What does a "relay" do?


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bohdan
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What does a "relay" do?

Postby bohdan » Fri Sep 23, 2016 7:28 am



Greetings Gents,

Trying to learn the electrical schematics of a 93 Aspy. Notations, connectors, etc. Seems like the manual does a pretty good job. What specifically does a relay do? Does it do anything but act as a conductor between a source and a ground? Mighty obliged....



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Re: What does a "relay" do?

Postby WingAdmin » Fri Sep 23, 2016 8:00 am

A relay is basically a switch, but instead of being operated by your fingers, it is operated by an electromagnet.

This has the benefit of being able to control one circuit from another circuit, with no actual electrical connection between the two circuits. This is most commonly used to allow low-amperage circuits (like a handlebar switch) control a high-amperage circuit (like a headlight). The handlebar switch switches power on or off to the relay, which in turn switches the high amperage headlight circuit on or off.

Many relays have multiple throws. A single throw relay (notated as ST in the relay type) turns power on and off to a single circuit. A double throw relay (notated as DT) switches incoming power between one of two outgoing circuits - for instance, incoming power being switched between low and high beam headlight circuits.

Relays can also have multiple poles. This basically means the innards of the relay are duplicated, so that the electromagnet (or magnetic coil) actuates multiple switches at ones, each switch connected to its own circuit. These are notated as "SP" (single pole), "DP" (dual pole) or for more than that, the actual number involved - for instance "4P" (four poles).



Put the notations together, and you'll be able to tell what each relay does:

SPST - simple single pole, single throw relay
SPDT - single pole, double throw - this and the SPST are the most common kinds you'll find in your bike.

4PDT - double throw relay with four poles. This one has lots of connectors on it - two for the coils, and 4 x 3 connectors for the poles, for a total of 14 connectors!


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bohdan
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Re: What does a "relay" do?

Postby bohdan » Fri Sep 23, 2016 11:59 am

Wow thanks Wing Admin. I have a little bit more of an understanding. I will let to have it digest a bit. Cheers

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Re: What does a "relay" do?

Postby Wilcoy02 » Sat Sep 24, 2016 12:17 pm

Thank you both for asking and answering.
I did not know what a relay did either.

Learned one thing today.

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Re: What does a "relay" do?

Postby Mh434 » Sat Sep 24, 2016 1:39 pm

To make it easier, a relay is a heavy duty switch, able to handle heavy current. The relay is turned on (completes a circuit) when a low-power circuit it's connected to, as well, is turned on.

By way of illustration - on a car I had, the headlight switch kept burning out when I upgraded the lights, as there was just too much power going through the switch. Instead, I ran the power to the headlights directly from the battery, via a cheap relay. The relay was activated by the original headlight switch wire. No more switch burn-outs!

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Re: What does a "relay" do?

Postby hugger-4641 » Sun Sep 25, 2016 11:04 pm

Very good question and answers. This is one of those things that takes a little time to understand if you don't already have a good grasp of electrical principals, especially with Direct Current (DC). DC requires larger wires than a comparable AC circuit. The starter circuit is a good example. Especially on a car, it takes several hundred amps to turn the starter and crank the engine. If you didn't use some kind of relay to activate the starter, then those huge battery cables would have to go all the way to the ignition switch and back to the starter. And, the ignition switch would also have to be huge to handle that current. Using a relay lets you save weight and space by using small wires to control those large circuits. Just imagine all those switches on the handlebars of a Goldwing, the wiring harness would be the size of your arm if you ran all those circuits directly through the switches instead of using relays!

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Re: What does a "relay" do?

Postby offcenter » Mon Sep 26, 2016 11:54 am

hugger-4641 wrote:The starter circuit is a good example. Especially on a car, it takes several hundred amps to turn the starter and crank the engine. If you didn't use some kind of relay to activate the starter, then those huge battery cables would have to go all the way to the ignition switch and back to the starter.


If any of you are familiar with old cars from the 1930s & 40s, they had the starter switch on the floor.
You "stepped on the starter". The heavy battery cables went directly through that switch to the starter motor.
From the floor mounted switch, it was only a short distance to the starter motor which was often
mounted on the left rear of the engine, right ahead of the drivers feet and the
floor mounted starter switch. Short cables and a heavy duty foot operated switch
meant that no relay was needed.
In some cars, I believe that the switch was actually part of the starter motor with
the pedal sticking up through the floor.
When they started making the start function part of the ignition switch, a relay was
necessary so the battery cables didn't have run through the small key switch on
the dashboard.
George in Jersey.
99 Goldwing GL-1500 SE
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77 Honda CT-90 "Trail 90"

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Re: What does a "relay" do?

Postby hugger-4641 » Mon Sep 26, 2016 3:07 pm

I actually have an Allis Chalmers tractor from the 1930's that uses exactly that, a rod that is pushed with your foot which activates a switch lever built into the starter. Can you imagine having to start a Goldwing this way? Lol.

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Re: What does a "relay" do?

Postby spiralout » Tue Sep 27, 2016 11:41 am

hugger-4641 wrote:I actually have an Allis Chalmers tractor from the 1930's that uses exactly that, a rod that is pushed with your foot which activates a switch lever built into the starter. Can you imagine having to start a Goldwing this way? Lol.

Could you imagine have to start that tractor with this?

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Re: What does a "relay" do?

Postby hugger-4641 » Wed Sep 28, 2016 4:39 am

LOL, that might be better than using the hand crank, which it also has and I actually still use most of the time. Then again, if you do it right, if the engine kicks back it just pulls the crank out of your hand. If it hiccupped with that kick starter, you'd end up 30 feet in the air. :o

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Re: What does a "relay" do?

Postby WingAdmin » Fri Sep 30, 2016 10:35 pm

Here is the inside of a common 20 amp automotive relay. It might give you a better idea of just what's going on inside:

Image

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Re: What does a "relay" do?

Postby WingAdmin » Fri Sep 30, 2016 10:36 pm

This is also a really good explanation of the working of a relay:




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Re: What does a "relay" do?

Postby tylers883 » Sat Oct 01, 2016 8:43 pm

The signal lights rely on a 'flasher relay' which is just a special purpose relay designed to flash your signal lights instead of holding them in a steady ON state.

I have found that some people will call it a 'flasher', or a 'relay' or sometimes something totally different like 'turn signal controller module'. This can be a bit confusing but shouldn't be so long as you keep in mind what a basic relay does.




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