Recently I received this photocell switch that was not working. I opened the machine and start to study to see why is not working. And the result is this article:

Automatic photo cell jobs

-Automatically on/ off the lights in the entrance of buildings / parking /gardens / yards and or billboards…..

-Automatically on / off the lights inside the stores and shopping stores.

-To save money in consumption of electricity and keeping life span of lights.

– Automatically switch the light of streets and .public passages.. so and so.. the power supply of this machine:

Is a very good example of transformer and mosfet less power supply. is very cheap and light weight  the architecture is based on just using the resistors diodes and caps  with very precise calculation of values of components

LDR: Light dependent resistor:

The principal of photocells are based on a chemical compound (selenium sulfide:  SeS2 ) that shows different resistance value  in front of flow  of photons .in another word in day time and enough light this compound shows resistance and cut  the circuit and in night time during the darkness  lets the electron flow in the circuit and act as a switch and trigger the relay and relay make contact inside and let the live line of electricity reach to the lamps. In the circuit two C945 series NPN transistors are installed and their emitters joined together to amplify the difference s of voltages of photo cell and deliver and translate these for relay to let the lights on or off

Diagram of circuit of photocell switch

The relay of machine is: JQC3FF this is a subminiature power relays single – pole 10 Amp 24 Volts that I found it defected

Four diodes 1N4007 acts as part of DC power supply and rectify the AC entrance voltages .one pot.56k is present in this machine by changing the value of the resistance of pot the sensitivity of photocell against light can be change and desire on/off mod of lights can be achieved.

R9 biggest resistor 1 watt in the circuit act as decreasing entrance AC voltages since this resistor has a full tension job seems get very hot and PCB color around the resistor  was turned to dark brown and even black color but the value of resistor was good.

The machine has two incoming wire and one out going:

Incoming wires:

One is white color wire that is neutral line of electricity

That goes directly to polyester cap 684/600 volt

That cap is installed parallel with R1 resistor 560 ohm ¼ watt that act as a filter for entrance AC and act to prevent unwanted harmonies of AC

I have to mention: that this white wire is a sub extension of neutral wire that goes directly to the lamps. Another entering wire to machine is black wire.

Black wire: that is live line and directly goes to one pole of relay here also 10 AMP fuse is present to protect the machine against unwanted spikes.

Outgoing wire is red:

Red wire is live line that is coming out of the machine and directly coming from another pole of the relay and by commend of relay this wire will contact with black wire and will light up the lights. Zener diode 11 volt also act as a voltage regulator and supplying voltages for photocell. On the PCB there are 3 electrolytes caps that their job is purifying the DC voltages.

By replacing the relay the machine returned to life all other component were good to know how to test the relay I refer you to page 163 of Jestine Yong’s Ebook here.

Note:  I repaired this machine with ohm check method only and with no power on it.

This article was prepared for you by Mr Beh from Iran

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Note: You may check out his previous repair articles in the below link:

http://jestineyong.com/led-lamp-repaired/