Re: [TCML] Homebuilt Transformer - Can you add shunts?

["Christoph Bohr" <cb@xxxxxxxxxxxxxxx>]

Hello Phil.


> circuit it will (dramatically) increase the current that the transformer
> draws with no load connected and it will give poorer regulation (change in
> output voltage vs. output current."
I tried this, too, and even a small gap can have huge effect. If the transformer was
designed to be air gapped from the very start, it seems to work for certain
applications, but just "throwing in a gap" seems to be problematic.

> Doing some basic tests today with wire around the core and shimming it apart
> confirms this. The shunts in an NST aren't an actual air gap as I understand
> it, having never de-potted one.
yes, this is a completely different subject and has to do with some sort of
shielding arcross the flux path, others may be able to explain this better than me.

> Also it's not good news regarding the placing of a secondary coil on each
> outside leg, as this means they will only get half the flux from the
This is true, I almost fell for that once, too. But using two secondary windings
in fact doubles the wire length for a given voltage. However, insulation may
become easier.

> primary, as the two outside loops 'meet' in the centre of the primary and so
> have twice the area inside the primary.
yep...this is not optimal for "distributted" windings...
You might consider to rearrange the core for one double wide U.
Would result in an odd shape, but give you an evenly distributed cross section.
You then could wind pri on one side, sec on other for a self limited device or
just wind both on one side.....

> " leakage flux would be excessive, and the transformer would have poor
> regulation" quote from an interesting page at
yes, but it can be helpfull, too. I wound my transformer that way and
the result was a self limited transformer. Maybe a bit lossy but very tame,
just like a big NST.

> As the original winding window was pretty full when it was wound originally
> for 8.25kv, it leaves little scope to up the voltage that way, so I may
> still go for a secondary on each leg and accept the downsides.
Hm I don't see any real problems with winding the traditional way either.
If you wind your pri directly on the core, then the secondary directly on top
of the pri, ground the inner end of the secondary ( or connect to end of pri )
the only thing you have to worry about is arcing to the core...
Or am I missing something?
However, this is not helpfull in regards of your attempt to shunt the xformer...
Maybe I missed a point, its late in the evening, but don't let troubles stop you from
persuing your task. I "wound my own" and didn't regret it.

sincerely

Christoph Bohr

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