Re: Motorized Variac question . . .

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

> I bought a used 120VAC, 20A motorized variac which I

> plan on using in my power controller.  The motor runs

> off of 12VDC.  Just had a few questions as
> I have not dealt with these motorized variacs before:
 
> 1.  I assume

	I wouldn't.  Test & find out.  cf below

> if I put +12VDC/Gnd into the motor for one direction and
> Gnd/+12VDC into the motor for the opposite direction?

	Maybe.

>  Is this correct????
 	Maybe.  Some DC motors reverse when the voltage applied

	is reversed.  These are the ones with permanent magnet
	motors.  (eg as used in many model rr trains.)
	Others require reversing the connection of the field
	relative to the armature.  Given that this motor is
	designed to be reversed, if any of its control gear is
	presen, it should be able to be figured out.
	Alternately:
	If two leads (only) come out, probably reversible by
	polarity change, as you propose.
	If FOUR leads come out, probably two are armature, two
	are field.  Reverse EITHER with relation to the other.
	
	In any case, some testing with any old 'more or less 12v'
	supply should settle it.  (eg battery charger....)


> 2.  Do these motorized variacs have mechanical limits on them,

> or do I risk damaging the variac and/or motor if I continue to

> run the motor once a variac limit has been met???
	Dunno.  Good thing to be sure of, inspect the insides.


	Another thing to think on:
		Assume the system is up and running.
		Assume the 12vdc supply fails.
		Is there a way to render safe the system with
		not 12v supply?
	(A manual variac can ALWAYS be spun down.  An motorized
	one...)

	best
	dwp

...the net of a million lies...
	Vernor Vinge
There are Many Web Sites which Say Many Things.
	-me