Using Arduino to control a 6A motor

Hey all,

I'm working on a bot with some friends, and we need to find a way to interface an Arduino Mega PWM singal and a 6A 12V motor signal so that It can control both direction and speed. I think we've decided on a H-Bridge format ('cause that's all we know of.. haha, I'm a novice in electronics... and I'm designated to work on the electrical work: figures). Anyway, we need to build an H bridge that can handle the 12V 6A current, but is signaled only by Arduino's 5V PWM output? Should we go for BJTs or MOSFETS? and furthermore, what transistors will work? Like I said, i'm a novice at circuit design, and I've fried too many transistors to help! I understand vaguely what the H-Bridge Circuit entails, but I still need help working through the discrete components! Please Help! :-/

An H-Bridge for a 6A motor really isn't a beginner project. You will be much happier, and working quicker, if you just buy the correct motor driver shield, and plug it in.

Like I said, i'm a novice at circuit design, and I've fried too many transistors to help! I understand vaguely what the H-Bridge Circuit entails, but I still need help working through the discrete components!

Ultimately, at your level, you are likely to burn thru more components, and money to boot. Unless your goal is to understand discrete component h-bridge design, and money isn't an object while you learn, cut your losses now, and buy an h-bridge.

Pololu (http://www.pololu.com/) has a decent selection, although the one you would probably want:

http://www.pololu.com/catalog/product/705

...is currently out of stock, and more won't be available until February at the earliest (according to the site).

There are plenty of other vendors of h-bridges, so do some googling until you find one for your budget and needs...

If you're intent on building your own, you could probably use this design:

http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-circuit.html

But substitute transistors in a TO-3 case (with appropriate heatsinks as needed) instead of the smaller TO-220 package; a good common complementary pair would be the 2N3055 (NPN)/ MJ2955 (PNP) for this. You will need to include the diodes, by the way. Be sure to use optocouplers for switching the power transistors (4n25/26 would be OK).

You could probably do a MOSFET h-bridge, but in order to do it right you need to either use complementary pairs (and P-types can get expensive), or you can use an all n-type bridge, but then you have to implement a charge-pump on the top end to get it to work properly.

Good luck.

:)

Good advice from the Gods. I've built dozens of 'em but after following that link I'm just gonna buy from now on.