SCR dimmer control for portable electric heater??

[Andy]

Andy comments:

The heating element may be non-linear, so the current may not be linearly reduced along with the voltage, and will be different...

I did some experiments with an old stove top burner which , the small size, is 1000 watts when powered by 220V..... I found that the current drawn was linear with voltage, which means that running it from 110V made it a 250 watt element.

However, light bulbs, for instance, are not linear, and the same wouldn't apply....

Just felt like typing --- it's easy enough to characterize your heater if you have a voltmeter and a current meter.....

By the way, I have a great application for old stove burners mounted on a metal paint bucket filled with sand..... Really good heaters that don't put out enough light to keep you awake at night.... and keep your coffee warm.....

Andy in Eureka, Texas

[George]

More efficient in what regard? It takes xxx BTUs to warm the space. Assuming the space heater is providing the heat it costs the same to provide those BTUs whether the heater is operated at a higher output for short periods or a lower output for longer periods.

[Gary H]

That doesn't suggest much knowledge of electricity.

[Monty B]

A dimmer doesn't reduce the voltage. It reduces the duty cycle.

[dean]

You can buy a 2000W dimmer. I have one, and I use it to control a

1500W tungsten light bulb (as part of a light bulb collection, nothing more). They were hard to find on the web a few years ago, but search a little and you'll get one. If you want I can look at the brand name on mine.

[George]

Depends what "voltage" is being discussed. It reduces the RMS voltage. RMS voltage is the voltage displayed by a typical meter. Attach a load to a dimmer and then connect your meter to the load. You will note that the displayed voltage does drop as you lower the dimmer. RMS is used because it approximates the DC value which is what we need to perform easy power calculations.

[George]

You can buy them at any real supply house. Had two in an office. They had a large external heatsink. Not as common anymore as we move away from incandescent light.

[dean]

Yep, big heat sink! Would look ugly on a wall,

[Jim Yanik]

"John Grabowski" wrote in news:4ba609b7$0$22526$ [e-mail]:

no,because triac dimmers -shut off- current flow during part of the AC cycle,so there's no power dissipation while the triac is OFF. It dissipates only when it's on and conducting,and it's ON resistance is very low,so that's not a lot of dissipation.

[Jim Yanik]

[e-mail] wrote in news: [e-mail]:

well,it's a triac,not an SCR.

SCR would only work on half the AC cycle.

Or you could say thyristor....

[dean]

e quoted text -

The 2000W dimmer is made by unenco.

-D

[me]

Yes..... SCR only

[me]

I don't want to control the heater with a thermostat at all cause I come and go so much that I just turn the unit off/on when leaving/coming.

I would turn thermostat all way up.....and control heat with pulses from Triac

[me]

Yes.... you are correct.....it is a Triac

I had forgotten it was a Triac and could only think abt the SCR name

[me]

Good point..... could be the case!

I realize it may NOT be worth pursuing.....especially if there does not exist off shelf Triac control at low price.

But since I come and go so much.... I turn the little heater off and on a lot.....so a thermostat does little good for me.....and was thinking a Triac would allow me to "tweak" very small increments of heat....and then just keep at that setting.... and turn heater off/on when leaving

Probably not worth messing with..... but it was an "idea"

[me]

YES!!!

I think that is what some people are missing....

The Triac only controls duty cycle...... on/off

[me]

OK.... was hoping to find something off shelf at Lowe's or Walmart

If I cant do that....will scrap the idea

[clare]

An SCR (or more correctly a Triac) type dimmer will work very well for controlling the output of an electric heater. The control will NOT be linear - but it will be effective and quite efficient as the triac control turns the power on and off at different points of the sine wave. There is very little dissipation.

There IS, however, significant electrical "noise" and a standard residential dimmer will not do the job because they are generally rated for 600 or 700 watts. You need a 1500, or preffereably 1800 watt dimmer to do the job. They will get WARM - but only dissipate a few watts if running within their design parameters.

[clare]

You would still use a thermostat to controll the heat, but the heat would be more even as, if properly adjusted, the heater would be on almost constant and there would not be great fluctuations. A bit like the units that switch from 1 to 2 to 3 elements for low, medium, and high - 500 watts each for 500, 1000, and 1500 watts. There is a radiant heater made in Turkey and sold in North America that DOES have variable heat output - and IIRC (only saw them once) it does use an SCR type phase switching control.

[clare]

The diode would need to be in series with the thermostat, so would have no effect if it shorted on. The thermostat is stll "wearing the pants".