Problem with Bafang hubkit 500W48V

[Mardsjo]

I have a Bafang hub kit with 500 W 48 V that I mounted on a 26" mountain bike. I throttle with a thumb control. Everything worked perfectly for six months when one day the motor suddenly started to chop. I then changed to a new similar motor controller and everything worked again for a couple of months until the same thing happened again. A few months later I tried again, everything worked for a couple of days but then the same problem returned.
I haven't opened the engine but don't think the problem is there.
Anyone recognize the problem and know how to fix it?
Can I maybe change to a controller for 750 W if it can withstand more?

 

[Chalo]

Everything worked perfectly for six months when one day the motor suddenly started to chop.

By "chop", do you mean stutter and run roughly, or do you mean it turns off briefly, and then comes back on?

The first problem would most likely be Hall sensor wires, plugs, or the sensors themselves (for instance from heat damage). The second problem would most likely be battery weakness or cell imbalance.

Neither one would be improved by the use of a more powerful controller, and might become worse.

 

[Mardsjo]

By "chop", do you mean stutter and run roughly, or do you mean it turns off briefly, and then comes back on?

The first problem would most likely be Hall sensor wires, plugs, or the sensors themselves (for instance from heat damage).

Thanks for quick reply!
It runs choppy or bumpy. That it hacks its way forward and then finally stops going. I don't think the battery would be bad.
Don't really know what is meant by, Hall sensor wires, plugs, or the sensors themselves... How do I check it?

 

[James340]

Thanks for quick reply!
It runs choppy or bumpy. That it hacks its way forward and then finally stops going. I don't think the battery would be bad.
Don't really know what is meant by, Hall sensor wires, plugs, or the sensors themselves... How do I check it?

I have had same problem with the motor and it was a bad hall censor connection.This tool is helpful.

 

[amberwolf]

If the battery is dropping in voltage under load, you can get stuttering operation for two reasons.

If the voltage drops enough, the BMS may actually power off the system to protect the cells from damage that can lead to a fire. That usualy turns the screen, lights, etc off as well as the motor.

If the voltage doesn't dip far enough down to trigger the BMS to turn power off, it may still dip enough to trigger the controller LVC and shutdown the motor but still leave it turned on.

In either case when the load is removed (motor off) the voltage rebounds and the system works again.

If it's the battery, changing to a higher power controller will just cause the problem to be worse, and put more stress on the failing battery.


You can verify if the battery is a problem by checking the voltage of each cell (group) inside it. If they are all identical and normal at full charge, then it's probably ok. If any of them are different in voltage, then the battery has a problem. the amount of difference can indicate how bad it is.


Another common fault is connections and cables. You can unplug and replug every cable (especially for battery and motor) one at a time, to see if it's just a bad connection. Cables take more testing, usually with a multimeter.

Sometimes you can see cable damage, especially at the wire exit from the motor itself at the axle--this gets damaged easily especially if the bike falls over or crashes.

 

[Chalo]

Thanks for quick reply!
It runs choppy or bumpy. That it hacks its way forward and then finally stops going. I don't think the battery would be bad.
Don't really know what is meant by, Hall sensor wires, plugs, or the sensors themselves... How do I check it?

Hall sensors are position sensors that tell the speed controller where the rotor magnets are in relation to the stator phases. They are the most vulnerable part of the motor to excess heat, and they depend on steady connection to +5V, GND, and signal wires to the controller. If any of them is damaged or disconnected, a controller that depends on them won't be able to run the motor smoothly or at all.

The easiest workaround is to use a sensorless or dual-mode controller instead of what your bike already has.

 

[Mardsjo]

I have had same problem with the motor and it was a bad hall censor connection.This tool is helpful.

Thanks for the tips!
Did it come with clear instructions on how to use it?
How did you fix the problem with the Hall sensors?

 

[Mardsjo]

Hall sensors are position sensors that tell the speed controller where the rotor magnets are in relation to the stator phases. They are the most vulnerable part of the motor to excess heat, and they depend on steady connection to +5V, GND, and signal wires to the controller. If any of them is damaged or disconnected, a controller that depends on them won't be able to run the motor smoothly or at all.

The easiest workaround is to use a sensorless or dual-mode controller instead of what your bike already has.

Thanks for the great info!
Is it possible to fix if the Hall sensors are bad or does the motor have to be replaced?
If I were to switch to sensorless or dual-mode controller instead. How do I know what to choose one that fits my motor?

 

[fechter]

Often hall failures are just a bad connection in one of the connectors. Trace the wires coming from the motor and look for any plugs. Unplug the connector and visually inspect the contacts. Look for any signs of damage or corrosion. Fully reconnect the plug and test.