Constant Voltage Transformer Question

Maybe not silly, but wrong. A triac-based controller does not control voltage level; it is a phase controller, varying duty cycle. A triac, once triggered (assume before 90 degrees and 270 degrees for any brightness at all), stays triggered until the line voltage crosses zero. This means that it delivers full peak voltages to the load. Sorry, Dan. Don't have access to alt.binaries.schematics.electronic.

I had that happen at our old house, the neutral corroded (underground utilities) and became resistive... some lights brightened, some lights dimmed, when the furnace blower ran.

...Jim Thompson

Get the power company to fix their regulation. I don't know about AZ, but in WA, voltage at the point of service is 120 V +/- 5% for a maximum voltage of 126 at the meter.

I read in sci.electronics.design that Richard Crowley wrote (in ) about 'Constant Voltage Transformer Question', on Sat, 1 Jan 2005:

I don't see how you can have a CRI of 90% with a CT of 3000 K.

I think I meant 'All warm-white CFLs that I tried had a very noticeable difference in colour temperature'

(snip)

Hmm. Well then, maybe I am having a CRI problem as well.

(snip)

BTW, I have a question regarding dimming CFLs. One of the effects of dimming an incandescent lamp is that the colour temperature drops as the lamp dims. Depending on the application (a romantic dinner for example) this can be a desired effect. I wonder if this is true for dimmable CFLs. Has anyone here tried dimmable CFLs, and if so do they have a pleasant light output when dimmed?

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Greg Neff VP Engineering

I read in sci.electronics.design that Greg Neff wrote (in ) about 'Constant Voltage Transformer Question', on Sun, 2 Jan 2005:

The light comes from the phosphor coating and changes colour very little with excitation level.

You might have a patent there; a phosphor formulation could be devised to produce the effect you mention. You'd sell a jillion. (;-)

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At work I've found this happens with three phase, and I've seen the neutral wire carrying substantial current, especially when I measure the current near areas where there is one or more copiers. They seem to have a very high current draw at times, when the fuser comes on. I've seen several volts diff between the neutral and ground. Check to see if you nave a situation where the neutral and ground are not close to the same voltage. Run appliances to see if that makes a diff. And if you find that there is, it can be fixed with some rearrangement of the loads on the breaker panel.

Back in the '70s a friend got a microwave oven, and I noticed that his kitchen lights would dim and brighten when the microwave was on. And I also noticed that at half heat settings, the lights would dim and brighten at about ten second intervals, which led me to the conclusion that all the microwave was doing was switching the magnetron on and off, and not 'dimming' it on a per cycle basis.

AFAIK, that's the way most, if not all, microwaves adjust "power".

...Jim Thompson

Best regards, Spehro Pefhany

I read in sci.electronics.design that Spehro Pefhany wrote (in ) about 'Constant Voltage Transformer Question', on Sun, 2 Jan 2005:

It's very true that there is nothing new under the sun. But Powergen is a UK electricity supplier company and I've certainly not seen any sign of the product being marketed.

Maybe it emitted too much mains harmonic stuff. Or caused flicker. (;-)

I read in sci.electronics.design that Watson A.Name - "Watt Sun, the Dark Remover" wrote (in ) about 'Constant Voltage Transformer Question', on Sun, 2 Jan 2005:

Yes. I don't think you can phase-control a magnetron. DON'T TRY!

"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...

Power Co fixed it. There was a bad splice in the feed coming off the pole into the house. You have a point about copiers and printers. I had to run a separate feed to the color laser printer.

Tam .....................

Jim Thompson wrote: led me to the conclusion

Back in the early '80s, a company I worked with made a "precision" microwave that did the power adjustment on a per cycle basis. It was a simple thing that could go from 10 to 100% power by dropping full cycles from the transformer's input.

The nice thing about that microwave was it didn't burn small things when you were running at reduced power. One demonstration they used was filling a watch glass with saline and running at 10% power using a conventional microwave, and then the "precision" microwave. The conventional microwave would spit and spatter as it blew up the water around the edges of the puddle, the "precision" microwave heated everything nice and evenly.

-Chuck Harris

Or, they really _do_ work, and are being withheld from the hoi polloi, so the lords and ladies get them all to themselves. ;-) Kinda like big oil suppressing the Pogue carb. ;-)

Cheers! Rich

I did a neon light dimmer that way... feed the transformer with full cycles (to avoid saturation), and switched them in and out as groups (with TRIACs).

...Jim Thompson

I've seen series-modulated magnetrons in military jamming transmitters, but they have real DC for the plates. The rectifier in the last microwave oven I took apart was half of a voltage doubler, and the maggie was the other diode.

Fil. winding C----| |--+----+UUU+ C C | | | C D v Fil. If you think I'm going to try to draw C --- Anode a magnetron, think again. ;-) C | | C-----+---+------+ | GND

I wouldn't even want to try integral-cycle control with a klooge like that!

Cheers! Rich

Have you considered low voltage Halogen's? They used to come with a linear transformer, to drive the halogen bulb at 12V. Common wattages were/are 20 and 50W. Newer ones use a SMPS with a crude unrectified output. Power density of such SMPS is extremely high. We have a under cabinet low voltage halogen system, which uses 3 x 20W bulbs, all run off of a single SMPS that's about 1" x 3/4" x 2", including the standard size replaceable fuse! Most of these newer low voltage halogens with the SMPS should last much longer, since the SMPS should give a regulated output, and the filaments in the halogen bulbs are much heavier for a given wattage.

John, at least here in Canada/US, fluoro tubes are rated for 40W, for a standard 4' tube. Energy saver tubes, which seem to be the only ones that are commonly available now are rated for 34W, which fit the same fixture without modification. The 34W tubes are junk, since the seem to only give out 1/2 the light. New, T8 fluorescent tubes are rated for 32W, and are significantly brighter then the older 40W tubes, they are also much skinnier, with a diameter of about 1".

Helluva good idea! Maybe automotive headlamps? They're quite rugged.

...Jim Thompson

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Very rugged indeed, but at the expense of efficiency, since they don't run as hot as other halogens. They also will be difficult to adapt to normal fixtures.

Commercially available low voltage halogens should be available all over the place, at hardware stores and lighting centers - just look at the fixture to see if it has a designed in, vented box or hump to hide a SMPS, or look at the bulb spec's. Low voltage bulbs are generally always 12V.

A quick google search for halogen fixtures found this site:

Most fixtures that are labeled "low voltage" should have a SMPS to convert line voltage to 12V. Watch out for the ones labled with magnetic transformers, since they won't help much. Line voltage fixtures don't use step down techniques. An added advantage of the 12V lights, with good quality bulbs, gives a nicer white light, at least IMHO.