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identical failures in two appliances mystery

R

rabbit killer

Jan 1, 1970
0
My clothes dryer is not heating and I found the problem: two normally
closed thermostats have failed open. Several weeks ago this group helped
me with my dishwasher which also failed with the thermostat open...

I replaced the part on the dishwasher and it now works and I could
replace the parts on the clothes dryer but I'm wondering why these parts
failed, within several weeks of each other, on two separate appliances.

Both these appliances are plugged into the same (unnecessary?) GFCI
outlet in the kitchen and they share the plug with the refrigerator.

The failed parts are normally closed bi-metallic thermostats wired in
series with the heating element. The parts are these:

http://www.alliedelec.com/search/productdetail.aspx?SKU=5570010

....for the dishwasher (which I replaced and it now works) and identical
ones for the dryer except they open at a higher temperature.

I don't believe this is mere coincidence but I don't know why both
appliances would fail in identical ways...
 
R

rabbit killer

Jan 1, 1970
0
rabbit killer wrote On 10/23/2010 12:04 AM:
My clothes dryer is not heating and I found the problem: two normally
closed thermostats have failed open. Several weeks ago this group helped
me with my dishwasher which also failed with the thermostat open...
....

I'm not sure now how they both thermostats could fail - they are wired thus:

power--> thermostat --> heating element --> thermostat --> power


I don't know how these things fail, but it seems that the first one to
fail would cut off power to the other and render it safe. But both of
these are open circuits and I'm pretty sure they are normally closed.

Could the refrigerator motor be causing voltage spikes when it goes on/off?

Could the GFCI outlet be the culprit somehow?
 
T

Tom Biasi

Jan 1, 1970
0
"rabbit killer" wrote in message
My clothes dryer is not heating and I found the problem: two normally
closed thermostats have failed open. Several weeks ago this group helped
me with my dishwasher which also failed with the thermostat open...

I replaced the part on the dishwasher and it now works and I could
replace the parts on the clothes dryer but I'm wondering why these parts
failed, within several weeks of each other, on two separate appliances.

Both these appliances are plugged into the same (unnecessary?) GFCI
outlet in the kitchen and they share the plug with the refrigerator.

The failed parts are normally closed bi-metallic thermostats wired in
series with the heating element. The parts are these:

http://www.alliedelec.com/search/productdetail.aspx?SKU=5570010

....for the dishwasher (which I replaced and it now works) and identical
ones for the dryer except they open at a higher temperature.

I don't believe this is mere coincidence but I don't know why both
appliances would fail in identical ways...

There are just too many variables to make any intelligent hypotheses about
this condition.
I think maybe that's what John Fields was saying in his own way.
Tom
 
R

rabbit killer

Jan 1, 1970
0
Tom Biasi wrote On 10/23/2010 11:33 AM:
There are just too many variables to make any intelligent hypotheses
about this condition.
I think maybe that's what John Fields was saying in his own way.
Tom

What about the refrigerator on the same outlet? I would think there
would be internal something-or-other to keep voltage spikes out...

How do these thermostats fail anyway? All I can guess is too much
current deforms the bimetallic strip too much and it stays open...

Can I rule out the GFCI outlet? I don't know how these things work
internally or how they could change the nature of the power being
supplied to my appliances.
 
J

Jamie

Jan 1, 1970
0
rabbit said:
Tom Biasi wrote On 10/23/2010 11:33 AM:


What about the refrigerator on the same outlet? I would think there
would be internal something-or-other to keep voltage spikes out...

How do these thermostats fail anyway? All I can guess is too much
current deforms the bimetallic strip too much and it stays open...

Can I rule out the GFCI outlet? I don't know how these things work
internally or how they could change the nature of the power being
supplied to my appliances.
How about if something was wrong with his thermostat controller and
only the safety over temperature device was doing the regulating, until
it wore out.!
 
R

rabbit killer

Jan 1, 1970
0
Jamie wrote On 10/23/2010 12:45 PM:
How about if something was wrong with his thermostat controller and
only the safety over temperature device was doing the regulating, until
it wore out.!

