"Bert Hyman" > wrote in message
...
> In "FDR"
> > wrote:
>
>>
>> "Bert Hyman" > wrote in message
>> ...
>>> In "Douglas Reynolds"
>>> > wrote:
>>>
>>>> Anderson noted that an oven's heating elements are either on at
>>>> full power or off-with no middle ground.
>>>
>>> In this age of cheap semiconductors, why ->don't consumer ovens have
>>> "proportional controls"?
>>>
>>> I'd think that solid-state temperature controls would be cheaper and
>>> more reliable than the relay switching that's used now.
>>>
>>> Or, maybe the newest ones do; our Thermador oven is 5 years old.
>>>
>
>>
>> Solid state power control is basically like what you get with a light
>> dimmer switch. The sinusoidal voltage is turned on and off during the
>> sine wave to achieve a reduction in power.
>
> Well, that's one way to do it.
>
>> In the oven the relay switches the power on and off too, but since
>> heat in the oven reacts more slowly than a lightbulb on the retina,
>> the switching can be done slower too.
>> So there's really no benefit in applying the technology.
>
> Of course there would be, assuming that a continuous temperature in the
> oven that actually matched the temperature you set it for is a
> "benefit".
>
> Simple full-on/full-off switching of the heating element causes
> significant temperature over and undershoots, although the long-term
> average might match the dial setting.
>
> A proportional control could apply full power to the cold oven, reduce
> power as the oven approached the desired temperature and then continue
> to apply just enough power to maintain a constant temperture in the oven
> to balance heat loss.
>
> Would you accept a stove-top element that only had a full-on or full-off
> setting?

A stove top element has a much much quicker response time, and would need to
be more tightly regulated. An oven doesn't need the same regulation. Aslo,
the stovetop works by you regulating the temperature, whereas in an oven you
set the temperature and let the oven maintain that temperature. They are
two totally different environments.

As inaccurate as a stove may be, they really don't need to be dead on for
your baking to work. Now if as the OP siad that he never gets anything to
really cook right and the fluctuations are really large, then you will have
problems. But even the lowest tech gas ovens from years ago could make a
good cake or roast.

>
>> Relays seem to be good enough that they don't need service also.
>
> Relays, being mechanical with moving parts, break far more often than
> conservatively designed power control circuits would.
>
> --
> Bert Hyman St. Paul, MN