Re: Ballast and wire stuff

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

Original poster: "Bunny Killer" <bunikllr-at-bellsouth-dot-net> 

Hey Matt...

I made an inductor for my bigPIG transformer out of a huge transformer EI 
core and 3 spools of #10 wire 250' each. The secret was to use three rolls 
of wire at the same time when winding the core...   sooo  you end up with 3 
"paralelled" wires sharing the load ( 60 sumodd amps capacity) .  Sure 
beats trying to wind a #4 or thicker wire on a core form. Even when I pump 
50 -60 A into the transformer, the inductor stays cool ( well it does get 
warm ... about 100F)

IIRC the center core leg was 5"x5"   ( 25 sqr inch area) so there is little 
chance of saturation on this puppy...

I had to play around with the gap on the EI core untill I found a 60 A draw 
at full power ...

see if your local salvage yard has some large control cabinets and just 
maybe you can find a large enuf core in it ...

I got mine for 7.50$

Scot D



Tesla list wrote:

>Original poster: Mddeming-at-aol-dot-com
>Hi All,
>
>     Well, I'm finally getting ready to retire my NST farm, the OBIT farm, 
> the MOT clusters, and plate-supply transformer, and start using my pole 
> pig for something more than a doorstop/conversation piece. This brings up 
> some questions:
>
>1) I know there is a rule-of-thumb that a couple of 500' spools of #10 
>wire can be hooked onto the primary side as ballast and "all will be 
>well". However, I was wondering, " Is there a way to calculate the 
>inductance needed to limit the current draw to say, 30 Amps, even in the 
>case of a dead short on the secondary?"
>
>2) What transformer parameters are needed to do the calcs beyond the 5 
>KVA, -at-60 Hz. primary 240 V, secondary 14400 V?
>3) The off-the-shelf wire spools each measure 0.5 Ohm resistance and ~7.4 
>mH inductance.
>and #10 wire is nominally NEC rated -at- 30 Amps. In a multi-layered ballast 
>coil, inside a cabinet, would these be subject to overheating? Will I need 
>a Hollywood-style wind machine and thermal relays in my control cabinet to 
>keep from smoking the system?
>
>4) I vaguely remember a posting to this list from Fr. McGahee ca. 1998 
>that said #10 bare copper wire could only handle ~24 Amps Max and about 21 
>Amps steady load, and that was with plenty of free air space. Anybody 
>remember why the discrepancy?
>
>Thanks,
>Matt D.
>
>