Electrical Engineering - How stove controls work?

Author

How stove controls work?

ranck@vt.edu

2007-02-12, 5:25 pm

In a sort of indirect follow up to the crossposted article about
electric stoves with constant temperature, I wonder if anyone has
a good basic explanation of how the mechanical stove controls
actually work. I have taken them apart and looking at the internals
they have a little coil of wire and a bi-metal spring contact which
rides on a cam on the control shaft. So, I assume it just sets up a
on/off cycle based on the spring being heated while the switch is
on and shutting off until it cools enough to make contact again.
The cam changes the spring tension, and thus the duty cycle.
Is there any sort of feedback from the heating element itself?

I searched the web for an explanation, but found nothing at the
detail level.

Bill Ranck
Blacksburg, Va.

Paul Hovnanian P.E.

2007-02-13, 3:25 am

ranck@vt.edu wrote:
>
> In a sort of indirect follow up to the crossposted article about
> electric stoves with constant temperature, I wonder if anyone has
> a good basic explanation of how the mechanical stove controls
> actually work. I have taken them apart and looking at the internals
> they have a little coil of wire and a bi-metal spring contact which
> rides on a cam on the control shaft. So, I assume it just sets up a
> on/off cycle based on the spring being heated while the switch is
> on and shutting off until it cools enough to make contact again.
> The cam changes the spring tension, and thus the duty cycle.
> Is there any sort of feedback from the heating element itself?

For what you have described, no.

I have seen electric stoves with temperature sensors and feedback
control, but these are easy to spot. They have a temperature sensor in
the center of the calrod element (the stove heater) that is usually
spring loaded to maintain contact between the bottom of a pot and the
sensor.

I don't know if these are all that accurate, as there might be a
significant temp difference between the inside and outside of the pot.
This difference will vary significantly depending on the pot's
construction.

I think there are some stoves (and ovens) that have plug in sensor
probes like meat thermometers or immersion sensors.

The details of these sorts of systems vary significantly between models
and manufacturers.

> I searched the web for an explanation, but found nothing at the
> detail level.
>
> Bill Ranck
> Blacksburg, Va.

--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
I want to die quietly in my sleep, like my grandfather,
not screaming in terror, like his passengers.

John Gilmer

2007-02-13, 9:25 am

The electric stove burner "control" it very much like the "control" for an
electric blanket (or at least the "old technology" ones.) It is also the
"technology" used in the old style electro mechanical flasher.

Within the controls is a heater and a control thermostat. The heater wire
is wound around the thermostat "bi-metal" loop so the only temperature that
is being regulated is that of the thermostat's sensor. If reasonably
designed, the case of the control unit doesn't get all that "hot" to the
touch.

As you increase the temperature setting the duty cycle of the heater
increases.

The only step(s) necessary to turn this glorified flasher into a burner
controller is to increase the capacity of the contact which control the
internal heater and connect your burner element in parallel to the tiny
little heater in the controller. The burner just goes along for the ride.

As in the "electric blanket" case, if the burner controller is "warm" it
will require less additional heat to satisfy the thermostat. The effect of
this is that often when you turn the oven on (or its very HOT in the
kitchen) , the "middle" setting of the burners will end up a little cooler.
That's one reason cooks prefer gas ranges over electric: the heat setting is
more re-producible.

<ranck@vt.edu> wrote in message news:eqqnvf$cec$1@solaris.cc.vt.edu...
> In a sort of indirect follow up to the crossposted article about
> electric stoves with constant temperature, I wonder if anyone has
> a good basic explanation of how the mechanical stove controls
> actually work. I have taken them apart and looking at the internals
> they have a little coil of wire and a bi-metal spring contact which
> rides on a cam on the control shaft. So, I assume it just sets up a
> on/off cycle based on the spring being heated while the switch is
> on and shutting off until it cools enough to make contact again.
> The cam changes the spring tension, and thus the duty cycle.
> Is there any sort of feedback from the heating element itself?
>
> I searched the web for an explanation, but found nothing at the
> detail level.
>
> Bill Ranck
> Blacksburg, Va.
>

Long Ranger

2007-02-15, 3:25 am

<ranck@vt.edu> wrote in message news:eqqnvf$cec$1@solaris.cc.vt.edu...
> In a sort of indirect follow up to the crossposted article about
> electric stoves with constant temperature, I wonder if anyone has
> a good basic explanation of how the mechanical stove controls
> actually work. I have taken them apart and looking at the internals
> they have a little coil of wire and a bi-metal spring contact which
> rides on a cam on the control shaft. So, I assume it just sets up a
> on/off cycle based on the spring being heated while the switch is
> on and shutting off until it cools enough to make contact again.
> The cam changes the spring tension, and thus the duty cycle.
> Is there any sort of feedback from the heating element itself?
>
> I searched the web for an explanation, but found nothing at the
> detail level.
>
> Bill Ranck
> Blacksburg, Va.
>
If your stove element is in two pieces, and the control "clicks" into place,
chances are it is using a combination of series and parallel connections
utilizing 220, and 110 volts to get about 10 distinct heat ranges.

John Gilmer

2007-02-15, 5:25 pm

> If your stove element is in two pieces, and the control "clicks" into
place,
> chances are it is using a combination of series and parallel connections
> utilizing 220, and 110 volts to get about 10 distinct heat ranges.

Yep!

My grandmother had a range like that.

I haven't seen them for sale for a LONG, LONG time.

The "duty cycle" control is just about standard with, perhaps, a few true
thermostatic controls.

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