Say I have a 48v motor/controller and I'm just coasting downhill which is now causing regen. Will this harm any of my circuits? I'm not sure if my board has regen or not... or does it not matter?

 

A properly-designed motor controller won't be harmed.

 

Is the downhill speed rate causing over-speeding of the motor?

 

No it's not. it's probably around 25% of what the motor can handle.
I just wasn't sure because the controller just died when I started going down hill more than usual. Didn't smell anything burning.

 

If it is an issue, you could fit a disconnect relay every time you take the control to zero, which presumably it will be when coasting downhill.

 

https://www.ebay.com/itm/122112318908

I've used this controller for a couple of years without any issue. It's only when "regen" starts kicking in.
The thing is that I don't have a physical brake on my machine as I just rely on the motors to go backwards.

 

What I have done for a regen brake is via relay, open the supply to motor and place a short (or braking resistor) across the the motor

 

For quicker braking you want to create a negative resistance load on the motor.

 

There are three basic methods of braking a motor , Dynamic, Regenerative and plugging

 

thanks for the help. I'll do more digging into this.

 

Most PWN motor controllers are what they calling single quadrant. You can supply volts and amps TO the motor. If you overspeed your motor, it may damage the output switch because of too high volts from the motor (its acting now as a generator)
The next type is a two quadrant controller, but i wont describe it
The bells and whistles is a four quadrant controller, It will control the speed of the motor and provide braking if the commanded speed is less than the motor speed. It also has the advantage that you can electronically put the motor in reverse.
You can tell this type because it will have four output switching elements. Not easy to implement as it needs motor speed feedback.(and not just the back emf of the motor)

 

Years ago I DID destroy two motor controllers because the motor was over-running and there was no braking load resistor in place. so you might have done that.