As you make your decision, please note that polarity switching isn't an optimal dc motor control method, especially if its immediate (via DPDT Relay or whatever, with a minimal time delayin contact changeover). It works, but doesn't control the field build up or decay of either a permanent magnent or shunt wound motor. The end result can be a more severe arc when switching which shortens motor life.
Polarity switching of a fixed source voltage also negates accel or decel control and fixes speed (voltage is speed to a dc motor). A regen drive (4 Quadrant as Al mentions) provides accel, decel, variable speed, and better torque control at low speeds. Possible mfg's of these include KB, Baldor (many of the Baldor units are KB), Dart, Minarik, Fincor (now part of Emerson), etc. While I have put a pile of the KB #KBMG212D out there successfully in many automation projects, I am sure any of those manufactures would have a suitable offering.
If you decide to spend the money on a real drive, skip the non-regenerative (2 Quadrant) types. A KB #KBIC120 can be had new for $80... but the performance isn't as nice. Good Luck!!  |