Re: Using a variac for current control

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Terry,

The reason people like to cut variacs is core saturation.  "I" don't have
much advice there since I am playing with all that too for the OLTC...
However, If you don't want to chop a nice variac, this place sells nice
bare cores brand new for very good prices:

http://www.alphacore-dot-com/stcores.htm

I have ordered a few from them with no trouble at all.  Probably want to
get slow ground shipping since your basically ordering iron ;-)  I have not
cut one "yet" so I am not sure they will not unravel or do anything bad.
I'll report back...  I note they sell split cores too but not off the shelf:

http://www.alphacore-dot-com/images/Special%20shapes.JPG

You will have to figure out how to wrap a bunch of wire on a toroid core.
I starred at the machines for an hour or so and finally figured it out ;-))  

http://test.urs-dot-com.tw/demo/Weyhwang/product.htm

If you split the core (use cobalt tipped hack saw, my band saw "gums"
didn't work past the first 1/4 inch...) winding the wire is much easier.

You could simply have taps coming out for various inductances.  Or, you
could just make the whole thing like Finn:

http://home5.inet.tele.dk/f-hammer/tesla/museum/variac/variac.htm

Just some ideas ;-)

Cheers,

	Terry




At 09:27 PM 9/9/2002 -0500, you wrote:
>Hi all,
>
>I am working on a power control panel for a pole pig (I'd like get one
>someday), and would like to have a knob to control current.  I have this
>cool book from J.H. Couture (Tesla Coil Construction Guide) that provides
>the plans for a control panel.  The panel is made up of two variacs; one for
>voltage and another (in series with the load) for current.
>
>My question is; do I have to make a cut in the toroid of the current variac?
>Mr Couture makes no mention of this operation.  Is it necessary?
>
>Anything else I should know about this sort of thing before I screw up a big
>variac?
>
>Confused as usual.
>
>Terry Blake
>Coiling in Chicago.
>
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Monday, September 09, 2002 7:11 PM
>Subject: Re: defective caps?!?!
>
>
>> Original poster: "J. B. Weazle McCreath by way of Terry Fritz
><twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>
>>
>>
>> At 11:54 AM 09/09/02 -0600, you wrote:
>>
>> >Original poster: "Steven Ward by way of Terry Fritz <twftesla-at-qwest-dot-net>"
>> <srward16-at-hotmail-dot-com>
>> >
>> >I now have a very sick feeling in my stomach,
>> >
>> >I may have bought about $120 worth of bad caps!  While my GE 42l series
>> >3000v caps have lasted for a looooong time, the 42l 1200v caps may not!
>> >I may send one to Terry so he can check it out.  Heres the story.
>> >
>> >I just finished up a medium coil powered by a 12/60 and a static gap.
>> >My MMC is 20 in series of 1200v .33uf caps for .0165uf -at- 24kv.
>> >
>>
>> <big snip>
>>
>> >
>> >I just upgraded to 2 strings of caps on my big coil, but never ran it
>yet.
>>  >Each string is 24 X .68uf -at- 1200v for a 0.0283uf -at- 28.8kv.  By the way,
>> >is a .0566uf cap too big for a 15/120 system with a blower gap?
>> >
>>
>> <snip>
>>
>> >I like the idea of that huge cap for some huge current handling, unless
>> >these are "crap caps" and they will all fail soon anyway.
>> >
>> >
>> >Steve Ward.
>> >
>>
>> Hello Steve & Coilers,
>>
>> Maybe I'm all wet, but it seems to me that you're asking a lot of just
>> one or two strings of caps in your MMC.  It's generally not the volts
>> that kill a cap, but rather the amps and you'll sure have plenty with
>> using only one or two strings.  I have six strings of 16 caps each in
>> my MMC and I worry about it!
>>
>> 73, Weazle, VE3EAR/VE3WZL
>> G-1#1214
>>
>> Listening: 147.030+ and 442.075+
>> E-mail:    weazle-at-hurontel.on.ca
>>            or ve3ear-at-rac.ca
>> Web site:  http://www.hurontel.on.ca/~weazle
>>
>>
>>
>