Hello, I use a hub motor (HT3525) with 45V lifepo4 battery p

[peters]

Hello,
I use a hub motor (HT3525) with 45V lifepo4 battery pack, and I have a problem:
during downhill above 40..45 kph the back-emf is higher than the battery voltage, so the back-emf charges the battery with uncontrollable current through the controller's MOSFET freewheel diodes and the BMS. Unlike the regen braking, the current can be very high because it is not limited (only by the serial resistance of the motor) and I'm afraid it may damage the battery at high speed.

What is the usual solution for this?

(if I put a diode on the power supply line, then normal regen would not work and the DC bus voltage may increase and damage the controller at regen. )

(moderator edit: Since it is not a circuit schematic or really a request for one, your post has been moved out of "Upload Your Circuit Schematics & Requests Here..." and into it's own thread so people can see it and you can get the help you are after.)

 

[John in CR]

For high current to go back to your battery then you have a strong braking force. It must be an extremely steep hill.

 

[peters]

Well, I think if the motor needs 50A on a hill upwards then it will produce also 50A downhill when back_emf > Vbat, because the torque is the same, just opposite direction (not taking into account the losses). Although I did not try it, I rather pulled the brake when I saw -10A on the display.

 

[Alan B]

1) use a higher voltage battery

2) use a diode to prevent REGEN altogether

3) use a contactor to disconnect the motor from the controller

4) use larger rims/tires

5) There is so much air resistance and other losses that the current back in will be much less than the current out, monitor it and unless it is more than your batteries can take, enjoy it.

6) slow down, this is a bicycle not a motorcycle

 

[Alan B]

Well, I think if the motor needs 50A on a hill upwards then it will produce also 50A downhill when back_emf > Vbat, because the torque is the same, just opposite direction (not taking into account the losses). Although I did not try it, I rather pulled the brake when I saw -10A on the display.

Not likely.

On a 12% hill I use 3500 watts going up at 25 mph and get 500 coming back down at 11 mph.

 

[peters]

I choose option 1: higher voltage, higher speed