'll be charging to around 4v or 4.1v max to prolong life, so total of 28.7v.
29.4V x 12Ah = 352.8Wh (FULL charge to 4.2V)
28.7V x 12Ah = 344.4Wh (90% charge to 4.1V)
justaperson76 said:
Seeing I am only charging at 0.5c, then I think that means I will only need a PSU that does half the above quoted figures.
A charge rate of 0.5C (1.5A for 30Q 3000mAh) or 1.0C (3.0A for 30Q 3000mAh) to 90% (4.1V)
still requires 28.7V (7s). The difference in charge rate is not a change in voltage, but rather the time it takes to charge. Charging 90% means the cell capacity is also reduced ...
Charging to 4.10V the cell capacity is reduced to say 2700mAh ... 4p x 2.7Ah = 10.8Ah
28.7V x 10.8Ah = 309.96Wh (90% charge to 4.10V) ... Full charge = 352.8Wh
https://battlebornbatteries.com/watt-hours-to-amp-hours/#:~:text=Here's%20the%20equation%3A%20
On another thread i believe it was
fechter that suggested discharging p-groups to 3.00V which is AOK. The reason i charge my 30Q pack only 90% and Controller Cut-Off at 3.20V (p-group voltage) is because Samsung 30Q cycle life may only be good for say 250 c/d cycles when charging battery pack to 4.20V (FULL) and discharging to 3.00V (p-group voltages).
Here is another way of figuring discharge voltage and capacity rates. Whatever the Controller Cut-Off it's considered 0.00V and 0000mAh for the sake of the following comparisons. There is very little useful Ah capacity below p-group voltage of 3.00V ...
4.20V - 3.00V = 1.2V divided by 10 = 0.12V
4.20V, 4.08V, 3.96V, 3.84V, 3.72V, 3.60V, 3.48V, 3.36V, 3.24V, 3.12V, 3.00V
100%...90%....80%...70%....60%....50%....40%....30%....20%....10%....0%
3000mAh (3.0Ah) divided by 10 = 300mAh
3.0Ah, 2.7Ah, 2.4Ah, 2.1Ah, 1.8Ah, 1.5Ah, 1.2Ah, 0.9Ah, 0.6Ah, 0.3Ah, 0.0Ah