burnt MiniMotor

[pieroh]

...It seems that a continuous current of 15-20A overheats the motor windings and damages it beyond repair...

By now we have 'killed' some 5 MiniMotors -
 

Hi,
I am riding my bike with a 250 minimotor for half a year now, I use it for my daily way to work (one way 13,5km). Total distance is 1000km with this motor without any faults.

I run the motor with two Bosch LiIon battery pack of 2Ah each, connected in parallel.
I installed a "Watts up", to be able to monitor Ah, currents etc. and use a main fuse directly at the battery of 21A.

The mini motor has an inrush (surge) current of 22A and a peak power of ~820Wp when you push the throttle all way up from standstill or when slightly cycling.
When pedalling I try to keep the current below 5 to 6 A (48 - 13 transmission ratio) which is easy, when not going uphills or against strong winds.
Speed is about 31km/h then (28" wheels) and I enjoy every trip!

The only odd thing I experienced up till now is, that the motor seems to run harder (stiffer) when it is cold outside (below 5°C) which equals in a higher energy demand and total consumption.

[Russell]

Seen lots of burnt mini motors, Time to check with the factory and to find the cause.

My 36V 250W Bafang QSWXB failed after 3,000 miles, the problem wasn't with the gears, they looked great, or the windings but with the HALL SENSORS and their wiring. When I opened the motor I found frayed hall sensor wires which may have led to the failure of the "yellow" hall sensor.

Now why I'm posting this info on the GM site. I had an extra GM Mini 24V 250W motor core sitting around because the first mini-motor GM sent me had a cracked flange. Though I suspected the Mini to be a Bafang I was pleasantly surprised to find the Mini core was the same size as my Bafang core. I installed the Mini core into the Bafang case and was ready to roll again.

The 24V is lacking low-end grunt even at 36V/22A so on my first long ride with the new Mini core I used my 48V LiFePO4 battery. The motor still lacked low speed torque but it was pretty fast at around 29 mph on the flats. After a few high speed runs I settled back to a more conservative pace for much of the ride. Near the end of the route I used full power up a series of hills (max 1,086W) then for about a mile afterwards. It was at this point the motor up and quit. My Watts-Up meter showed a higher than normal current draw at idle which dropped to normal when the hall connector to the motor was disconnected.

When I got home I found there was a short between the red and black pins on the motor hall sensor connector. When I opened the motor I found the heat had fused two tightly looped red and black wires together. While I realize I was operating the motor well above spec this problem could have been avoided if the hall wires had a high-temperature insulation rather than a standard insulation which melted easily.

I was able to repair the motor and I'm off for a ride now so wish me luck

[rolf_w]

...While I realize I was operating the motor well above spec this problem could have been avoided if the hall wires had a high-temperature insulation rather than a standard insulation which melted easily. I was able to repair the motor and I'm off for a ride now so wish me luck

we started to repair the 'burnt' MiniMotors too: those with intact windings but melted hall element harness we replaced all connections with high temp insulated cables and in case we broke of pins whilst dismantling we replaced the hall elements too. and ... it works!! by the way, if the hall elements are shorted you might think to simply disconnect the hall sensor connector and let the MiniMotor run in the 'sensorless' mode. Unfortunately this doesn't work as the motor is free wheeling and the rotor doesn't spin thus the coils do not produce the signals required by the controller to run the motor...

[Russell]

When I got home I found there was a short between the red and black pins on the motor hall sensor connector. When I opened the motor I found the heat had fused two tightly looped red and black wires together. While I realize I was operating the motor well above spec this problem could have been avoided if the hall wires had a high-temperature insulation rather than a standard insulation which melted easily.

I was able to repair the motor and I'm off for a ride now so wish me luck

The repaired hall wiring in the GM 24V Mini Motor held up however I missed the torque of my previous 36V Bafang so after 93 miles I removed the Mini Motor core from the Bafang case.

My 36V 250W Bafang QSWXB failed after 3,000 miles, the problem wasn't with the gears, they looked great, or the windings but with the HALL SENSORS and their wiring. When I opened the motor I found frayed hall sensor wires which may have led to the failure of the "yellow" hall sensor.

My plan was to convert the Bafang to sensorless operation. I have a controller capable of working sensorless and it will operate a freewheeling Mini Motor however it takes a light throttle to get smooth take-offs and the controller loses the motor position with the throttle off and has to reacquire it when the throttle is engaged again. In a word it's a pain. There are supposedly other controllers out there which work better with freewheeling motors but since a hall sensor was already fried in my Bafang I ripped out all of the hall wiring and locked the clutch up so it would NOT freewheel. The 36V Bafang works like a champ again only now it's sensorless The same thing will work with a GoldenMotor Mini Motor if someone want to go sensorless or they could try one of the sensorless controllers to see how they work. Has anyone tried a GM Magic controller in sensorless mode on a Mini?

-R

[rolf_w]

... Has anyone tried a GM Magic controller in sensorless mode on a Mini? -R

Yes, I tried and it didn't work. One needs to block the freewheeling, which I haven't tried - How did you do this?

[Russell]

... Has anyone tried a GM Magic controller in sensorless mode on a Mini? -R

Yes, I tried and it didn't work. One needs to block the freewheeling, which I haven't tried - How did you do this?

There are now sensorless Bafang motors being sold and people are using them and claiming they freewheel so running without halls on a freewheeling motor is possible however the controller I have works far better when the motor is not of the freewheeling variety.

Anyway it's a simple matter to lock up the clutch mechanism if you have a welder however I didn't and resorted to JB Weld which so far is holding up. See this post on E-S for more details;

http://endless-sphere.com/forums/viewtopic.php?f=4&t=10458&start=45#p212576

The gear/clutch assembly is slightly different on the Mini Motor I have (see attachment) but the internals should be the same.



-R

[Perbear]

Instead of replacing damaged minimotors, should it not be smarter to put on a temperature sensor on the stator that can derate power input when the temperature is rising above a set (and safe) level? Sensor input can easily be added to existing Hall sensor wires and handled by a revised Magic controller.

This is a method that has been used for almost a century on other motors