Where/how to build or buy a relay for 24v AC?

I need to drive a solenoid that requires 24v AC (sprinkler valve).

Can someone point me to a specific product that I can buy that will drive this, or specific instructions on how to build something like this?

Thanks in advance!!! :slight_smile:

Most normal relays can switch 24V AC.
What current needs to be switched ?

Most normal relays can switch 24V AC.
What current needs to be switched ?

Agreed. A 5V relay usually has contacts rated for 10A @ 120VAC, which should be plenty for a 24V solenoid.

There are many premade relay modules on the market. Those are the easiest to use, as they already have the switching transistor and flyback diode taken care of for you.

SPST relay like this would work: Mini Relay SPDT 5 Pins 12VDC 10A 120V Contact
schematic for connecting relays: Arduino Playground - HomePage

Here's another option: Most (all) of the sprinkler valve solenoids I have played around with work happily on 12v DC, so I switch the solenoid with a simple transistor (2n2222 or s8050, costs less then 5 cents) and power it from the same source as the Arduino. Don't forget flyback diodes
schematic for connecting transistor switching using DC power source: Arduino Playground - HomePage

There are two "sides" to the relay, and the specs are interpreted differently.

The "input side" is a coil (on a mechanical relay). It needs to be run at it's rated voltage and it will draw it's rated current. The Arduino outputs put-out 5V, and can supply up to 40mA. To drive a relay directly from an Arduino output, the relay needs a 5V coil rated at 40mA or less. Most relays actually require more voltage & current, so you need a transistor or MOSFET to drive them.

The contacts on the "output side" have maximum ratings. Contacts rated at 240V and 20A will work at lower voltage and lower current. If you are switching AC, look for a relay with contacts rated for AC. (There are also relays with AC coils.)

Take a look about relays and controlling power with Arduino HERE:

Relay-specific stuff is here:

No problem with switching the 24VAC with the relays on boards like this:

DISCLAIMER: Mentioned stuff from my own shop...