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Can you connect an AC load to a 5V DC relay?

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dav456

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I have made a 8051 circuit which will turn on/off a 5v dc relay according to to sensed temperature.

currently the relay has a 12v input and drives a 12v lamp.

can I connect it to 220v ac and drive something bigger?
 

You'll review the relay datasheet. It's not a matter of relay coil voltage, more contact size.

There are 5V driven relays switching e.g. 230 VAC and e.g. 1 or 2 kW. You should however be aware of contact arcing, particularly with inductive loads. It can easily upset a microcontroller circuit with insufficient noise hardiness.
 

The relay will be driven with specified voltage of 12 volts or 5 volts for its energizing coil. The contact are naturally isolated from the later and thus you can even use it to switch an AC load. But make sure the current capacity of the contacts are not over driven by the given load.
 

Normally relay contacts can handle AC better than DC. So the relay can drive 220V and perhaps 100-200mA (please check the details).

On the other hand, relays can be driven by AC or DC and that cannot be exchanged or interchanged. If the relay coils can support 5V DC, you cannot change it to 12V AC or even 5V AC.

Good relay contacts are made of gold, sliver, platinum or tungsten, depending on the current and voltage. Take a good look at the contacts and you will most likely be able to decide yourself whether the contacts can support high voltages / high currents.
 

If you're driving a motor (as FvM said, an inductive load) the relay will be severely de-rated from the maximum resistive load that's usually printed on the relay. Make sure you look up the maximum motor size you can switch.
 

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