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Topic: 120V Relays (Read 17998 times) previous topic - next topic


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.  ;)



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!


Dude, I can't find crap... I found the 6 amp one that you already showed me, but I need one that does 15, too.


5 volt coil @ 15 amp contacts is going to be a hard find I bet. You know that 15amps is pretty much the maximum rating of a standard AC wall outlet? You can always use the 5volt 3-5 amp relay to then switch a larger 120vac coil relay that has higher contact amp ratings.

This one has two pairs of 12 amp contacts, so if you wire the contacts in parallel you should have more then enough to handle 15 amp load.



Dec 02, 2010, 04:48 am Last Edit: Dec 02, 2010, 04:48 am by Jeremy1998 Reason: 1
I actually think that I have found some good ones at DigiKey for cheaper that those others.

5 Amp
15 Amp

Do they look like they are any good?


They look fine. Make sure you use large wire (or large traces if building a PCB) on the 15amp contact wiring (see chart link) and try and make extra strong solder connections. AC power wiring especially at high current values needs to be carefully planned and build. Normally we give long speeches to someone as young as you about electrical safety and not fooling with AC power until your old enough to drink or smoke.  ;D




Thanks, but I'll skip that lecture. I have had my shocks... And beleve me, I remember every one! I can tell you the awg of wire to use fro how many amps. You need at least 14 awg or larger to safely do 15 amps. I will probably run 12 awg to be safe.

One more thing: how should I power the arduinos? They will be inside of the boxes. There will not be 5 volts (normally). I could strip down a regulated wall supply and tap the 2 input wires. Does that seem Ok if I insulate everything?

If I do it so that the arduinos are external, what size wire should I use for signal?


Dec 02, 2010, 05:42 am Last Edit: Dec 02, 2010, 05:42 am by retrolefty Reason: 1
They will be inside of the boxes. There will not be 5 volts (normally). I could strip down a regulated wall supply and tap the 2 input wires. Does that seem Ok if I insulate everything?

Sounds OK, I've been finding 5.1vdc regulated wall warts used to charge cell phones at Goodwill stores stores recently for a buck or two each. Clear silicon glue can make a good insulation material that you might find useful instead of just electrical tape alone.

If I do it so that the arduinos are external, what size wire should I use for signal?

Signal? you mean the wire from the transistor that powers the coils? At some point you really need to draw up your design to clearly explain further questions.


Well, I am going to have an arduino or 2 in my house, with a set of transistors to amplify the signal. After these transistors is where the wire comes in. After the wire, I will have a 2nd set of transistors that go to the relays.

how big should that wire between transistors 1 and 2 be? I know it doesn't have to be big at all, but I don't want an uber small wire... Would 18 be good for this?


I know this might sound crazy, but I do what you want to do with Christmas lights with an Arduino 2009 an X10 TW523 powerline interface and a bunch (about 12) X10 plug in appliance modules. Even use the lamp modules to dim and fade different lights. Maybe 50 bucks on ebay for all the stuff. I assume you already have an Arduino. Works great for home automation the rest of the year. You just can't do a high speed light show. Takes about a second for each module to go from off to on and about 3 seconds from bright to dim...etc, etc. Works like a champ.

aroma of tacoma

One cheap way I use to switch 120vac lighting (chicken coop heat lamp)on and off is to hack the $12 generic remote control outdoor outlets from the hardware store. You can interface with an Arduino at the remote control or at the outlet itself (where the receiver interfaces). They look like short extension cords with a bulge in the middle. They're weatherproof and will switch a pretty large 120vac load.


Actually, 2 dollar relays are cheaper.

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