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400 Hz HURTS

>From chip Fri Jan 19 09:16 MST 1996

>Greetings,

>I saw a gang of 3 phase variacs for a reasonable price ($15) at the local
>electronics surplus/supply place.  However, the variacs are 400Hz instead
>of 60Hz.
	THAT explains the price.

>Does anyone know if they will work ok for 60Hz?

	[Danger Chip Robinson, Danger...  (obscure joke.]

	Short answer NO!
	Longer answer, they are usable, but with serious constraints.
	I am semi familiar with folk using 400Hz synchros on 60 Hz.  It can be
	done but the usual rule of thumb is that the 400Hz units must be run at
	about 10% of their nameplate voltage, which means 10% of the power
	handling capacity.

>I thought the main considerations with different frequencies for transformers
>are eddy current losses.
	Thats one thing.  There are others, like the core material used is
	optimized for 400Hz so it will have higher losses at 60Hz. (means
	more heating.).  I can't do a REAL GOOD mind dump on this, tho i am
	99% sure i understand it.  FOlk in the olde 'surplus hacker' community
	tried hard to find use for 400Hz stuffe and its NOT easy.  For
	references IEEE Trnasactions, just before, during, and after WWII,
	when 400 Hz was common in a/c work are where i would start.

	IF the $15 is 'expendable', I would buy them to experiment with.  IN
	GENERAL. the limitng factor is heating, or will show up as heating.
	Use them, stick a thermometer on them and see how hot they get and
	don't let them get any hotter than (ohhhh, guessing here) 100F above
	ambient (there may be temp rating on them...).  Ferinstance, they
	MIGHT make a 'fine sdjust' to go with 'course adjust' by a stepped
	welder.

	regards
	dwp