Widewheel 2019 - rear motor "shuts off"

[Dishwashertaco]

Greetings,

I recently purchased a Mercane Widewheel 2019 model, but there appears to be an issue with either the battery, controllers, or rear motor.

I disabled the kick&go, unlocked full speed, and put the scooter on a chair (so the wheels are free) to make it easier to troubleshoot. When accelerating, the front motor works fine, but the back motor "shuts off" after 0,5 - 5seconds. I then have to reset the throttle to zero position, and accelerate again, and the rear wheel will spin for another second or two before it stops with a thud. The process can be repeated several times with the same result, and the rear motor always fires - but it only lasts for a few seconds. The back wheel is not blocked, and spins "freely" only with the resistance of the motor itself.
In addition to this, i took the scooter (fully charged) for a test ride, and it shut down after about 2km, and i was unable to turn it on before charging it again.

I might be able to post a video later to further examplify my issue:
https://www.youtube.com/watch?v=RxsjpMac6f0&feature=share

As i bought the scooter cheaply with no warranty the seller refuses to take it back (them regrets...), and I am left to fix it myself. Initially i thought this might be a controller isolated issue, but the fact that the scooter dies on me entirely after not even reaching 10% of its range, makes me worried maybe i need a new battery. Any ideas? Is it physically possible to swap the controller cables for the front and rear motor? I.e. connect the front motor to the main controller, and the rear to the secondary controller. I suppose if the front motor starts acting the same way, I would know for sure i need a new main controller.

 

[Dishwashertaco]

Added a video now, which might explain the problem better. Actually i just realised - sometimes even the front motor shuts off without me letting go of the throttle (illustrated 30 seconds into the video).

https://www.youtube.com/watch?v=RxsjpMac6f0&feature=share

 

[amberwolf]

most likely controller shutdown from lvc due to voltage sag in battery.

recharge the battery first, then use just bare minimum throttle in the offground "chair" test. just enough to make the motor spin at all.

if it doesn't shutdown (or not as quickly or as often) like that, vs higher throttle settings, then the battery most likely needs to be replaced.


but before you do that, you could try just leaving the battery on it's charger at least overnight, and potentially for days (or weeks) if it's really badly unbalanced (meaning the cells are not all the same voltage). that assumes it has a balancing bms, which it may not (cheaper batteries may not, more often these days it seems).

if it doesn't change after leaving it on the charger for overnight, or days, then the battery isn't able to fix it's own issues, and would need to be replaced (assuming an unbalanced battery or one that won't fully charge).

 

[Dishwashertaco]

most likely controller shutdown from lvc due to voltage sag in battery...

Thanks for your reply, amberwolf! I did like you said, charged the battery fully, and did some more testing. I also went out and bought a cheap multimeter to be able to pay attention to the voltage. At first, your theory seemed correct. I gave the scooter as little throttle as i could, and both wheels spun for about a minute straight before I stopped the test. However, during my testing, the back motor started changing behaviour, and now it doesn't start at all, and if so, just a tiny jerk. I managed to get a voltage read from the battery while both motors were working, and the voltage went from 54,6v fully charged(no load) to a minimum of maybe 51-52v (full accelation, off ground). To my knowledge this is a "normal" voltage drop, and not something that should shutdown the controller(?).

I dont believe the Mercane Widewheel has a proper BMS, but will check into that further.

Any other testing i could do with a basic multimeter? I found a tutorial on youtube ( https://www.youtube.com/watch?v=lTssCn5YyTw ) on how to recognise faulty mosfets in the controller, although i'm not sure this type of behaviour is typical for a faulty mosfet. Anyhow, I got a reading of about 6000ohms when checking between the minus of the battery wire to all the phase wires, but didn't get any reading when checking the plus wire on any of the 3 phase wires on the two controllers. Not really sure what this means. As you can tell, I have no idea what i'm doing...

 

[amberwolf]

there's also info on http://ebikes. ca in the learn - troubleshooting section that may help.


if it's not the voltage sag, then there is probably something mechanically wrong with the motor itself, or electrically wrong with teh controller, wiring, etc.


mechanical stuff isn't likely since the motor spins freely without power.

electrical stuff could include a lot of things, but the most common thing is simply connections. that includes everything from inside the motor where phase and hall (if any) connections start on the wiring that goes out to whatever connector is between the motor and controller, to the controller board itself (solder joints, pcb pads and traces, etc).

if it's a sensored motor, then anything wrong with the sensors or wiring can cause either shutodwn of controller (or failure ot start under load), or loss of sync and high currents that could then cause shutdown. this happens more often at high currents or speeds than low ones, if it's got a connection but just not a good one. very gently wiggling or moving wires and connections while running the motor may help find a problematic one (but not always).


it's highly unlikely given ti's a factory setup, but if there are sensors in the motor and they are not in the correct wiring order for the phases in the motor, it will do something similar. before you go down that rabbithole, check all the wiring and connections first.

 

[Skaiwerd]

I have one and have had it apart. Mine had a non working front motor from new. I was sent two dead ones and the third worked. Seems unlikely to be the battery as it’s shared by both motor controllers so wouldn’t the problem affect both motors? The two motors and controllers use the round plugs so swap them around to isolate the problem part. Trial and error, I don’t think you can screw it up as the parts are the same for front and back. I vaguely remember the front motor wire did not have a plug at the controller and required removal of something to make it connect, a motor or controller, no big deal, you’ll see.