Reduce Refrigerator bills with this Simple circuit

Refrigerator is a common household electrical appliance. When we buy refrigerator we try to minimize the electrical power consumption by looking for BEE 4 or 5 star rated ones which also tells us estimated total units consumption for a year.

But the bitter truth about that fact is that they mention performance under test conditions and the power consumption varies due to usage. Often we end up consuming much more electricity.

The refrigerator I have in my home has BEE 4 star label and that mentions 151 units per year.

So, it's 151/365 = ~ 0.42 units per day right? But I've installed a kwh submeter in my refrigerator's power supply outlet for 15 days straight and found that it was consuming nearly 0.90 units per day on average.

That's a huge 114% over the advertised figure. My refrigerator was put in cooling capacity minimum (0 at the dial) and there was on average 2/3 water bottles, vegetables on the bottom and occasionally some cooked stuff put overnight.

Then I called the customer service for a visit and the technician checked all parts and told me the refrigerator has no problem, and he couldn't explain the electricity consumption, so he made guesses like voltage problem, meter problem, or I open fridge too often and other excuses.

The next day I monitored the compressor cycles and noticed that compressor turns on and off at regular intervals irrespective of the stuff inside. It runs around 50% of the time even with the lowest settings that's 0 on the dial. I somehow need to reduce the ratio even lower.

The above circuit does that. It's a simple astable multi-vibrator controller but at much lower frequency than usual. We need long duration because hitting on and off the compressor frequently may damage it. The on and off time and it's ratio is determined by the resistance values and the capacitor value which we can adjust manually according to our need. It's a simple 555 timer based astable multivibrator circuit with 75% duty cycle and ON time approximately 707 seconds and OFF time 236seconds. The value for C is 1000µF and R1 is two 680kΩ and R2 is 340kΩ(two 680kΩ in parallel). Since I need 25% duty cycle I'll have to invert the signal. But I want the circuit to be as simple as possible so I am running a 12V 7Amp PCB relay through this by a transistor BC548 as driver. I'll be using the N/C contact of the relay to get 25% cycle for the refrigerator. For 12v supply for the circuit I've used a 12V 300mA transformer I had lying around. You may use a 12V adapter too.

First we need to bypass the integrated thermostat and duty cycle controller.

Look at the back of the fridge for a two wires that go inside like and act as a switch between mains and compressor.

Just short those two wires. This way the compressor will be on 100% of the time AC is supplied through our circuit.

Now we install the above circuit in series with the power supply going to the refrigerator. And we're done.

I've adjusted the compressor cycle to around 25% by adjusting the values of R1, R2 & C and I've run that for another 10 days straight and the average electric power consumption was just 0.49 units per day. That even includes the power consumption of this circuit board.

It's almost half of the previous power consumption. I've noticed no performance problems in the refrigerator itself just except that the water bottles take more time to cool.

But that's ok considering almost 45% energy savings in my case which translates to 150 units saving per year or Rs. 900 per year considering Rs 6/unit. Overall this circuit costs approx Rs. 200 only.

If you build this, let me know in the comments how much you saved on electric bills.