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> Electric Stovetop Burners, temp control?
MacFromOK
Posted: February 07, 2010 01:32 am
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Hey guys,

We have a built-in electric stove (GE) that was installed in '76 (so there are no fancy electronics involved). Pots and skillets are placed directly on top of old-fashioned exposed-coil stovetop heating elements when cooking, and temperature is set by adjusting their rotary control knobs.

However, I'm wondering how temperature control is achieved. There's an audible "click" when the appropriate temperature for the dial setting is reached, but there are no mechanical thermostat tubes at the burners as there is inside the oven.

My question(s):

Is each burner's temperature monitored by the element's changing resistance as it heats/cools (utilizing a bi-metal current sensitive gizmo perhaps?), or is some other method used?

All the cooking elements work fine btw, I'm just curious... smile.gif


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GPG
Posted: February 07, 2010 03:43 am
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MacFromOK
Posted: February 07, 2010 04:04 am
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"An electrical control device which turns a heating element such as a stove hotplate or grill on and off in a fixed cycle."

Ok, so it's sort of a crude PWM equivalent and doesn't actually respond to temperature. Thanks. smile.gif

But what provides the "fixed" cycle? As mentioned, it periodically "clicks" like a regular thermostat. huh.gif


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GPG
Posted: February 07, 2010 04:11 am
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Bimetal heating and cooling, biased by a ramp controlled by the knob.
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MacFromOK
Posted: February 07, 2010 05:17 am
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So the bi-metal piece carries the full burner current?


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CWB
Posted: February 07, 2010 05:54 am
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some of the controls i have seen use a method similar to that used in the bimetal signal flashers in cars .
insulated resistance wire is wound around the bimetal that causes heat generation when the contacts are closed .
the method above is used to vary the temperature .


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MacFromOK
Posted: February 07, 2010 07:05 am
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Huh. All the non-electronic auto flashers I've taken apart just conducted directly thru the bi-metal strip IIRC.

So using the wire as a heater allows a smaller bi-metal strip to control a larger current then.

Thanks. smile.gif


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CWB
Posted: February 07, 2010 03:15 pm
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i should have mentioned that it was a method i have seen .

when i was a wee kid i watched the action of one of those 7.5 watt flashing christmas tree lamps (after i had scraped off the paint) ... it was fascinating .

i asked my dad how it worked ... he did not know .
i think this was the start me researching stuff .


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tekwiz
Posted: February 07, 2010 08:46 pm
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Those Infinite Heat controls are crude thermo-mechanical PWM devices. They have no temp sensing at all. Whether the load current flows thru the bimetal or not is another story, but there has to be some heat source for it. I'm thinking seperate heater, as the controls are pretty well universal, they work the same no matter what the burner power is.



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MacFromOK
Posted: February 08, 2010 12:03 am
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Interesting bit of history Larry. smile.gif

Thanks again guys, this has been very informative (as usual). thumbsup.gif


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undidly
Posted: February 08, 2010 01:41 pm
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QUOTE (tekwiz @ February 07, 2010 08:46 pm)
Those Infinite Heat controls are crude thermo-mechanical PWM devices. They have no temp sensing at all. Whether the load current flows thru the bimetal or not is another story, but there has to be some heat source for it. I'm thinking seperate heater, as the controls are pretty well universal, they work the same no matter what the burner power is.


The bimetal heater is across the contacts.
The heater element is wound to match the voltage not the load.
At switch on the contacts are open ,the heater for the bimetal is on ,the load is passing the small current that goes through the bimetal heater but this hardly heats the load at all.
After a few seconds the bimetal switch closes and full voltage is applied to the load and the bimetal heater is shorted so starts to cool.
Few more seconds and the cooling switch opens.
The cycle repeats.

An adjustable screw pushing on the bimetal alters the on,off ratio.

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