Hi,

 

I have an ebike that's got a Bafang 250w hub motor, 7A KT controller and a 36v battery. I set the LCD controller to max speed (about 40 mph i think) but the wheel won't spin faster than 20 mph when the bike is on the stand, 18 mph riding it.

Is that normal what could be holding it back? Should I upgrade something to get it to about 23 - 25mph?

 

Cheers

only 7 amps is your problem get a 20A controller if the batt can handle that much!

Or it could be the winding code of the motor.

The winding code should be within the code number on the motor casing.

Motors can only rotate as fast as their construction allows. Once it reaches it's design maximum rpm it produces enough back EMF to equate to the supply voltage, so cannot spin any faster. If this is the case the only way to get more speed is to increase the voltage, which means a new battery and controller and display.

That's a lot of expense to make something ilegal !

Thanks for the info. The motor has code RM G020.250.DC 31 1. stamped on it.

Probably not a lot you can do safely, you'd need a more powerful hub motor (1000-1500W), controller (17-20A continuous, 35-40A peak) and a higher voltage battery (48-52V) and safe charger. Also a new controller.

 

You can't really mix and match these safely, if you really need the extra few mph then I'd look at a new kit / donor frame.

 

Gl!

No matter how fast I can go city traffic slows me right down to average 8.5mph.

No matter how fast I can go city traffic slows me right down to average 8.5mph.

try the country lanes the speed limit round our race track is 60mph.

 

All motors have their own maximum speed that depends on the windings. Bafang normally have their winding code as a number in brackets stamped onto the motor. The numbers are in the range 16 to 6 from slow to fast.

 

Your motor is wound for 20 mph at 36v, which is fairly normal for a 15 mph bike because it gives best efficiency and power.

 

The 7A you quoted is the rating of the controller, not how much current it gives. It'll be a 14A or 15A controller.

 

14A and 15A KT controllers are normally dual voltage, which is indicated as 36v/48v. If it just says 36v, bad luck.

 

To get more speed, you have two choices:

1. Change the motor to a higher speed one. Your system will work just about any motor with the 9 pin connector. The problem with that is that 36v and 15A is only enough for around 18 mph unless you're light or fit, so you'll only get the higher speed in favourable conditions, so not the best solution unless you're light and/or fit.

2. Get a 48v battery. If your controller is dual voltage, all you need to do is connect the new battery, and you'll get a max speed of 26 mph and extra torque to be able to cruise at around 22 mph. If it's a single voltage controller, you'd have to buy a new one as well as the battery. Also look at the back of the LCD for its voltage rating.

Wow, thanks Saneagle! I have dual voltage LCD and KT Controller (7A / 15A) , so I need to look for a 48v battery.