How to Generate a Safe 220V AC Supply

If you are working on electronics projects that need regular house voltage 220V AC.

This voltage can be dangerous.

To make it safe to use, you can connect a special device called a step down transformer.

This transformer lowers the voltage to a safer level for your project and also includes safety features to protect you from shocks.

Circuit Working:

Parts List:

When working on any project involving a connection to the mains it is crucial to observe all safety precautions to prevent electric shock.

This project operates at 220V AC with current limited to 60mA when using a 15 watt transformer.

While the output can deliver a dangerous shock and the voltage is potentially lethal the circuit offers isolation from the mains.

In the event of a short circuit the circuit will not blow a fuse, however, the transformers will become very hot and start to buzz.

You can use any two identical transformers with the wattage of either transformer determining the maximum output wattage.

If non identical transformers are used the output voltage will differ from the mains voltage and the wattage will be limited by the smaller transformer.

Although this setup is not entirely safe, it is the best option for projects like switch mode power supplies and capacitor fed downlights.

Formulas:

From the above circuit diagram the turns ratio is a crucial factor in determining the connection between a transformers input and output voltage formula:

V_s = V_p * (N_s / N_p)

where,

• Vs is the secondary voltage, or output voltage.
• Vp is the principal voltage, or input voltage.
• Ns is number of secondary coil twists
• Np is primary coils number of twists

This formula basically says that the number of turns in the secondary coil (Ns) divided by the number of turns in the main coil (Np) is equal to the ratio of the secondary voltage (Vs) to the primary voltage (Vp).

Knowing the Formula:

Vs will exceed Vp (step-up transformer) if Ns > Np (more spins in the secondary coil).

Vs will be smaller than Vp (step-down transformer) if Ns < Np (fewer spins in the secondary coil).

Vs will equal Vp (the isolation transformer, which maintains voltage but separates circuits) if Ns = Np (the equal number of turns).

Important Information:

This formula makes the assumption that the transformer is perfect, ignoring practical considerations like copper and core losses.

Because of these losses, the output voltage in actual transformers will be marginally lower than the computed value.

How to Build:

To build a simple how to Generate a Safe 220V AC Supply you need to follow the below mentioned steps:

Safety First:

• Before starting ensure you are familiar with working with mains electricity and take all necessary safety precautions such as wearing insulated gloves and using a circuit breaker.

Transformer Connection:

• Connect the primary coils of both transformers in parallel to the mains supply 220V AC.
• This will ensure that the transformers receive the same input voltage.

Output Connection:

• Connect the secondary coils of both transformers in series.
• This will effectively double the output voltage while maintaining the same current rating.

Load Connection:

• Connect your load such as a switch mode power supply or downlights to the output of the transformers.
• Ensure the load does not exceed the maximum power rating of the transformers.

Testing:

• Before connecting your project to the mains double check all connections.
• Once you are confident everything is correctly wired you can power up the circuit and test its functionality.

Monitoring:

• During operation, monitor the temperature of the transformers.
• If they become too hot it may indicate a problem with the circuit or that the transformers are overloaded.
• If this occurs disconnect the power immediately and troubleshoot the issue.

Note:

• Even though the setup is safer compared to AC mains from AC outlets please note that working with mains electricity can be dangerous and should only be attempted by individuals with the necessary knowledge and experience.
• If you are unsure seek the help of a qualified electrician.

Conclusion:

To generate a safe 220V AC supply use a step down transformer with proper isolation, current limiting, grounding and enclosure.

Regular maintenance and compliance with safety standards are essential for safe operation.

If unsure, consult a professional electrician.

References:

Detecting 240vAC – best way?

Mains electricity