"David Farber" wrote in message
...
This Whirlpool electric stove, model number RF0100, appears to be an
older model. If you were wondering what blasted the ground lead of my
Kill-A-Watt
meter which I posted about two days ago in the thread about the
Phillips security screw, this is the culprit. The schematic is he
http://members.dslextreme.com/users/...tric-stove.jpg
as
I photographed it from the back of the stove.
I used to have the stove hooked up to a 240 volt circuit as
indicated in the
schematic and it worked ok. But, now I don't have a 240V line. Or at
least not yet. I was trying to at least get it to work on 120V
because only the oven will be used and at very low heat, probably
around 200 degrees to cook
some ceramics. The stovetop and broiler wires have been disconnected
because
they are not needed. This particular model does not have a light or a
clock
as shown in the schematic. I wired it so that L1 went to hot
(black), L2 went to N (white), and N to ground (green). The load
across the electric plug, hot to neutral, with the oven switch on,
is 17 ohms. That makes sense
to me. However the impedance reading from neutral to ground makes no
sense to me. I've tried two different dvm's and they both give
bizarre results. When starting at the 2M ohm range, the meter starts
at about 700k and counts
down to about 300k and holds there. When I move the switch over to
the 20M ohm range, the meter starts at about 2.3M ohm and counts up.
The other meter
which is a portable meter counts backward too and then the minus sign
appears on the meter as if current is coming into the meter. From
what I can
see, there aren't any capacitors or semiconductors interfering. The
oven thermostat has a thermocouple wired to it which for some reason
is not shown
in the schematic. I opened the thermostat and found an interesting
mechanical coupling that moves a slider bar that depresses either
the oven element switch, the broil element switch, or both. Then
there is the thermocouple wire which is wrapped(?) internally around
the rotating control
that selects the oven temperature. I don't usually open oven
thermostats so
I'm not sure what exactly is going on inside because once you open
the thermostat,
there is a spring inside the device which displaces everything. In
any case, at room
temperature, there is a connection from L1 to the bake and broil
terminals so I know
it's sending power through to those elements.
Not trusting anything about these electrical readings, I first
plugged the oven into my Sencore PR57 isolation transformer. The
transformer can only supply about 300 watts but I was more
interested in measuring leakage current. No surprise when the low
side leakage to the metal frame measured full deflection even with
the power off to the oven. Not exactly the best situation. The high
side leakage was zero. I turned up the voltage slowly and the
current seemed to rise proportionately to the 17 ohm load until I
stopped at about 300 watts. I should mention that the heating
element did not seem to get warm. Also, the heating element
impedance matched the load across the power plug so that seemed like
a good sign. Then I plugged it directly into the wall outlet via the
Kill-A-Watt
meter. I
turned on the oven switch and an instant trip of the circuit breaker
at the
sub panel occurred. So where is all this extra current coming from
to cook the ground plug on my Kill-A-Watt and trip the breaker? I
must be missing something very obvious.
Thanks for your reply.
--
David Farber
Los Osos, CA
Wild_Bill wrote:
I'm not really sure which heating element is still connected. Most of
the elements' wattages are listed on the wiring diagram, but the two
on the left side (bake, broil) of the diagram aren't (that I could
see). It could be, that the wattage of the element being used exceeds the
total wattage of the circuit breaker.
I would check to see if there are any other loads applied to the same
AC supply circuit.
Those temperature control symbols may represent the type that have
internal heated bi-metal type switches in them (dunno what they're
called in the trade, but commonly used in cooking appliances with
heating elements). In some Corning laboratory type hot plates that I have,
these types of
switches make a fairly distinct sound.. a sort-of "tink" when the
when the switch's internal heated bi-metal strip opens the switch.
I believe a cam closes the switch contacts, then the heated bi-metal
strip opens the switch (a calculated/designed time delay, I guess).
The small bi-metal heater wire (inside the switch(s) will naturally
have a DC resistance. I wouldn't think that internal heater wire
resistance would change from just a DMM test lead voltage, but maybe
they do. If I could get to those lab hot plates, I'd do some checking
instead of just speculating.
Hi WB,
There's an upper and a lower element in the stove section. The top one is
called the broil and bottom one is the bake. When you turn the stove knob
from off to on, both broil and bake elements get energized. I disconnected
the broil element because I will not be doing any broiling. So what's left
is the bake element at the bottom. That presents about a 17 ohm load which
translates into approximately 850 watts. If the supply voltage were 240V,
that would increase the power to 3,400 watts. I'm not even sure 850 watts
can raise the temperature to 200°F (assuming I can get it working) in a
reasonable amount of time. Regarding the circuit breaker, there was really
nothing else on that circuit at the time it tripped. Even so, why would the
ground terminal be the one to take the hit? There shouldn't be any current
flowing through there, right? The way the stove is wired now is that the
neutral wire of the stove is connected to where L2 was before so the circuit
path is from L1, through the oven switch, through the heating element,
through L2 which is now wired to neutral.
Thanks for your reply.
--
David Farber
Los Osos, CA