Thread: What is a RELAY?!?

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i see these every where. WHAT ARE THEY???

THANKS!

-BYH

A relay is a switch.

It is electromechanical or can be solid state.

In the basic electro mechanical configuration, there is a coil of wire that surrounds a core of metal. By providing current to the coil the core becomes magnetic. This is known as an electromagnet. A set of contacts are moved by this electromagnet to close and or open and act as a switch. The contacts are labeled Common. Normally Open and Normally Closed.

Now why do we have relays. A relay allows the use of low voltage to switch or activate devices that require higher voltage or higher current flow than the circuit used to control the device can handle. So for instance you can have a 12volt DC solenoid that can control a 110 volt AC motor as an example. Or you can have a 110 volt AC solenoid control a low voltage DC circuit.

The solid state variety of relay use transistor n+ n- type logic to open and close gates to pass current. I am a bit less informed on the Solid State arena, so one of the circuit guru's can correct me on terminolgy.

they are an electromagnetically control switch.

the electromagnets (or coils) are made to handle different voltages (such as 5VDC, 12VDC, 24VDC or even 120VAC).

the switch can then handle a different voltage and usually more current.

for example a relay can interface to computer with 5VDC and then control 120VAC light.

everyone above gave great answers. here is the example that i hope helps. if you put off-road or fog lights on your truck/car they take huge amounts of power (amps) and require heavy duty wires and switches. BUT you dont want a massive switch on the dash or run the heavy wires inside..... so the cute little switch on the dash activates the relay under the hood which electronictally switchs on the heavy duty stuff you dont want inside the car/truck.

What you learned is that you can use one set of wires/switches that have very little current to turn on a different set of wires that are using a different type or level of electricy.

Fron there, that first set of swtichs might not even look like a switch to you and me, but might actually be part computer or electronic circuit board turning on and off items whos power requirments would destroy the computer.

best example of this i can quickly think of (and easy to see) is "KIT 74"


the blue boxes are the relays. this board hooks to your computer printer port and with some software (vixen) can then turn on and off 8 electrical items (like lights)

Parallel Port Relay Board

my guess is you search this forum for "kit 74" you will find lots of examples of it being used on the low end to control lights, fogmachines, etc... for halloween and (GASP) chistmas.

ok i see but how do you trip it? does it save like switch pattens

You should have asked: "What is Wikipedia?" and "How do I use it?". (This may be a bit callous, but I'm just sayin'....)

I find that asking questions to real people gets me an answer I understand better. Besides, this is a forum of like minded people who are here to help. Just sayin...

Originally Posted by BackYardHaunter

ok i see but how do you trip it? does it save like switch pattens

Typically, in Halloween terms, you would use it in a programmed circuit card. The Prop-1 is a good example. You have a 12VDC power source (input), but you want to trigger a 120VAC fog machine. You could use the solid state relay (SSR) on one of the outputs, and when that output goes high, it would trigger the relay, then turn on the fog machine.
Another good example was the Kit 74 card shown above. This card has the relays built onto the card. They are the large blue boxes. They take the 12VDC input voltage and "switch" the SSR on/off depending on the timing sequence. This allows you to use 120VAC lights on a 12VDC circuit.

Originally Posted by dpeterson

You should have asked: "What is Wikipedia?" and "How do I use it?". (This may be a bit callous, but I'm just sayin'....)

It's really not the same, is it?

Whilst Wikipedia and other such sites can give you a basic insight into what a relay does or how it works, it can't offer advice on practical applications for specific uses, or explain in depth if there's some aspect that you don't understand or are having trouble with.

That's why forums like ours are such great and useful places...
First hand advice from like minded people with practical experience in the subject field is an extremely useful resource, and can prevent costly or even dangerous mistakes.

Originally Posted by BackYardHaunter

ok i see but how do you trip it? does it save like switch pattens

Not sure if you mean how with software do yo trip it on the 74 board or just any relay. If any, then it could be a motion detector, a pressure mat, or just a plain switch. Normally there would be other things involved like timers (search prop1 controler)!that would do things like keep the relay open for a set time or turn on ther relays for lights or air valves. If you are talking about the kit 74, it wold be hooked up to a computer the entire time running software that has need programmer to activate one or more of the relays as part of a show. Go to YouTube and search for singing pumpkins as an idea. Or using the same concept with a ton more cash search here for LOR