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Constant Voltage Transformer Question

J

Jeff

Jan 1, 1970
0
Jim Thompson said:
[snip]
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.
[snip]

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

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:

http://www.pegasusassociates.com/products/HalogenFixtures/HalogenFixtures.ht
ml

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.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
pernews.com>) about 'Constant Voltage Transformer Question', on Sun, 2
Jan 2005:

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

Yeah, maggies like to have their voltage constant. So they need a nice
flat topped pulse. But the pulse width can be varied to get diffetent
power levels. It's just that the microwave oven doesn't care much about
the freq, just as long as it's microwaves. So just feed it 60 Hz pulses
(or 50) and let it do its thing. Like the makers treat the transformer,
magnetron, HV rectifier and the capacitor as a unit. It wouldn't be
cost effective to try to gate the HV, so just use a SSR and turn the AC
to the transformer on and off.
 
J

John Stewart

Jan 1, 1970
0
Watson A.Name - \"Watt Sun said:
Yeah, maggies like to have their voltage constant.

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
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Tam/WB2TT said:
in message
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
.....................

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.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
pernews.com>) about 'Constant Voltage Transformer Question', on Mon, 3
Jan 2005:
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 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.
 
Z

Zak

Jan 1, 1970
0
Chuck said:
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.

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
 
C

Chuck Harris

Jan 1, 1970
0
Zak said:
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.


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
 
Z

Zak

Jan 1, 1970
0
Chuck said:
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.

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
 
C

Chuck Harris

Jan 1, 1970
0
Zak said:
Chuck Harris wrote:
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
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
pernews.com>) 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.

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

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
pernews.com>) about 'Constant Voltage Transformer Question', on Mon, 3
Jan 2005:
It felt like 50 or 60 volts to me. Shocking.

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.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
pernews.com>) 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.

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.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
pernews.com>) about 'Constant Voltage Transformer Question', on Tue, 4
Jan 2005:
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.

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.
 
C

Charles Edmondson

Jan 1, 1970
0
Jim said:
Do they make those with floodlight shaping?

I haven't been impressed with the light output of the CFLs I've seen.

I have 5x 75W halogen floods just over the cooking area... 15' up,
that's barely adequate.

...Jim Thompson
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.
 
M

Mark

Jan 1, 1970
0
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
 
D

David Lesher

Jan 1, 1970
0
Ferroresonant transformers have terrible efficiencies. If you want to
double your power usage, they're great! Although Jim T's description of his
house seems to indicate that power usage is the least of his worries. :cool:


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...
 
D

David Lesher

Jan 1, 1970
0
Good point. You're right, they almost always fail at turn-on.


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....
 
D

David Lesher

Jan 1, 1970
0
But it's cool watching a ferroresonant tranny regulate, especially when
you've got a variac and an AC ammeter. As soon as you apply any voltage at
all, the current goes WAY up. The first time I did it, I kinda panicked
when it was drawing 7 amps on the primary at about 3 VAC in. "It's
regulaging!" he said. He was beaming, probably because he designs them.
Of course, the current went to practically zero at no load and full V.
They were also inherently short-circuit protected. Well, current-limited;
I'm not sure if those are really technically different things.


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.....
 
D

David Lesher

Jan 1, 1970
0
AFAIK, that's the way most, if not all, microwaves adjust "power".


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

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