What would be the easiest way to use an Arduino to control a 24AC solenoid, when I only have access to 220VAC mains?

Question

I do also have the Arduino power supply and output pins at 5 or 3 volts to control, for example, a mosfet gate voltage.

Sorry if this is a nooby question - I am an electronics noob

Answer 1

You have (at least) two problems to solve.

1. You need 24VAC (or thereabouts) to power the solenoid. That problem is solved by a 220:24 VAC transformer rated for the solenoid VA (or more).

2. You need to switch either the 24VAC or the 220VAC. That can be accomplished with a relay or an SSR that is suited for inductive loads. Or you could make your own SSR with an alternistor and perhaps an optocoupler.

3. If you use a relay you need to power and switch the relay.

4. If you use a relay or most SSRs you should add some suppression across the load to reduce arcing. An RC snubber, for example.

A suitably AC-output SSR with isolation and rated for inductive loads is probably the easiest and safest option. Most can be driven directly from the MCU.

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An alternative option if you have only a single solenoid to power and are willing to devote the transformer to it is to use a bridge rectifier and a MOSFET.

^{simulate this circuit – Schematic created using CircuitLab}

R2/R3 are optional but somewhat reduce the likelihood you'll have certain problems. M1 should be a logic level MOSFET.

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In some cases you can run an AC solenoid from a much lower DC voltage and it will work well enough. If you apply 24VDC to a 24VAC solenoid usually it will overheat and burn out.