Build Safer Electrical Systems with Electrical Relays
Mark Simpson
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Electrical relays are essentially electrically operated switches. They have been used in a wide array of electrical systems for over 200-years. Early classic cars had little need for electrical relays and often even lacked fuses or circuit breakers. As cars became more sophisticated and the electric systems more robust, relays proved an effective means to deliver large amounts of electric current without having to go through a conventional switch.
There are several advantages to using electrical relays when building or adding on to your electrical system and they include: Shorter heavy gauge wire lengths, deliver higher amperage to components, take load off of switches, reduce electrical fire risk. Relays have proven themselves reliable in many automotive applications, including horn, starter and cooling fans. Today most modern cars include dozens of relays for nearly every system on a car.
When you're doing any kind of electrical work on a classic car, sooner or later, you're gonna need to wire in some heavy amperage components, like an electric fan for your radiator. You know, some of these components can draw a lot of amperage and you don't wanna run a switch or a wires all the way back and forth, using a 10-gauge or 12-gauge wires. So rather than have all that amperage to your switches, you use a relay. And what a relay does, it acts like another switch. And in this case, let me kinda point this out here on a basic 4-pin relay.
There's two pins on this relay that will serve to... Actually, there's a wire inside this little block that has it's a little electromagnet. And what does electromagnet does is it pulls closed a switch. So the electricity can flow from two other points. So this is very low voltage.
The amount of voltage to actually activate that little electromagnet is very small. So that switch on your dash, it's maybe pulling just a fraction of a amp of electrical draw, but it's completing a circuit that may be a 30 or 40 amp draw. And now you don't have all that voltage going up to your switch. You're not running huge heavy cables back and forth. You know, you instantly, you've got your power close to, you know, the point of use.
And the another benefit is this is whenever you're running wire, the longer the wire, you start to lose amperage as you go through. It's called line loss. And what the way to get around that is keep your heavy gauge wires as short as possible. If you have a relay mounted close to like your electric radiator fan, when you flip that little switch inside which is just a low voltage switch then you can have a short distance from your battery or from a circuit, from a fuse block out in your engine compartment to the electric fan and keeping that circuit real short like that, will increase the amount of voltage available or amperage available for the actual device itself. And again, that's the way a 4-pin works.
A 5-pin works much the same way. 5-pinners used a little less common. Okay, as you can see in this relay, the fifth pin which is actually cut off or ground off in here because it's not actually available in here is also operates the same way. It can operate, so it can send voltage either on or off. And this would be used like in a situation where you may need like a high or low beams on headlights.
So once you hit your high beams, it would flip over or flip from low to high and it would complete the circuit differently. It can also be used for variable speeds on fans and some various other wiring schematics. Okay, let's look at how a relay is actually wired. You know, your power comes into your switch through the 86. In this, the switch is your low voltage side, low amperage side.
So this is relatively thin wire. You know, your 86 is just going in. Then your ground then becomes the 85 terminal. So your 86 is your power in, 85 is your ground. And all those to do is activate that a little electromagnet inside the relay.
Then the real power of this is your 30 which is your heavy wire in or heavy amperage in, and then out to your accessory is your 87. So 30 and 87 are your two main leads to complete that connection. And 86 and 85 are the switched connections. Okay, that kinda explains the basics on how to wire a relays in. And the advantages of having a relay, kinda go without saying, keep your main power lead short.
You know, you can reduce your fire risk by having low voltage wires running to switches and various other components. And, you know, the relays themselves are fused. They'll like, if you look at any fuse, any relay, they're usually rated for a maximum amount of power. And like this one here is a 30 amp. And this one here is marked 40.
So when you're buying a relay, you wanna make sure you buy a relay that's rated for the amperage of whatever you're want it to operate plus about 20%. So you don't wanna be right at the limit. If it's a 30 amp fan, you don't wanna buy a 30 amp breaker. You wanna be there plus 20% or whatever. So you might wanna look at like a 35 amp breaker.
So consider using relays whenever you're doing any kind of electrical work that involves heavy load electrical devices.
Please find an electrical teacher that actually knows what they are doing.
I understand what he's saying, but for beginners watching this, I suggest being specific about low and high amps, not high and low voltage. Don't call a relay a breaker
RELAYS are the reason why some cars could not shut off. Contacts are notorious for welding themselves together. In the old days, the key switch directly disconnected the ignition circuit and the key would ALWAYS control the ignition without fail. This guy needs to learn the difference between voltage and current. Long wire lengths create a VOLTAGE drop. BTW, the whole car is 12-volts, not low and high voltage. A relay uses a 'controi' signal to energize a 'power' circuit. For instance, the horn relay energizes the relay coil through the steering wheel ring. When the horn is pressed, the relay contacts control the horn power. It's all 12 volts but horn current would melt the steering column wiring and destroy the brush spring without a relay. Because the key switch cannot control power windows, power seats and convertible tops, Ford added a relay that is controlled by the key switch. When the relay coil is energized, contacts connect battery power to the accessories.