12VDC, 12Amp Relay... what does this mean?

[Szech]

Does this mean that it activates on 12VDC, and can handle up to 12 Amps going through it? I'd like it to activate a 115 VAC source, how many amps can it take going through it?

Also, what does SPST, DPST, SPDT, and DPDT mean?

Thanks! http://www.sysopt.com/forum/smile.gif

[DanU]

These numbers describle the circuit that is being controlled. It can control up to 12 Volts DC and up to 12 amps can pass through it. Don't use it for 120VAC circuits. Get one specifically rated for 120VAC or higher.

Single pole single throw, double pole single throw, single pole double throw, double pole double throw. The number of poles is the number of circuits you can control with one switch. The number of "throws" is how many "on" positions you can put the switch in. OK... it's a bad explanation. Maybe someone can point Szech to a better one.

[Szech]

So if I need it to handle 115VAC, and activate on 12VDC, get one with a 115VAC coil?

[DanU]

The relay contacts should be rated to handle 115VAC or greater. If the contacts are not rated at a high enough voltage, then current may arc across the contacts, damaging them. Also, if the current of the load (be it a lamp, motor, etc) exceeds the current rating, the contacts will overheat.

So let say you want to control a 120W load. It will draw 1A at 120VAC. You'll want a relay that has contacts rated for 120VAC, 1A. In practice, you'll probably want one that can handle maybe 2 to 10 times more current. Motors in particular can have very high starting currents. A 1A motor can easily draw 5A or more until the motor gets up to speed.

The coil, which is part of the control circuit, should be rated for 12V if you are going to use a 12V control signal. Otherwise the coil might burn out.

[Graham]

Szech,
Danu is right about the rating.
Relays are quoted in terms of their coil (operating)voltage, and contact current rating (obviously large currents need larger contacts). They dont usualy include the contact working voltage in the simple description because, as Danu suggested the voltage and current switched are inter-related, eg the contacts maight be OK for 1A at 12V but only 0.1A at 50V.

Relays are quite cheap, if you cant be sure of the rating of the one you have, get the right one, like Danu says, arcing, and contact burnout are potential problems.

what do you want to switch ??

I'll add my explanation here, perhaps between us Danu and I may get it so you can understand,

SP single pole... one line (wire) switched .

DP double pole .. two lines switched, just like two SP operating together.

ST single throw.. just two positions, on or off.

DT double throw.. on in both positions but to different circuits, either or. Imagine a light switch, one way lights on in the kitchen, the other way on in the batroom.

Why anyone would want that ?...... http://www.sysopt.com/forum/smile.gif


G

[Szech]

Ooh... I think I see... So the voltage rating is what the relay can handle when current is going through it?

I wanted to do something like this: http://www.overclockers.com/tips242/ , except connect it to my surge protector switch instead of a pump. Basically, I want everything to turn off when I shut down (Monitor, printer, Zip drive, speakers, etc.). When I went to Radio Shack to buy the part in question, the guy said, "What's a relay?" Geez. So I'm looking for an equivalent part off http://www.allelectronics.com or http://www.meci.com . Since it will be switching on/off a surge protector, I should get a 115VAC high amp DPST or DPDT relay, right?

Thanks!

[This message has been edited by Szech (edited 05-16-2001).]

[Kuasimodem]

Schech,

With a relay controlled by the PC shutting down the surge protector (and everything else) at computer shutdown, unless you have the computer on a different surge protector, you will not be able to power back up again.

You could buy one of those cheap power bars, wire the relay into that, and have all your peripherals on the power bar, which is plugged into the surge protector. Then have the computer (tower) plugged directly into the surge protector. This way, the computer always has power to it, but will shut down the printer, scanner, speakers, monitor and whatever else you have.

As for the relay, just get Radio Shack catalog number 275-218 (http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F010%5F008%5F005%5F000&product%5Fid=275%2D218) . It's a 12VDC relay with contacts rated 15A @ 120VAC

Here's the specs (http://www.radioshack.com/SupportGate.asp?SupportPage=%2Fsupport%5Fsupplies% 2Fdoc9%2F9525%2Ehtm)

[This message has been edited by Kuasimodem (edited 05-16-2001).]

[Szech]

My surge protector has two constant-on ports. My tower and my alarm clock are plugged in them. I did go to radio shack, but the guy didn't know what I was talking about, but it looks like I can order it online, so I think I'll do that.

[tonym]

Szech,

You can **** around with RS relays, but the quality you get isn't that hot!!

If you want a good relay, pick a Magencraft (www.magnecraft.com), CII Technologies/Midtex (www.ciitech.com)or an OMRON (www.omron.com) or a similar quality vendor's product. You can do some research at the EEM (Electronic Engineers Master) web site (www.eem.com). Just click on the relay link and take a look at the products. They are by no means all that are available, but you can get a good idea of the products available out there!

Also, if you need samples and are unable to get them...let me know and I'll be happy to get them for you and send them along.

Good luck and have fun...


Tony