Motor issues under heavy load

[clueless987]

Hi all,

A friend was kind enough to give me his old, broken e-bike. It's a foldable "hopper" with a geared, brushless, sensorless hub motor on the front wheel.

Battery and controller were both screwed from water damage, and were only 7S/24V anyway. Being the fool I am, I opted to build a new 14S3P/52V battery for it, purchased a cheap 48V square wave controller with a sensorless mode and wired everything together.

Initially it was absolutely glorious. 8 miles of pure delight. The motor was fairly loud during operation but had loads of power and stayed cool to the touch. Applying throttle at very low speeds just gave dodgy noises and no power, due to the lack of hall sensors, but I was very happy with my creation... Then it broke. :lol:

Below is a video is what happens now during use. At very low throttle levels, the ebike works fine. If I raise the front wheel in the air and apply some throttle, the motor works fine and spins up to a high speed. But if I try and apply more than a very small amount of throttle during use I get an initial ~0.5 second surge of power, then some pretty dodgy noises and no power. Seems like something might be still shorting somewhere as the current rises?

https://youtu.be/RxASG8ohZQM

First thing I found was this https://imgur.com/69fgAqR - spade connectors connecting the phase wires had melted and presumably shorted a little during use. So I cut them out and soldered the wires together, as I should've done in the first place. This didn't fix anything.

So I presumed I'd probably fried some FETs the controller by shorting the phase wires under load. Purchased a new one, wired it in, still no change.

I noticed the 3 pin HiGo connector on the front fork connecting the motor/wheel to the phase wires was getting warm, so I've chopped it out and hard soldered the wire there too. No change.

I've taken the motor apart, and visibly it looks fine to me - though admittedly I'm pretty clueless with electric motors. A couple of pictures are below:

https://imgur.com/l89CslV
https://imgur.com/8DtUFPH

Does anyone have any ideas on next troubleshooting steps? I'd very much rather not replace the motor if possible. It's only a 16" wheel and I've had real difficulty in finding replacements for a reasonable cost.

Thanks in advance for any advice you can offer.

 

[Hwy89]

My guess is that your puny 3s battery was no match for the loads you were putting on it. Melted wires are a reliable clue that you are pushing too much current through them. The battery is now on it’s last leg and is so saggy that the low voltage cutoff is triggered in the controller. Before you melt everything else in the system I would suggest that you back off to 12 or 13 s and have more cells in parallel.

 

[clueless987]

You're very much right that the battery is pretty puny! Not sure it's causing this issue though.

I tested the cells before building the pack, they're good for 10A continuous each with ~0.4-0.5v drop. At 50V nominal that's still 1500W of continuous power. No way the controller/motor are pulling more that, the controller is supposedly good for 17A continuous, 30A peak. The pack doesn't even get warm, and the battery charge meter never drops from full bars.

 

[ZeroEm]

Not an expert but most geared motors are not built for 1500w. The issue would be the plastic gears. Have you opened up the other side to check the gears. What I get is it starts to pull then makes a noise and does not pull any more. If it was cutting off would't the noise stop?

 

[clueless987]

The gears look perfect, no obvious marks or issues there. Though I understand there's a little clutch hidden somewhere that could be knackered? Very true, the controller/battery definitely aren't cutting out at all.

You're completely right though, the gears are plastic and the motor was never going to take the increased power forever, but was hoping for a little more than 8 miles! This issue doesn't necessarily seem like the motor is actually dead either, it appears in good health from first sight/smell, and still works find under no/low load. It never even got very hot. It seems like something minor has gone, possibly causing shorting at higher currents, but I can't for the life of me see what it might be. From the sound made, it seems like some sort of phase lock or something?