Using Relays Properly

Well i figured since questions have been popping up recently about relays I would create a thread on what they are, how to use them and when to use them.

So let's start with the basics: What is a relay? Well I'm glad you asked because I just so happen to know the answer to that question. A relay is basically a automatic switch that when powered by an external source creates a connection to whatever you are powering. Now this may sound confusing at first but it is quite simple. The way this "switch" works is by the use of a electromagnet that when powered switches the circuit. Pretty neat stuff is you ask me.

Now for what you really want to know: how to wire them properly. Well if you look on any relay there are 4 - 5 poles. Each pole has its own function. Here's a diagram to illustrate what I'm talking about:

Now that you can visualize the 5 poles, I can explain what each does. Let's start off simple; pole 30 is your constant power. This means that there will always be power moving through the relay at all times. Now it does not necessarily mean it has to be plugged directly into the wall socket or anything, just that it should be tapped of a power with constant power. Such as the wires directly from the power supply.

Pole 85 is the ground. No need to explain a ground.

Now here is were most people have a problem with relays and end up catching wires on fire. Pole 87 is the accessory turn on. This means that it is connected to the whatever you want to have automatically turned on. I.e. fans, lighting, whatever.

Pole 86 is the accessory turn on wire. This means that whatever this source of current is, will switch the relay and apply the constant power to the object you are trying to turn on. This may sound confusing but a simple diagram follows showing what I mean.

Now the question I always receive is why would you want to use a relay when you could use a switch. My answer is always because I'm lazy. But the real answer is because switches cannot always handle the current necessary to power some components. A relay can handle 30-40 amps while a switch can only handle 3-3.5 amps. Also a relay basically automizes everything. This way if you only want your sweet lights to turn on when the case is on AND when a switch is turned on, the you can do this with a relay. Well that is all for this post. This is just basic relay wiring which is why I did not get into the 87a pole. It really is not necessary for basic use but if there is a response and you guys seem to want to learn more, I will create a more advanced post discussing more advanced techniques on relays and also the diffrent types of relays.

I'm interested! :)

While the information is correct, I (as an electronic engineer) found it confusing. For one thing, it's only relevant for automotive relays. Other types don't have those terminal numbers.

For real simplicity, if you know how a switch works then you can understand relays.
With a switch, you use a finger to move its position. With a relay, you use a voltage instead. That's pretty much all there is to them. The voltage energizes a coil, creating a magnet which moves the position of the switch.

xmastree
nicely put +rep

I liked the wiring diagrams ans I find things like that extremely helpful. I may go about making wiring diagrams for alot of the simple circuits that people will run into in modding.

Quote:

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Originally Posted by xmastree

While the information is correct, I (as an electronic engineer) found it confusing. For one thing, it's only relevant for automotive relays. Other types don't have those terminal numbers.

For real simplicity, if you know how a switch works then you can understand relays.
With a switch, you use a finger to move its position. With a relay, you use a voltage instead. That's pretty much all there is to them. The voltage energizes a coil, creating a magnet which moves the position of the switch.

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yeah I noticed that but English is not my first language so i have the idea's in my head but stating them is a bit on the difficult side. I do realize that those are only for automotive relays but we would only need automotive relays considering computers run on 12 volts.

Automotive relays would work, but they are rather large. Using smaller, multi-pole ones would allow you to switch 5V to one thing and 12V to another simultaneously.
Or even switch mains voltage, which car ones aren't rated for.