Asked — Edited

Controlling A 12 Volt Servo With Outside Power Source

Afternoon All

So I need to control a 12 volt servo using an outside power source. I'm assuming I need an H-bridge to handle the power but I can't wrap my head around the wiring specifically the signal wire. I have standard Pololu H-bridges (see below). I've worked with H-bridges and EZ before.

If my assumption is wrong could it be as easy as wiring my servo to my 12 volt power source (with a common ground to the EZ) but use a fuse (for protection) and then use a signal wire to my EZ for control? I've seen postings here that seem to say that. The action is to raise and lower a robot head. It will require 12 volts.

Any advice is always welcome.


Daniel User-inserted image

Skip to comments


Upgrade to ARC Pro

Your robot can be more than a simple automated machine with the power of ARC Pro!


From what I understand if it's a 12V servo you can wire it to a 12V battery. fuse? sure.


If you are going to use the new EZ-B board, you will be able to plug it right into the board provided you supply the board with 12 volts.

If you are using one of the previous boards, or you are using a different voltage to the new board, or you do not want to draw too much amperage from the board, your second assumption was correct. Here is a picture. I left the fuse out, but you get the idea. User-inserted image


As illustrated above, you don't need an H-bridge to operate a servo. The H-bridge is used to control electric motors.


To break this down a little more, H-Bridges are used for stand alone DC motors only. A servo is cool as it already has a control board in it that will reverse it's DC motor. It also has a little pot in there that sends positioning info back to the EZB.


Ah. So flyback is not a problem. I'm still ansy from earlier when I wired my servo directly through my board and the battery pack exploded. So the servo handles the change in current safely.

Thanks everyone :D



Correct but you still need to be careful as to how large a servo you attach directly to EZB. If your servo needs more voltage and amps then the EZB will supply you need to use a external power supply for them. However the signal wire from the servo still attaches to one of the signal pins of a Digital port. ;)


@mulberry , glad your ok , I've never caused a battery pack to explode before outside of purposely doing it. Did any electronics get damaged.


No electronics damage. Just my nerves :-)

This is my last question of the day.

So my heavy duty servo just grinds when I activate it. The head seems to be locked in position and I can't even force it.

I've restarted EZ but no change. It just whines and grinds.

Is it likely shot?


United Kingdom

If it is stiff/stuck when no power is applied then I assume it's seized for some reason (12v may be different, I've not used 12v servos yet, so check with others or take their word over mine if they say I'm wrong).

If that's the case, open it up and check the gears inside to make sure they are all aligned nicely. I had a few Tower Pro MG90s which were stuck and needed to be opened up and reassembled before they wanted to work.


Thanks Rich. You've bee a tremendous help as always.



I had one explode on me once. It was like a shotgun. It went through the ceiling. I was seeing if you could charge an Alkaline Energizer. But, it was a regular one, not a re-chargeable one.

I was very lucky. ;);)