Overvolting Bafang SWX02 to 59V after 1000 miles

[WheezyRider]

Been overvolting my Bafang SWX02 36V 250W hub motor to 59V at 15A and completed 1000 miles on it. Now I have replaced it with a Bafang G020250 DC, so I can fit a cassette and make full use of my 8 gear shifters again.

In the process I had a strip down to see what the insides looked like. I was worried that there might be a lot of wear on the nylon cogs. So here are some pictures of what it looked like after cleaning the grease off:









So it looks completely fine.

What is interesting if you look inside the brand new G020250, the marking on the clutch is "G020350", so it looks like the clutch can handle more power than the "250W" motor is supposed to produce:

 

[vfr400]

By 59v, do you mean 14S?

It takes a lot to wear those gears. forum member Cwah ran a high speed Q100 at 20 amps and 48v for some time in a bike that he never pedalled and did around 30 mph. when the motor was decommissioned, I disassembled it to find it full of rust and some wear on the gears, but its gears are much smaller than Bafang ones.

It's the torque that damages the gears, as long as you keep the current down as you increase the voltage, they'll be fine.

 

[WheezyRider]

By 59v, do you mean 14S?

It takes a lot to wear those gears. forum member Cwah ran a high speed Q100 at 20 amps and 48v for some time in a bike that he never pedalled and did around 30 mph. when the motor was decommissioned, I disassembled it to find it full of rust and some wear on the gears, but its gears are much smaller than Bafang ones.

It's the torque that damages the gears, as long as you keep the current down as you increase the voltage, they'll be fine.

Yes 58.8 max voltage.

The original SWX series had smaller cogs, and there are lots of examples of SWXH motors out there with stripped cogs. However, the 02 version and the G0 series seem to have bigger cogs, which helps.

I still am trying to get my head around things in terms of torque. From experiment and instinctively, it seems a lot better to keep the amps down and volts up. By over volting I get loads of torque...if there is something heavy on the back rack and I start off in PAS 6, you can feel the front wheel lifting off the ground. Hill climbing is great.

Both increasing the voltage gives more torque and increasing the amps gives more torque. The reasons for more amps giving more torque are quite obvious, but it's a bit more subtle with increasing the voltage.

I think it's because the motor is an inductor and inductors don't like rapid changes in current, but by increasing the voltage it is easier to drive a rapidly changing current through it. Also, due to transformer effects in the motor, voltage gets converted into "armature amps", so increasing the torque.

I like the fact that I can still use the same 36V controller and it barely even gets warm. I've tried shunt soldering, but the controller gets stressed with the extra heat it generates.

 

[vfr400]

It can be explained in simpler terms. The controller is firing PWM pulses of energy at the motor. Each individual pulse has a width, which you can call the current and a height, which is the voltage direct from the battery. The energy in each pulse is the width times the height. it's the total amount of energy getting into the motor that makes the torque. In other words, increasing the width is the same as increasing the height. By way of example, I had two similar motors. One did 260 rpm at 36v and the other was the 48v version that also did 260 rpm. When running the 36v one at 36v and 20 amps, it had identical performance to the 48v at 15 amps - the same torque, power and speed. Maybe there was the 3.33% theoretical difference, but that was unnoticeable on the road.