Hello,
I was recently asked about how to connect a relay to a DIY project. The relay can be found here , or with it's over load protection (full video spin of the device) here . I was ultimately not able to answer the question and I suggested another relay module for the project, but I'm both curious and puzzled regarding this relay.

I've attached some pictures of it and, as you can see, it has only one pin. Now a relay needs four pins, three if you're using the same power source for input to both the relay, and the load being driven by it. But only one pin?!

How does this weird relay work?

Thanks!

PS: The title of the listing is, "New QP2-4.7 Start Relay Refrigerator PTC Ohm 1 Pin for Vissani Danby Compressor."

 

The compressor motor has two windings that runs the start winding it heats up then laches the run winding it totally useless for anything else

 

Relay turns on initially while PTC is cold. then PTC heats up and its resistance increases so current drops. So relay is only on for short time on power up. it is sort of a crude timer that helps start compressor.

 

Hello,
I was recently asked about how to connect a relay to a DIY project. The relay can be found here , or with it's over load protection (full video spin of the device) here . I was ultimately not able to answer the question and I suggested another relay module for the project, but I'm both curious and puzzled regarding this relay.

I've attached some pictures of it and, as you can see, it has only one pin. Now a relay needs four pins, three if you're using the same power source for input to both the relay, and the load being driven by it. But only one pin?!

How does this weird relay work?

Thanks!

PS: The title of the listing is, "New QP2-4.7 Start Relay Refrigerator PTC Ohm 1 Pin for Vissani Danby Compressor."

It has three pins. The one obvious one, and then the two recessed ones on the bottom (look at your third picture) which connect to pins sticking up out of the motor where the relay mounts to it.

 

Confusion is because it is a more of a thermal resistor named PTC 'positive temperature coheficient' , not a relay. It conducts with its low resistance when cold and presents a high resistance when heated by a load in series to it.
Connected in series to a start motor winding, conducts when cold : energizes that start winding only for a short time (usually 5-10 seconds) until it gets to temperature and then has poor conductivity barely passing current but the motor is already running and then not needed to keep energizing that winding. PTC = more temperature = more resistance.
The reason a vast majority of equipment gets discarded instead of just replacing the part that can restore functionality for little cost.
Simplified wiring : It is always powered but its resistance changes from few ohms to many.

 

They have called them relays for more then 50 years I remember playing with one then i was boy the run heated a switch that latched when switched to run. So it's a heat relays lol power off it switched back to run. I fixed a lot of old R12 refrigerators those things would never die but that little black box would go bad and they throw them out to the street replace the PTC and it run 50 years