2nd Gen Non-Engine/Transmission What's a relay? Educate me!

[dieselvet]

I am electronically challenged, what is a relay. Hows does it work, what does it do. Thanks

 

[csevers]

A relay is a form of a switch it has two circuits the control and the load. Relays can be 4 prong or 5 , 5 prong can be wired normally open or normally closed. The purpose of using a relay is you can control a higher amperage with a much smaller control amp control circuit, smaller wires. Inside the relay it has 4 sets of contacts with a miniture sized magnet that closes the circuit when you apply voltage to the control side. Make any sence??



Craig

 

[John - K5AWO]

DieselVet;



This all takes a lot longer to say than to show.



Don't worry about the lack of electronics knowledge. I'm not a vet either and I needed one in the worst way six weeks ago when my dog was hit by a car. She's all better now after $2400 of vet bills.



Visualize a relay as being a large 16 penny nail with a lot of small guage (26-32 ga. ) insulated wire wrapped around it. Let's assume that the nail is one side of our contact and that a bare wire is wrapped around the end of the nail and run to a light bulb. Assume the light bulb has a wire run to the battery hot side.



Now if we were to cut a piece of thin sheet metal about a 1/4 inch wide and maybe 2 inches long. And we positioned that metal strip about an 1/8-3/16 inch from the nail head- we could call that the moving armature and the point at which it could touch the nail head, the contact.



This armature will have a wire connected to the end of it and will be our "ground" contact. We will take this wire to the negative side of the battery.



Now, if a voltage is applied to the "coil" (wire that is wrapped around the nail) the current in that wire will induce a magnetic field in the nail. This will cause the metal strip to be attracted to the end of the nail and when it makes contact, you will have current flow to the light bulb.



This little exercise is usually part of a lab in 1st semester basic electricity. You have now passed Electricity: Relays 101.



confused?



Typically in your Dodge truck, a relay will be a plastic device about an inch square by maybe an tall. It will have a minimum of 3 leads, usually four and sometimes five. Depends on the circuit requirements.



John

 

[John - K5AWO]

When I started al that, I was first. But Craig beat me to the posting, and just may have done a better job of it.

 

[Gary - K7GLD]

That small square box mounted to my firewall is a relay, used to control my Carter pusher pump...



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Commonly available at places like Radio Shack rather cheaply...

 

[B.G. Smith]

And: http://www.humanspeakers.com/audi/headlight-simple.htm bg

 

[Joe G.]

The big deal about a relay is the difference in the current required. The trigger circuit only draws about . 1 amps so you can connect almost anything to it without over loading the signal circuit. The output side usually can handle a lot of current. 30 amp relays are common. 70 amp are easy to get too. This way you can run stuff like a set of 100 W running lights from your light switch without burning the switch up. Just connect the switch to the trigger circuit and the output contacts between a fused battery terminal supply and the lights.

 

[Sixpack]

This may help you understand. It did for me.

 

[jwgary]

Basically, a relay is an electromagnet that operates a switch. All you need is enough power to turn on the electromagnet and that will close the switch on the larger circuit. This was the idea behind the telegraph from 100 years ago. A switch closed a circuit that turned on an electromagnet that closed another switch somewhere else to operate another object. In the early days, the clicking of the relay was the transmision medium and you just listened to the clicks, but then they made ways to record the clicks on paper and to operate a buzzer for as long as the telegrapher's key was held down. I hope this helps in the analogy.

 

[dieselvet]

Thanks, you all did a great job explaining it to me (and others I guess too). I hate working on stuff I don't understand.

 

[rrausch]

I've installed 4 relays on my truck so far:



One to run the clearance lights on the roof and take the load off of the light switch. For this one I also ran the relay ground wire through a switch so that while I am running at night, I can flash my roof clearance lights off and on.



Another relay to run the blower motor and take the blower electrical load off of the ignition switch.



Two more to take the load off of the headlight switch--one relay for Dims and one for Brights, for my Sportlights.



The 12v+ power source for these has been 2 MadElectrical Insulated Terminal Blocks. They are only $5 from MadElectrical.com

Each terminal block has room for 5-6 accessories.

I installed the Terminal Blocks next to each Battery, and ran a 10Gauge wire from each + Battery cable to the Term. Block. I soldered the 10G wire into each Batt cable, and then sealed the solder joint with liquid elec. tape, and then regular elec. tape.