MP5 26” fat bike front hub current draw problem

[C.White]

Hi,  I’ve had my MP5 front hub for 8 month’s. It works but I can only get 750 watts of power out of it.  The battery I am using is a 16s8p lifpo4 30 ah. Battery is rated at 3C draw continuous.  Controller is set to 30 amp draw, 360 rpm, 70 amp phase, 100 percent acceleration, 48v, 62v high, 42v low.  Here’s the problem.  At full throttle with my 6’2” 230 lbs bulk sitting on the bike. The cycle analyst is only reading 15 amp maximum draw and 750 watts of power. I double checked these numbers by hooking a 100 volt/100 amp shunt on the battery and it also reads a 15 amp maximum draw.  What could be limiting the controller to a 15 amp max draw? 

I left all the settings the same on the controller but I reduced the rpm to 250.  On the test run from full stop to full throttle on a slight inclined hill, the amp draw was reduced to 12 amps maximum. The bike never got over 10 km/h. It appears that reducing the rpm settings also lowers the maximum amp draw.   I’m pretty certain the motor should be drawing 30amps of power until it reaches the set rpm limit at full throttle.   Please correct me if I’m wrong.  I’m a big guy and I need all the torque I can get.

[Bikemad]

Hi andto the forum.

I suspect that you may not be getting a high enough voltage output on the throttle signal wire, which is sometimes caused by a low +5V supply. 

If the +5V output from the controller is too low, the throttle would be unable to output sufficient voltage to allow the controller to run at full power, as it needs an output voltage of at least 3.25V for maximum rpm and power.





If possible, check the +5V supply for the pedelec (measured between the Red and Black wires) or between pins 1 and 2 on one of the brake connectors on the control harness and see what voltage reading you get (it should be ~4V).

If it's below 3.25V, a weak +5V regulator inside the controller is probably failing, and you are not going to achieve the required full throttle output to produce maximum power (i.e. maximum current).

However, if the voltage reading on the +5V wire is above 4V, it may be a problem with the throttle itself.

With the wheel raised off the ground, see if the wheel speed reduces when you release the throttle very slightly, as the very last part of the throttle movement does not typically affect the motor speed as most throttles will output the maximum required 3.25V before the throttle reaches the full extent of its available movement.

If you release the throttle from 100% to 80% and the maximum rpm instantly begins to slow, this would confirm that the controller is not receiving the maximum required signal voltage from the throttle.

Check out Tommycat's Guide to Hall Sensor Throttle operation, testing, and modification for further information on typical throttle voltages.

Alan