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RE: [TCML] Winding a filament transformer expertise needed

  Jim , I have wound other size filament transformers for ham stuff so you
will find you might need a little trial and error to get the secondary
voltage right on but you will need a different "load" wire for the test.
You might try an old dryer heater and tap as required. You need nichrome for
a load not 18ga copper.
Rich ,KDØZZ ,
 from the middle of Missouri , out in the sticks with the hicks and the

To: 'Tesla Coil Mailing List'
Subject: [TCML] Winding a filament transformer expertise needed

Hello esteemed coilers,

The following a bit boring but may be educational for some:
Requirements: 10Vac @ 50amps stiff.

I pulled the cover off my old 10V filament transformers and noticed the
insulation was tired:-(  I have a dual stack a 1x1" C Cores from an x-ray
transformer, the core cross section becomes 2"sqrd so the current at 240
volts should be around @3amps/1"sqrd*2=6 amps... 240/10 =24 so ratio being
24 the 10volt out should be 24*6amps or 144a theoretical. I want 50 amps @
10v for a 10 amp+ head-end room (40amps@10v required). The winding window is
a nice 2x4". 

I have wound 190 turns of #18awg (this is the suggested inductor winding
density for current chokes from the archives 240v/190=~1.2 volts/turn. Am I
ok so far? I am ready to wind the secondary if so.

Figuring the resistive loss for this length of #18awg I think I need around
21 turns 190t/[19]=10v +2 turns. I plan to use #6 stranded standard
insulated wire (around 15 feet). ***Should the winding on top of the primary
be wound in the same direction or opposing? I don't have knowledge here on
if mutual inductance comes into play in stacked transformer windings and how
to leverage it.***

The transformer will be run on a 240v variac but I would like to have a 50a
load delivering 10v from the transformer out of the gate. I plan to use 31
feet of #18 for a test load. Calcs are based on the wiki AWG chart and on
3amps/1"sqrd core for 240v we use on current limiting inductors. Can someone
concur or challenge my calculations and speak to the mutual inductance
secondary question? BTW, this is to drive my 4x833c coil.

I have taken a procrastinating break from my 7500VA 12" pig coil for a few
days ;-^) (the control and HV cabinets are complete) I want to keep this fun
not work! 

If the current sags or runs too warm
 I'll next try a 15kv/60 (900va) neon core with the secondaries removed and
the primary in tact which was provided by a benevolent list member:-)

Thanks much,
Jim Mora


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