Yes indeed, power factor caps can help a lot. For reference, I use 240uF
with my single 15/60 120VAC NST, so ideally you want on the order of 480uF,
but the exact value isn't really critical. It's not like there's some
resonant value. I once tried metering the current and varying the array of
caps to find a sweet-spot, but the current was so chaotic I came away with
nothing useful. Just be sure to use motor run (not start) caps.
Regards, Gary Lau
MA, USA
On Thu, Apr 2, 2015 at 3:56 AM, Yurtle Turtle via Tesla <tesla@xxxxxxxxxx>
wrote:
> You can use a power factor capacitor to reduce your amperage.
>
> From: Jon Danniken <danniken@xxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Wednesday, April 1, 2015 9:01 AM
> Subject: Re: [TCML] Mid sized Tesla Coil using a 20A variac
>
> 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.
>
>
> Jon
>
>
>
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