I have a Jetstream countertop oven that expects 110V at 60Hz. I have
been using it lately in 230V country courtesy of a pretty massive
stepdown transformer that is rated at 1500W but of course outputs 110V
at 50Hz.

The oven seems to work okay (the electronics are fine of course since
they are DC) and I suspect the motor is okay also since I would expect
that to be DC also. But the perspex oven cover gets uncomfortably hot
and has started to crack from the heat. I am wondering if this is
because the actual heating element is rated for 110V at 60Hz operation
and doesn't like 110V at 50Hz? From a distant past I recall that power
for DC was Volts*Amps or I**2*R. But for AC you had to take the RMS
value of the voltage rather than the nominal voltage? So potentially
the heater is operating at a higher power (heat output) than it was
designed for?

As an aside I recall my US house had to have 240V at 60Hz for a drier
since not enough power could be supplied at 110V whereas in my local
house abroad, since the entire house is wired for 230V 50Hz there is no
need for a separate line for high current draw appliances.

Anybody who is more familiar with some of the basic electrical theory
able to cast some light on this?

Thanks

Larry

wrote in message
ups.com...
I have a Jetstream countertop oven that expects 110V at 60Hz. I have
been using it lately in 230V country courtesy of a pretty massive
stepdown transformer that is rated at 1500W but of course outputs 110V
at 50Hz.

The oven seems to work okay (the electronics are fine of course since
they are DC) and I suspect the motor is okay also since I would expect
that to be DC also. But the perspex oven cover gets uncomfortably hot
and has started to crack from the heat. I am wondering if this is
because the actual heating element is rated for 110V at 60Hz operation
and doesn't like 110V at 50Hz? From a distant past I recall that power
for DC was Volts*Amps or I**2*R. But for AC you had to take the RMS
value of the voltage rather than the nominal voltage? So potentially
the heater is operating at a higher power (heat output) than it was
designed for?

As an aside I recall my US house had to have 240V at 60Hz for a drier
since not enough power could be supplied at 110V whereas in my local
house abroad, since the entire house is wired for 230V 50Hz there is no
need for a separate line for high current draw appliances.

Anybody who is more familiar with some of the basic electrical theory
able to cast some light on this?



Most likely the motor is AC and will run slower on 50 hz. The heating
elements don't care what the frequency is. They will put out the same
ammount of heat with any frequency that is in common use.

Without really getting into it, the stated voltages are RMS. That is also
the DC equivilent heating voltage. That is for a heating element 110 volts
DC or AC (any frequency) RMS will heat the same

I don't know anything about your particular stove, but it may be the slow
running motor is causing the problem by not moving enough air.

On Nov 12, 11:00 am, "Ralph Mowery" wrote:
wrote in oglegroups.com...

....

Without really getting into it, the stated voltages are RMS. That is also
the DC equivilent heating voltage. That is for a heating element 110 volts
DC or AC (any frequency) RMS will heat the same


I guess that makes sense. Shows up how far in the distant past my
physic was :-(
I don't know anything about your particular stove, but it may be the slow
running motor is causing the problem by not moving enough air.

I hadn't thought of that. The motor runs fairly fast - I am guessing at
over 500 up to 1000 rpm. I presume with the right windings on the
motor, it can be configured to rotate that fast based on the mains
frequency? But what puzzles me is, the motor has two speeds (low and
high) controlled by an electronic switch. Perhaps that switches from
one to another set of coils on the motor to give the two speeds?

The actual unit is a later model of this

http://nesco.com/products/?category=600

the difference apparently being the motor now drives the fan directly
rather than via a belt that is susceptible to breaking