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Running a 208V radiant ceiling heater from 240V

I've always wanted radiant ceiling panel heat in our basement, but those panels are expensive. Recently, I found a supply of used panels for a reasonable price, so I bought one to play with. (It's a Qmark Aztec 375W panel.) Unfortunately, it is rated for 208V, and our house has 240V. I hooked it up, and it worked. But, the surface temperature in the middle of the panel reached a maximum temperature of 250F, which might be beyond the safe operating range.

So, I'm wondering how I can reduce the power supplied to these panels. Although this won't be perfect, I thought about some diode arrangement that would supply power to a pair of these panels in parallel for one half of the cycle and in series for the other half. So, they would be getting 240V half of the time and 120V half of the time. That should average out to less than their rated capacity, but it's better than setting them on fire.

I also thought about a more complicated circuit using triacs or something that would let 208 out of every 240 cycles pass through.

What about a 240V light dimmer? (Each panel is 375W)

Bulky, expensive transformers aren't an option, because I'll most likely be better off buying the correct 240V panels at non-surplus prices.

Ideas? John

Reply to
John Sevinsky
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Sounds like a reasonable choice, but you have to worry about someone cranking it all the way up. And cheap light dimmers make a lot of RFI.

Can you just run the panels from 120V (say, put two in series if from

240V)? If they really are surplus/cheap it might make sense to spread out the panels anyway.

Tim.

Reply to
Tim Shoppa

If I did use a light dimmer, I would install it above the suspended ceiling so nobody would mess with it.

Yes, I could run them off of 120V, but that would reduce these 375W heaters to 94W if I did my math right, so I would need four times as many. And the surplus price is more than 1/4 the new price.

John

Tim Sh> > What about a 240V light dimmer? (Each panel is 375W)

Reply to
John Sevinsky 

--
Very clever; I like it!

Easy to do, too.

Use a free-running 8 bit counter clocked by the mains, and when it
overflows set a latch which turns on a zero-crossing TRIAC driver
which turns on a TRIAC which turns on the panel.  Then, when the
counter gets to 222, decode that and reset the latch.  That'll turn
off the panel until the counter overflows and the cycle begins anew.

Want a schematic?
Reply to
John Fields

The triac or SCRs will cause RFI and will generally fail "on". They will probably see a lot of thermal cycling if you are using a conventional thermostat to control them.

I suggest a ~32VAC buck transformer or a(n) (about an order of magnitude heavier) surplus stepdown transformer, from safety considerations. Such tranformers can sometimes be had for the asking from companies. It's part of your house-- do you really want to compromise safety (and probably violate code)?

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

Back in my disco days I dimmed neon by cycle skipping. Caution: If a transformer is involved pass WHOLE cycles only.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

I'm sure we'd love to see some pictures of that on ABSE, Jim. :-)

I had a co-worker once who claimed he and his fraternity arranged a "headphones only" dance night... he built a huge distribution panel/amplifier, and everyone dancing had to wear headphones plugged into the ceiling to hear the music.

And supposedly women actually attended this shin-dig. (This would have been in the late '70s/early '80s.)

Which I find quite surprising...

It sounds like a scene out of Revenge of the Nerds...

Reply to
Joel Kolstad

BC, before CAD... I MAY have pencil schematics somewhere.

But really quite simple, TRIAC's driving the transformer... pass whole cycles, skip cycles... ratio determines dimming... worked quite well.

Around 1980, installed in Bobby McGee's on I17, along with my fabulous boom-box.

Don't know if it's still there or not.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Pass 7 cycles, skip the 8th

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

I'll bet that system used 1/4" jacks for the headphones. :)

John

Joel Kolstad wrote:

Reply to
John Sevinsky

After the fire when the insurance investigator is looking at the remnants what will your story be? Find some code approved way to run them off a split

240 V system - it might be worth a chat with the local electrical inspector.
Reply to
Homer J Simpson

It might be possible to install a small disc thermostat to the panel to shut it off at a safe temperature.

You could use a small buck/boost transformer. You only need one with 240 VAC input and 24 VAC or 32 VAC output at about 1.5 A. This should be a standard control transformer of 36 VA. The output is wired to "buck" the input voltage, so you will get 240-24 = 216 volts. Close enough. Or 240-32 = 208 volts.

Paul

Reply to
Paul E. Schoen

So, let's see if I got this right. One 375W 240V panel would use a little over 1.5A. Let's say I need six for the room in our basement. That would a little over 9A, so let's round it up to 10A. If I wanted to use a 32V buck transformer, that would be 320VA or 0.32KVA. Is that correct?

John

Paul E. Schoen wrote:

Reply to
John Sevinsky

Were you able to construct such an arrangement? I do not think it can be done with just diodes, unfortunately.

The 208v 375w panel, when hot and running at the correct voltage, would draw 1.8A. So, how about putting 3 12v 20watt light bulbs in series with each? The light bulbs themselves will also provide heat at nearly perfect efficiency, and presumably the light can be productively used somehow.

Reply to
Terran Melconian

"Terran Melconian" wrote in message news:slrner29b8.6mj.te_rem_ra_ove_an snipped-for-privacy@There-Are-Many-Things.consistent.org...

There will be 240 V across these if they blow - they may not be rated for that. Be careful with such a set-up.

Reply to
Homer J Simpson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

I actually meant that we'd love to see pictures of you disco-ing. :-)

Back in the '80s I built a phase-controlled TRIAC dimmer... no filtering, just hard-switching of the gate, etc. The old WW-II vet running the electronics shop told me it was a horrible design, that I'd create RFI all over the place, just turn on the radio.

So we did (a big old tube set with a foot-wide spider web antenna).

No significant RFI.

Being a young punk I concluded he didn't know what he was talking about.

But now I know better. :-)

Plus I now have access to spectrum analyzers!

Reply to
Joel Kolstad

I think I did, but my ASCII art isn't so good, so I'll to describe my sketch.

Represent the heating elements by drawing two resistors in series stacked vertically on the paper, making a top, middle, and bottom node.

One leg of the AC goes to a diode "pointing to" the middle node. The same leg also goes through another diode "pointing away from" the bottom node.

The other of the AC leg gets directly connected to the top node. The same leg also goes to a third diode "pointing away from" the bottom node.

I hope that's not too confusing.

John

Reply to
John Sevinsky 

--
Early-on PDM, no?
Reply to
John Fields

Me ?:-) I'm a nerd... I designed that stuff, and actually enjoyed that variety of music, but I'm not a dancer.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson 

--
It\'ll run a little hot...
Reply to
John Fields

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