Automatic Changeover Controller (ATS) Control Card with PIC16F88 (Version 1)

🔌 Automatic Changeover Controller (Prototype V1)

1. Terminal Blocks

• 12V DC Input Block (2 screws):
  
  
  Supplies regulated 12VDC to the circuit, typically from the GENSET battery, to power the controller.

• AC Sensing Block (3 screws):
  
  
  Used for sensing 220V AC signals from both mains and GENSET.
  • Middle screw → Neutral line (common for both supplies).
  • Side screws → Phase line of mains and phase line of GENSET.
  • Each screw is clearly labeled on the PCB.
• Relay Control Blocks (2 screws each):
  Connected to:

  1. Switch Relay

  2. Crank Relay

  3. Changeover Relay Driven by microcontroller GPIOs.

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2. Transformers

• Step-down Transformers (220V → 12V):
  
  
  Used to reduce mains and GENSET phase signals to a safe level for the microcontroller.

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3. Rectifiers

• Two rectifiers (1A rating):
  
  
  Each phase signal passes through a separate rectifier, converting 12VAC → 12VDC for conditioning.

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4. Voltage Regulators

• 7805 Regulators:
  Convert rectified 12VDC signals to 5VDC.

• Signal Conditioning:
  • Each sensing line includes a 10kΩ pull-down resistor (ensures clean logic levels).
  • 470µF capacitors are used on each line for stability and noise suppression.

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5. Microcontroller (PIC16F88)

The PIC16F88 monitors input signals and controls relays accordingly.

Controller Logic:

1. Case 1 – Mains Present, GENSET Off
   
   
   → Keep all relays OFF.

2. Case 2 – Mains Off, GENSET Off
   
   
   • Wait 30s, energize Switch Relay.
   • After 2s, energize Crank Relay for 4s.
   • Check GENSET signal for 10s.
     
     
     • If not detected, repeat crank cycle (up to 6 attempts).
   • Once GENSET detected →
     
     
     • Keep Switch Relay ON, Crank Relay OFF.
     • Energize Changeover Relay → Load shifts to GENSET.
3. Case 3 – Mains Restored
   
   
   • Detect mains presence.
   • Wait 10s, then turn OFF Changeover Relay (load back to mains).
   • After 3s, turn OFF Switch Relay → GENSET turns off.
4. Case 4 – Both Supplies Off
   
   
   • Retry GENSET startup process (same as Case 2).

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6. Relays

• Relay 1 – Switch Relay: Turns ON GENSET.
• Relay 2 – Cranking Relay: Engages GENSET starter motor.
• Relay 3 – Transfer (Changeover) Relay: Switches load between mains and GENSET.

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7. Relay Driver IC

• ULN2003:
  Acts as an interface between 5V microcontroller outputs and 12V relay coils.
  Provides current amplification and safe isolation.

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