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Re: Cheap Variac Substitute?/ vs Expensive.
Tesla List wrote:
> I recently purchased 4 MONITOR ISO-V-AC III model WP 32 isolated power
> supplies that go to 150 volts-at- 10 Amps. These can function as variacs as I
> can turn the voltage up from 0 to 150 with a dial.
Not sure how those are built. There are some problems with the solid state
devices being used for this when attempting to control a transformer. You may
want to do a little more checking before hooking them up to a coil. I wouldn't
want you to fry anything expensive. ;) At the least include a circuit
breaker or
fuse inline to prevent them from running away with you.
> I have several questions
> regarding operation. Do all variacs represent an isolated power supply? Is
> there an advantage to using such a supply
> to a NST primary and does this consist of a means of protection against RF
> kickback such that only a safety gap should then be needed
> as protection to NST damage on secondary?
No. Variacs are autotransformers. There is no isolation when using them. Nor is
there any protection for the NST in cases of kickback. Safety gaps and other
means are required for that. To keep HF from getting into your power lines you
should also use line filters on the input.
> Could I put all 4 in series to get
> 600 volts, or would there be any problems with having to simultaneously turn
> up the voltage on each device?
You would probably have to turn them all up and down at the same time to
prevent
them from fighting each other. When I wanted to parallel 2 variacs someone
mentioned this problem to me. They sugested getting a 'paralleling choke' to
make them be nice. Looks like a large center tapped inductor to me. Although I
haven't verrified that. What would you run 600 volts into anyway? The NSTs
wouldn't like that, you'd probably burn out the insulation on the secondary.
Travis