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Re: Self-built power transformer

*smacks self on head* I should have thought of insulating between the wire
and the
core. Thanks for bringing it to my attention. I'll have to re-wind, but at
least
it won't fry the insulation. Would 60 mils of polyethylene do the job? It's
only
one layer, so at least that won't be a problem. I'm putting about 5 24 AWG
windings on top of each other and paralleling them, so current won't be an
issue.
32 AWG, according to my information, can take an amp or so. As for current
limiting, I've done the math, and thanks to the oil, it shouldn't fry even
if it's
shorted. I'm not aware of oil increasing arc-overs until it's outgassed--am I
mistaken? It wouldn't depend on the oil to prevent arcovers-it's only to
increase
thermal conductivity to the outside.

Tesla List wrote:

> Original Poster: RWB355-at-aol-dot-com
>
> Snip
>  > I'm currently building a power transformer for my coil, and I'd like to
>  > get some reactions on it. It's wound on a 15" long, 1" diameter
>  > commercial iron core with 1600 turns of 32 AWG magnet wire for the
>  > secondary, and 5 windings, 8 turns each, of 24 AWG (they're on top of
>  > each other) for the primary. I'll probably wind a second primary so I
>  > can run it on 240V as well as 120V. The whole thing will be immersed in
>  > motor oil. Please reply with your opinion--I want to be sure it won't
>  > fry on me when I power it up.
>
> Snipel
>
> Hi Dave, All
>
>  There are several things to consider when "homebrewing" transformers. First
> and most important: You must treat these transformer as non shunted types
> (which it really is). If you short the secondary, you WILL burn it out,
due to
> the too high current drawn. Remember the spark gap in your tc will short out
> your xformers´ secondary, when it conducts. This means you MUST current
limit
> your xformer or else you will see smoke rise, have a cuss of first
quality on
> your lips and tears in your eyes.
>
> My next question is: Did you wrap a layer of insulation between:
>
> a.) The core and the form
> b.) The wire form and the first wire layer
> c.) In between each wire layer.
>
> You MUST do this when building HV xformers, other wise you will get arc
overs
> and ruin your lengthy winding job.
>
> Last thing to consider: If you oil immerse your xformer you have two
choices.
> You either dump it into a pot of oil and wait at least two weeks before
firing
> her up or second (better) choice would be to evacuate the container and back
> fill it with oil. After a 3/4 fill up (completely covering the xformer) run
> your trusty vaccum pump again for another 30 minutes to help outgas the
setup
> completly. The constant vacuum "pull" will help the oil penetrate into the
> deeper layers and prevent internal arc overs.
>
> My last question: What is your expected current output? The wire sizes you
> have mentioned are very thin (both primary and secondary). This will limit
> your current capability. I mean AWG 32 is a lot thinner than I would use
even
> on the Tesla secondary.
>
> Here are some values I will build my xformer with:
>
> Input: 240V-at-50Hz
> Output: 15000V-at-500mA (7.5KVA)
> Primary: 124 turns of AWG 13 (middle leg)
> Secondary: 7792 turns of AWG 24
> (This is total, I would ct it, so I would need 3896 turns per outer leg)
> Crosssectional area of the biggest leg: 2.87 inch^2
>
> Okay, this is a pretty hefty transformer, but I like going on the safe side
> (with power to spare) in case I build a new TC. The primary (no load)
current
> draw on this sucker is slightly heavy, but it is built to bullet proof specs
> and I am sure I could overrate it for shorter runs, altho I don´t see a need
> for this at 7.5kVA.
>
> If you want to give me your required voltage/current specs, I will try and
> calc an xformer to fit your needs.
>
> Hope I could be of help,
>
> Coiler greets from germany,
> Reinhard



--
           --Doug Brunner
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