Why does a Refrigerator need a stabilizer? Is it that Sensitive. . . than a Computer?

Many of us think that the only duty of a stabilizer is to keep the parent equipment safe from voltage surges and drops. . . But actually that’s not it is all about.

The Compressor of the refrigerator is nothing but an Induction motor and it can much easily tolerate voltage surges as good as a fan or washer. But still we are compelled to get a stabilizer along with our new refrigerator ? Why is it so …? Lets get it clear now!

Electrical Circuit of a Refrigerator
  • 1- Mains
  • 2- Door Switch (Push to Break)
  • 3- Lamp Inside
  • 4- Thermostat with adjustable knob(Opens the circuit, once required cooling level attained)
  • 5- Thermal relay.
  • C1- Starting Coil of Compressor
  • C2- Running Coil of Compressor

So what is that Thermal relay?

We must have studied that Single phase induction motors are not self starting and we must provide a means to start it? Appliances like Fans have a capacitor to shift phase and start the motor but a Capacitor of that size installed in fans is not powerful enough for a 250 W machine like Refrigerator Compressor and also the lifetime of such capacitors are not more than few years or months and definitely you won’t be willing to buy a refrigerator that breaks down once a year because of “Capacitor” problem.

So what are the other solutions to start an induction motor ?(note: without using a capacitor)

What about Resistance start motor? Oops but Resistance consumes power unlike a capacitor?

So, there is a requirement that the resistance must be removed after the motor is started? But who will remove it?

Now comes the thermal relay into action saying, “Let me take care of it. I will heat up myself and open the circuit of starting coil few seconds after current flows through me ! Is it fine…”

Thermal relay
Thermal relay. The disc in the middle conducts current from left to right, but while doing so gets self heated along with heating the metallic fins touching it, making them bend and thus opens the circuit.

So the entire working is as follows…

When you turn on the Refrigerator, current starts flowing through the thermostat (assume the required cooling level is not attained) and then through running coil and starting coil, thus turning the compressor. But within few seconds, the thermal relay gets heated and disconnects the starting coil, with running coil still running and powering the compressor.

But a trouble in this too… Assume a case where the power supply is cut off just after the compressor gets started and re-established immediately. Since the compressor has just started, the thermal relay must be in the “hot — open” condition and hence it cannot allow current through the starting coil and hence the compressor won’t be started. But the running coil has no such bar and hence current passes through it but remember the compressor is not running and this is nothing different than a stalled induction motor. So in this condition the running coil gets extremely heated up and the motherboard of your refrigerator, i.e compressor will be reaching its end of life.

Here comes the need of stabilizer…

It is a notorious device that won’t provide output soon after the input is given, right. So it protects the Compressor from such a condition of “Power supply cut- off and immediately restored” and thereby make you not blame the Electricity board for spoiling your refrigerator.

Sorry, if you had lived your whole life so far believing “the stabilizer delay” is a drawback about it… and just got to know that it is the prime purpose of the whole stabilizer itself. LOL!

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Engineering student