What is this thing; Single-phase motor starter?

[5ubtle]

What is this thing called? I'm fairly certain that it selectively sends power to the "starting winding" on my fractional HP single-phase motor (on a HF benchtop belt sander). The current for the motor "run winding" runs through the external coil of wire in the device. I haven't made any measurements yet on the energized circuit, so I can only assume what this device is doing. At startup (maybe?) this device sends power to the motor "start winding"? The device has "up" and an arrow molded in, so it is mounted properly. There seems to be a "core" which can slide up and down inside the device. When "rightside up" the "S terminal" is disconnected. When "upside down" the "S terminal" is connected. This suggests to me that the device switches on the "start winding" when current flows though it's coil.

 

[john.k]

Youd assume the rising back EMF allows the core to drop ..........a cheaper alternative to a centrifugal switch in the motor.

 

[bonneyman]

Looks like an induction starter for a small compressor like one would find in a refrigerator.

 

[micromind]

It's called a 'potential relay' and yes, it does indeed control the start winding of a single phase motor.

Most single phase submersible well pump motors have one of these in the control box, that way there's no centrifugal switch to fail when the motor is inaccessible.

A lot of single phase refrigeration compressor motors have them too.

 

[5ubtle]

Youd assume the rising back EMF allows the core to drop ...

I think that is it. I couldn't figure out how the 'start winding' gets dropped out.

It's called a 'potential relay' and yes, it does indeed control the start winding of a single phase motor ...

The 'potential relays' that I am familiar with have their 'coil contacts' across the motor 'start winding'. They 'sense' the potential across the 'start winding', so the term 'potential relay' makes sense there.



If John.K is correct, this device would perform the role of 'potential relay', but it seems to be 'sensing' the motor 'run winding' current. In this situation, the term 'potential relay', doesn't make sense.

After further investigation, I think that the term would be 'current starting relay'. As bonneyman and micromind pointed out, they are used in refrigerator compressors.

Thank you for your help, gentlemen.

 

[Dagny]

Nope it's called a current relay normally open contacts close due to large amount of current that the run winding draws when the start winding is not hooked up this current closes the contacts which hooks up the start winding causing motor to start which lowers current then start winding unhooks