# Re: [TCML] Ballasting my Homemade Transformer.

```Hi Jim,

```
Yep, sure. Realize this was just an analogy (like say a water analogy for current flow). Magnetics has aspects like any discipline, but it seemed like an analogy that would make some sense to the electrical minded (why cross sectional area dictates magnetic core size for current flow in the core).
```
```
Yes, you want to avoid saturation of the core as losses will sky rocket (and damage will eventually occur to the coils). If you mean by "pulling a second dual E core against another" as putting the two cores side by side, then your cross sectional area will double and it will take far more current in the core to saturate it. But the core ends will need to be handled (they can't be open on the ends). I'm not sure on the linearity of this (you would have to do the math). But, the core could maybe handle twice the current. You do lose out on the winding window however. There is always a trade off.
```
Take care,
Bart

Jim Mora wrote:
```
```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@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] 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@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] 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@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] 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>
```
```
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