Discussion thread for Schematic drawing posted for ECN's Member "Nick", in the Technical Reference area under the topic heading:

Balanced Power Schematic - Per ECN Member

Feel free to post comments and / or questions in regards to Nick's drawing.

Scott SET. 07/07/2001 07:12:00

edit= embedded hyperlink to schematic

[This message has been edited by Scott35 (edited 10-02-2001).]

Is the Q how to 'balance' the120V loads?

This is just a quick dirty one line of a typical system described in the new article 647 in the 2002 NEC (formerly part of Article 530) It's use is now expanded to commercial/industrial buildings and not limited to article 530 occupancies now. We will probably be seeing more of this in the near future.
One note: in order to take full advantage of the noise reducing capabilities of this system the transformer coils are wound in what is called a tortodial coil. (I think the spelling is right) You car and home audio buffs should no what I am talking about. More on this later.

Nick:

Do you mean "toroidal" ?

Or to use the real technical terminology, "donut shaped!"

That's the word I'm looking for! Thanks Paul.

You're welcome.

I've used toroidal xfmrs quite a bit in building power supplies for amplifiers and radio equipment. The design of them results in lower levels of EM radiation that with an equivalent size conventional xfmr.

The only drawback is that they tend to have quite a high switch-on surge. It's also important to watch the mountings carefully. They're usually clamped with a neoprene washer and plate through the middle. If the bolt is electrically connected to chassis at both ends it effectively forms a shorted turn.

Mabey thats why the 400KVA units tripped out the UPS when energized? I wrote it off as normal inrush but mabey they draw a little extra.

I did see some data on this a few years ago, but I can't remember the details now. I certinly always make the fuse on the primary an anti-surge or "slow-blow" type, otherwise it needs to be so much larger that close overload protection is lost.

A while back I used a 500VA toroidal xfmr to step-down from 240V to 120V to run imported U.S. equipment. I never measured the in-rush current, but just turning it on with no load made the lights dim momentarily, and they were on a different branch circuit, so the surge must have been quite high.

[This message has been edited by pauluk (edited 10-05-2001).]

Paul,

Have you ever wound your own Toroids? Man, that's a heck of a job!

My Brother-In-Law gave me a Toroid winding machine, which makes the task become somewhat pleasant!

I like the way Toroids retain their fields and don't have such a drammatic Inductive Coupling effect with other circuit elements.

I made a set of crossovers once, using Toroids for Inductors instead of the more commonly used Perfect Layer stacked Inductors.
Was great space saving, but the PL Inductors were easier to wind.

As you all mentioned, the Toroids have a high inrush value. Let me get out the Theory books regarding this, then I'll post a little data about it. I read about it back then [when?? even I don't remember!] and just can't recall the fine details.
Seems like the initial difference is the difference of overall conductor / winding length, then the alternate core material.
Let me verify this baloney.

Scott SET

Thanks Scott. I probably have the data here somewhere as well, but it could be anywhere in about 20 boxes full of manuals and journals!

No, I've never tried the dubious pleasure of winding my own toroidal xfmrs. I always chickened-out and bought ready-made.

I like the well-contained field as well. It's great for xfmrs closely spaced to sensitive audio circuits, e.g. P.S.U. for a pre-amp fitted right underneath a turntable with a magnetic cartridge.