Brian Scearce wrote:

> An easier trick I've seen used (but I haven't done it myself, so
> I can't give you a "here's what to watch out for") is to use relays
> as the H-bridge switches, then add just *one* MOSFET or BJT at the
> "bottom" of the bridge,

> If you don't want to do active braking, you can even use just two DPST
> relays (one relay per diagonal) instead of four SPST relays.

  If you *do* want to do active braking or even if you don«t, you use
two *dirt common* SPDT relays.

  Otherwise, one DPDT relay to reverse.  Arguably, a relay is as
efficient as an H-bridge in most cases.  If for example you rarely want
to reverse, it«s *very* efficient!
-- 
  Cheers,
        Paul B.