Running Home Refrigerator on Inverter Supply

[george_leon]

Normally our Home Refrigerator Motors are Resistive start and induction run type which draws heavy current during starting cause to trip inverter. So by converting that motor to Capacitive start induction run motor the starting current can be reduced and it will run on home inverter. For that we need to connect 10 MFD/400V capacitor in between PTC and starting winding for typical 70W refrigerator motor. Running winding circuit need not be disturbed. I have tested and working fine.

 

[srizbf]

a resistive start type ? or resistor to control starting current?

can u post an image of your work?

 

[c_mitra]

Most of the refrigerators I have seen so far have an integrated motor - compressor. Yes, they are capacitive start but the motor is basically a vibrator and it works like a fish tank air bubbler (diaphram valve type). The compressor (about 100W or often less) draws high current because the capacitors need to be charged up and that takes only a few milliseconds. Adding a series inductor can help the inverter not to trip.

 

[tsan500]

Perhaps resistive start motor means a split phase induction motor where auxiliary/starting winding is made to have a high resistance and rather low inductance when compared to main winding. This creates required phase shift for start. More information

https://www.studyelectrical.com/2014/07/split-phase-induction-motor-working-characteristics.html

I guess my refrigerator may have a split phase motor as starting current is really high. Anyway, here are images made from data collected during start of normal (lower part is a freezer) household refrigerator. Power rating of the refrigerator is 130 W and nominal supply voltage is 230 VAC. Images are from the same start and it is from normal start initiated by the fridge itself. I have not turned power off-on myself.

 

[FvM]

According to a Danfoss compressor data sheet, there are two start circuits in use, a contactor controlled capacitor start circuit and a "resistive" PTC circuit. The OP apparently supplemented a start capacitor to the PTC starter circuit and achieved lower inrush current.

Industry standard compressors have rotating induction motors, not oscillating armature drive. Otherwise they won't need a starter circuit.

 

[Warpspeed]

A bit of caution may be required here.

Normally with the motor stopped for a reasonable period, the refrigerant pressure equalizes across the compressor. When the motor starts up, initially it sees zero back pressure.

As the motor quickly accelerates up to full running speed, the back pressure rises very steeply within a couple of seconds up to full working differential pressure.
Induction motors generally produce very low starting torque without a heavy start winding.

The problem is, that you cannot soft start a piston refrigeration compressor with an induction motor. It will simply stall against the steeply rising pressure at start up, then burn out with a locked rotor. It needs fast violent acceleration up to near synchronous speed before the back pressure can rise sufficiently to be a problem.

You can certainly try to reduce the inrush, and it may just work. But one day it may fail to start, and then the motor may be in trouble.

The expensive oscillating piston compressors now recommended for off grid use do not have this problem, because the amplitude of oscillation reduces under high back pressure but it can never completely stall into fully locked rotor the way an induction motor driven compressor can stall.

I know my own 120 watt capacitor start induction motor compressor has an inrush of 10.6 amps rms (2.5kW) and it takes fully two seconds to creep back down to 120 watts.

My home brew 1.8 kW sine wave inverter handles that inrush easily even with other loads.

 

[george_leon]

with capacitor in starting winding the phase angle between running and starting winding improves which compensates reduced staring winding current. so net result no reduction in starting torque.

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