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Re: Self-built power transformer

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