On Saturday, September 3, 2011 7:45:47 AM UTC-7, Ian Field wrote:
"whit3rd" wrote in message


NO NO NO!
DC excitation of an AC-rated coil is never a good idea.

As long as you alter the voltage to take into account no inductive effect,
its probably not as bad as running a DC contactor with AC.

There's a subtle difference, though, in an iron pole piece that gets
permanently magnetized by repeated DC excitation, and the same
pole piece that gets AC and is repeatedly demagnetized. I'd worry
about the DC causing, maybe after weeks, a failure of a perfectly
good AC component.

The 'no inductive effect' means that only the wire resistance, not the
resistance plus inductance, limits field current. That means the
field current with DC isn't predictably proportioned to the field
current with AC (though THAT could be quickly tested).