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Post by coldspaces on Mar 12, 2016 3:49:06 GMT
So I though to buy a RO-81 today and found that with the help of a pocket knife and screw driver I was able to open it up without harming it. So now we will know just how they wired it inside.   As you can see the two leads on the top are the power. The right power lead simply feeds on through the housing and becomes the common lead to the compressor.  The left power lead is the one going through the overload.  Here is my hand drawn diagram of it. Also note that this overload is made to stay off longer than most. I do not see that this overload is sold by itself.  |
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Post by ChrisJ on Mar 12, 2016 3:55:52 GMT
So wait,
The black common is 1 piece of wire, that's all? Can it be pulled out without taking the unit apart?
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Post by coldspaces on Mar 12, 2016 3:59:04 GMT
So wait, The black common is 1 piece of wire, that's all? Can it be pulled out without taking the unit apart? Yes I think it could. There is nothing stopping it other than the 90 degree turn it takes. Push in on the power lead end the same time you are pulling on the compressor end and it should come out. Eddit: Stripping most the insulation off the power end might make it go even easier. |
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Post by ChrisJ on Mar 12, 2016 4:00:21 GMT
So wait, The black common is 1 piece of wire, that's all? Can it be pulled out without taking the unit apart? Yes I think it could. There is nothing stopping it other than the 90 degree turn it takes. Push in on the power lead end the same time you are pulling on the compressor end and it should come out. That must be what Mike Arnold did. Yanked that useless lead out and wired it into the relay base. Wonder what other stuff he knew............  |
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Post by coldspaces on Mar 12, 2016 4:02:01 GMT
Yes I think it could. There is nothing stopping it other than the 90 degree turn it takes. Push in on the power lead end the same time you are pulling on the compressor end and it should come out. That must be what Mike Arnold did. Yanked that useless lead out and wired it into the relay base. Wonder what other stuff he knew............ I never met or talked to Mike but he knew plenty from what I have heard. Bet he would have loved to see the progress on our forum. |
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Post by ChrisJ on Mar 12, 2016 4:04:40 GMT
Thanks for taking the time to do this Gill.
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Post by Travis on Mar 12, 2016 4:39:26 GMT
That's interesting. Now I understand the magic of your relay with only three wires connected Chris.
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Post by coldspaces on Mar 12, 2016 4:58:03 GMT
Thanks for taking the time to do this Gill. This time of year I have more time than any other so its no problem Chris. By the way I pressed it back together and the wire will pull through pretty easy. |
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Post by cablehack on Mar 13, 2016 22:59:39 GMT
I thought that would be the case with the black wires - just for wiring convenience. Two wires in from the supply & three out to the compressor means the fridge mechanic is less likely to be confused.
One could obviously use the overload thermistor on its own such as for when having to put modern thermostat guts into an early control.
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Post by ChrisJ on Dec 1, 2020 13:48:09 GMT
I wanted to add some info I received from Supco a few years ago.
The overload protector in a URO81/RO81 has a steady state RLA [run load amps]
of 4 amps.
This means that the UTC [ultimate trip current] is 4 amps. If the
continuous draw amps exceeds 4 amps the URO81 will trip in about 15
seconds at a 70 degrees.
The LRA [locked rotor amps] protection is 12 amps, this will trip in
about 2 seconds. The URO81 is a PTC device and runs hot to the touch as
all PTC relays do.
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