Hi Bud,
I ended up taking the iron core of an old style DOA x-Ray transformer (it was of the two piece "C" or "U" design) and winding each of the two "legs" with about 105 turns of #8 THNN insulated and stranded cable and paralleling the two windings. The core cross section is about 11 sq inches, IIRC. I also affixed a cooling fan to blow down on the homemade ballast. I can easily churn out 80 amps continuously through it and it doesn't even seem to get warm.
Also, I did separate each layer of the hand wound coils with ~1/4" thick wooden spacers, which kept the coil layers more organized and allows for more cooling air flow between the coil layers.
Finally, I ended up adding about 1/8" thick spacers between the faces of the two "C's" of the core to adjust the maximum current flow that the ballast would allow to flow into a dead short (I adjusted for about 100 to 110 amps at 240 VAC input).
I run my Green Monster coil with this setup and get great results!
Hope this helps,
David
Sent from my iPhone
> On Jul 31, 2015, at 7:21 AM, Buds tape mail <bud@xxxxxxxxxxxx> wrote:
>
> Hi Phil and others, I have been reading thru your web site and Richie's very thoroughly. I have built a 12" X 51" secondary #18 wire and have finished a 56" toroid and will have this thing ready to go very soon. I have a rotary spark gap (copy of Ed's in Rochester) and a 14kv pole pig. I have been reading extensively about primary inductive ballast. I do have two 225 amp buzz boxes I could use in parallel as ballast like others have done. I understand the principle series on the primary side limiting the power to the pig.
>
> I saw how and why you wound your own ballast. My question is this........can we just use a very large welding transformer........say 400 amp unit as the ballast while shorting the secondary or should we just bite the bullet and wind a huge ballast from an older transformer with a huge iron core? I have my own machine shop.......... www.tape-inc.com ..........and can do almost anything once I know what it is I need to do. I think most of us do not know the how and whys of ballast design.....you know the core size min/max and wire size min/max for a pig of this size.
>
> Bud Mohrman
>
> -----Original Message----- From: Phil
> Sent: Friday, July 31, 2015 5:16 AM
> To: 'Yurtle Turtle' ; 'Tesla Coil Mailing List'
> Subject: Re: [TCML] Variable Ballast
>
> Jon,
> The modern cheap import ones you see knocking about are generally not up to the job for a pole pig, without getting pretty hot during use. I melted and shorted the windings of one a while back while running @ 10.5kv / 400mA - (hardly pig output) simply because I left it running for several minutes (they normally have a thermal cutout to disconnect the mains input during normal use)
> Their duty cycle is very low sometimes, especially as Yurtle mentions, if Alu' conductor is used; also the resulting voltage drop from lossy windings gets multiplied up by the pig, so you could potentially be losing 0.5kv at the worst case.
> Winding your own ballast is a better option.
>
>
> Regards
> Phil Tuck
>
> www.hvtesla.com
>
>
>
> -----Original Message-----
> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Yurtle Turtle via Tesla
> Sent: 30 July 2015 20:52
> To: GENE GARRAGE; Tesla Coil Mailing List; Tesla Coil Mailing List
> Subject: Re: [TCML] Variable Ballast
>
> I got a 225 amp Lincoln welder at a garage sale.It was old enough to have copper windings. I chose to short the welding leads internally, and eliminate the cables.
>
> From: GENE GARRAGE via Tesla <tesla@xxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Wednesday, July 29, 2015 6:53 PM
> Subject: Re: [TCML] Variable Ballast
>
>
> From: Jon Danniken <danniken@xxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Thursday, July 2, 2015 2:28 PM
> Subject: Re: [TCML] Variable Ballast
>
>> On 07/01/2015 11:14 AM, Miles Mauldin wrote:
>> Do I need to find an old welder, or will an inexpensive new one work
>> just as well. Read many posts about shorting the secondary and using
>> the primary in line with a pole pig. Thoughts, ideas or suggestions
>> all wanted for a variable ballast.
>
> You can get an old 220V arc welder for cheap on craigslist if you are
> patient, less cheap if you are not patient. As a bonus, you also get a
> welder.
>
> Jon
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