toroidial transformer winding question

They're isolated electrically, just because the wires are insulated. The thing that would change with the different winding patterns would be interwinding capacitance and possibly the mutual inductance, or the magnetic coupling between the windings, which would only affect effeciency.

Hope This Helps! Rich

You are not thinking correctly. Any winding or windings can be primary(s) or secondary(s). It does not matter where on the core they are wound except for issues like capacitace and leakage inductance. All windings should cover as much of the core as possible depending on the number of turns and the wire thickness. Each 115 winding may go more or less than half way or they may go more than one complete layer, again depending on the turns required. It is possible that the two 115 windings are in three or four layers. It is not knowable with the information provided. If you provide the physical size of the transformer(s) the power level and frequency, typical windings can be estimated, both number of turns and wire size. Of course there are other factors complicating the issue such as allowable temp rise, maximum flux density, allowable leakage flux, maximum inrush current, necessary magnetizing current, efficiency, acoustic noise, allowable waveform distortion, creepage distance and other factors that can complicate a real design. Bob

Usually one winding is wound, pretty much evenly all around the core, making the donut fatter. A layer of insulating tape goes next, then the next winding, also more-or-less evenly distributed around the core. And so on.

Yes, the two 115v windings can be used to make an isolation transformer.

John

All the winding go fully around the toroidal core.

The primaries are wound first then the secondaries wound over the top.

The two 115 volts windings are insulated from each other, but with not as much polyester wrap as the secondary to primary insulation.

....... Phil

the insulation between thhe two 115V winding s may not be as good as between the 115 and 25V windings.

to make an isolating transformer hook the 25 windings of wto of your several transformers together (in parallel) and feed 115V in one end and you'll get most of it out the other end.

Bye. Jasen

You can't legally use it that way for isolation since the insulation doesn't meet safety regs.

Graham

Until you load one transformer only whereupon there will be a burning smell.

Graham

Best coupling is acheived with all windings going 'all the way round'.

Don't use 2 primary windings for isolation. The insulation used isn't intended for safety isolation.

Graham

"Pooh Bear"

The plastic ( ie polyester tape ) wrap insulation used on typical toroidal transformers is merely functional insulation. It can and will fail if the transformer is ever subjected to a serious overload - in some cases, especially with low VA units, this takes only a few seconds.

A "safety isolation " transformer is one with a secondary voltage less than

Obviously, a 115 volt secondary winding is * UNSAFE * for human contact at ANY time.

........ Phil

Will the Insulation Police bust me? Will they, er, put me into isolation?

John

Given today's liability issues, I wouldn't even suggest this in a casual newsgroup discussion. Note the use of your company in your email addy. Liability lawyers will note that too and possibly claim it was professional advice.

Graham

I'm shocked, shocked that you suggest such a thing.

John

doesn't

Liability

I didn't think that you had the capcity to be shocked. ;-)

doesn't

Liability

doesn't

Liability

How did you induce that?

John

doesn't

Liability

With my magnetic personality! ;-)

doesn't

Liability

I can easily resist that.

John

doesn't

Liability

Haven't got that capacity to admit it, eh?

;-)

He's reluctant to.

Tim