How to not kill my electronics with voltage spikes

[Chris Baker]

I had a circuit setup to control the motor and a few other electronics from a 24v battery. The motor was connected to a motor controller from polulo and I also had a micro-controller connected to the 24 volt battery (motor controller: https://www.pololu.com/product/1456) The micro-controller had a power regulator rated at 5-36v (https://www.pololu.com/product/3104). Everything worked fine for a few minutes and then the power regulator on my micro-controller board quit functioning. The micro-controller itself still works fine if supplied with 5v but the power regulator is not outputting any voltage anymore.

I am assuming that there was a voltage spike from the motor that exceeded the voltage rating of the power regulator.

I've attached an imaging showing the circuit layout.

Is there anyway to predict what the maximum voltage spike would be from the motor? and what is the best way to handle the voltage spike? Should I just get a higher rated power regulator, or use a snubber diode? and if so how to size the diode?

 

[Harald Kapp]

I am assuming that there was a voltage spike from the motor that exceeded the voltage rating of the power regulator.

I doubt it. A good motor controller should have the required overvoltage protectio diodes on board.
Anyway, in case it hasn't, there are two protectionms you can add:

1. A zener diode (e.g. 28V) across the power supply input of the microcontroller, anode to "-", cathode to "+" to prevent overvoltage spikes (or to limit them).
2. A silicon diode (e.g. 1N4148 or 1N4001) across the motor, anode to "-", cathode to "+" to limit the negative flyback voltage when the motor is turned off.

Edit: This particular motor has no protection diodes on board because it is an H-bridge controller meant to drive the motor in both directions, hence both polarities of voltage are required (a protection diode as I described above would short circuit teh power in one direction). For this application this motor driver board is "overkill". A simple transistor as described in our ressource here will suffice.

 

[Alec_t]

A suitably-rated bi-directional Transient Voltage Suppressor (TVS) across the motor might help.

 

[Ragnar Már]

Use a separate power source for the micro controller, if you only want to run the motor one direction use the silicon diode as described above and a simple transistor, I think a tip 120 should do the trick.

 

[tilup367]

A good practice is to never run an inductive load directly from a micro-controller. It could burnt all the semiconductors, meaning the output pin you are using. Your best bet is to run it with external power supply with transistor and diode. Easiesy way and cheapiest way. How to choose the diode? 10x higher is to minimal. Exemple : motor 24v 0.05A, take diode 200v 0.5a. Because what happen when turn off, the inductive load is "eating" his intensity to maintain a tension. So amps is lowering and voltage is going higher and higher until all amp is consume.