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craigmillard 16th July 2013 04:19 PM

Toroid Rewind
Hi Guys,

Im looking to rewird a toriod secondary to be a center tapped 6.3v... I just cant figure out the best way to wire it.

Should I:
a- get two lengths of wire and loop them together around the toroid
b- wind one then wind the other..

Im hoping "a" isn't an issue as will save alot of time:)

Cheers all

BobEllis 16th July 2013 04:41 PM

A will work, just remember that the two windings will be in phase. So for center tapped you connect one starting winding with the other end winding. That will be the center tap.

craigmillard 17th July 2013 08:11 AM

Cheers Bob!

Is that the same for HV windings such as 250v?

Also is it recommended to tape between each layer of secondary winding for extra insulation between the secondaries?

DF96 17th July 2013 09:16 AM

Bifilar winding (or thereabouts) may not give enough voltage isolation for a high voltage secondary. OK for heaters, though.

My personal rule with mains transformers is that unless I am sure I know what I am doing I will leave it to the professionals.

craigmillard 17th July 2013 09:27 AM

So i will wind the secondaries in this order -

6.3v ct wound together
glass isolation tape
250v single wind
glass isolation tape

I like to learn by doing:) just very carefully!! Trying to get all the information to make sure its right and this forum is great for that!:)

CT HV secondary would be nice as it would half the turns required which is in the thousands! Glutton for punishment:) Any ideas on how high you can go with Bifilar winding before voltage isolation becomes an issue?

DF96 17th July 2013 12:06 PM

Depends on how thick and uniform the wire coating is. Thinner wire, as used for high voltage windings, usually has thinner insulation. Off the top of my head, without investigating it, I would not want to go much above 20-50V for bifilar.

craigmillard 17th July 2013 03:22 PM

Cheers DF96, i will go with this approach then:

6.3v ct wound together
glass isolation tape
250v single wind
glass isolation tape

AndrewT 18th July 2013 10:01 AM

I would agree substantially with DF and suggest that wire to wire insulation must never see excessive voltage difference.
<=50Vac may be a good guide, but I suspect <=100Vdc is acceptable.

But with thousands of turns could the ONE winding overlap at the beginning/end where 250Vac of difference would exist? If your 250Vac is done as two layers, then you have 125Vac between the layers. I would insulate one layer before adding the second layer.

Then repeat for other windings.

This results in:
layer1 sec1
layer2 sec1
layer1 sec2
layer2 sec2

You will need a long mandrel to get that length of 125Vac winding onto a slim through the hole bobbin.

Note if you swap the phase of a winding, you can get 250Vac difference between adjacent ends.

DF96 18th July 2013 01:31 PM

Yes, I would add insulation within the high voltage winding. The traditional material is high quality paper but there may be better modern plastics.

hotironsmoke 8th November 2013 10:04 PM

toroidal winding
What I often wonder is, would there be advantages in segregating the secondary windings to separate segments of the toroid, or conversely shared evenly.

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