I've got a bit of a weird problem with a kit I put together for a guy recently.
It's a crystalyte HT35, running on 18S lipo.
I've done a fair bit of testing with this configuration and they normally run quite cool and efficiently with the lower speed wind.
So the guy assembled the kit on his bike and after the first ride he said the motor was boiling to touch and the battery quickly went flat. When I checked the CA the top speed was only around 40km/hr but the whr/km was up around 45 (should be sub 20 on this config). The current limit was only around 40 amps so it certainly shouldn't have been running that hot.
He bought it back with a stuttering problem which I assumed was halls. At first I thought it was a wire cut issues but the wiring looked fine. Each hall voltage changed with the wheel spun but not quiet as it should - only slight voltage changes. I figured maybe the heat cooked them and took the easy way out and fitted a sensorless controller. I took it for a spin down the driveway and back and it ran smooth and fine so handed it back to the guy.
A few rides later he says it's scortching hot again when he tries ride it now it just shudders. Cooked windings.
So, I'm kinda stumped as to what the problem is. Given I replaced the controller with a sensorless one it really has to be the motor.
I've never seen it before (contrary to popular opinion I try *not* to blow up motors
) but my guess would be a short in the windings somewhere from new. It ran smooth on the bench and under load on the short test I gave it but apparently was just dumping all the current the controller allowed as heat.