Pololu Robotics & Electronics
My account Comments or questions? About Pololu Contact Ordering information Distributors

Pololu Forum

Back EMF of Motor Driver 24v18

We are using a Pololu Dual G2 High-Power Motor Driver 24v18 Shield for Arduino to control two
bi-stable electro magnets (solenoids). The resistance of the magnets is 3.8 Ohm. Pole changing is used to change the direction of the magnetic field (pull/push).

To get a good force response we apply a step voltage using a 12 to 24 v boost DC-to-DC power converter (step-up converter) in a test vehicle. (We are considering using a 36 v converter in the future.)

Considering that our design involves driving electromagnets we are concerned that the electromagnet will store energy when powered and will generate a “back EMF”, or counter EMF (CEMF), when the supply is switched off. It is our understanding that if this back EMF is not controlled or suppressed it will generate very large voltages that in turn can cause damage to electronics or loss of data.

Initially we considered ramping down the voltage after applying the step voltage to the magnets but because of PWM nature we don’t think this will work. Instead we are considering putting an RC element in parallel with the magnets. Our idea is to use a 10 micro Farad capacitor and a 7.5 Ohm resistor.

From the forum we have learned that the output MOSFETs have integral diodes that will provide fly back protection. Will this be enough?
Currently we have some problems burning a servo that we are using in parallel with the magnets so we are trying to find the root cause for this problem.


The driver’s built-in flyback diodes are generally enough protection, but depending on your setup, there could be other related issues. Could you post a diagram or schematic of your full setup? Could you also post datasheets or other documentation for your solenoids and servos?


A post was merged into an existing topic: Possible to recover from over-current short-circuit?