8FUN motor needs help to get spinning

[pilotg2]

I cleaned up a 8FUN front 250w geared hub motor that was badly rusted internally, I mean really badly. I'll post some pics later.

After the clean up, it ran fine on the bike for a few days. After briefly stopping on a ride, I set off again and the motor was noisy and ran rough for a short while then died. Then worked again but it felt like it wasn't pulling at full power. Then died and is now intermittently faulty.

Got home and have done some testing. Luckily, I have another identical bike so the motor is definitely the problem.

I've opened the motor up. With the throttle sometimes the motor will start spinning on its own. Other times it won't spin but I can hear it hum and then click. Like it's trying to start spinning. Once going providing i keep it spinning, I can back off the throttle to just before it stops spinning and it'll keep going.

It seems in some positions it won't start spinning but in others it will. What does this mean?

From the rust the bearings sound rough and are loose but they run freely. The only other difference is this motor when unplugged doesn't run quite as smoothly when turned by hand as the non rusted one. Like the magnets are sticker. Buts it's consistent, there are no positions that are sticker to turn.

I don't think it's a short as providing the motor doesn't stop spinning I can vary the speed without any issues.

 

[amberwolf]

Sounds like hall sensors. Either hte sensors are bad, or there's a bad connection between them and the controller.

 

[pilotg2]

You were right, at least I think so, by my diagnosis, which could be wrong. Just like to say this forum is amazing, 2 days ago I knew nothing about Hall Sensors and now I'm attempting to replace one.

One hall sensors voltage did not change when I placed a magnet over it. The other 2 went from 5v to 0v and then flipping the magnet back to 5v. What I believe is the faulty sensor always stayed at 5v.

I have ordered some SS41 Hall Sensors but they'll take over a month to be delivered... so I found a local chap who repairs electric bikes and picked up 3 Hall Sensors with model number 3144 C5221.

However I'm not sure they will work as I have discovered they are non-latching and uni-polar. Will they work and if so, would it be safe to use one. I think the sensors should be latching and bipolar, but how does this guy use them to repair electric motors?

I'm out of my depth here so love to hear back before I test it out tomorrow - i'm keen to ride with the family.

 

[fechter]

I looked at the datasheet for those hall sensors. Those should work fine. Good for up to 150C.

 

[docw009]

You want a non latching sensor. I believe a latching unit will turn on and stay that way til it sees a second magnet come by with the correct polarity of field.

 

[amberwolf]

Latching bipolar is actually the normal type for most ebike hubmotors (all the ones I've worked on, for instance, used some version of SS411A, so I keep a bag of them around).

I'm sure some systems use other types, but I haven't run across any.

But any digital output, open collector hall sensor will probably work fine in most applications. I expect the generic controllers only care that they get the right pattern of signals for the phase combo being used.

Since two of your sensors work fine, I would only change out the non working one. They are kind of a PITA to change, and break leads off easily. So anything you don't have to touch is better.

 

[pilotg2]

So it definitely was the hall sensor as now the motor starts to spins from any position and ran perfectly during a ride.

And the sensor works fine even though it has different behaviour to the existing two, which I didn't bother changing.

During discovery and testing, the existing two sensors would stay at either 5v or 0v, even when the magnet was moved away and only changed with the magnet polarity alternated. I guess that's latching.

The new sensor always switches back to 5v automatically and only stays at 0v with the magnet in contact.

Anyway I thought I'd mention my understanding of it as you are right, it worked and the controller seems happy to accommodate the different new sensor.