# [TCML] Ballasting my Homemade Transformer.

Jim Mora wavetuner at gmail.com
Tue May 5 20:26:28 MDT 2009

Hi Bart, et al,

Thanks for paring that down! So we want a big core and a short-like
geometry; sort of like a MOT. Now I suppose we don't want to push the
current without saturation.

Lets consider a second dual E core pulled against the other. This relatively
creates a "tighter window" and doubles the cross section.  What is the
function as we add to the core geometry? ... Clearly, this not linear. Given
that function and the other stated info, one could get in the ballpark for a
choke or transformer.

Jim Mora

-----Original Message-----
From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On Behalf
Of bartb
Sent: Tuesday, May 05, 2009 5:30 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Ballasting my Homemade Transformer.

The cross sectional area is the determinant. For an analogy of sorts,
think of current in the core as a very large conductor whose geometry is
a single loop. The current in this loop is the same at all points along
the loop (series circuit). Cross sectional area is what you want to
concentrate on. Actually, you will have higher core losses with a long
core versus a short core (Eddy and Hysteresis). This is a good reason to
keep cores as small and practical as possible from an electrical
standpoint, but the major reason would be weight and cost.

But yes, it certainly does open up the winding window, and for high
voltage transformers, this is a good thing because it allows some area
for the windings (you don't have to put 10 pounds of _/you know what/_
in a 5 pound box).

Take care,
Bart

Jim Mora wrote:
> Hi Bart,
>
> Great shot! That almost says it all. Clearly, this opens the winding
window
> to get the copper in there! Stacking the E cores affects the current by a
> mathematical function, yes? This discussion simplifies the math challenged
> such as myself :-^)
>
> It seems weird to me that the cross section area is mostly discussed in
this
> vein. If I knew the answer to this, the simplified, pseudo functions of
core
> geometry would be clear to me.
>
> Thanks Much,
> Jim Mora
>
> -----Original Message-----
> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On Behalf
> Of bartb
> Sent: Monday, May 04, 2009 6:40 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Ballasting my Homemade Transformer.
>
> Hi Jim,
>
> I should show an NST 12/60 broken down:
> http://www.classictesla.com/photos/nstrepair/Image4.jpg
>
> There you can see the two E cores.
>
> Take care,
> Bart
>
>
> bartb wrote:
>
>> Hi Jim,
>>
>> Sure. For example a Franceformer 12/60 NST uses 2 E-cores in just this
>> fashion. The primary is located in the center leg and center to the E
>> cores. There is a secondary on the same center leg to each side of the
>> primary (with of course shunts between the primary and secondaries top
>> and bottom of the center leg).
>>
>> As Phil mentioned, it may not make the most ideal transformer and some
>> slight leakage if the cores do not butt together nice and flat, but
>> that's not a big deal if you used the cores for a high voltage
>> transformer. If the ends are not flat, then you'll certainly want to
>> ensure it's potted to prevent buzzing. BTW, if you use a potting
>> compound like wax or other that gets relatively hard, when the potting
>> material is about half cured, energize the transformer (this will pull
>> the two cores together nice and tight and any potting material that
>> had seeped between the two cores is squeezed tight providing a nice
>> packed seal between the two cores). Makes for a silent running
>> transformer. I energize the tranny two or three times for about 5
>> seconds at different stages during the curing process (while the wax
>> or whatever is still very soft).
>>
>> Take care,
>> Bart
>>
>> Jim Mora wrote:
>>
>>> Hello,
>>>
>>> Good reference material! Since we are on the topic, I was wondering
>>> if (2) E
>>> cores could be used (opposing each other) without the I core. This would
>>> double the winding window and still allow for some leakage spacing. (4)
>>> would double the core size yet again (two deep). I have a number of
>>> beefy
>>> transformers from an inverter cabinet.
>>>
>>> My goal is to make a seriously stiff filament transformer, So in
>>> review: 150
>>> -200 turns for 240, wired sized for current in and out, 2.25-2.5
>>> inch^2 for
>>> each kwatt. Good stuff!
>>>
>>> Jim Mora
>>> Anyone see issues with using dual inverted stacked E cores?
>>> -----Original Message-----
>>> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On
>>> Behalf
>>> Of David Rieben
>>> Sent: Sunday, May 03, 2009 6:37 AM
>>> To: Tesla Coil Mailing List
>>> Subject: Re: [TCML] Ballasting my Homemade Transformer.
>>>
>>> Hi all,
>>>
>>> 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,>>>
>>> <snip> <Snip#2>