AndyH
Well-known member
The 'nominal' voltage is open circuit voltage at 50% state of charge - 3.6V. The cells can be charged to over 4.4V per cell, but it costs cell life. These numbers are for regular LiPo not LiMn (a LiPo variant):
at 4.1 volts, you get over 2000 cycles.
at 4.2 volts, you get roughly 500 cycles.
at 4.3 volts, you get under 100 cycles.
at 4.4 volts, you get less than 5 cycles.
The LiMn cell has a 'sloped' discharge curve similar to lead - not like the more 'flat' or 'horizontal' curve of LiFePO4.
This is comparison between a 36V LiFePO4 battery (black trace) and a 36V sealed lead acid battery.
This shows the typical LiMn curve. This data is from EIG - not from Nissan's battery company.
Unlike lead or LiFePO4, LiMn carries most of the power at higher voltages - so we want to keep from overcharging, but we do want to use as much of the first half that we can.
I don't know enough about the voltage range for Nissan's cells so can't get too specific. IF they track fairly closely to other manufacturer's LiMn cells, then 90% state of charge will be around 4.1V per cell and 10% should be about 3.5V per cell. (The voltage and SOC guesses are just that - somewhat educated but probably not likely to be verified until someone gets some cells to play with.)
Back to AESC and their numbers. Some cell manufacturers report the full voltage and capacity range for their cells, others report only the voltage and subsequent capacity available to the 'consumer' without revealing the 100% and 0% voltage/capacity limits. While it's possible that the cells actually are 33Ah each, it's also possible that they're closer to 40Ah and the 33Ah number is the "80% available to the consumer" number.
I look forward to learning more but that's all I have at the moment.
Andy
at 4.1 volts, you get over 2000 cycles.
at 4.2 volts, you get roughly 500 cycles.
at 4.3 volts, you get under 100 cycles.
at 4.4 volts, you get less than 5 cycles.
The LiMn cell has a 'sloped' discharge curve similar to lead - not like the more 'flat' or 'horizontal' curve of LiFePO4.
This is comparison between a 36V LiFePO4 battery (black trace) and a 36V sealed lead acid battery.
This shows the typical LiMn curve. This data is from EIG - not from Nissan's battery company.
Unlike lead or LiFePO4, LiMn carries most of the power at higher voltages - so we want to keep from overcharging, but we do want to use as much of the first half that we can.
I don't know enough about the voltage range for Nissan's cells so can't get too specific. IF they track fairly closely to other manufacturer's LiMn cells, then 90% state of charge will be around 4.1V per cell and 10% should be about 3.5V per cell. (The voltage and SOC guesses are just that - somewhat educated but probably not likely to be verified until someone gets some cells to play with.)
Back to AESC and their numbers. Some cell manufacturers report the full voltage and capacity range for their cells, others report only the voltage and subsequent capacity available to the 'consumer' without revealing the 100% and 0% voltage/capacity limits. While it's possible that the cells actually are 33Ah each, it's also possible that they're closer to 40Ah and the 33Ah number is the "80% available to the consumer" number.
I look forward to learning more but that's all I have at the moment.
Andy