Presume you have a solar panel that charges a battery, but you do not want to overstuff it!
An SCR Solar Charger Controller is like a smart switch.
It uses special components called SCRs to only allow the perfect amount of electricity from the solar panel to reach the battery keeping it healthy and charged without overflowing.
Circuit Working:
Parts List:
| Category | Item | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 1M, 3.3k, 18k, 62k | 1 each |
| 100k | 10 | |
| 47Ω | 2 | |
| 10k | 3 | |
| 1k | 2 | |
| Potentiometer 10k | 1 | |
| Capacitors | Electrolytic 10µF 25V | 1 |
| Ceramic 70µF | 1 | |
| Ceramic 0.1µF | 1 | |
| Ceramic 0.47µF | 1 | |
| Semiconductors | IC TL431 | 1 |
| Transistors 2N6027 | 2 | |
| Transistors 2N3904 | 3 | |
| Transistor 2N3906 | 1 | |
| SCRs S2800A | 2 | |
| Diode 1N4148 | 1 | |
| LEDs | LED green 5mm 20mA | 1 |
| LED red 5mm 20mA | 1 | |
| Power Components | Solar panel 7A (up to 100W) | 1 |
| Battery 12V | 1 |
This article describes a unique design for a solar charger controller circuit that uses a special type of switch called a force commutated SCR.
Traditionally, relay or transistor switches have been used for this purpose but this design offers some advantages.
Advantages of SCR based design:
- Robustness: SCRs are known for their durability.
- Simplicity: Only one SCR is needed to perform three functions: switching, latching and acting as a reverse polarity diode.
How it works:
Main SCR: This SCR controls the flow of charging current from the solar panel to the battery.
Commutation SCR: This second SCR turns off the main SCR at the end of its conduction period.
Control Circuit: This circuit, made of readily available components, uses programmable unijunction transistors PUTs to control both SCRs.
Important considerations:
- While innovative, this design is not the most efficient or cost effective solution for modern solar charge regulators.
- However, it is a great educational tool for understanding SCRs and their applications.
Electrical characteristic of SCR S2800A
| Characteristic | Symbol | Min | Typ | Max | Unit |
|---|---|---|---|---|---|
| Peak Forward or Reverse Blocking Current (VAK = Rated VDRM or VRRM, Gate Open) | IDRM, IRRM | – | – | 10 µA (TC = 25°C) <br> 2 mA (TC = 100°C) | µA |
| Instantaneous On-State Voltage (ITM = 30 A Peak, Pulse Width ≤ 1 ms, Duty Cycle ≤ 2%) | VT | – | 1.7 | 2 | Volts |
| Gate Trigger Current (Continuous dc) (VD = 12 Vdc, RL = 30 Ohms) | IGT | – | 8 | 15 | mA |
| Gate Trigger Voltage (Continuous dc) (VD = 12 Vdc, RL = 30 Ohms) | VGT | – | 0.9 | 1.5 | Volts |
| Holding Current (Gate Open, VD = 12 Vdc, IT = 150 mA) | IH | – | 10 | 20 | mA |
| Gate Controlled Turn-On Time (VD = Rated VDRM, ITM = 2 A, IGR = 80 mA) | tgt | – | 1.6 | – | µs |
| Circuit Commutated Turn-Off Time (VD = VDRM, ITM = 2 A, Pulse Width = 50 µs, dv/dt = 200 V/µs, di/dt = 10 A/µs, TC = 75°C) | tq | – | 25 | – | µs |
| Critical Rate-of-Rise of Off-State Voltage (VD = Rated VDRM, Exponential Rise, TC = 100°C) | dv/dt | – | 100 | – | V/µs |
Circuit Breakdown:
Voltage Reference:
- A TL431 chip is used to regulate voltage to a precise level.
- A transistor compares the battery voltage with the reference voltage to ensure proper charging.
Commutation Capacitor:
- This capacitor plays a crucial role in turning off the main SCR.
- Its size is important for proper operation.
SCR Turn off Time:
- The design considers the turn off time of the SCR to ensure proper commutation.
Minimum Conduction Period:
- The circuit design ensures there is enough time for the capacitor to charge and turn off the SCR effectively.
Holding Current:
- The design needs to consider the holding current of the commutation SCR to ensure it turns off properly.
LED Function:
- LEDs are used to indicate the status of the circuit.
Overall, this document provides a detailed explanation of a unique SCR based solar charge regulator control circuit highlighting its advantages and limitations for educational purposes.
How to Build:
To build a SCR Based Solar Charger Controller Circuit follow the below mentioned steps :
Components:
- Gather all the necessary components for the circuit, including SCRs, resistors, capacitors, transistors, TL431 and LEDs.
Circuit Design:
- Use the provided description to create a schematic diagram for the circuit.
- Place the components according to the circuit layout and ensure proper connections.
PCB Design:
- If you plan to create a printed circuit board PCB design the PCB layout based on the schematic diagram.
- This step requires knowledge of PCB design software.
Component Placement:
- Place the components on the PCB according to the layout design.
- Ensure that the components are oriented correctly and solder them in place.
Wiring:
- Use hookup wire to make the necessary connections between components on the PCB.
- Follow the schematic diagram carefully to avoid mistakes.
- Before applying power, double check all connections and components for errors.
- Use a multimeter to check for continuity and shorts.
- Apply power gradually and monitor the circuit for proper operation.
- If the circuit does not work as expected, use troubleshooting techniques to identify and fix any issues.
- This may involve checking components, connections and signal paths.
Final Testing:
- Once the circuit is working correctly perform final testing to ensure its reliability and functionality.
Note:
- Building this circuit requires advanced electronics skills and knowledge.
- If you are not familiar with electronics or PCB design consider seeking assistance from someone experienced in these areas.
Conclusion:
An SCR based solar charger controller circuit offers a robust and efficient solution for charging batteries from solar panels.
By using SCRs as switches and incorporating control circuitry this circuit can regulate the charging current based on the batteries voltage and other parameters.
While this technology may be considered old, it remains a viable option for those looking to create a reliable solar charging system.
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