120V Relays

Well, Christmas is too close to do this this year, so I want to do a big project next year.

For that, I need 120 volt relays. I need about a 3 amp rating each, just to be safe.

Before you go all nuts on me saying “Mains are dangerous! You can kill yourself!” I want to state something that I am quite proud of:

I have meen woking with mains since before I was out of diapers. I am 12 now… I have had my share of shocks, and I know how to work mains.

Relays have two key specifications, coil voltage and contact ratings. Did you mean with 120vac coils or some DC voltage coils?

If 120vac coils then these are pretty attractively priced:



DC coil, AC contacts / whatever you call them… Should’ve mentioned that.

Also, I only need SPST.

The coil needs to be 5V DC to be interfaced with Arduino through a transistor.
The switch part needs to be 120VAC, for mains voltage. I am expecting about 2 amps, so 3 would be safe.

5vdc coil relays with that large a contact rating are not as common but this one is well priced and should work fine.


Will those handle 120 VAC though? As in on the switched contacts?

It seems that little rectangular blue relays are popular…

Will those handle 120 VAC though? As in on the switched contacts?

Typically questions like that are best answered by reading the manufacures datasheet. Typing the part number in for a google search will usually find a datasheet like here: http://www.hascorelays.com/electro_klt_series.asp

And reading the contacts tells you, yes, the contacts are rated for 120vac. So it’s a good question but did you think I would recommend a part that wouldn’t match your specs? :wink:

So learn to fish grasshopper and you will never go hungry for lack of information.


A) No, you wouldn’t tell me anything that woudn’t work.
B) Did you really call me a young grasshopper? I don’t hear many people say that anymore.

I have no idea how young you might be grasshopper. :wink:

12… I’m like a baby grasshopper.

Have you considered solid state relays ?. Much easier to interface to the arduino…

Notice that solid state relays don’t switch 100% off.

Notice that solid state relays don’t switch 100% off.

What? I’m so confused.

A solid state relay don’t switch off the same way as a relay with moving parts in.

When a ‘normal’ relay is switched off, it is switched off, and absolutely nothing going through it.

But when a solid state relay is off, it is still a bit on, but with such a high resistance that most things wont be able to do anything. But if you connect a power saving bulb, neon light, or something like that, they might just turn their brightness down when you switch them off.

What about Christmas lights? That is the main use. That and blow up thingies (santa, ect.).

Also, I need some of them rated at roughly 15 amps, to run the air pumps to those blow-ups.

SSR’s would be nice, but (yes, there must be a but) they seem expensive. I checked ebay, and they’re $8 each… Doesn’t seem like a lot, until you realise that I’ll use it 1 moth of the year, and that I need over 10.

If you know of a cheaper source for ones rated at 3~ and 15~ amps, please share.

SSRs are nice and I have used a few to good effect. But as you have seen they tend to be a little costly compaired to surplus relays. Once in a while I’ve seen some $2-3 surplus ones but they tend to have one amp ratings or so. Also something that many miss is that to use a SSR at anywhere near full current ratings requires that you mount it to a substantial heat sink, just like with large power transistors. This adds size and costs to projects and makes the old elecromechanical relay worth looking at again. :wink:


Ok, I’m back to normal relays. Can you point me to some that are rated at about 3-5 amps, and some that are 15 rated? It is a plus if they are similar size, and are available from the same store.

Well I tend to like All-electronics and electronics goldmine. These tend to be surplus or new old stock as the prices are below normal retail, however they may not be available the next time you look to buy a specific model.

four pages of relays here:

Lots here also:

Still searching, but I already like Goldmine better… They hav sort by voltage… I like things that make my life easier!