connecting primaries in series

[Lazybutt]

Originally Posted by KatieandDad

WOOOAAA.

You would be better to sell on the different transformers and buy the correct one in the first instance.

You're probably right....
but these toroids are second hand, and I don't think I could find such high quality as such low price so easily.
I especially liked the fact that they are sealed, which is rare and that I was like for low hum....

Nevermind... I found another pair of quality toroids :P (but a bit more expensive and not sealed... )
Thanks!

[DF96]

You can only connect transformer primaries in series when the secondaries have identical loads, or are tightly coupled together (usually by being wound on the same core!). Identical loads is almost impossible to achieve: you need not just identical circuits taking identical currents, but also identical smoothing caps (note that big electrolytics usually have very loose tolerances). This balance needs to be maintained under all conceivable fault conditions.

Paralleling secondaries should only be attempted when they are on the same transformer or with ballast resistors to aid current sharing.

The quick answer, as others have said, is don't do it!

[AudioSan]

Originally Posted by Lazybutt

You're probably right....
but these toroids are second hand, and I don't think I could find such high quality as such low price so easily.
I especially liked the fact that they are sealed, which is rare and that I was like for low hum....

Nevermind... I found another pair of quality toroids :P (but a bit more expensive and not sealed... )
Thanks!

and if it works okei. the transformers will be 337VA/2 pr pc.
so 168.5VA pr transformer

[KatieandDad]

Originally Posted by AudioSan

and if it works okei. the transformers will be 337VA/2 pr pc.
so 168.5VA pr transformer

Not quite. The transformers will still be at rated power but the drawn power will be as you suggest.

[elic]

When four 200 VA transformers cost you around $10, you don't ask too many questions :-)

[AndrewT]

The transformers each have 2off 115Vac primaries. These can be wired for either 110/120Vac, or for 220/240Vac. You don't have to mix up windings on different transformers.

[KatieandDad]

Originally Posted by AndrewT

The transformers each have 2off 115Vac primaries. These can be wired for either 110/120Vac, or for 220/240Vac. You don't have to mix up windings on different transformers.

He's trying to reduce the secondary output.

[AndrewT]

one does not mix up windings on different transformers.

There are better ways to reduce the output voltage than mixing up primary windings.
I have described the method previously and I can confirm that method does not lose any VA rating of the secondaries. But the description does have a warning. It is not for beginners who cannot recognise the dangers inherent in mucking about with mains transformers !!!!!!!!!!!!

[kevinkr]

Originally Posted by KatieandDad

Theoretically it seems OK. However, my experience of connecting transformers in series has always been poor results.

What KatieandDad says!

Check out this inexpensive Antek: Antek - AN-3218 Even with shipping it should not be too bad.

[KatieandDad]

You will always be better off with the correct transformer.