ATS Control Card with PIC16F88 (Prototype 3)

Terminal blocks: as you can seen in the pictures, i would like to start from terminal blocks as the right most terminal block with three screws on it, is being used for sensing the presence of 220V supplies from the mains and the GENSET. The middle screw is for neutral wires which are jumped together from both power sources. Whereas the side screws are for phase wires from both power sources. It is labelled on the board which screw is for mains and which one is for GENSET. Second terminal block from the right is for providing any 5V logic input to the controller from any outside device which may be required for any other function. The third terminal from right is being used to provide power to the circuit board it is usually 12VDC and comes from the battery of GENSET. Next terminals consisting of two screws are respectively for switch RELAY, crank RELAY and changeover RELAY driven by microcontroller's selected GPIOs.

Transformers: In this prototype we used 220V to 12V step down transformers for shifting down the level of input signal, suitable for PIC16F88 microcontroller sensing.

Rectifiers: we used two rectifiers of 1Amp to convert the signal from 12VAC to 12VDC for further conditioning, each line has a separate rectifier on it after transformer.

Regulators: after rectifiers input signal is further passed through 7805 voltage regulators and 5V signal is then applied to the selected GPIOs of PIC16F88 supported with 10K pull-down resistors. These input power sensing lines also have 470uf capacitor on each line for signal stability.

Microcontroller: in this prototype we used PIC16F88 microcontroller which senses the presence of mains or GENSET power signal on its selected input GPIOs and performs the following functions.

--> If mains is present and GENSET is not present just make sure to keep all output RELAYS in off position.

--> If mains is off and GENSET is also off, controller waits for 30 seconds and then energizes the switch RELAY, waits for another 2 seconds and then energizes the crank RELAY for 4 seconds, looks for input power signal from GENSET if it is not present for 10 consecutive seconds, controller again energizes the crank RELAY for 4 seconds and repeats the same check and do process for 6 times if it senses the power signal input from GENSET is present then keeps the switch RELAY on, keeps the crank RELAY off and energizes the changeover RELAY for shifting the utility load to the GENSET.

--> in third case when mains supply is restored, the controller senses its presence via one of its selected input GPIO and waits for 10 seconds then turns off the changeover RELAY then waits for 3 seconds and then turns off the switch RELAY which causes the GENSET to turn off.

--> if both supplies are off the controller tries to start the GENSET via same process described above in case two.

🔶 Relay 1 (Switch Relay) 🔶 Relay 2 (Cranking Relay) 🔶 Relay 3 (Transfer Relay) :

in this prototype, big RELAYS were used for a specific purpose, we came across the RELAY switching and power handling issues in 1st and 2nd prototype therefore we decided to improve the design by adding big L-Type RELAYS.

LED indicators: in this prototype, we also added the LEDs for separate functions, Red LED indicates the mains power and one of the Green is for GENSET power. While the other Green LED is for switch RELAY. Orange LED indicates for the crank RELAY and the white LED is for changeover RELAY.

IC sockets: a UlN2003 i.c is also present between the outputs of PIC16F88 and output RELAYS, which helps driving the 12VDC relays with the 5V logic signal from the microcontroller's output pins.

Note: Specifically in this prototype more effort were put in improving the PCB design of the circuit