Rear Bafang hub motor speed hack?

R

Ramonplutarque

10 µW
Joined
Mar 22, 2019
Messages
5
Hi, I have a 750w Bafang rear hub motor setup. But I’m a little disappointed by the top speed. As it turns out the motor has a 36km/h (22mph) speed cap. Which I find pretty stupid. I have a 850c display in which I put the speed limit to 99kmph, but that changes nothing to the speed. So I’m guessing the speed cap is programmed in the controller ? Or maybe a physical cap? (Extra part soldered that is limiting speed?)
The controller is a 10A, 20A peak.
My question is how can I remove this speed limit?
Thanks
 
I was willing to do a shunt mod, but with this speed cap I’m pretty sure it would be useless, besides getting me a little faster to 36kmph
 
Ramonplutarque said:
I was willing to do a shunt mod, but with this speed cap I’m pretty sure it would be useless, besides getting me a little faster to 36kmph
Click to expand...

Probably not a speed cap in the way you are thinking. Based on the physical parameters of the motor (windings, etc), the motor will only spin up to a certain speed with a given voltage. The only time current comes into play is because being able to propel a vehicle and maintain its speed, energy/power is required (voltage times current). But no matter how much current you make available at a certain voltage, you'll never go faster than the wheel can spin at that voltage with no load (wheel off the ground).
 
Ramonplutarque said:
As it turns out the motor has a 36km/h (22mph) speed cap. Which I find pretty stupid. I have a 850c display in which I put the speed limit to 99kmph, but that changes nothing to the speed. So I’m guessing the speed cap is programmed in the controller ?
Click to expand...
Run the bike off ground (upside down, etc), so the wheel isn't loaded.

If the speed is *exactly* the same at full throttle there as it is on ground while riding, then it is a speed limiter in the controller.

If the speed is higher (a few percent or more), then the limit is your battery voltage and possibly the controller current limit.

If it is battery voltage, then it will also drop in max speed as the battery discharges.

If it is a speed limit, it will always have exactly the same max speed thru the discharge (assuming the speed limit is below what the battery voltage at that moment would allow).
 
amberwolf said:
Ramonplutarque said:
As it turns out the motor has a 36km/h (22mph) speed cap. Which I find pretty stupid. I have a 850c display in which I put the speed limit to 99kmph, but that changes nothing to the speed. So I’m guessing the speed cap is programmed in the controller ?
Click to expand...
Run the bike off ground (upside down, etc), so the wheel isn't loaded.

If the speed is *exactly* the same at full throttle there as it is on ground while riding, then it is a speed limiter in the controller.

If the speed is higher (a few percent or more), then the limit is your battery voltage and possibly the controller current limit.

If it is battery voltage, then it will also drop in max speed as the battery discharges.

If it is a speed limit, it will always have exactly the same max speed thru the discharge (assuming the speed limit is below what the battery voltage at that moment would allow).
Click to expand...

Good tips!
 
amberwolf said:
Ramonplutarque said:
As it turns out the motor has a 36km/h (22mph) speed cap. Which I find pretty stupid. I have a 850c display in which I put the speed limit to 99kmph, but that changes nothing to the speed. So I’m guessing the speed cap is programmed in the controller ?
Click to expand...
Run the bike off ground (upside down, etc), so the wheel isn't loaded.

If the speed is *exactly* the same at full throttle there as it is on ground while riding, then it is a speed limiter in the controller.

If the speed is higher (a few percent or more), then the limit is your battery voltage and possibly the controller current limit.

If it is battery voltage, then it will also drop in max speed as the battery discharges.

If it is a speed limit, it will always have exactly the same max speed thru the discharge (assuming the speed limit is below what the battery voltage at that moment would allow).
Click to expand...

Thanks for the tip!
Indeed the max speed seems to follow the battery discharge (when the wheel is lifted). Which means my top speed is determined by the motor’s max spin rate (related to the voltage)?

So im guessing if i want to maintain the top speed for longer i would need a bigger battery? Its currently a 52v 14ah. If i get a 19-20ah i would cruise at the maximum top speed for longer?
 
E-HP said:
Ramonplutarque said:
I was willing to do a shunt mod, but with this speed cap I’m pretty sure it would be useless, besides getting me a little faster to 36kmph
Click to expand...

Probably not a speed cap in the way you are thinking. Based on the physical parameters of the motor (windings, etc), the motor will only spin up to a certain speed with a given voltage. The only time current comes into play is because being able to propel a vehicle and maintain its speed, energy/power is required (voltage times current). But no matter how much current you make available at a certain voltage, you'll never go faster than the wheel can spin at that voltage with no load (wheel off the ground).
Click to expand...

Thanks for the info!
 
Voltron said:
Does the controller have a pair of single, usually grey, wires that plug together?
Click to expand...

Nope. But i think i see what you are talking about. I had a cheap ancheer chinese ebike for about a month which had those. I had to send it back because the build quality was really too poor.
 
With a hub driven bike, it's not about the display you use, it's the controller that determines the speed limit - if there is one.

If I'm reading this right/understanding, your display setting is not affecting the controller's setting. If that's the case, there's a very good chance the controller isn't completely compatible with the display, or it's locked down, with that parameter hard set in the controller.

That being the case, you'll need a different controller, with fully compatible display, to go faster.
 
ltfereau10@aol.com said:
All great info but how do we make it go faster?
Click to expand...

More money. You could buy a controller with field weakening, which would allow the motor to run past the normal rpm limit, but will use a lot of battery when it kicks in. Or you could buy a higher voltage battery and a new controller that works with it. Or both; the sky's the limit if you have money to throw at it.
 
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