# Regenerative braking: reverse polarity protection for Arduino

Hi all,

I'm using a Sabertooth 2x25 motor driver which supports regenerative braking.
This means that it will charge my 4S Lipo when the motor (max 20A stall current) decelerates.

I'm using the same battery to power my Arduino, through a switching/buck convertor (VMA404) which steps down the voltage to 5V. So this circuit is connected in parallel with the motor circuitry.

Now I'm wondering how to deal with the fact that regenerative braking will reverse polarity of the battery. I suppose that will either fry my buck convertor or Arduino.

I could put a diode in front of the switching convertor to protect it, but even then I'm stuck with the problem that the Arduino won't get power during braking events.

What is the typical way to deal with this? I did my research, but can't seem to find much about this.

Edit: The Sabertooth itself has a 5V output but that one can only supply 10 milliamps, which is not enough for my needs. So I would like to tap off the main battery directly, through my BEC.

Thanks a lot!

I just realized that my question is based on a misunderstanding of how regenerative braking works.
So I'll just answer it myself because it might be useful to others too.

Basically, back EMF does not reverse polarity. In fact, it is of the same polarity as the applied voltage. When running normally, this voltage is lower than the applied voltage. When braking, it can be (much) higher and can therefore charge the battery.

So there is no reversal of polarity, hence no problem to be solved :).

Actually no! The reverse EMF is always there. IT is what keeps your motor from an infinite speed. When you remove the normal power, that just leaves the the back EMF to continue. Regenerative braking shorts the back EMF through a variable resistor, that may be ZERO Ohms resistance, or a short circuit for ultimate braking.

Paul

Thanks for replying, I'm learning every day! I finally finished my first robot, so since you made the effort of responding, I wanted to share the result with you

Video 1: https://youtu.be/vIddskon6ic
Video 2: https://youtu.be/s3aa-ipn5Z0
Video 3: https://youtu.be/rJf3yibiXUA

Regen braking has the ability to DESTROY components unless they are designed to cope with such EMF.

Be very careful in using it to apply holding torque to motors.

For large motors the braking is done via a PWM'd switching device, with the current continuously