Battery was drained by unplugged charger.

[e-lmer]

This is a 48V Golden Motor pack model: LFP-4812S
It's worked perfectly for a couple of years.

Somehow the chargers power plug came out of the wall,
draining the battery, possibly since November.

First ride this year, the battery cut off.

I tried charging, but the charger light does not come on.

I disassembled it and found:
The open circuit output voltage is 34.8V

The balancer is hot while the connector is plugged in.

The balancing connector open circuit values are all 4.22V
(The middle of the connector has 10.9V where the polarity reverses.)

My second battery seems to charge on the same charger.

Anyone have suggestions on the next step?

[Bikemad]

Hi Elmer,

First of all, your pack is a LiMn type not LiFePO₄ (13 cell groups @ 4.2V =54.6V).

I suggest that you check the voltage of each of the cell groups to see if they are all ~2.67V.



On your battery, you will only be able to check 11 of the 13 cell groups from the 12 pin balance connector.

If your BMS is getting hot, make sure it is left disconnected again when you have finished checking the cell voltages.

If they are all ~2.6V, I suspect that the BMS may have discharged them, as the charger itself should not be able to discharge the battery because the voltage/current should not be able to flow in the reverse direction (unless the charger itself is faulty).

It should be possible to bypass the BMS to allow the charger to raise the voltage of the low cells by temporarily connecting the C- and B- connections together and leaving the balance lead disconnected.

Try this for a few minutes and recheck the cell voltages again to make sure they are increasing.
Repeat this process until the cell voltages are over 3.5V, but do not allow any weak cells to exceed 4.2V.

If the cells are all above 3.5 volts, plug in the balance connector and remove the temporary link between the C- and B- and see if it will then charge properly.

Alan