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Re: [TCML] Ballasting my Homemade Transformer.

Hey Phil...

2 main concerns when making your own inductive ballast are wire size to be used and the number of turns required to have about 1-2 volts per turn... ok well there are 3 things to think about.. core size!

First off, how much current do you plan to pump thru the ballast? A #10 THHN solid copper wire is good for 25A at 180 turns on a core of about 12 sqr inches. more amps needed?? go to a thicker wire ( # 8 or 6) keep turns in the 180 -210 value, and increase the core area to 16 - 18 sqr inches....

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.

Best bet, use wire to meet the maximum amount of current you need to supply the trannie with, keep the volts per turn to about 1 - 1.5 and keep the sqr inches of core to handle 3 amps per sqr inch, this should set you in a good direction and you will have a happy inductor....

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 up
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 say
that when using an inductive ballast for my transformer, the only voltage
drop across the ballast will be caused by the ballast's resistive component
In other words if I wind an inductive ballast coil of the correct mH rating
(using chunky wire on a 4 square inch core so it has low ohm resistance) I
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 a
laminated core. It will still be a bit of a guess as I don't know the cores
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.




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