Inrush current limiters for AC compressors

[sdowney717]

https://www.ametherm.com/blog/inrush-current/ac-motor-inrush/
Cut the starting amp load in half.

At $10, the part has potential use versus buying a $300 soft starter.
For a wet system on a boat, this part would go on the common line of the compressor versus the incoming power line for an RV system with no water pump.

I don't need this, my gen starts it fine. Some people may want to run their AC on marginal power, like a Honda 2000 gen or an inverter or they have crappy shore power.

 

[gsholz]

Looks like an interesting solution. It will drop voltage by about 1Volt at steady state amps. Should not be an issue. Will get surprisingly hot (~500 deg F) at steady state. One would have to make sure of adequate air flow to cool the thermistor.

 

[sdowney717]

Yes, gets hot. These are being used more and more. For awhile now in PSU for computers. Finding more applications elsewhere.
Soft starting your compressor will put less load on the motor, does not spin up as fast, far less current inrush = less component stresses. May help it last longer.

If I did this, would place it on the hi pressure cut out switch, like screw down one lug and solder other wire to other lug. Or I would make a small pcb board attach board in the electric box above the hi pressure switch.

Also was mentioned, you can make a circuit that bypasses the NCT resistor once motor spins up, then it is only used for starting the compressor.
https://www.instructables.com/id/Controlling-the-Inrush-Current-Required-by-Large-T/

Cooldown time is about 2 minutes. So if you shut it off, and immediately restart, then very little amp draw improvement over not having this.

 

[BIG CAT]

i wonder how they compare to a good start capacitor.

 

[sdowney717]

i wonder how they compare to a good start capacitor.

You wont notice the difference, but your compressor and power supply will. Instantaneous amp draw is half what it is without the resistor.
when you start the compressor, it is like a dead short to the electrical system.
Typically lasts about 1/10 second, but that instantaneous huge amp draw is enough to prevent starting on inverters or small generators.