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?

> 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