How Does a Whirlpool Moisture Sensor Work?

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Old 04-09-13, 12:57 PM
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How Does a Whirlpool Moisture Sensor Work?

Model Nr. LG7681XSW2.

This sensor consists of 2 metal strips, each about 3 inches long and about 3/8 inch wide. These are mounted on a curved plastic part that is visible from inside the drum.

One strip is connected to a wire, the other to ground. There is no continuity between these strip.

The only way I can see this sensor working is that current is available at one strip, and when the clothes are wet enough and brush by the sensor they complete a circuit to ground (through the 2nd strip). Is this correct?
 
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Old 04-09-13, 01:44 PM
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I believe you are correct...but it's probably more complicated than just an open or closed circuit. I imagine there are electronics connected that actually measure the resistance as the clothes tumble.

I think some of the fancy new models actually adjust the heat to help prevent wrinkles and such?
 
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Old 04-09-13, 04:12 PM
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Wet clothes complete the circuit. Depending on dryer there may be more parts involved.
 
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Old 04-09-13, 06:13 PM
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Like Don said.....wet clothes complete the circuit. Completing the circuit causes the timer to lengthen the drying time and when the clothes are dry the timer completes the cycle normally.
 
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Old 04-09-13, 08:16 PM
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Thanks! I reinstalled the sensor.
 
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Old 09-05-13, 08:50 AM
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Moisture Sensor on Kenmore (Model 110.65944400) Dryer - SHOCKINGLY simple?

My sister was recently shocked when unloading clothes from a Kenmore washer with the humidity / moisture sensor feature. I've learned that her hands were damp and she was shocked when touching the inside of the dryer, below the door. On this dryer, this is where the moisture sensor elements are located. I'm reading 60VAC between the two elements. This is whether the timer is set to "OFF", or not, whether the door switch is depressed, or not. It seems strange to me that this circuit would remain live when the door is open. I've traced the connected wire back to the control circuit card, and there's no obvious damage, but who knows what's going on inside (somebody out there knows right!?!?)

I guess I really don't need to know the specific internal workings of the circuit, beyond that the 'charged capacitor means the clothes are dry enough > advance timer, and a discharged capacitor, due to damp clothes shorting the sensor bars/elements to ground, means the clothes aren't dry enough yet > don't advance the timer yet', but I would like to know if these elements/ bars are supposed to be energized at all times; i.e. circuit not broken by the door switch or the timer 'off' setting. Does anyone out there know? If you have a dryer with this feature, could you take some readings on yours and let me know?

Thanks sincerely.

BTW, I realize 60VAC isn't terrible, I've been hit by far more, and less (checking phone connections (tip/ring) while standing barefoot in damp grass - 48VAC ...not real smart I know ...I considered it a valuable safety lesson), but still, it just seems odd to have even 60V sitting there, always, and so accessible.
 
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Old 09-05-13, 09:13 AM
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Welcome to the forums.

Yes......60vac IS terrible. There should not be that high a voltage on an exposed part.

I'll look for the schematic so we can check this out.
 
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Old 09-05-13, 11:55 AM
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Thanks Pjmax. I saw the schematic -actually took a picture -but all I can say is that it's an output of this separate circuit card. Have no idea what the IC is doing. I'll attempt to post the pic. Have been tempted to drive up to sears, plug in one of their floor models, and take a reading. Do you think these bars may have an insulative coating that my meter probes pierced, and sister's wet hand overcame? Or simply a bad part somewhere? Btw, this dryer is a couple hours away and, for safety reasons I went ahead and disconnected the sensor bars for now so they can still dry their clothes. I'll be back in a few days with hopefully a better fix.

Name:  Schematic s.jpg
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Name:  Control Circuit Card -smaller file.jpg
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Size:  31.8 KB (Card pic, Yellow-Red (Y-R) is from sensor)
 

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Old 09-05-13, 03:15 PM
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Now, having taken some time to study the circuit a bit, I'm not seeing the door switch having any effect here, and unless the sensor bars have some type of insulation that my probes penetrated, I may have a bad 'dryness' control board. Hmmm, shall I replace this board for $100+ or leave the sensors disconnected? Hopefully someone can tell me about those sensors, or whether their sensors read the same, or that I'm missing something, but until then, sister won't be using 'automatic' mode anymore!
 
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Old 09-05-13, 03:54 PM
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Check to see if your neutrals and ground at terminal block are connected right.
 
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Old 09-06-13, 12:52 AM
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The door switch only opens the neutral...... the hot is still connected.

The sensor bars are bare metal......no insulation or they wouldn't sense moisture from the clothing.

Looks like the board is defective. It's available all over ebay.


Genuine FSP Part 8558180 60S01870002 Kenmore Sears Whirlpool Dryer Control | eBay
 
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Old 09-06-13, 06:12 AM
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Thanks for the suggestions.

[PJmax]
Was thinking the bars might have had some type of thin resistive or capacitive film that had deteriorated. Just hard to accept that the manufacturer would use a circuit design that, upon failure, would present an energized component so accessible to a user.

Thanks for the link to the ebay board. I'd seen one there as well (~$4 for the part and $35 for shipping - interesting marketing strategy), just a little skeptical when it comes to buying used electronic parts - I'll probably run a few checks on this board this weekend.

[pugsl]
As to neutral and ground connections, unless something shook loose, all should be good there as this appliance used to work fine, and prior to me, it's not been 'cracked open'. The power side of things also tells me that's all fine. Nonetheless, I'll give those a check, especially at this control card, where poor connections could have significant effects.

Will post back what I ultimately find ....
 
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Old 09-08-13, 12:20 PM
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Go to Appliance Parts Pros.com Discount Appliance Parts for your spare parts.

Been there.
Done that.
Fully satisfied.
 
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Old 09-09-13, 04:17 PM
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Lots of reputable online parts companies.

I was kind of surprised too that the board would allow leakage to that extent. I couldn't find an online schematic and I don't have one to test.
 
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