Another thing that I might add about the addition of PFC caps the input to your NST transformer(s). Their power factor correction action only kicks in once there is an established significant inductive reactance (XL) load (transformers energized with the coil firing) to balance out. Until the significant XL load is established, PFCs draw more current from the incoming line feed than no PFCs, since they are individually only capable of adding a capacitive (XC) load, when there is little L to "balance" their XC. And of course, the larger the capacitance, the more amperage that the PFCs will draw from the wall. I ended up adding an additional contactor, wired to a panel mounted toggle switch to engage the PFCs when I choose to (after the coil starts firing) on the control panel of my big pig coil. Otherwise, my 500 uFds' worth of PFCs (5 ea. of paralleled 100 uFd, 370 VAC rated run style capacitors) are immediately pulling 42 amps from the 240 volt mains as soon as I turn on the main power switch of my control panel to my Green Monster coil. Of course, once the XL load is established (the coil starts firing) then their PFC action will significantly reduce the actual amperage that is pulled from the wall (but not the amperage that is circulating in the circuit downstream). My panel ammeter (whose CT "donut" is around one of the 2 input leads to the inductive ballast coil) still shows the same amount of current flow irregardless of the "upstream" PFCs' engagement (or disengagement).
David Rieben
Sent from my iPhone
> On Nov 25, 2015, at 4:12 AM, wt5y <wt5y@xxxxxxxxx> wrote:
>
>
>
> I had 2 12kv 60ma NST that were blowing 20amp fuses in my variac. I can now run 3 12KV 60ma NST because I added 10 50uf 370V ac caps for pfc. I put a amp meter gauge on the incoming 120v feed. Then Ikept adding he air conditioning run caps till I got what I wanted the lowest current draw which was around 9 caps, used 10 cause it was a even number. But I can run it without blowing fuses or tripping circuit breakers again.
> John Cooper
>
>
> Sent from my Samsung GALAXY S5™, a Cricket 4G LTE smartphone
>
> -------- Original message --------
> From: David Speck <Dave@xxxxxxxxxxxxxxxx>
> Date: 11/24/2015 21:58 (GMT-06:00)
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Subject: Re: [TCML] Recent variac problem.
>
> Vincent,
>
> What is the rating of the fuses you are using? 10 amps?
>
> Are they slow blow or fast blow fuses?
>
> Many old-school name brand variable autotransformers (Variac, Powerstat)
> can handle double their rated nameplate current ratings for short runs
> of 30 - 60 seconds without being damaged. Can't say the same for some
> of the cheap Asian imports, though.
>
> A Variac is not the part of the circuit that provides current limiting.
> That is established by the NSTs themselves.
>
> If you want to run 4 NSTs simultaneously, you will need a Variac big
> enough to provide the all current they require.
>
> Adding power factor correction capacitors (PFC) to the transformer input
> may help manage their current drain.
>
> Dave
>
>> On 11/24/2015 7:46 PM, Vincent D'Amore wrote:
>> Hi All
>>
>> Recently I've been running my coil controlled by a 10amp variac. I'm running two parallels 12/30 franceformer neons sign transformers and have been running this way for several years but as of late I keep blowing fuses on the variac about every 4th run. I'm not sure if or what has weakened over time. I would like to run my coil with a much larger power supply but that obviously won't go over well with my 10amp variac and I certainly don't want to move forward until I know the weakest point. Any suggestions? Also if I do go with a larger supply I'm thinking of 4 12/30's in parallel but don't know what to do for current limiting. Larger variac? Something else? Thanks for any advice.
>>
>> Vincent
>
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