Thread: Relay Help

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Ok masses here I am again begging for help. I am wiring relays into my project and what I have is 12VDC/125VAC 10A SPDT Mini Relay from Radio Shack, Model: 275-248. I am starting to wonder if this is the proper relay for my application or should I use the 12VDC/10A DPDT Plug-in Relay Model: 275-218. Then only use one pole.

Thanks.

I am not sure what you are trying to control -

but, the first relay is a SPDT - That means that you will have a common connection, a normally open connection and a normally closed connection. If you just want to light a light when the relay is active, hook the hot (Black) from your AC source (Wall Outlet) to the common relay connection. then hook your neutral (White) from your AC source to the light bulb. Lastly hook your normally open contact to the other side of the lamp.

On a side note if you want to drive two lamps that flip flop on and off - then hook a second wire to the normally closed contact and to a second light bulb and the other side of the light bulb will go to neutral. this light bulb will be on when the relay is not energized.

Both relays listed have a 10 amp rating, that is 1200 Watts or 12 100 Watt light bulbs. So you can drive most things with this relay, unless you are driving motors.

The second relay is a DPDT, That means that there are two switches like the prevoilsy mentioned relay enclsosed in one relay. So you have two normally open connections, two commons, and two normally closed connections. this enables you to turn two things on at the same time - one set of contacts can feed a lamp, the second set can click play on a modified MP3 player.

I should also note that the first relay is designed to be installed in a printed circuit board, so while you can use it soldering it will be a little difficult. The second relay can easily be soldered or you can by the optional socket for it. Relays were typically socketed because they wear out and need to be replaced fairly often. However when it comes to haunting the relays are used maybe 100 times on the big day and then go into storage until next year so it will take 50-100 years for them to wear out.

I hope this helps -

Originally Posted by chillingham_manor

Ok masses here I am again begging for help. I am wiring relays into my project and what I have is 12VDC/125VAC 10A SPDT Mini Relay from Radio Shack, Model: 275-248. I am starting to wonder if this is the proper relay for my application or should I use the 12VDC/10A DPDT Plug-in Relay Model: 275-218. Then only use one pole.

Thanks.

It's hard to help without more info.

What are you attempting to switch on and off with the relay?

With a relay you have two sides: a coil side (the 12 volt side in your case)
a switch contact side (125VAC contacts)

When you apply power to the coil (12 volts), the switch contacts open or close.

SPDT means one center pole contact that switches between two throw contacts (one opens and one closes when the relay coil is energized like an on/off switch). You normally wire to the center pole contact and one throw contact.

DPDT mean two separate center pole contacts that switch between two sets of throw contacts (one set for each pole). This one is like having two SPDT relays in one that can switch two separate power feeds to two different devices.

If they supplied a pin diagram, the center pole is usually designated by an arrow or straight line near or between the throw contacts.

I'm sorry I should have been more clear (it all worked in my head). I am powering a washer valve, lights, computer speakers (on and off). After I got the mini relay I thought "crap how am I going to solder that?" I think I may just return the unopened ones and get the DPDT instead.

For simple on off applications SPST relays are all that's needed, as they can just turn something on and off

SPDT can also be used to turn something on/off, or it could be used to switch between a pair of lights maybe left/right in one position it turns the left light on and the right light off in the other the its left off and right on.

DPDT you would use for something like a reversing circuit, where you want to switch the two wires of a motor simultaneously, or you could use it to switch on a high voltage circuit for maybe a motor and use the other pole to switch on a low voltage circuit that turns on an indicator light

DPDT can do everything SPDT can do and SPDT can do everything SPST can do, so if you have DPDT don't worry you are fine

here is a quick relay guide I put together

Excel Control

in case it helps here is the guide i did under the how to section haunting with relays

also we need to know what you are using it for

Thanks. It all helps a lot. I just returned my mini relays and got DPDT and sockets. I may even be able to get by with 2 relays instead of 6.