38v GM LiFePO4 has 12 cells

[iamsofunny]

I removed the case from my Golden Motor "36v" "LiFePO4" battery.
The key switch was defective so I removed it and went to the wires.
through the shrinkwrap it looks like 12 rectangular cells.
Voltage measures 41.5 after charging.

Do you think they are selling LiMnO2 batteries and calling if LiFePo4

[dnmun]

did they actually state that it is lifepo4? or did they just say lithium ion?

is that charger the one they included with the battery? what is the output voltage of the charger?

you need to post up pictures of the pack and the BMS.

[iamsofunny]

I don't have the battery with me, but I was curious due to a post I saw yesterday about someone's problems with their GM battery. Someone asked if it was real 10s Lifepo4 or the old 12s limno2. I remembered what my pack looked like when I removed the case. I bet you it's not lifepo4.

[Russell]

A "36V" LiFePO4 battery pack uses 12 cells and the other lithium chemistries use 10 cells for 36/37V packs. Check the output of the charger to be sure it's at least 43.8V for LiFePO4 (3.65V/cell). Also check the voltage of each cell to be sure the pack voltage is not low due to one or more low cells. If one or more cells are low and the charger output is fine then leave the pack on the charger overnight to see if the BMS will bring up the low cells and balance the pack.

( Do note that 41.5V/12 cells = 3.458V/cell which is NOT out of line for a 36V LiFePO4 battery that has been sitting for a while. Hot off the charger a 12 cell LiFePO4 battery pack will usually be over 43.2V (3.60V/cell) however they are pretty much fully charged at a bit over 3.4V/cell with the excess just a "surface charge" that burns off very quickly and represents very little stored energy. This is in contrast to the other lithium chemistries which charge to 4.2V per cell and then hold that voltage.)





-R

[SamTexas]

Check the output of the charger to be sure it's at least 43.8V for LiFePO4 (3.65V/cell).

I don't think there's an exact standard for LiFePo4 upper cell voltage. I have a 12s LiFePo4 pack that comes with a 42.0V charger, and I did verify the voltage. So that works out to 3.50V per cell.

[Russell]

Check the output of the charger to be sure it's at least 43.8V for LiFePO4 (3.65V/cell).[/i]

I don't think there's an exact standard for LiFePo4 upper cell voltage. I have a 12s LiFePo4 pack that comes with a 42.0V charger, and I did verify the voltage. So that works out to 3.50V per cell.

It really depends on the the voltage at which the BMS shunts activate. Just from my experience this voltage has been 3.60V/cell so the charger needs to be above this level for a bleeding type BMS, the most common type, to be effective. I've read that Ping for example uses even a higher charge voltage which will result in quicker balancing when used in conjunction with a BMS with higher shunt current capability.

-R

[dogman]

I'd say that anywhere between 42v and 46v is "normal" for a 36 volt lifepo4, 12cell pack.

Just depends on exactly what the designers set the bms and such for. I have noticed though, that after a year or more of daily use, charger output may drop a volt or more. So eventually you end up undercharging a bit compared to when it was new.