Winding torroidal transformers

[dkemppai]

Originally posted by jackinnj
Kiwi man -- oftentimes the only way to get the transformer you need is to roll your own -- this is particularly true from SMPS supplies for which inductance, leakage are important. But generally, if analyzing the problem as time = money, it's easier to just pull what you need from a catalog.

Agreed! Keep in mind that for SMPS transformers you usually deal with less than 2 dozen turns. For a 60Hz transformer, you need many many more turns. So, if you plan on building a SMPS transformer, winding it yourself is the only way to go. If you plan on a 60Hz transformer, You may not want to spend the time.

(In all honesty, I have several transformers collected because they are a EI cores with screws holding the laminations together. I'm keeping them just so I can wind a 60Hz transformer when I need a custom unit!)

-Dan

[jackinnj]

to loosen the laminations? of course they all must remain isolated.

Nat Semi and others give you the primary inductance from their switcher software which is a big help. An impedance bridge or LCR meter is a necessity to calculate the minimum impedance.

[Jared]

i used to work for a comopany that made power transformers. I hate to say it, but the bigger toroids were mostly hand made.. a machine wrapped up enough wire for each winding on a H shaped piece that could go through the center of the ferrite ring, and then a minimum wager wrapped it around and a round. For the smaller torroids, and all other laminate and filters and such there were bobbin winding machines that pretty much did it all. Soi it is very diy-able, its just time consuming as hell
edit - typos

[miguel2]

I have this 800 VA 220 primary, 47-0-47 secondary toroidal transformer. It gives 65-0-65V after the bridge. As I only need 50V can I unwind some coils? It also buzzes a bit, even when at no load. Is there anything I can do to fix this?

Thanks.

[Jeff R]

Originally posted by miguel2
I have this 800 VA 220 primary, 47-0-47 secondary toroidal transformer. It gives 65-0-65V after the bridge. As I only need 50V can I unwind some coils? It also buzzes a bit, even when at no load. Is there anything I can do to fix this?

Thanks.

Yes, you should be able to remove some windings to lower the voltage. Be sure to remove an equal number of winding from each side to maintain the same plus and minus output voltage.

Humming is generally due to mechanical resonances and can be difficult to eliminate. Be sure to fasten it down snugly to the chassis. Another coat of varnish might help, too. Hopefully others can some some other suggestions.

[peranders]

Originally posted by miguel2
I have this 800 VA 220 primary, 47-0-47 secondary toroidal transformer. It gives 65-0-65V after the bridge. As I only need 50V can I unwind some coils? It also buzzes a bit, even when at no load. Is there anything I can do to fix this?

You could also wind a "counter winding" with the opposite sign. Normally you have 0,3 V / turn.

The buzz may come from DC on your mains. Maybe you need a DC-trap? Fat Cap with two diodes in parallel across the cap.

[miguel2]

I'll try to unwind it a bit and put some extra rubber underneath it to see what happens. Thanks.

[miguel2]

This weekend I made this unwind and could lower the voltage around 10%, which is quite acceptable. But now it makes a lot of noise, I believe from mechanical vibration. I was carefull in puting back all the tape, but it really was already making noise before. Any suggestions?