Motor locks and unlocks(at high speed) magnetically problem

[Bigbikebob]

While I was going up a steep hill my power was cut and I heard and felt the motor resisting to foreword motion.
I tried to turn on and of the controller and nothing changed, the bike was dead. the motor itself resisted to motion by hand.

On my way back I was going down the same hill (with the controller off) and the motor was resisting the motion more and more until I picked up some speed at which point i felt the motor stooping to resist to motion and when I stooped and turned on the controller I got power back and my bike was working with no problem.

I commute the same way everyday and what I have described happened twice so far (about 5 weeks ago and once today). both times the power was cut at same height point of the hill and in both times the power got "unstuck" at the same speed.

about the same time as the problem started the controller had cut the power under extreme stress few times but with no motor resistance.

I do know that usually when the motor resists to rotating by hand it means that phases of the motor are in contact with each other but then why does it happens only under stress at irregular times and I am able to "fix" this just by turning the wheel really fast?

 

[amberwolf]

I would guess that your battery voltage is dropping below the controller's LVC, so the controller shuts down, until the motor has spun fast enough to regen high enough voltage to bring voltage back up to where it can turn on again. (even with power off, as long as the battery is connected, the FETs will pass motor voltage back to the battery once it is high enough from the motor spinning fast enough).

It may be more likely that it is the battery's BMS, detecting a cell (or the whole pack) dropping below LVC under the high load. The same still applies for why it comes back; though it's the BMS that comes back on rather than the controller (or rather, in addition to).



Now, neither of these explains why the motor becomes higher resistance, unless it is simply that the controller goes into a "lock mode" of some sort when it loses power, as a security measure, though I'm not sure how it would work without any power.



IF the motor feels "locked" even with the phase wires not connected to the controller, then the problem is in the motor itself, either wiring or a bearing or some other mechanical issue.

If it does not, then it is in the controller (or battery).

 

[Bigbikebob]

Now, neither of these explains why the motor becomes higher resistance, unless it is simply that the controller goes into a "lock mode" of some sort when it loses power, as a security measure, though I'm not sure how it would work without any power.

As you say, when I turn off the controller I literally pull the plug and any security measure should be cut off.
Now if there were a problem with the phases touching each other then the wheel should have remained locked regardless of the speed I was sniping it.


I already took a wrench (to open the battery / controller case) with me, next time this happens I am going to try to unplug the phases and battery and see what happens.

*I am going to program the controller to work at a lower amperage to put less stress on the battery.