Simple Refrigerator Protector - Making and Installation Guide

This simple refrigerator protector circuit is actually a delay ON timer circuit which makes sure that whenever a power failure occurs or in case abrupt power fluctuations take place, the refrigerator is never allowed to switch ON instantly, rather after a delay of a few moments.

Conventional Protection Features


Today most modern refrigerators are equipped with a protection feature which prevents the fridge from suddenly switching ON or OFF due to sudden power fluctuations or a sudden power restoration.

However, for those fridges which are not equipped with this feature, the following simple delay ON timer circuit can be applied to enable the refrigerator to switch ON after a certain delay, and only when the mains power has become stable.

Until this happens the circuit keeps the fridge switched OFF and monitors until the power has returned to a perfectly normal status.





WARNING: CIRCUIT IS NOT ISOLATED FROM MAINS... STRICT PRECAUTIONS MUST BE OBSERVED WHILE HANDLING THE DEVICE, WHILE IT'S IN AN UNENCLOSED CONDITION.

Simulation and Working


Referring to the above shown refrigerator protection circuit, we are able to witness a two transistor circuit which forms a very basic yet effective delay ON timer circuit, meaning this circuit switches ON its output after some delay, after power is applied to it.

The power supply to the circuit is derived from the mains via a transformerless power supply circuit
which is appropriately stabilized at 12V and fed to the delay circuit.

Whenever power is switched ON, may it be during the first initialization, or during a power failure situation, the associated 1000uF capacitor prevents the BC547 from switching ON at the onset, which in turn keeps the BC557 and the triac switched OFF. The load is therefore unable to receive power and stays switched OFF too.

However, the 1000uF now gradually begins charging via the 330K resistor and when the potential difference across it reaches the approximate total of transistor's biasing limit plus the emitter zener value (0.6 + 3 = 3.6V), the transistor begins switching ON which prompts the BC557 also to switch ON.

The triac now begins acquiring the required gate voltage and within moments switches ON the fridge.

The 1000uF capacitor stays charged as long as power is available to the circuit, and during power failures the capacitor discharges through the parallel 100k resistor so that it can get into the standby mode for the next delay ON cycle operation.

The time delay period can be accomplished by appropriately selecting the values of the 330K resistor, the 1000uF capacitor and the 3V zener diode, as per the user's preference.

This concludes the explanation for the proposed simple refrigerator protection circuit, for any related query please feel free to use the comment box.

PCB Design


refrigerator protector PCB design

Need Help? Please send your queries through Comments for quick replies!




Comments

NvD said…
sir pls help
In your pir (https://homemade-circuits.com/2014/09/automatic-pir-controlled-fan-circuit.html) you mention that there is a delay in switching of fan..i dont want that delay..i need to switch off instantly..pls give me changes in circuit..so that i can use it for automatic faucet to prevent wastage of water
Swagatam said…
NVD, you can remove the 470uF capacitor for eliminating the delay effect
Sir mera laptop charge nahi ho raha hay mene dosra adptor lagaya tu thori dair charge howa phir nahi ho raha hay agar ap ko is k baray me maloom hay tu please help kar dain thank u.
Swagatam said…
Syed, the problem could be with the battery or the internal laptop circuit...can't say precisely without checking.
NvD said…
last question sir..i think i m not disturbing you..in below circuit

https://homemade-circuits.com/2016/07/touch-free-faucet-circuit.html

sirwhat is the value of resister R8 and R9 (not shown in fig)..sir is thereany substitute for 1uF 16v (cant find in store)..p1 and p2 are variable resistance is it right..is all resisters 1/4watt...i am going to make this circuit..hope itworks
Swagatam said…
you can use 10K for both the resistors
the 1uF is a filter capacitor so it's not critical, you can use any other higher value...
p1/p2 are presets, or trimpots
all resistors are 1/4 watt
NvD said…
thank you very much sir
Sherwin Baculi said…
Sir. The triac needs a heatsink?
Swagatam said…
Yes it will need a heatsink
Anirudh Kundu said…
Sir i made a refrigerator delay on circuit using a 555 ic. I'm using a transformer based power supply and regulating it via 7812.

The problem am facing is i'm using a 25volts 1000mf cap with the transformer and the bridge rectifier.

When there is a change of power from genset to mains power, the circuit doesn't shut off as the change takes place in a second and the capacitor compensates this no power state and doesn't shut the circuit off.
I just wanted to know what rating of bleed resistor should i use. And should i use it before the ic 7812 or after the ic 7812.

Thanks.
hello swagatam,

the 3v, 1watt zener is not available here in my place. can i parallel 2x3V,1/2W zener instead?
Swagatam said…
Anirudh, you can try with a 1K 1/4 watt directly in parallel with the 1000uF capacitor and see the response
Swagatam said…
hello jade,

1 watt is not required....1/2watt will be fine without issues.
Thank you so much sir
hello Swagatam,

Can I use 225 capacitor instead of 105?
Swagatam said…
hello jade, you can try it, if the triac fires correctly with it then it you can continue with it.....
KSR Discoveries said…
dear sir i want this circuit for giving input to 12 V relay
Swagatam said…
please modify the above design as per the following design

https://homemade-circuits.com/2013/02/make-this-simple-delay-on-circuit.html
Noel said…
Sir,
Regarding the fridge protection circuit what are the wattage of the resistors.
Thanks
Swag said…
Noel, all resistors are 1/4 watt rated
Noel said…
Hi
Can the fridge protection circuit also be use for other items like tvs, other electronic equipment.
Regards
Swag said…
yes it can be used for any desired appliance or gadget.
Noel said…
Hi,
Can you design a circuit that can be used in a db box so that if there is load shedding or some power surge the entire plug points go off until voltage is stabilized at 240v when power comes back on.
Regards
Swag said…
Hi, I think you could apply the concept discussed in the following article and see if it suits your requirement.

https://www.homemade-circuits.com/highly-accurate-mains-high-and-low/
Noel said…
Hi
Thanks for the invaluable info really appreciate it.
Regards
Swag said…
It's my pleasure!
Noel said…
Hi sir,
With regards to the high/low mains cut off circuit using two relays can the out put be connected direct to the db thereby protecting all appliances or must it be connected to each individual appliance.
Regards
Swag said…
Hi Noel, the 2 relay circuit is not required, you can use the single relay circuit and configure the relay contact in series with one of your DP lines and then you can apply it for safeguarding all the associated appliances.
Noel said…
Thank you much appreciated
Swag said…
You are welcome!
Noel said…
Hi sir,
Hope you are well.
Just want to know if you have a circuit to test eeproms.
Regards
Swag said…
Hi Noel, I have seen a few of them in some old magazines with me, if possible I'll publish them here, but I am not sure whether the designs are still relevant or not.
Noel said…
Thanks appreciate it
Noel said…
Hi
Do you have a circuit for a 100w bass guitar amp.
Regards
Swag said…
Hi, you can try the following concept

https://www.homemade-circuits.com/how-to-make-outstanding-home-theater/

you can replace the shown amplifier design with the following circuit
https://www.homemade-circuits.com/how-to-make-simplest-100-watt-mosfet/

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