[TCML] Homebuilt Transformer - Can you add shunts?
follies at ntlworld.com
Sat Mar 28 07:22:22 MST 2009
Bart wrote>> "In Richie's Ballast, you can see the top core and the hard
polystyrene shims he used for the gap. These shims are across both sides"
Yes - I REALLY do need to get my glasses changed. I looked at that several
times and thought the bit extending across was part of the bobbin!
However it may all be immaterial .......
Quoting from one reply in the thread at
http://4hv.org/e107_plugins/forum/forum_viewtopic.php?28717 at 4HV.org "If
at all possible you should not introduce an air gap into the magnetic
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."
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.
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
primary, as the two outside loops 'meet' in the centre of the primary and so
have twice the area inside the primary.
I have tried some tests today and using the currently unused outside legs
for a new secondary gives me 0.95 volts per turn, but winding a secondary
around the core again as the original was, gives 1.76 volts per turn.
Putting a secondary on an outside leg means there is also an issue regarding
" leakage flux would be excessive, and the transformer would have poor
regulation" quote from an interesting page at
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.
It is certainly a most fascinating subject, a lot of it over my head at
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