Power a 12-volt relay directly from 230VAC mains voltage

Summary

In this video, the creator demonstrates how to operate a 12V relay directly from 230V AC mains voltage without the need for an external 12V power supply. The simple circuit uses a capacitor to drop the voltage and a bridge rectifier to convert AC to DC, allowing the low-voltage relay to function. The process is explained with tips on fine-tuning voltage using a resistor or capacitor adjustments. This setup is useful for safely switching or detecting mains voltage using low-voltage components, providing a cost-effective and practical solution for electronics enthusiasts and DIYers.

Takeaways

• 😀 You can operate a 12V relay directly from 230V AC mains voltage using a simple circuit without a 12V power supply.
• 😀 The circuit uses only a couple of diodes, a capacitor, and a relay to step down and rectify the voltage.
• 😀 A capacitor dropper circuit is used to reduce the 230V AC mains voltage to around 12V DC for the relay coil.
• 😀 12V relays are inexpensive and easily salvaged from other electronics, making this circuit cost-effective.
• 😀 This method is useful when you need a relay for switching low voltage circuits but don’t have a high voltage relay.
• 😀 The circuit includes a bridge rectifier made of four diodes to convert AC to DC, followed by a capacitor to drop the voltage.
• 😀 The voltage can be adjusted by experimenting with the capacitor value or using a resistor across the relay coil to fine-tune the voltage.
• 😀 The setup offers electrical isolation between the mains voltage and the low-voltage circuit, making it safer to use in certain applications.
• 😀 A resistor can be added to dissipate the charge stored in the capacitor after the power is removed, preventing any shocks.
• 😀 The circuit can be made more compact by using a ready-made bridge rectifier and adjusting components to fit specific needs.
• 😀 This circuit can be applied in scenarios like mains voltage detection or when switching larger loads with a low-voltage relay.

Q & A

What is the purpose of using a capacitor in the circuit?

The capacitor acts as a voltage dropper, reducing the 230V AC mains voltage to approximately 12V DC, which is required to power the 12V relay coil.

Why is a bridge rectifier used in this circuit?

The bridge rectifier is used to convert the AC voltage into DC voltage, which is necessary to power the 12V relay coil.

Can I use any 12V relay for this circuit?

Yes, most 12V relays can work within a voltage range of 9V to 15V, but you must ensure that the voltage drop across the relay coil is within this range for proper operation.

What is the role of the resistor in the circuit?

The resistor is used to load the relay coil slightly, helping to fine-tune the voltage applied to the relay. It helps adjust the voltage drop across the relay to get it closer to the desired 12V.

How does the capacitor affect the voltage in the circuit?

The capacitor limits the current flowing into the relay coil by dropping the voltage. This is what makes it possible to operate a low-voltage relay on high-voltage mains power.

Why not just use a 230V relay instead of this circuit?

230V relays tend to be more expensive, and they may not always be readily available. This circuit allows you to use an inexpensive 12V relay, which can be easily salvaged from other devices.

What happens if the voltage across the relay coil is too high?

If the voltage is too high, the relay coil may overheat and be damaged. To prevent this, you can adjust the capacitor or add a resistor to drop the voltage to the proper level.

What should I do if the capacitor holds a charge after power is removed?

To safely discharge the capacitor, you can place a 1MΩ resistor across the capacitor terminals, which will dissipate any remaining charge and prevent a shock when handling the circuit.

How can I fine-tune the voltage applied to the relay coil?

You can adjust the capacitor’s value or add resistors across the coil to fine-tune the voltage. Experimentation with different capacitor values or resistor combinations will help you reach the desired voltage.

Is this method of powering a 12V relay from mains voltage efficient?

Yes, the capacitive dropper circuit is quite efficient, as it doesn’t generate significant heat like resistive circuits. The voltage drop is capacitive, which minimizes energy loss.