Can I put a coffee warmer on a dimmer switch?

[J. Clarke]

Resistive loads don't draw ten times their normal current on startup, that's an induction motor starting stalled and even then 10x would be pretty high.

While one should use a dimmer rated for the load, the use of dimmers and similar devices with coffee makers works quite well.

The right place to ask such a question though is alt.coffee, where there are many people with expertise in the management and modification of coffee making apparatus of all kinds, including the fitting of temperature control devices to them.

[Boden]

Not likely.

[Square Peg]

Good point. I should have said that I don't think ti has a *variable* thermostat. That's what I thought you meant. There is no temperature control. But I am sure you are right that it may have some sort of threshold control to turn it off at some fixed temperature.

[tnom]

What are you talking about? This resistive load is a tungsten or nichrome or similar metal that with out a doubt changes resistance depending on its temperature.

[trader4]

A resistance element in a heater like this behaves a lot differently than a light bulb. The temperature change in a lightbulb goes from room temp when off to thousands of degrees when lit. That causes the resistance of the filament to change substantially from cold to hot. In the case of a resistance heater in a coffee pot, the resistance of the element is going to change much over the small temperature range from 70 to 150 or so degrees.

[trader4]

What he's talking about is that a resistive load in a coffee pot doesn't change in resistance by anywhere near 10X over it's operating range. If they did draw 10X, then the typical 1500W hair dryer would draw 120amps when first turned on and you'd have tripped breakers. A lot of this is probably being taken out of context from the case of light bulbs, which do vary substantially in resistance from cold to hot. But in this case, cold is room temp or below and hot is it glowing at thousands of degrees. That doesn't happen in a coffee pot, where the heating element is only going from 70 deg to maybe 200 and the resistance change can be ignored.

[JIMMIE]

Dimmers dont control light bulb intensity through variable resistance unless you want to call the difference between off and on a change in resistance. They control the intensity by controling the off/on duty cycle.

[tnom]

O

The element gets much hotter than 200 degrees. The inrush current depends on the particular element material.

[dpb]

Jeff Wisnia wrote: ...

... Ever done the dill pickle? :)

--

[trader4]

Exactly how much hotter than 200 deg? Would 300 deg F make you happy? The point is that you do not get anywhere near a 10X change in resistance over the temp range of the heating element in a coffee warmer. You do get that kind of resistance change in a light bulb, where the filament temp changes by 3000 degrees.

From your own source:

"Nickel-chromium alloys. These are the most common, and for control, the most docile class of resistance heater materials. Various formulations, which can include iron, aluminum and silicon, show useable element temperatures up to some 1400 =BA C.

Change in resistance from room temperature over the working range is only some 4 =96 6%. It also changes very little during service life, which also makes it easy to detect and warn of partial heater failure by monitoring the combined resistance of several parallel branches."

When you have something that says the resistance in a coffee warmer varies by 10X, post a link.

[terry]

Hi Jerry. Agree; the variac transformer type; not very common IMHO that's why we wrote "Some older style dimmers etc.". In fact got one of those auto-transformer types somewhere (Pretty heavy wattage, I think it came out of an assembly/dining hall); only reason not using it as an electronics bench variac is that we have another variac. Also need an odd sized shaft knob for the ex-lighting variac. Must make or adapt a knob sometime! Maybe a lever/pointer arrangement would work?

[terry]

[terry]

They really were HOT-dogs!!!!!!

[tnom]

[terry]

Where does the 1500 watts come from????? (Or go to)? The discussion is about a 'Coffee/tea WARMER'! Probably less than 30 watts?

Or maybe we have changed over to discussing a coffee 'pot' or coffee maker. If so the 'inrush' current during the first half or full cycle after first switching on from room temperature cold would be ................ what?

Maybe half the resistance, for momentarily twice the operating current? Maybe quarter resistance, for momentarily four times the current?

Doubtful it would be anything like one tenth the normal operating temperature resistance, even for that few milliseconds (1000/60 =3D 16.7 m/secs) =3D one cycle!

The temperature-resistance coefficient of typical (nichrome) resistance wire (alpha) is say 0.00017.

In other words for a change in temperature from room at say 20C to red hot at say 600C the amount of change of resistance would be about (600

- 20) x 0.00017 =3D 0.0986.

I think that means 9.86 percent lower resistance? Momentarily.

[tnom]

I never said it did. I said it may. There is a difference.

I originally said "The 1500 watt heater upon startup may draw as much as 10 times its normal current before the element heats up." I stand by that because I said "may". I said may because we do not know what the heating element is made of.

All you have to do is read the link. It gives resistance of various heating elements. Going by this link I should of said "may be 15 times" instead of 10.

.

[nicksanspam]

Not necessarily, with a short draw.

Nick