[TCML] Ballasting my Homemade Transformer.
drieben at comcast.net
Sun May 3 07:37:27 MDT 2009
I took the core of a gutted defunct x-ray transformer (I
seem to burn them out a lot ;^(), and rewound each
"leg" with 105 turns of #8 THNN building wire, in pa-
rallel. Since #8 is rated for 40 amps continuous current
flow, I should be good for 80 amps continuous, at least
from the wire guage perspective. This core was not the
alternately leaved "E" and "I" peice construction, but of
the two solid "U"s, which rendered rewiring considerably
easier. IIRC, each leg has about a 10 to 11 square inch
cross section and each are wound with a ballast coil, so
I'm assuming that the cross sectional area is additive ( >
20 sq. in. total). I simply experimented with a variaced 120
volt source while adjusting the gap spacing between the "U"s
to adjust for the desired current flow allowance. I found that
3/8" spacing allowed for enough flux leakage to allow about
95 to 100 amps to flow at 280 volts input to the ballast.
I also employed forced air cooiling to the finished home-
made ballast to assist in cooling. With this setup, I have
to run it at near max current for several minutes non-stop
before I am able to detect ANY warmth above ambient
temperature by hand. Oh yea, I forgot to mention that I
placed shim spacer sticks between each alternate layer
of the coils to maintain well-formed coils and also to
allow adequate ventiallation between the neighboring
layers. You can see the two reddish colored coils of
#8 THNN building wire of the ballast at the bottom of
the control panle in this "Green Monster Control Panel"
----- Original Message -----
From: "david baehr" <dfb25 at hotmail.com>
To: <tesla at pupman.com>
Sent: Sunday, May 03, 2009 8:00 AM
Subject: RE: [TCML] Ballasting my Homemade Transformer.
I also made a ballast a few years back, using a small book published by
Lindsay called 'how to design and build a 200 amp welder' as a guide. It
states a rule of thumb of 2.25 -2.5 sq. in. of core for every 1000
watts,..also the 1.2 - 1.3 volts per turn ( 180- 200) seems to be a good
rule(for 240v). Im pushing my #12 wire a bit,...as i push 12-14 amps
through it, but its low duty cycle :-) its a neat LiL' book, but i think
its out of print ??
> Date: Sat, 2 May 2009 22:15:04 -0500
> From: bunnikillr at cox.net
> To: tesla at pupman.com
> Subject: Re: [TCML] Ballasting my Homemade Transformer.
> Hey Phil...
> Im running a ballast with 3 #10 THHN solid copper in paralell on a 25
> sqr inch core at 200 turns... The "I" section is adjustable via PE
> "shims" ( used to be wood) for current control from 5 amps at 280VAC to
> 100 amps ( depending on where I set the I section of the core at,
> presently its set at 60 amps max). Granted, its a big core assembly,
> but it doesnt suffer from heating issues even at 60 amps at 5+ minutes
> run time....
> seems that the core size along with input voltage ( approx 240V )
> roughly equates to about 4 amps per sqr inch before saturation becomes
> an issue... but thats just my experiences I have noted.
> As far as voltage drop, my unit has about 5 - 10 volts difference
> before and after the inductor between an input of 120 -280 vac.
> Scot D
> Phil Tuck wrote:
> >I have finally got my homemade transformer running and now face the
> >delightful task of ballasting it. Its output, based on scaling up low
> >voltage readings, will be 10 to 11K (3.7kva approx) limited by the number
> >of turns and the window winding size unfortunately. Primary will be set
> >for 16 amps with around 375 m/a secondary (235v / 240v system). (Primary
> >Bifilar AWG 14, Secondary = AWG 27)
> >Two quick questions:
> >Question 1:
> >As a perfect theoretical ballast will have no resistance, is it true to
> >that when using an inductive ballast for my transformer, the only voltage
> >drop across the ballast will be caused by the ballast's resistive
> >In other words if I wind an inductive ballast coil of the correct mH
> >(using chunky wire on a 4 square inch core so it has low ohm resistance)
> >should get almost full voltage going into the tranny, with little voltage
> >drop across the inductive ballast?
> >Question 2:
> >There are various inductance calculators around, but they are all for
> >air-cored as far as I can see. Anyone know a link to one that caters for
> >laminated core. It will still be a bit of a guess as I don't know the
> >magnetic specifications, but it will be better than using an air cored
> >example. I am trying to avoid the hit and miss method of wind / measure /
> >wind / measure etc, as I will be winding onto a bobbin using a lathe.
> >Tesla mailing list
> >Tesla at www.pupman.com
> Tesla mailing list
> Tesla at www.pupman.com
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