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Interesting Discovery
By SparWeb, Section Diaries Posted on Mon Oct 23, 2006 at 06:12:31 AM MST
Constant Voltage Transformer

On Friday, I discovered a classified ad for some interesting power supplies and isolation transformers. I visited the guy on Saturday, and after drooling over the huge 15 kVA 3-Phase Solatron, I settled down to look at the 5kVA 240/120VAC Constant Voltage Transformers. He had two. I took one, and it's been totally fascinating to experiment with. I plugged the inputs to 120 VAC from the wall, and the X1-X2 output was bang-on 118V. The output from X1 to X3 was 238VAC. Its input normally draws nearly 15 Amps, even when not loaded.

At first I thought I could try feeding the house power through it to "smooth out" power spikes and brown-outs, but given the constant demand of 15A, I won't even try it. It also hums like a 200 pound bumblebee. Still, I can't quite figure out how it works: How can you vary the input voltage yet get a constant output voltage, without a control mechanism? When I look inside, I can see nothing but transformers and banks of capacitors. I'll be doing a bit of research on the machine to understand it better. I might learn some important stuff from this beast.
BTW, if anybody else wants one, the guy still has another, plus a bunch of phone company power supplies /w switching panels, and that giant Solatron, too. The Solatron may already be spoken for, but if that contact doesn't pan out, he'd really appreciate getting rid of it.

Solatron Line Voltage Regulator & Comm Power Supply - Calgary Electronics For Sale - Kijiji Calgary

Interesting Discovery | 7 comments (7 topical)

Re: Interesting Discovery (3.00 / 0) (#1)
by Nando on Mon Oct 23, 2006 at 07:54:53 AM MST

SOLA had the initial patent for a constant output voltage regulation.

The transformer has a choke, between the primary and the resonant winding that places the core of the choke in saturation to insure that the energy delivered to the resonant circuit is always the same = reason for the high current even when not loaded.

RESONANT circuit consists of a winding and a set of capacitors to resonate at the GRID frequency -- circuit is quite sensitive to frequency GRID variations, so not good for most AC supplied by generators.

The Sola was good for cleaning glitches, brown outs under/over voltages that were common in the 1940's up electric systems.

You may remove the choke between the windings and the capacitors for a normal transformer behavior.

THEY RUN HOT

Nando

Re: Interesting Discovery (3.00 / 0) (#2)
by SparWeb on Mon Oct 23, 2006 at 08:45:05 AM MST

Thanks for the info Nando. I was specifically going to look up those patents, too. A recent discussion between Jerry and Flux has also let me in on the secret of those extra windings in some transformers that saturate things or deliberately cause leakage flux, so I think I have enough vocabulary now to get a grip on this slippery subject.

Do I correctly identify the choke as the larger group of windings in the center of each transformer between the other (line) windings on either side ?

This has nifty square magnet wire in it, roughly 12 gauge.... wow.

Thank you.

Steven Fahey
[ Parent ]

Re: Interesting Discovery (3.00 / 0) (#3)
by robl on Mon Oct 23, 2006 at 03:06:44 PM MST

I've used some of the smaller (2KW) Solas. Two observations: Use sheet metal screws to mount a 115V muffin fan on the case, near the vents, they will last longer that way. Also, be sure you really, really, need Solas for your application. Mine were quite inefficient when lightly loaded.

Regards

Rob

[ Parent ]

Re: Interesting Discovery (3.00 / 0) (#4)
by inode buddha on Mon Oct 23, 2006 at 04:58:46 PM MST

Quite easily, this is very similar to the so-called "ferro-resonant" transformer cores. They never achieve complete saturation because the magnetic flux path is never completed. I've seen them used in hospital and laboratory equipment where stable power is critical and money is no object. They are not especially cheap to use, but the power quality is first class. Sometimes they are sold as "isolation transformers", but one should check just how much isolation is happening?

Re: Interesting Discovery (3.00 / 0) (#5)
by Tom in NH on Wed Oct 25, 2006 at 09:13:36 PM MST

Another thing those babies do is filter out harmonics, the upshot being a nice clean sine wave even if you feed it a square wave input. I have a 3kva a Sola transformer and it only draws 6 amps no load. --Tom

Re: Interesting Discovery (3.00 / 0) (#6)
by SparWeb on Fri Oct 27, 2006 at 12:36:39 PM MST

If I may ask: What do you do with it Tom?

Steven Fahey
[ Parent ]

Re: Interesting Discovery (3.00 / 0) (#7)
by Tom in NH on Tue Oct 31, 2006 at 07:03:58 PM MST

It doesn't do anything, sad to say. I got it thinking it would help my inverter produce a sine wave that my microwave oven would find suitable. It did, but the transformer draws just too much current (6A no load) to justify using it all the time. I tried to rig up a set of relays that would energize the transformer when the microwave was turned on, but I couldn't make it work the way I wanted. I may still be able to get it to work, but the project is on hold for the time being. --tom

[ Parent ]

Interesting Discovery | 7 comments (7 topical)

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