Thread-topic: Mid sized Tesla Coil using a 20A variac
> If you were blowing a 20A fuse, then the variac was only seeing an
> output of 20A fuse. The idea here is that you can increase the value of
> the fuse beyond what it is recommended, provided you A) do not leave it
> in, and B) you take into account the duty cycle.
> Of course then you are going to run into the limit of what the breaker
> on that branch circuit is rated for, and breakers tend to not behave
> well after being tripped a lot of times.
> That having been said, running two 15/60s should only be needing 1800VA,
> or about 15 amps at 120VAC, so it's possible you just have a very
> sensitive variac fuse. You might try a time-delay fuse, as they get
> along better with inductive loads, or just get a higher value fuse (just
> remember to take it out when you are not coiling).
Does the fuse blow after the coils has been operating for
'a few minutes' or on initial power up?
thanks
dwp
> > Wow Jon. So perhaps I was using much more than 20 Amps then being drawn
> > from the NSTs.
> >
> > Interesting.
> >
> > On Wed, Apr 1, 2015 at 8:01 AM, Jon Danniken <danniken@xxxxxxxxxxx> wrote:
> >
> >> On 04/01/2015 05:02 AM, Timothy Gilmore wrote:
> >>> When using my 20A variac, it is listed as 0-130vac but when I measure
> >> with
> >>> a meter it is 0-145vac. I can never bring the voltage past about 120 vac
> >> on
> >>> the dial (which is really about 130vac measured or so) because then the
> >>> variac 20A fuse blows when connected to my 2 15kv 60mA NSTs for my mid
> >>> sized Tesla Coil. During a tesla coil show at my home this week, I was
> >>> running it for about 1 minute increments and blew the fuse 3 times.
> >>>
> >>> Do I have to re-wire my garage outlet and/or circuit breaker for 30A via
> >>> hiring an electrician? or I'm assuming its at 15A now and live with it?
> >>
> >> Hi Timothy, one thing to keep in mind about variacs is that most
> >> domestic versions are rated for continuous duty. This means that a 20A
> >> variac is rated to control 20A 24/7.
> >>
> >> If you want to run them at a higher current than they are rated for, you
> >> can do this, provided that you limit the duty cycle of the variac (the
> >> limiting factor is the amount of heat that builds up). The manufacturers
> >> actually plan for this, and provide a duty cycle chart for the units.
> >>
> >> As an example, here is the duty cycle chart for GE Volt-Pac variacs
> >> (other manufacturer use a similar curve):
> >>
> >> http://i.imgur.com/2fOYa7N.jpg
> >>
> >> As you can see, you can run a variac at double the rated current,
> >> provided that you limit the duration to less than ten minutes. In Tesla
> >> coiling, this usually isn't a problem, because we generally limit the
> >> run time to less than a minute or two.
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