Constant Voltage Transformer Question

CW Magnetrons as used for cooking need a CC supply. I managed to destroy a very expensive Philips cooking magnetron rated at 2500 watts, 2.5 GHZ around

1960 running it from a CV, 4500 vdc, one amp regulated supply. Changed that to a CC supply & the next magnetron lasted a long time. The application was a research project where we needed a lot of RF in in small volume.

Far as I know you will find the PS in a Microwave Oven to be CC by virtue of the transformer having lots of leakage inductance. The microwave frequency is determined by the physical dimensions inside the magnetron. The power delivered to the load depends on the PS duty cycle selected.

The magnetrons Watson has referred to are for pulsed Radar applications. The amplitude of the output is controlled by the voltage stored in the transmission line (usually lumped constant), while the length of the pulse depends on the electrical length of the transmission line.

Cheers, John Stewart

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What really used to bother me was when I connected the thin ethernet T connector to a PC in the classroom. There were a dozen or more PCs daisychained to each other and to the network. I could see a spark when I touched the T connector to the jack in the back. Shocking.

I read in sci.electronics.design that Watson A.Name - "Watt Sun, the Dark Remover" wrote (in ) about 'Constant Voltage Transformer Question', on Mon, 3 Jan 2005:

I doubt that the voltage was literally shocking. The PCs are all connected together by the safety earth conductor, and current from filter capacitors from line to earth in each PC flows in the earth conductor. Contrary to popular belief, this conductor has finite resistance, so a voltage is developed across it. When you connect the parallel path formed by the net cable shield, you cause a proportion of the current to divert and flow in the shield. The voltage is very low, but so is the impedance, so the current can be appreciable.

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FWIW: Panasonic uWave ovens use solid-state power supplies. Very light weight. The variable power feature on mine went bust pretty quick and now it is 100% power 100% of the time.

More that this I do not know.

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I just checked a new Bosch 'InnoWave' microwave with a switching power supply. At the 90 watts setting it is 6 seconds on 16 seconds off approximately.

This would scale up to 330 watts. Indeed, at the 360 watts level, my CFL 'test tube' doesn't switch off.

Strangely enough at the 1000 watts setting it doesn't shine much brighter.

Obviously I also put some containers with water in the oven.

Thomas

Your "CFL test tube" has a capacitor filtered DC power supply, and adjusts its inverter to regulate the current going into the bulb. As long as the converter can make the 60 (or so) volt drop the plasma requires to stay lit, the bulb will stay lit.

-Chuck

Well... I checked the microwave by placing the CFL tube (sans electronics) in the oven.... the DC power suppy - if it would be inclined to rectify 2.4 GHz - was not there to do its job :)

Thomas

Hi Thomas,

That's an interesting use of technology ;-)

The same phenomon applies though: The plasma is lit by the E field of the 2.4GHz E-M wave. Once the E field gets to be large enough to make the plasma light off, further increases in E field have no great effect.

-Chuck

pernews.com>) about 'Constant Voltage Transformer Question', on Mon, 3

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It felt like 50 or 60 volts to me. Shocking.

I read in sci.electronics.design that Watson A.Name - "Watt Sun, the Dark Remover" wrote (in ) about 'Constant Voltage Transformer Question', on Mon, 3 Jan 2005:

Then somewhere in the system you had a piece of equipment that was not earthed. It might be a fault, or it could be a legal Class 2 product. The signal ground of such products normally floats at half the supply voltage, but the current available should be too low to cause a shock.

Vintage Danish audio test gear is another matter. Here, the supply voltage is 230 V and the capacitances to the signal ground are much higher. You can get a real bite from these products.

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Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

pernews.com>) about 'Constant Voltage Transformer Question', on Mon, 3

I think you may have hit upon something. The capacitors of many PCs in parallel, adding up to the point where the current and voltage are hazardous.

I read in sci.electronics.design that Watson A.Name - "Watt Sun, the Dark Remover" wrote (in ) about 'Constant Voltage Transformer Question', on Tue, 4 Jan 2005:

The effect is recognized in EMC and safety circles. I did a calculation, and obtained an unconvincing result for the likely voltage, but Y MMV.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Hi Jim, Do you have undercabinet lighting as well? In my kitchen, the only time I switch on the recessed lighting is when I have company! I just use the undercabinent lights (flourescents) all the time. I find it a lot easier on the old eyeballs than bright overheads that leave shadows.

--
Charlie
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Put a dimmer control on the bulbs.

That way you can turn them down or up as the mood strike you.

Even though a dimmer works as a phase controller , it WILL solve your problem. When you dim the bulbs down they will last longer because the RMS voltage is decreased.

Mark

Indeed...A 1000 watt Sola draws ~350 watts at no load. It gets better at full load, but that hum and heat come from somewhere. Be sure and put it near your CRT monitor for most fun...

I second the CF suggestion; esp. since most offer free replacements. Note the cheapest Home Despot ones will last a few days max in a 'top-hat' recessed fixture....you can guess how I know.

If you must waste heat with incandesents; a triac regulator would be the best bet, I'd think. Maybe [cough] someone here would suggest a design...

I've seen large servo driver Variac regulators, but that was 25 years ago and it was in a surplus store THEN...

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If I recall accurately, Nela Park says that's hokum. It's a perception issue; you always notice the ones that fail at turn-on....

-- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433

Lorain Products used to test their many tens of KVAs 3 phase UPS's with a 100HP motor. Drop it across the output, the UPS goes to limit and sits there. Motor does not move. Then you see it creeeeeep oh so slowly, then you can see it move. After many minutes the motor was going full speed.....

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

And inside the microwave is a ferroresonant xfmr.....

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

When HP-35's and such were first appearing; I read a story about a building where HVAC motors, fluorescent lamps, elevators, and you name it all failed regularly. Only clue was TI calculators would regularly crash if plugged in.

After a large effort; turns out the Mini-sized (as in British car) copier machine was putting nasty spikes on the line/neutral, nasty enough to degrade motor insulation and other windings. They fitted it with (!) lightning protection (Poly-phaser or such) and that solved the issue. One wonders how ?Xerox? got UL approval....

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433