Help- ebike started acting strange

[nedfunnell]

Hello all,
I recently decided to put my PMDC motor build plans on hold and get a cheap hub motor kit just to have something to ride until I have time for that. I picked up an Aotema hub motor with a no-name controller and 3 SLAs as a kit, used. It worked when I demo'd it, it worked when I tried it out first after installing it on my bike. However, today, when I went for a ride, it would not rotate. When I applied throttle, it would jerk to one position, hold it, and stay there. It'd do that for 3-4seconds then go limp. I tried powering the controller on and off, unplugging it from the batteries, spinning the wheel before applying throttle, and applying throttle while riding. Each time the result was the same- the motor would attempt to hold a zero RPM condition.

One other details which may or may not relevant- before this ride, I realized I'd left the controller on, draining the battery to 29v. I recharged it fully before my attempted ride.

Can anyone help me understand why this is happening and what I can do to fix it?
Thanks.

 

[nedfunnell]

Voltage is 39.4v OC, 37.1 minimum during the ~2-4 seconds the motor tries to hold position.

 

[d8veh]

You probably had a bad phase wire connection. The problem now is that by holding full throttle like that, you've probably damaged the controller. As a general rule, if your motor won't rotate but is taking power, you shouldn't try and run it. It's more or less the same thing as giving full power when it's stalled. A lot of current flows, which is confirmed by your 2v plus drop.

Being optimistic, the quickest way to find what's wrong is with an ebike tester. You can get them from Ebay or Em3ev.com. They don't cost much and can test that both your motor and controller.

Check that the phase wire connectors are tight. Maybe nothing has blown.

 

[nedfunnell]

Bad connection where? Between the controller and the motor?

I didn't hold the throttle down for long stretches of time, seconds only. You really think that'd have blown it?

 

[thewmatusmoloki]

In these kind of situations the first thing to check is the easiest thing to repair, in this case the wiring between the controller and motor.
You'll need a multi-meter to test for continuity on each of the 8 wires, the 3 phase (thick) and 5 hall (thin) wires.

In fact I had this same problem only yesterday. I put the motor on a bike I'm currently building and had the same result as you. Pulled everything back off the bike then took the motor apart to find that the blue hall sensor wire had broken near the axle, inside the motor, so I repaired the wire, tested for continuity and put everything back together only to find I still had the same problem so took it all apart again only to find that the blue hall wire had now broken in a different place just outside the axle . This time I replaced the entire blue wire (which was obviously stuffed) and the problem was solved.

If the wiring checks out ok it could be a blown hall sensor, which is a more advanced repair.

If the controller is still making the motor grunt briefly at the moment, then it seems likely that it's not damaged. Don't go holding it on full when the wheel isn't turning though. As d8veh say's it will damage your controller.

 

[nedfunnell]

In these kind of situations the first thing to check is the easiest thing to repair, in this case the wiring between the controller and motor.
You'll need a multi-meter to test for continuity on each of the 8 wires, the 3 phase (thick) and 5 hall (thin) wires.

In fact I had this same problem only yesterday. I put the motor on a bike I'm currently building and had the same result as you. Pulled everything back off the bike then took the motor apart to find that the blue hall sensor wire had broken near the axle, inside the motor, so I repaired the wire, tested for continuity and put everything back together only to find I still had the same problem so took it all apart again only to find that the blue hall wire had now broken in a different place just outside the axle . This time I replaced the entire blue wire (which was obviously stuffed) and the problem was solved.

If the wiring checks out ok it could be a blown hall sensor, which is a more advanced repair.

If the controller is still making the motor grunt briefly at the moment, then it seems likely that it's not damaged. Don't go holding it on full when the wheel isn't turning though. As d8veh say's it will damage your controller.

Thanks for the response. My motor has only three large wires. No sensors, apparently. I did check the connection from the controller to the motor, it seemed tight. How can I check the motor wire continuity?

 

[dnmun]

it is usually the hiside mosfet that burns up from the ones i have seen. but that is anecdotal. but i have this idea that the hiside mosfet is most vulnerable because if the commutation is stalled and the hiside gate driver drains all the charge off of the hiside charge pump cap then the mosfet gate voltage will drop off fairly quickly through one of those source resistors i bet.

anyway as the gate voltage sags the mosfet overheats as it continues carrying hi current through the transition phase.

the idea is that the charge pump would not be pushing charge up above the B+ of the battery because the circuit is not commutating so no charge is pumped up each cycle so the charge drains off the charge pump cap through the gate drive circuit for the hiside mosfet.

 

[dogman dan]

Definitely seems like you just have a poor connection to the motor, could be in the halls, or the phase wires.

If you blew your controller fets, it would show as lots of resistance when spinning the motor. If a gear motor, lots of resistance spinning backwards.

Then unplug the motor completely, if that resistance vanished, you have blown the controller.

 

[Ykick]

If you can use a DVM (meter) this info can help - http://www.ebikes.ca/learn/troubleshooting.html

 

[nedfunnell]

Definitely seems like you just have a poor connection to the motor, could be in the halls, or the phase wires.

If you blew your controller fets, it would show as lots of resistance when spinning the motor. If a gear motor, lots of resistance spinning backwards.

Then unplug the motor completely, if that resistance vanished, you have blown the controller.

No hall sensors on this motor.

I don't feel any significant resistance when turning the motor either forwards or backwards.

 

[nedfunnell]

If you can use a DVM (meter) this info can help - http://www.ebikes.ca/learn/troubleshooting.html

That page looks great! I will try the tests on it after I finish up making some Christmas gifts.

 

[nedfunnell]

I tried the test, looks like I've got some blown MOSFETs. That's pretty lame. I don't know how they could have gone bad with the bike just sitting there. Maybe I killed them on the last little climb into the garage and didn't notice. So strange. I bought this kit to be a relatively trouble-free situation, so much for that. How depressing.

 

[d8veh]

It's probably like I said earlier, not the fault of the stuff. You only have to have one phase wire not quite connected and all the troubles start. It's surprisingly easy to do, especially with those bullet/barrel connectors that you get on many kits. If the current can't go through one phase, the others are stalled. It's the same as giving full throttle with the brakes on to stop the motor. The FETs can't take that.

Controllers are not too expensive, so it's not the end of the world. It'll even give you the opportunity to get a better one.

I'll keep posting this in the hope that it might save somebody else: If you motor is stuttering, juddering, jerking or otherwise stopping, never give it full throttle or PAS until you've found the cause.

 

[Ykick]

There should be HUGE WARNINGS plastered on controllers warning about "pushing" a BLDC motor/controller which is obviously not operating properly:

View attachment 1


Check out this thread for carnage caused by incorrect Phase/Hall combination/operation:

http://endless-sphere.com/forums/viewtopic.php?f=2&t=48311&hilit=+phase+hall+combo

Bottom line, if your motor isn't running properly - STOP and check phase wire connections (Hall sensor wires if equipped). Whatever you do, don't push it until it's operating properly.

 

[dnmun]

and do not, DO NOT, sit with your hand on WOT while the bike is stalled on a hill and not moving. if the motor is not turning then you will burn up the hiside mosfet like i said. get off the throttle right away.