Testing controller using power tool batteries

[Neonnblack]

Hello, had a question about using power tool batteries in series to test a 72v 150a controller... I'll give a brief overview of my situation.

Bought a non working electric street bike for cheap to see if I could get it going again. It runs off of a 72v li ion battery. The battery meters at 50.4 v and I'm sure tripped it's low voltage protection and won't let the bike turn on.

I'm willing to just buy a new battery for it but I'd like to make sure the controller and motor are working before I waste money on it.

My thought was to connect my four milwaukee 18v 6ah batteries in series with wire for the sole purpose of seeing if it turns on and spins the motor. It will not be used to try and ride it.

I just want to make sure I'm not going to burn out my batteries doing this as they are expensive and I use them for work.

Appreciate the info and hope to be around here more as I work on this bike.

 

[amberwolf]

Some questions:

Do the batteries you want to use have an internal BMS?

If they do, and they use FETs to control the output on/off, then if the BMS trips while everything is in series and turned on, the full voltage of all the packs will now be across the FETs of the one pack. If the FETs are not rated for at least that voltage, they may fail. Diodes across the output of each pack like here:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=104687&p=1529921&hilit=diode%2A+series%2A+bms%2A#p1529921
may prevent that problem, by bypassing any pack that turns off it's output.

If the FETs are rated for the total system voltage, then there should be no problem.

If there is no BMS in the packs, then they should handle being in series without any issues.

A 72v system usually has a controller LVC somewhere around 60V or higher; it may be marked on the controller label.

A 72v battery usually has a BMS LVC (assuming balanced cells) somewhere around 56v or higher.

Does the battery already on the bike charge at all? If not, what symptoms do you have when connecting the charger?

Hello, had a question about using power tool batteries in series to test a 72v 150a controller... I'll give a brief overview of my situation.

Bought a non working electric street bike for cheap to see if I could get it going again. It runs off of a 72v li ion battery. The battery meters at 50.4 v and I'm sure tripped it's low voltage protection and won't let the bike turn on.

I'm willing to just buy a new battery for it but I'd like to make sure the controller and motor are working before I waste money on it.

My thought was to connect my four milwaukee 18v 6ah batteries in series with wire for the sole purpose of seeing if it turns on and spins the motor. It will not be used to try and ride it.

I just want to make sure I'm not going to burn out my batteries doing this as they are expensive and I use them for work.

Appreciate the info and hope to be around here more as I work on this bike.

 

[Neonnblack]

Some questions:

Do the batteries you want to use have an internal BMS?

If they do, and they use FETs to control the output on/off, then if the BMS trips while everything is in series and turned on, the full voltage of all the packs will now be across the FETs of the one pack. If the FETs are not rated for at least that voltage, they may fail. Diodes across the output of each pack like here:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=104687&p=1529921&hilit=diode%2A+series%2A+bms%2A#p1529921
may prevent that problem, by bypassing any pack that turns off it's output.

If the FETs are rated for the total system voltage, then there should be no problem.

If there is no BMS in the packs, then they should handle being in series without any issues.

some quick googling shows there is a bms on these batteries, so i probably won't mess with these particular ones since i need them

A 72v system usually has a controller LVC somewhere around 60V or higher; it may be marked on the controller label.

A 72v battery usually has a BMS LVC (assuming balanced cells) somewhere around 56v or higher.

Does the battery already on the bike charge at all? If not, what symptoms do you have when connecting the charger?

I do not have a charger for it right now. The person I got it from (a trustable source) said it just wouldn't charge after sitting for a long time and has since lost the charger. So i did some research and found out about the batteries having the LVC. So to answer that, i don't know for sure that it does/doesn't charge but I'm guessing it doesn't.

Hello, had a question about using power tool batteries in series to test a 72v 150a controller... I'll give a brief overview of my situation.

Bought a non working electric street bike for cheap to see if I could get it going again. It runs off of a 72v li ion battery. The battery meters at 50.4 v and I'm sure tripped it's low voltage protection and won't let the bike turn on.

I'm willing to just buy a new battery for it but I'd like to make sure the controller and motor are working before I waste money on it.

My thought was to connect my four milwaukee 18v 6ah batteries in series with wire for the sole purpose of seeing if it turns on and spins the motor. It will not be used to try and ride it.

I just want to make sure I'm not going to burn out my batteries doing this as they are expensive and I use them for work.

Appreciate the info and hope to be around here more as I work on this bike.