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Elec. Question - What's a relay?

  • Thread starter Thread starter J_C
  • Start date Start date
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J_C

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I honked my horns the other day and I got one quick honk before they went down. They were garbage anyway, so I was thinking about upgrading. Ive been looking at the Stebel Nautilus compact and the PIAA sport horn and a few others. Some of these say they require relays. Am I correct in my assumption that a relay is usually an inline fuse running direct from the battery to the new horn(s) and then to the frame or other ground?
 
yes, look in the tips and tricks section for the relay write up with great mods.

EDIT: well sort of, it's a way to run power directly to whatever you want. Basically a direct switch.
 
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J_C said:
I honked my horns the other day and I got one quick honk before they went down. They were garbage anyway, so I was thinking about upgrading. Ive been looking at the Stebel Nautilus compact and the PIAA sport horn and a few others. Some of these say they require relays. Am I correct in my assumption that a relay is usually an inline fuse running direct from the battery to the new horn(s) and then to the frame or other ground?
Click to expand...

It's a switch, controlled remotely by electricity. Like a starter solenoid, a small control wire can open and close a relay to switch huge amounts of power through the circuit it controls.
 
A relay uses a low current source (horn switch) to switch a high current device (horn). E.g., if you put 30 amps directly through your starter switch it'd melt fast. You do need a ground, power supply, and inline fuse. You might check if it's your horn or your horn switch that went bad, or something in between.
 
OHHHHH I get it, thanks guys! That makes a lot of sense.... so the horn switch, when pressed, just opens up the flood gates of the relay so to speak. I think I get it.

As for the old horns, they've always been crummy. I wasn't at all surprised to hear it finally go down. I'll trouble shoot it just to make sure it isn't the horn switch, but I was tired of that little old "beep beep"
 
What it is vs. what it does

What it is vs. what it does

An electrical relay most usually consists of an electro magnet with the metal slide connected to a shorting bar. For a refresher on electromagnets if you take a tube of non conductive material (e.g. plastic) and wrap wire around it (i.e. create a coil), and put a slug of metal near the end of the tube (but still inside), when voltage is applied to the coil there is a magnetic field created which has a tendency for the metal to be pulled into the center of the coil. This is what it is called an electromagnet.

http://science.howstuffworks.com/electromagnet2.htm


With a solenoid that slug of metal is also attached to a shorting bar that when engaged pulls the bar in contact with two contacts. One contact has a heavy gauge wire from the battery. The other contact has a heavy gauge wire to the load. So by switching the current in the (thin wire) outer coil (e.g. 2-4 amps) , you are able to control much larger
currents (25-100 amps) depending upon the size of the shorting bar/contacts. There is also usually a spring involved to force the contacts open when the coil is not engaged.

A starter solenoid is what is called a "Normally Open" relay. The Bosche type have two terminals with two sets of contacts. One set is normally open (shorting bar away from the contacts) and there is another shorting bar that is against the other side of the contacts that is making it "Normally Closed"

If you go to Matchless's "Relay modification for bike v23 pdf" file you will see two types of automotive relays a 4 in and a 5 pin.

The 4 pin is the simplest. It is electrically just like a starter solenoid or relay. It is "normally open" (i.e. not connected) but when energized the electromagnet sucks in the metal slug which shorts the contacts to drive the load (e.g. starter motor). The switch schematic indicates which way the current flows when not energized.

The 5 pin is a combination "normally open" and "normally closed" relay in one. You will note that the 87 terminal is "normally open" and looks just like the 4 pin relay schematic. But in addition the 87a terminal is a "normally closed" connection that opens when the relay is energized.

Hope that helps a little better. If you have an old starter solenoid it is relatively easy to take apart and with the big cables removed pretty safe to play with. :-D

Posplayr
 
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Thanks so much for another great response! Yes, I definitely get the hang of it now. So let me ask these two followup questions.

If I was going to create a horn relay, as mentioned in the PDF, and I wanted power running to two horns, using a 4 pin I would need to split off of the 87 so when it was triggered both would sound. If I used a 5 pin, I wouldn't want to use the 87a, because then the horn would always sound UNLESS the horn button was pressed correct?

The second question, say my horns draw 12 A. How do I termine which kind of fuse I need to install between the battery and the relay? I would use a 15A fuse, correct? (And not a 10A fuse, because then not enough electomagic* is getting through right?)


*Electromagic used in place of whatever the correct term might be. (Electricity? Voltage? Watts? Amps? Something?)
 
You are getting the hang of it

You are getting the hang of it

Correct on both questions.

1.) Yes, The 4 pin relay is "Normally Open" Only and the 5 pin relay has both.

2.) Yes, you want the fuze to be able to handle whatever current (amps) load you expect (through the fuze). If you had 3 lights hooked up (in parallel) each pulling 5 amps, you would want to use at least a 15 amp and probably a 20 amp fuse because the total normal current draw will be 3x5=15 amps.

Posplayr

P.S. we share a common hobby (brewskis)
 
The thing you want to look for is an external type relay with 4 pins.

25 years ago, when I did this to my GS, I used a Hella headlamp relay because it was external (made for under hood, rather than under dash), it was small and it had an integral mounting tab with a hole in it. I was able to find a bolt to mount it to, pulled the horn wires off one horn and attached to the relay, ran the big wire from relay to battery, ran a big wire from relay to horn and one from horn to ground. I've never used an inline fuse. Paired with Fiamm horns, car drivers hear me when I honk.

BTW, your current horns probably just need adjusting. Loosen up that little screw and locknut, try honking the horn and adjust the screw until you get the best sound. Tighten the locknut and you're good for a few years.
 
Thanks guys, this has been really helpful! I was planning on replacing the horns anyway, I know how to adjust them, and I'll do so to ensure that I don't have any other problems before doing the new ones. I wanted to just get some new booming horns. Just debating between the stebel nautica, or something like the stebel magnums or piaa sport horns. (Sounds like the magnums/sport horns option may be the easiest to mount, though nautica seems to have 3 more db)
 
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