Unused secondaries

[pilli]

Hi,
I remember reading something about this, but I can NOT find it again. So thanks for your patience...

I have a lot of transformers pulled from scrapped equipment, and often they have the secondary I need, but also several other secondaries.
Should anything special be done with these unused secondaries?
Leave them open? Something to "avoid ringing"?


The usage if for little power supplies, like dedicated power supply for a CD player output stage, or experiments with phono amplifiers, etc.
Nothing switching, just plain PSUs with a rectifier, caps, regulators.

Thanks,
G.



_

[richie00boy]

Just tape or heatshrink the ends of the wires up. Bear in mind that you do not gain any extra power for your used winding by not using these other windings.

[Geek]

Hi Richie,

Originally posted by richie00boy
Bear in mind that you do not gain any extra power for your used winding by not using these other windings.

Really? I always thought you gained 50% of the VA of the unused winding (if the wire size is OK with it)

[MRupp]

Not that I have tried this but you could - carefully - load the unused secondaries with a capacitor to dampen higher frequencies passing through the transformer and so improve line noise rejection? For more details see patent no 6087822 from Menno Van Veen.

[Zen Mod]

Originally posted by MRupp
Not that I have tried this but you could - carefully - load the unused secondaries with a capacitor to dampen higher frequencies passing through the transformer and so improve line noise rejection? For more details see patent no 6087822 from Menno Van Veen.

isn't better just grounding one end of winding........ ?

[richie00boy]

Originally posted by Geek
Really? I always thought you gained 50% of the VA of the unused winding (if the wire size is OK with it)

The wire size is usually the limiting factor not the core size, i.e. it's unusual to have much spare capacity in the wire size for more current.

[MRupp]

Hmmm - as I have not tried this I cannot really say. IMHO grounding makes sense if the unused winding happens to be between the primary (innermost ?) winding and the used secondaries, in which case it would be an additional shield winding (Schirmwicklung ?).

[Zen Mod]

Originally posted by MRupp
Hmmm - as I have not tried this I cannot really say. IMHO grounding makes sense if the unused winding happens to be between the primary (innermost ?) winding and the used secondaries, in which case it would be an additional shield winding (Schirmwicklung ?).

Ja, Schirmwicklung .

there can be benefits even if winding in case isn't between primary and used secondary ; many xformers have "cover" shield (often just one Cu strip) , besides electrostatische schirmwicklung

[MRupp]

Upon further reflection I would say that the "schirmwicklung" lowers capacitive coupling between primary and secondary windings, while the loading of additional windings alla Van Veen dampens the magnetic field in the core and hence the magnetic coupling of unwanted frequencies. Maybe the two could even be combinded?