RE: [TCML] Ballast -- Before or After Variac?

["Jim Mora" <wavetuner@xxxxxxxxx>]

PS. I have a 5KVA 240v slide choke for the transformer input (a bombardier
control). A cool way to go is to drive the reactor with an 18" satellite
actuator!

My big coil control cabinet uses a satuable reactor. Small knobs and big
changes are very cool!
Jim

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Dr.Hankenstein
Sent: Tuesday, April 28, 2009 9:54 PM
To: 'Tesla Coil Mailing List'
Subject: RE: [TCML] Ballast -- Before or After Variac?

On Zotzilla I have a ballast resistor and choke in series with the pole
xfmr; as the source of voltage is from the main variac. In reality, I
pretty much use the variac for tuning purposes only. Then I run the coil
"wide open". After all, once your coil is properly tuned, you really
don't need a variac at all, do you? Us old ham radio operators typically
use this same procedure for tuning up our amps as well. With some of the
variable chokes now available(very easy to manufacture) that are
adjustable from less than an amp to nearly 100 amps, you really don't
even need a variac in the first place. These chokes amount to nothing
more than a large slug of laminated iron designed to slide in and out of
a large coil of wire. Chokes of this variety make a great current
limiter....and that's what we're after!

Hank 

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of BunnyKiller
Sent: Tuesday, April 28, 2009 5:26 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Ballast -- Before or After Variac?

Hey Jeremy,

I have my ballast after the variac and before the piggie. I did it this 
way to have full voltage/current available to the variac and current 
limiting to the piggie...

Scot D



Jeremy Scott wrote:

>Hi all,
>
>I was just wondering where the optimal place in the circuit is for the
ballast?
>
>Should it go in series with the variac input, or series with the variac
output? 
>
>Modeling it in SPICE, it appears to function either way. 
>
>The ballast is an arc welder with a range of 6mH to 18mH (measured), 
>output terminals shorted.
>
>The variac is a 30A Powerstat with an input of 125mH to an output range

>of 0-180mH (measured - 120VAC in, 0-140VAC out.)
>
>I haven't hooked it up and measured the output for real yet, but SPICE
modeling shows some interesting results:
>
>When placed AFTER the variac on the variable voltage line, it limits
current to 35A on the low end to 50A on the high end. 
>
>When placed BEFORE the variac on the 120VAC voltage line, it limits 
>current to 28A on the low end to 45A on the high end.
>
>So, both results look okay -- this is a 50A circuit, so which is best?
>
>
>
>      
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>  
>


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