But for this to happen on two separate appliances (dishwasher and dryer)
seems unlikely
 
B

Baron

Jan 1, 1970
0
Its quite common for thermostat contacts to burn enough that they don't
pass any voltage to the heater, its also possible that the test meter
doesn't provide enough test voltage to overcome the contact resistance.

I had an issue with a boiler thermostat a few years ago. No heat ! But
if you tapped it with a screwdriver handle it would suddenly pass
current and the heater would work until the next on/off cycle.

The weird thing was that if you measured the resistance across the
contacts with the meter, one way round it measured a few ohms but an
open circuit with the meter the other way round.

I've seen the same behavior several times with various misbehaving
switches that have to handle heavy loads.
 
J

Jamie

Jan 1, 1970
0
Baron said:
Its quite common for thermostat contacts to burn enough that they don't
pass any voltage to the heater, its also possible that the test meter
doesn't provide enough test voltage to overcome the contact resistance.

I had an issue with a boiler thermostat a few years ago. No heat ! But
if you tapped it with a screwdriver handle it would suddenly pass
current and the heater would work until the next on/off cycle.

The weird thing was that if you measured the resistance across the
contacts with the meter, one way round it measured a few ohms but an
open circuit with the meter the other way round.

I've seen the same behavior several times with various misbehaving
switches that have to handle heavy loads.
Diode behavior.. Found in galvanic cases..
 
R

rabbit killer

Jan 1, 1970
0
Baron wrote On 10/23/2010 03:20 PM:
Its quite common for thermostat contacts to burn enough that they don't
pass any voltage to the heater, its also possible that the test meter
doesn't provide enough test voltage to overcome the contact resistance.

I had an issue with a boiler thermostat a few years ago. No heat ! But
if you tapped it with a screwdriver handle it would suddenly pass
current and the heater would work until the next on/off cycle.

The weird thing was that if you measured the resistance across the
contacts with the meter, one way round it measured a few ohms but an
open circuit with the meter the other way round.

I've seen the same behavior several times with various misbehaving
switches that have to handle heavy loads.

Thanks. I'm just going to replace these parts and hope for the best -
they are only $12.60 and I will no longer have to haul wet clothes to
the laundromat...

rK
 
R

Rich Grise

Jan 1, 1970
0
Baron wrote On 10/23/2010 03:20 PM:


Thanks. I'm just going to replace these parts and hope for the best -
they are only $12.60 and I will no longer have to haul wet clothes to
the laundromat...
Laundromat? Don't you have a clothesline? ;-)

Cheers!
Rich
 
R

rabbit killer

Jan 1, 1970
0
Rich Grise wrote On 10/23/2010 05:49 PM:
Laundromat? Don't you have a clothesline? ;-)

Cheers!
Rich

Clothesline? I can almost get away with that in the summertime, but I
live in a damp forest. It's raining now and it won't dry out till May.

rK
 
J

Jamie

Jan 1, 1970
0
rabbit said:
Rich Grise wrote On 10/23/2010 05:49 PM:


Clothesline? I can almost get away with that in the summertime, but I
live in a damp forest. It's raining now and it won't dry out till May.

rK

And besides, its being reserved for some one to hang themselves, incase
life gets rough out in that forest, as winter approaches! ;)



Jamie
 
R

Rich Grise

Jan 1, 1970
0
Rich Grise wrote On 10/23/2010 05:49 PM:

Clothesline? I can almost get away with that in the summertime, but I
live in a damp forest. It's raining now and it won't dry out till May.

Ew. Sorry for that. I grew up in Minnesota; we had a dehumidifier in the
basement, which we actually didn't need in the winter because the humidity
has all fallen out of the air in the form of snow. :)

Cheers!
Rich
 

shrtrnd

Jan 15, 2010
3,876
Joined
Jan 15, 2010
Messages
3,876
Refrigerator, dryer, and dishwasher all on the same line, ...
My experience at my place, is that when you run all those at the same time, you actually get the power wiring to heat up, .... which can trip your thermal protection.
My advice, unless you want to rewire with larger gauge wire, is to remember fridge is on, and NOT run dryer and dishwasher at the same time, ... you're drawing more current than what your wiring is set-up for. (You can check your service entrance, and
make sure all you wires are tight on the buss bar, for good connection, ...but ONLY if you know what you're doing).
 
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