What secondary circuit breaker should I use for my fridge compressor?

[stryped]

TL;DR Summary

I am replacing a broken inverter compressor with a regular compressor that has the standard electromechanical relay. I plan on controlling the compressor/electro relay with an ac to ac Ssr. The Ssr will be triggered by the condenser fan that is a 110v circuit.
The compressor looks like it runs on 2 amps, but has 15 locked rotor amps. I would like to install a self resetting circuit breaker between the compressor and Ssr. What amperage breaker would I need? 15 seems too high and 2 too low.

I am replacing a broken inverter compressor with a regular compressor that has the standard electromechanical relay. I plan on controlling the compressor/electro relay with an ac to ac Ssr. The Ssr will be triggered by the condenser fan that is a 110v circuit. The compressor looks like it runs on 2 amps, but has 15 locked rotor amps. I would like to install a self resetting circuit breaker between the compressor and Ssr. What amperage breaker would I need? 15 seems too high and 2 too low.

Reference: https://www.physicsforums.com/forums/electrical-engineering.102/post-thread

 

[Lnewqban]

Please, see picture of nameplate of an AC condenser unit, which fan's label shows MCA of 1.0 A
Note how much over the recommended maximum protection (30 A) is respect to the total MCA of the condenser (17.8 A).

I would see what breaker sizes are available to install between the solid state relay and the start circuit of the compressor (assuming the run circuit is left out of the additional protection).
Most compressors are damaged by overcurrent at the starting phase.

 

[stryped]

How do I determine the proper in line circuit breaker? This is a refrigerator compressor and it does not say much on it, other than it is 15 locked rotor ampsHere are some specs:
1/3- hp
Displacement 7.7cc
From 100W to 671W Cooling (341 to 2289BTUs) ASHRAE : 220w - 751btu
110-120VAC
50-60Hz
R134A
Low Back Pressure
PTC Starting Relay
Motor Type CSIR
Includes electricals, grommets and sleeves.

Cooling capacity ASHRAE
-35C (-31F) - 100w - 341btu
-30C(-22F) - 130w - 444btu
-25C(-13F) - 169w - 577btu
-23.3C(-10F) - 220w - 751btu - input power 165W - current 2.40 Amps - COP 1.35 - EER 4.55
-20C(-4F) - 275w - 938btu
-15C(5F) - 344w - 1174btu
-10C(10F) - 430w - 1467btu
-5C(23F) - 537w - 1832btu
0C(32F) - 671w - 2289btu
Certification : UL Underwriters Laboratories Recognized
Nationally Recognized Testing Laboratories (NRTL)
Reply

 

[Tom.G]

The 1/3 HP compressor will draw around 2 to 3A running.
With the locked rotor current of 17.8A (as @Lnewqban mentioned) I suggest a Thermal, Slow Trip (time delay), Auto Reset breaker rated around 8 to 12A. (I'm leaning towards the 12A range.)

That will yield a delay long enough for the compressor to reach operating speed but low enough to trip if the compressor gets fluid locked or the motor develops an internal short circuit.

Picking an exact breaker is not possible without details of the starting current and the delay curves of available breakers. The above values, however, should be well within the working range.

By the way, be aware that once the refigerant line is opened, the dessicator will need replacement, and the system evacuated with a vacuum pump before charging with refrigerant - otherwise the ambient moisture that enters the system will freeze in the evaporator (and also dilutes the oil in the compressor, sometimes causing it to foam).

Cheers,
Tom

p.s. Let us know what works -- or doesn't!

 

[stryped]

Would this work?

https://www.digikey.com/en/products/detail/e-t-a/1658-A00-00-P10-12A/3988695

 

[DaveE]

Would this work?

https://www.digikey.com/en/products/detail/e-t-a/1658-A00-00-P10-12A/3988695

Thermal CBs like this one don't always work well with normal outdoor temperatures. Look carefully at the trip characteristic curve at the temperatures shown.

For climate controlled spaces I think this one would be ok.

 

[Tom.G]

That looks like a decent option.

The actual current rating needed depends on the compressor starting (locked rotor) current. The breaker ratings so far are based on 18Amps peak load.

Let us know if your chosen compressor is significantly different.

After looking at the data sheet, I would suggest a 10Amp rating if it is used in a conditioned (living) area. If in an area that gets cold (close to freezing) then a 8Amp or maybe 6Amp is more appropriate.

As @DaveE noted, if it is in an un-heated or un-cooled garage or utility room, then the temperature extremes need to be accounted for because the time to trip depends on the ambient temperature.

Cheers,
Tom

 

[stryped]

One more question same project…..
If I wanted to use a varistor across the Ssr terminals to protect from voltage spikes, would this one be appropriate for this project?

https://www.digikey.com/en/products/detail/littelfuse-inc/TMOV20RP200E/1210654
Thanks for any help you can provide!

 

[Tom.G]

I just re-read this thread and realized your compressor is rated at 10A Locked Rotor. Based on this I change my Breaker suggestion to 5Amp.

Now to the MOV:
Sorry, neither DigiKey nor LittleFuse search pages will talk to my old browser.

However based on the information on the page you linked to, that MOV should be quite sufficient, Good Choice!

Cheers,
Tom