In my last post, I talk about compressor overload, and in this post, you will learn about PTC Relay which we use mostly for every refrigerator compressor starting. PTC means a positive temperature coefficient thermistor however we can call starting relay or compressor starting relay in simple words.
How a Refrigerator PTC Relay Working and Function
In the refrigerator compressor, we use the split-phase single phase induction motor and this motor has two internal types of winding which we called running and starting winding or auxiliary winding. We know that a single phase motor did not start without a starting capacitor or a starting current.
In simple words, the refrigerator PTC relay gave a current to start winding and when the motor starts up the PTC compressor relay removes the start winding from the circuit.
So the above is a simple and short explanation of refrigerator relay and its working, So let’s know the working method of a PTC.
As I wrote above that PTC means a positive temperature coefficient thermistor which means that a relay with working relation with temperature. Basically, a PTC thermistor is a resistor whose resistance increase with the increase of temperature.
So let’s explain it step by step
We know that the compressor motor or fridge compressor has a split phase induction motor which has two types of winding, the main winding which we called RUN Winding, and the auxiliary winding which we called START Winding. A fridge compressor requires a starting current to start normally and for this, we connect the starting relay.
Compressor three terminals called START, RUN, and COMMON. Common means the point where the start and run are connected.
We connect the overload protector to the compressor common terminal and the PTC relay to the run and start terminal. In the PTC relay the supply goes direct to the run winding but between the supply and start winding a thermistor is connected in series and when we switch on the refrigerator the current start flowing through the thermistor to the auxiliary and compressor start-up, this current flows heat thermistor and due to temperature, the resistance of thermistor high and thermistor remove the start winding from the supply.
E.g Example: If you start your fridge and then you switch off and then start it, you will note that the compressor does not start again because of the heat thermistor or relay. And when you switch it off again and try after 5 to 10 minutes you will find the fridge compressor starts normally.
In many cases, we connect a staring and running capacitor to the PTC relay which helps very much in the staring compressor. With the starting capacitor, we connect the PTC relay thermistor in series which makes removes of start capacitor from the circuit. In many PTC compressor relays have a connection point for the run capacitor and we connect the run capacitor in parallel with a relay which helps in better starting and running the compressor.
I hope you learn something from this post about the PTC compressor starting relay and its working, however, I will guide you about all types of PTC relays and their wiring methods with complete diagrams.