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What happened to Rheostats in Electric Stoves? None
Old 10-21-2008, 07:46 PM   #1
Bioplasmoid
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In pondering the frustrations of my current electric cooker/stove, I have found myself wondering why on earth do manufacturers not use Rheostats in such appliances anymore?

Perhaps my recall is at fault, but I'm certain that back about 50 years or so, there were several brands that used a variable voltage control to determine the amount of heat emitted by the ceramic heat coils on the top of the stove. My current stove (Simpson Columbo) has the typical thermostat design on a rotary dial. It seems such an absurd way of controlling heat, to have it either off or on (binary cooking anyone?) at a rough approximation of temperature via the control dial. I want variable and constant heat, not heat that is regulated by a piece of thermally sensitive metal connected in series with the electricity. Gas is not an option at my current location. I have searched at least one major search engine on several occasions seeking an answer to this question, to no avail. I have looked at the latest appliances available in this country, and they all seem to use the typical thermostat control system regardless of the technology used for the actual heat emitting source. Maybe I have missed the obvious in my brief forays into the local appliance world and the internet, in my quest for answers, but I'm certain someone here can clear up my confusion, in less than 50 words or so...To summarise:

a) Are there any Manufacturers in the World that make stoves with variable yet constant heat control of the heating element,that are powered by electricity ?

b) If the answer to a) is no, then why is this the case?

c) Why are electronic designs using triac circuitry or similar, preferred in general over good old rheostat technology, for control of the intensity of incandescent globes or heating elements?
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Old 10-22-2008, 06:15 PM   #2
Cicatrix
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Have you tested the range of temperatures the oven produces on the on/off cycle? You could do it pretty easily with an oven thermometer. Just a guess but considering how well insulated ovens are and that you also have a fan that works to keep the temperature consistant across the whole volume, I would guess that the temperature would remain pretty constant.

It has me interested though. I might check with my oven and see what it does.
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Old 10-22-2008, 08:29 PM   #3
Kisai
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Rheostats waste power.

If you use a rheostat for voltage control, you're still drawing the same amount of power required for using the stove at full power, you're just dissipating the unwanted wattage across the rheostat as heat. I'm assuming that the rheostat is transferring the heat(Q) to a material with a high specific heat(c).

With the triac, you're using pulse width modulation to send pulses of power. If you set the duty cycle of the oven's to 50%, you'd only draw 25% of the power used at full blast because P = VI. Voltage and current are only active 1/2 the time.

1 = 1*1 vs. .25 = .5 * .5
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Old 10-22-2008, 09:32 PM   #4
Bioplasmoid
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Cicatrix - You are totally correct, the oven DOES retain heat very effectively, which makes it a lot easier to cook with 'intuitively' , in terms of getting to know its typical cooking time for different food types. Im the kind of person who likes to cook without a recipee or guide, after i've learnt the initial arrangement. So being able to learn my appliances 'behaviour patterns' is kind of handy. I check food regularly, and use my nose to detect when things are smelling 'cooked'. Its kind of hard to explain...My issue is not with the oven at all, but with the Ceramic heat Elements on top of it...(Maybe the hot plate is a better term to use here.)

Kisai - Thanks for reminding me of PWM. That explains why old dimmer designs have such a noticeable flicker, at certain intensity levels. I can only look forward to the future of room temperature superconductivity, so that Rheostats can regain their original lofty status.
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Old 03-10-2010, 03:15 PM   #5
johnjeez
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  Originally Posted by Bioplasmoid
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In pondering the frustrations of my current electric cooker/stove, I have found myself wondering why on earth do manufacturers not use Rheostats in such appliances anymore?

Perhaps my recall is at fault, but I'm certain that back about 50 years or so, there were several brands that used a variable voltage control to determine the amount of heat emitted by the ceramic heat coils on the top of the stove. My current stove (Simpson Columbo) has the typical thermostat design on a rotary dial. It seems such an absurd way of controlling heat, to have it either off or on (binary cooking anyone?) at a rough approximation of temperature via the control dial. I want variable and constant heat, not heat that is regulated by a piece of thermally sensitive metal connected in series with the electricity. Gas is not an option at my current location. I have searched at least one major search engine on several occasions seeking an answer to this question, to no avail. I have looked at the latest appliances available in this country, and they all seem to use the typical thermostat control system regardless of the technology used for the actual heat emitting source. Maybe I have missed the obvious in my brief forays into the local appliance world and the internet, in my quest for answers, but I'm certain someone here can clear up my confusion, in less than 50 words or so...To summarise:

a) Are there any Manufacturers in the World that make stoves with variable yet constant heat control of the heating element,that are powered by electricity ?

b) If the answer to a) is no, then why is this the case?

c) Why are electronic designs using triac circuitry or similar, preferred in general over good old rheostat technology, for control of the intensity of incandescent globes or heating elements?

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Old 03-11-2010, 02:20 AM   #6
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There is a very interesting new technology to cook with electricity. It's a magnetic induction system and it as the one great advantage to share with gaz.

You can change the heat quickly and it's also more precise while still using electtric power. I dream of owning an induction stove some day.
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