Noob Question:

I have planned an arduino mega which will be driving several motors, two of them are quite large (12v, 25A stall current) I don’t need variable speed on these, though it must be reversible, just a simple, cost-efficient reversible on/off. If it matters, I will also be plugging in an adafruit motor shield for the other motors, which obviously won’t handle these 2. how best to do this?

Some 12V relays and transistors to drive them might be the most cost-effective way of controlling the two big motors.

http://rockingeeks.org/index.php?option=com_k2&view=item&layout=item&id=3&Itemid=61

Grab some car relays, they are quite cheap and usually rated pretty high

that wouldn't allow for the motors to operate in 2 directions would it? also, would they just be plugged directly into the arduino?

Any DPDT relay can do two directions, but do you need stop as well?

would they just be plugged directly into the arduino?

No, at this size you'd need a transistor to drive a relay.


Rob

Definetly gonna need those transistors, and youll need two but they are isually alot cheaper

It may be worth considering configuring some MosFETs in a H-bridge.

that wouldn’t allow for the motors to operate in 2 directions would it?

Yes, it would. That’s why I provided a pointer to an article about wiring two relays so that you can drive a motor in both directions.

also, would they just be plugged directly into the arduino?

Not if the relay coil requires more than 5 volts or 35 milliamps. I’d be surprised if you could find a 5V <35mA relay whose contacts could handle 12V 25A. I just checked DigiKey and such relays only had contacts up to 16A. That’s why I said you would need transistors to drive them. Using a transistor you could power the coil with the same 12V you were switching. The coil current will be about 50 to 150 milliamps so you don’t need a BIG transistor. The relays should cost about $4 each.