Lots of drag on a direct drive rear hub motor

[fitek]

I tried to resurrect an Eton Eco folding ebike I bought off Craigslist a decade ago. Battery is toast but I ran it off a bench supply @24v w/ the original pedal first controller. The bike has a direct drive rear hub motor-- massive copper monster. I tried spinning the wheel by hand and it feels like there's a ton of drag on it. Even pedaling I feel a lot of resistance, like an exercise bike. I took off the side cover and no obvious issues. Powered up, the weak controller could hardly overcome the drag. Finally it just popped.

Any ideas on what's up with this motor?

 

[e-beach]

If is is not something like rust or a bad bearing then check the phase wires to make sure they are shorted. When the phase wires short if feels like the breaks are on.

 

[fitek]

Ok, thanks, I'll throw an ohm meter on the power wires. Been out of ebikes for many years and couldn't think what to test.

My DIY orange Makita powered folding bike is still running 11 years later. Keywin 72v. So I haven't had to do much troubleshooting, but I'm moving and this Eton Eco has been sitting in the corner of the garage for 12 years. Worst case the scrap metal guys will be happy to pick up 60 lbs of steel and copper.

 

[amberwolf]

If brushless, an ohmmeter will read a dead short even on a working motor; it's just how they're wired.

To test for shorts ensure you have unplugged the motor from controler first. If the motor isn't dragging then, then connect one of the motor's phase wires to another motor phase wire. If it doesn't change the feel, then those two phases are shorted somewhere else, too. Probably at the axle where the wires come out; possibly inside the motor.

If it does change hte feel, then they're not the problem. Try connecting it to the other one. If that doesnt' do it, try connecting the other two (not icnluding the first one).

If nothing changes regardless, then all the phases are already shorted together inside the motor; perhaps the insulation is burned off the windings.


If the motro is brushed, then similarly you'll read a dead short. but there will only be two wires to do the test above with, instead of three.

Usually the rpoblem seen with those, if jammed up, is rust inside them. (whcih cna also happen to the brushless kind).

 

[fitek]

It's brushless. A short sounds possible-- the stock controller was really pitiful but both of the keywin controllers I threw on it blew FETs on a phase IIRC. I swapped in FETs a couple times but then just shoved it into the back of the garage and forgot about it. Some massive torque out of that motor (when it wasn't blowing up the controller), I had planned to swap it onto a recumbent.

 

[e-beach]

Disconnect the phase wires from the controller and see if the wheel spins freely.

 

[fitek]

It had drag when I started (with no controller).

I tried shorting the phase wires in different combos and then all together. No noticeable difference. It feels almost like there's some indexing. I'm gonna guess there's a mechanical problem.

Worth trying to figure out what's up with the bearings in an unbranded Chinese direct drive motor or time for the scrap heap?

 

[dogman dan]

Shorting the phases, no difference. There you go, you just proved that they are already shorted. Most likely a cooked off winding, or at least some kind of damage in the core.

 

[fitek]

All right, thanks dudes. I will harvest the other usable parts (the frame is an incredibly heavy steel monstrosity) and move onto finishing my RC motor driven folding bike

I see I need to update my sig.