As Rossw posted all it takes to reverse a DC motor is a DPDT relay, to swap + and - and a way to turn power on/off. Or if you want to get sexie use an H-bridge. It uses 4 transistors to effect both power and reverse control.
Here is an eBay link to one I used for a window controller. Mine is only rated at 2A per channel, if you really need 5A there are higher power versions. But be careful of current ratings posted by eBay venders, some are shall we say rather creative.
http://www.ebay.com/itm/L298N-Dual-H-Bridge-DC-Stepper-Motor-Drive-Controller-Board-Module-for-Mega-UNO-/351285863187?pt=LH_DefaultDomain_0&hash=item51ca44e313
A few thoughts from my experience using a L298 based H-bridge:
1) It is a two channel unit. A lot smaller and quieter then relays.
2) The chip does current sensing but the board does not implement it. The chip current sense leads are at the extreme ends of the L298 so it was pretty easy to lift the leads and install a .1 ohm current sense resistor. I can post a picture of my mod if you want.
3) It is over current protected (die thermal) but not short circuit protected. I blew one up during debug by being careless with test leads, but for a couple of bucks letting out the magic smoke did not break the bank.
4) Sounds like you application is a lot like mine, where the H-bridge has an extremely low duty cycle so thermal management is trivial. Lots of thermal mass in the on board heatsink.
/tom
Here is an eBay link to one I used for a window controller. Mine is only rated at 2A per channel, if you really need 5A there are higher power versions. But be careful of current ratings posted by eBay venders, some are shall we say rather creative.
http://www.ebay.com/itm/L298N-Dual-H-Bridge-DC-Stepper-Motor-Drive-Controller-Board-Module-for-Mega-UNO-/351285863187?pt=LH_DefaultDomain_0&hash=item51ca44e313
A few thoughts from my experience using a L298 based H-bridge:
1) It is a two channel unit. A lot smaller and quieter then relays.
2) The chip does current sensing but the board does not implement it. The chip current sense leads are at the extreme ends of the L298 so it was pretty easy to lift the leads and install a .1 ohm current sense resistor. I can post a picture of my mod if you want.
3) It is over current protected (die thermal) but not short circuit protected. I blew one up during debug by being careless with test leads, but for a couple of bucks letting out the magic smoke did not break the bank.
4) Sounds like you application is a lot like mine, where the H-bridge has an extremely low duty cycle so thermal management is trivial. Lots of thermal mass in the on board heatsink.
/tom
