ebike battery troubleshooting

[eatcarbs]

I'm a noob/ametuer trying to get my battery pack working for about a week now, and I'm reaching my wits end.

I hit a pothole while using a rear hub motor and I'm not completely sure what happened to the motor, The motor seized up and made a loud humming noise while turned on. I ended up pushing it home and got it in the garage to check it out. I had left the display at home because I hadn't mounted it yet. Plugged it in hoping to get an error code so I could at least find out whats wrong, but the battery lasted about 5 seconds before shutting off.

At this point, I haven't even touched the motor and have focused solely on the battery, because I have other functional motors that I can use. The battery has an external button that has LEDs that give an estimation of remaining power. This ceased to function, and the battery would not take a charge, or output any power. I've since disassembled the pack and tested connections between all the batteries, and they're giving consistent voltage. Checked the fuse with a multimeter and it's still reading. Some quick research led me to believe that something may be wrong with the BMS. After recieving a new BMS, I hooked it up to no avail - all the problems still persist.

I guess I need to start peeling all the glue out and checking out every wire/connector. The reason I'm posting this is hopefully someone with more experience than I may know whats going on with my pack and maybe point me in the right direction.

 

[Philaphlous]

I don't actually have an ebike or hub motor yet but sounds to be like something got knocked loose in the actual motor...my guess maybe an actual magnet got dislodged? Does the rear tire spin freely? any odd noises?

 

[Ykick]

Can you temporarily bypass the BMS and power a working system?

Have you ever installed a BMS before? Was this wire for wire or was it different from the BMS you were replacing? Hopefully, you tried connecting the charger briefly even if the output was showing nothing?

 

[999zip999]

Where you live ?

 

[eatcarbs]

Can you temporarily bypass the BMS and power a working system?

Have you ever installed a BMS before? Was this wire for wire or was it different from the BMS you were replacing? Hopefully, you tried connecting the charger briefly even if the output was showing nothing?

Bypassing the BMS isnt something ive done before, but ill look into it. As for installing the new one, all the wires have plugs so it was a simple swap with no souldering required.

There is a video from lunacycle on checking for a bad bms, its pretty much the exact bms and i get the exact same results with a multimeter. Dont have the link right this second because posting mobile sucks.

EDIT: https://www.youtube.com/watch?v=3Jkm0tfihe0

 

[eatcarbs]

I don't actually have an ebike or hub motor yet but sounds to be like something got knocked loose in the actual motor...my guess maybe an actual magnet got dislodged? Does the rear tire spin freely? any odd noises?

Yea thats what im thinking. The wheel hardly spins, its enough resistance i cant even pedal on the easiest gear. At the moment im focused on the battery though.

 

[amberwolf]

Unplug motor from controller, see if it spins normally. If so, controller is shorted inside (blown FETs).

If not, then motor wires might be shorted to each other, most likely at the axle exit. It's not uncommon for new installs to not be tightened down enough, and sometimes hitting a bump could cause just enough extra stress (or relaxation of it) to allow the axle to spin in the dropouts, twisting up the wires and ripping thru the insulation, which shorts them together.


Sometimes that also damages the controller, but not always immediately--sometimes the damage happens when the controller is repeatedly powered up with the motor wires still shorted together. Sometimes there is no controller damage at all, and just fixing the wires fixes the problem.

Mostly it depends on which wires get shorted together---teh worst case is when one of the phases that at that moment happens to be connected to battery power ends up shorted to the 5v line for the halls, which can blow teh 5v regulator and sometimes the 12v one and also the halls in the mtoor, throttle, PAS sensor, the MCU, etc. But that doesnt' happen very often.



If there's no wire damage, there could be internal damage to the motor but that's not very common--it'd take quite an impact to do that, or a badly designed (or poorly manufactured) motor.



If there is wire damage, but no controller damage, then with the motor disconnected, teh controller should power up normally--if there was a short in the motor wiring that cuased the controller to draw too much power it could cause your BMS to shutdown too.


If the BMS shutdown is when it is not connected to teh bike at all, then there's a separate problem in the battery itself somewhere. It could be a low cell or cell group, whose voltage is low enough that when any load is placed on the battery (even that of the BMS), it drops below LVC and the BMS shuts down to protect itself.


There's other possible issues too, but I'd start checking from those and see what happens.

 

[dogman dan]

Ditto above, it sounds like a short on the phase wires, not a battery problem. check the wiring to the motor, look for cut wires like at the axle in particular, that could be shorting.

if the heavy resistance on hand spinning the motor goes away when you unplug, you blew the controller. On cheap kits, they do sometimes last only a few min.