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Re: [TCML] Mid sized Tesla Coil using a 20A variac


I notice if I run the variac for a minute or two on my tesla coil, the fuse blows sometimes most likely when I increase the dial past 120 (which may actually be 130 or so vac) the end dial position is 130 which generates a measured 145 vac. I'm assuming the increased voltage from the variac is what's causing the increase in current

Thanks, Tim

> On Apr 1, 2015, at 3:25 PM, dave pierson <dave_p@xxxxxxxxxxx> wrote:
>> 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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