What is the difference between an induction furnace and an induction ccoktop

Extensive. Cooktops are low-Q coils with high inductance, in other words, they're made like transformers. The control circuit is also useless because it's made to sense if a pot is on top. If you tried, say, using one with an average work coil, made of a few turns of copper tubing, at best you'll simply get no power out; at worst you'll start a fire from the exploding transistors.

Such a furnace BTW would certainly work for a cooktop, you just have to turn it down a little so you cook the food instead of melting it. :)

Tim

-- Deep Friar: a very philosophical monk. Website:

ds,

Hey, If I might hijack this thread. I've got an electric stove with spirals of resistive heating elements that get hot. The knob on front controls the amount of current (or something.) What does the knob control? How is the current/ voltage varied? Is it a traic or some such thing?

Thanks, George H.

Probably adjusts a saturable reactor. Oh, no, wait, this isn't the

Cheers

Phil Hobbs

From my understanding: The induction furnace has a 'built in' cauldron, a carbon sink, you put the metal stuff into. The resonant frequency heats the sink, the sink heats the metal. The stove top is more like the primary side of a broadband current transformer. Sitting there looking for something to put the current into. YOU supply the pots and pans.

Be careful of the induction furnace. It will heat a metal washer, melt it, and burn through any metal mounting hardware. Make everything using nylon type bolts and hardware.Even a hole drilled into metal will heat, so use ABS or such. Out to at least 3 diameters away from the induction furnace coils.

words,

using

at

m the

to

Grin, yeah the stove is not quite that old. I sorta know how to deal with a few watts of power. (In my inefficient 'class A' style.) Hundreds / thousands of watts is harder... I first think of a Variac, but that=92s not in my stove either.

George H.

t -

The old ones had a bimetal thermostat that was heated by the current flowing through the main heating element. The knob adjusted a spring on the thermostat. You could tell these because the stovetop heater made faint creaking noises as it cyclically heated and cooled.

The new ones use a triac dimmer type circuit.

Jon

The obvious modification is to reduce the power? And a cooktop is not a furnace? The same principle of using induced eddy currents to heat the ferromagnetic cooking container which then heats the food applies?

The old ones are closer to your car's turn signal blinker. A heater and bi-metal strip, with the knob adjusting the tension of the bi-metal strip with a cam. Slow PWM.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

ords,

ing

the

Sounds like you have an electric radiant cooktop:

You just can't beat the bimetallic element where the knob adjustment presse= s on the bimetal adding a bias to the amount of heat required to trip it. T= his is because all these controls have time constants in the 10s of seconds= .

My stove is about 35 years old. It has spiral resistance elements. The controller for an element can be heard to click on and off from time to time while operating. I experimented with it this morning, removing the heating element. There is still a clicking on and off, coming from the control knob, and it will click on and off at different points on the dial, depending how long it has been at a particular setting. I infer that there is a thermostat with its own heater within the control, since it doesn't depend on having a heating element installed.That thermostat must control its own heater as well as the stove heating element.

OK thanks Jon. I've never noticed the AM radio interference that I get with light traic dimmers.

Maybe just cheaper?

George H.

her words,

less

y, using

g, at

from the

ve to

:)

th

ront

some

Yeah! I hear it clicking.

I'm cooking up a big pot of spaghetti sauce. It's the boys annual fishing trip to Oneida lake this weekend. I'm testing out my theory that you can never put too much onion or garlic in the sauce. (Three cloves, the kitchen reeks! tastes OK, should be great by Friday night)

George H.

It's called an "infinite heat control" and is essentially an electromechanical PWM. There's an internal heater, typically in series with the external load.

Best regards, Spehro Pefhany

All commercial cooktops AKA stoves use plain resistive heating elements which are good from DC to 400Hz (ie: anywhere in the world if voltage matches). An induction furnace system WOULD work in a cooktop configuration. Fer eggzample, the RF generator drives the induction loop, which is then loaded with the cooking pot. Might not be as efficient as a properly configured (industrial) furnace at the same power, but it would work OK.

Overall efficiency should be excellent -- they use a lot of ferrite and litz wire in the coil, no need for water cooled copper pipes.

Tim

Yep, thermal oscillator with a duty cycle control...

And some of the really old ones used a big element, and small element, and connected both (in parallel) to 240V for high heat, and connected one or both to 120V and/or 240V to achieve intermediate heat outputs. 120V to both elements in series would be 'low heat'.

That's completely untrue. Bimetal element controls dominate the market. There are a few high end cooktops that regulate the temperature of the element, versus the power, and those may use an electronic control, but the vast vast majority do not.

You did say 3 cloves of garlic, not three bulbs? My cooking would be = more like 3 bulbs, about 20 cloves, maybe a lot more depending on what i made. Assuming about 8 quarts of product.

?-)