Selecting the right relay

I’ve been looking for the right relay to power my solenoid. Here are the specs.
24VAC, 0.2A Holding 0.4A In Rush current

I’d like it ideally to be powered off the Arduino along with maybe an indicator led on the same pin. The valve will be powered for 1-10 minute durations a couple times per day.

So my first question is for this purpose what kind of relay should I look for SSR, Reed, Electromechanical?

Second I was looking at SSRs it appears that the load must operate at a specific voltage range it 75v-240v. eg: Is the proper operation of the SSR dependent on the loads voltage. Some SSR’s look like they would be the right fit for me but some have a load voltage range outside the 24VAC.

I was looking at a few that might work. Thoughts? <-TSC-105L3H,000 <-LC241 kinda pricey

You need a relay that can switch at least 24v ac and at least 0.4 amps.

I would generally choose a relay with an amp rating that is a few times higher than the absolute minimum. if it was my project I would probably look for a relay that can handle 2 to 5 amps. A 100v relay will have no problem with 24v.

SSRs have the advantage that they can probably be driven directly from the Arduino I/O pin because they need very little switching current.

Relays with coils require too much current for direct connection to an I/O pin so you need to use a transistor to translate the small Arduino current into enough current for the relay coil. Google should find you plenty of detailed examples.


You need to think about how you are going to power the coil. You will need to use a transistor on the arduino output pin, the energise the coil of the relay, to close the contact on your actual load circuit.

There are several alternatives. You can provide power for the relay coil from your arduino power supply ( but not actually through the arduino ), or you can provide power for the coil from the same 24V source you are switching, or from some other source ( perhaps not a relevant scenario in your low-voltage case ).

Your decision on this alternative will be a factor in which relay will work for you, more so than the voltage or current capability of the relay output.

This SSR needs only 15mA @ 5VDC for control and could be directly connected to 5V Arduino output pins. It can switch 12VAC to 280VAC @ 2 Amps.