Originally Posted by
graycenphil
I tested it today, and got erratic and varying readings, from 0 to30 volts, jumping around. So maybe a bad battery? I opened it up looking for a bad connection but didn't find anything obvious. I was surprised that it had a printed circuit board in there too; I'm not used to such a sophisitated battery. I was expecting a positive and a negative terminal, and not much else.
Another thought I had would be to run a battery directly to the motor, maybe a 12 volt or two 12 volts in series with an on/off switch. Can I do this? Will it work, and will it damage the motor?
1.) Battery NEEDS to be at LEAST 38.4 volts to operate the bike properly.
2.) The printed circuit board is a BMS, it stands for battery management system. It is supposed to protect the battery from overcharging and low voltages while riding. (That's why the motor cuts out when you go full throttle.
Did you test the voltage on the line AFTER the BMS (nearer the controller) or BEFORE the BMS?
Were you using an analog or digital volt meter? The voltage shouldn't be "jumping around"..
Some pics of you checking the voltages would help.
Also take a bunch of close up pics of the battery, it's wires and the BMS and show where you are checking the voltages.
There sounds like a lose wire somewhere in the battery or on the BMS. But can't know for sure without pics.
Edit: You would need THREE - 12v batteries in series for 36v (and at least 20AH batteries).
Let's go with pics first.