Jan-Erik-86
100 W
- Joined
- Jan 23, 2019
- Messages
- 110
Hi,
I'm currently putting together a battery pack for my e-bike to extend the capacity of my current battery and reduce the currently rather high voltage sag.
I'm using older/used 18650 laptop cells mainly from Samsung, LG and Panasonic, so finding the datasheet is not difficult, and neither is finding the max rated charge and (more importantly) discharge current. Therefor it should be rather simple to calculate how many cells in parallel I need to be inside the safe discharge zone.
However, as charge and discharge current is often referred to as a C-rating, one question popped up in my head, and I've been unable to find a clear answer after searching a bit online.
Take for example this cell: ICR18650-28A. Capacity: 2,8Ah, Max charge: 2.8A, Max discharge: 5,6A.
Now these ratings equals to exactly 1C charge, and 2C discharge, which is all fine when the cell is new and actually have 2.8Ah capacity, but what about my used cell that only have 2,1Ah of capacity?
Is it still safe to charge it at 2,8A, which would then equal to 1,33C, and discharge it at 5,6A, which would then equal to 2,66C, or should I follow the current capacity of the cell and set the max safe charge to 2,1A, and max safe discharge to 4,2A to maintain the 1C charge and 2C discharge rating?
I know common sense tell me "when in doubt, add extra parallel row(s) to be sure", and I will probably do that anyway, but I'm asking in general to also learn the theory behind how rated specifications are affected by a degraded battery.
I'm currently putting together a battery pack for my e-bike to extend the capacity of my current battery and reduce the currently rather high voltage sag.
I'm using older/used 18650 laptop cells mainly from Samsung, LG and Panasonic, so finding the datasheet is not difficult, and neither is finding the max rated charge and (more importantly) discharge current. Therefor it should be rather simple to calculate how many cells in parallel I need to be inside the safe discharge zone.
However, as charge and discharge current is often referred to as a C-rating, one question popped up in my head, and I've been unable to find a clear answer after searching a bit online.
Take for example this cell: ICR18650-28A. Capacity: 2,8Ah, Max charge: 2.8A, Max discharge: 5,6A.
Now these ratings equals to exactly 1C charge, and 2C discharge, which is all fine when the cell is new and actually have 2.8Ah capacity, but what about my used cell that only have 2,1Ah of capacity?
Is it still safe to charge it at 2,8A, which would then equal to 1,33C, and discharge it at 5,6A, which would then equal to 2,66C, or should I follow the current capacity of the cell and set the max safe charge to 2,1A, and max safe discharge to 4,2A to maintain the 1C charge and 2C discharge rating?
I know common sense tell me "when in doubt, add extra parallel row(s) to be sure", and I will probably do that anyway, but I'm asking in general to also learn the theory behind how rated specifications are affected by a degraded battery.