Why is a relay necessary for driving lights

[fwbpastor]

Here’s my question.

Why have a relay for the driving (passing lights).

 

My front fairing is still apart and I can change my wiring easily.

 

I bought the Kuryakyn Master Cylinder switch and have the hot connected to the Red wire with yellow strip (power on all the time when key is turned on). One of the switch wires I connected to the driving lights.

 

The hot wire to the switch has a 30 amp fuse and the wire going to the lights has a 10 amp fuse.

 

There is power to the switch when I turn the key on and I can toggle the driving lights on and off with the switch. If I ever forget to turn them off, the power is cut as soon as I turn the key off.

 

I don’t know a lot about electrical draw and amps, but was just wondering why I needed to put in a relay.

 

Other than the fuse being in the fairing, is there any problems with the way I hooked it up?

 

Thanks

Melvin

[bongobobny]

OK I'm sure you are going to get varied opinionson you're question but here's the facts in a nutshell. The main reason to use a relay is to protect the switch that controls the lights. Relays aren't needed for low power lights such as LED's but are a good idea for heavier current drain. Any switch contact is not a perfect zero ohm connection but has a small amount of resistance. The more the current, the more voltage drop occurs across the switch contacts resulting in heat being developed at the contact point. The more the heat, the more the damage to the contacts, the more the voltage drop across the contacts, the more the heat. It's like a snowball efect. Also, as more current goes thru the contacts, the contacts begin to pit because it sort of acts like a mini welder on itself.

 

So, to answer your question, although not necessarily needed. it may be a good idea. Also, it's generally a good idea to run the hot connection directly to the relay coil and switch the ground on and off to prevent the remote chance of 12 volts being shorted to ground thru the switch or the wires...

[MiCarl]

OK I'm sure you are going to get varied opinionson you're question but here's the facts in a nutshell. The main reason to use a relay is to protect the switch that controls the lights. Relays aren't needed for low power lights such as LED's but are a good idea for heavier current drain. Any switch contact is not a perfect zero ohm connection but has a small amount of resistance. The more the current, the more voltage drop occurs across the switch contacts resulting in heat being developed at the contact point. The more the heat, the more the damage to the contacts, the more the voltage drop across the contacts, the more the heat. It's like a snowball efect. Also, as more current goes thru the contacts, the contacts begin to pit because it sort of acts like a mini welder on itself.

 

So, to answer your question, although not necessarily needed. it may be a good idea. Also, it's generally a good idea to run the hot connection directly to the relay coil and switch the ground on and off to prevent the remote chance of 12 volts being shorted to ground thru the switch or the wires...

 

Well said.

 

In summary - Your switch will last a lot longer if you use a relay.

[jointventure]

EXACTLY what bongobobny said.

 

Very well stated.

[Seaking]

bongobobny put it well..

 

Two other schools of thought goes with the use of switch and relays.. in layman's terms. (I call it juice as I couldn't tell ya if it's the amp current or voltage word that applies

 

A lot of electrical juice gotta flow from the bike to the lights, and you can use a switch to turn them on and off but you would need a large heavy duty switch that can handle the heat and juice without burning out.. using a relay solves a lot of problems.. Basically think of it as the LARGE switch you can hide somewhere that gets operated by the little switch you place on your handle bars and such.. It doesn't take a lot of juice to push the relay into the open or close position to turn on the lights, that's why you can use the smaller switch to operate the relay.. In a nut shell that's how I learned to use a relay and why..

 

My OLD school of thought was always based on the Electrical Theorem of Smoke.. If you didn't use a relay you had a better chance of letting all the smoke out of your light circuit and that it would be expensive to put all that smoke back into the circuit..

 

That's still basically why I use relays.. the smoke..

[dingy]

Below is a schematic that shows how to run the wiring for your lights.

 

If you want some information on relays and their use in a Venture check this link on this site.

 

http://www.venturerider.org/forum/showthread.php?t=43150

 

The switched shown has an indicator light in it, yours may not, so just eliminate light in switch and the wire to ground.

 

Use care when routing wires, check that handlebars will rotate fully in both directions without putting stress on new wires.

 

If at all possible, solder all wires. I am not a fan of the crimp to connect wire splices, (Scotchlok is one trade name).

 

The relays and switches are available at most auto parts stores. Radio Shack has a few nice miniature switches also.

 

Check the rating on the switch, you want at least 10 amp rating for a pair of 50 watt lights. The circuit should draw about 8 amps.

 

Gary

[Rick Butler]

Melvin,

 

The main reason that I like using a relay to power a circuit (extra lights, horns, etc) is for the switching element of the circuit.....especially when you have a set of handlebar switches (especially the one that mounts on the reservoir cover) like you have installed.

 

Like any automotive accessory relay, you use the correct size wire for the accessory you are powering for posts 30 and 87 (power in and power out). Then on the coil switching posts 85 and 86, you can use smaller wire because the coil only pulls milliamps. So, this means you can run a very small wire for the switch. I usually use a dual conductor 22 guage speaker wire to switch the ground wire from post 85. This way you don't have a wire with current going to a switch and you can use one of the two wires to go from post 85 on the relay to one side of the switch and the other to go back to ground on the frame. This just makes for a much simplier and cleaner job (using a set of very small wiring), especially when you have a gang of 4 switches on a handlebar mount.

 

Hope this helps,

 

Rick

[fwbpastor]

Thanks for all the replies. I've just had a hard time getting my brain around the idea or necessity of a relay. I will install a relay today on the bike for the driving lights.

 

Again thanks for all the help.

Melvin

[Carbon_One]

In Gary's drawing I like to put the activating switch between the ground & # 85 post of the relay. Doing this there's no power going thru the switch then. I still use a fused line going to terminal 86.

Larry

[Flyinfool]

In Gary's drawing I like to put the activating switch between the ground & # 85 post of the relay. Doing this there's no power going thru the switch then. I still use a fused line going to terminal 86.

Larry

 

Actually by putting the switch on the ground side of the relay you have increased the potential for a short to ground since more wires will be hot all of the time whether the switch is on or off. If you are using a lighted switch, you then have to run another unswitched power wire for the light again increasing your chances for a short somewhere. Electrically there is no difference as to whether the switch is located on the power side or the ground side of the load. It is still switching the same amps and volts.

 

As far as the voltage drop across the switch contacts, the relay is nothing more than a switch that is moved by a magnet instead of your finger and has the same voltage drop issues.

 

I like Dingy's diagram as the best way to do it if the switch is going on the handle bars since it allows you to have a tiny switch and thin wires to hide. If you are using the switch with no relay you have to run a big enough switch to handle the power and you have to run the big heavy wires for all parts of the circuit.

 

So to answer your original question. A relay is not necessary but is more convenient.

[djh3]

I have been thinking about addig the relay to my fog/driving light system. The way I understand this all I really need to do is run a new larger "hot wire and fuse" line from say the battery to the relay and from relay to the existing light wires. My light bar is already installed and operational. However the wires for this light bar once while doing some other work in the fairing area got moved around and got pinched in the stops for the handlebars. Now I have them tied up out of the way.

[wes0778]

Just my

I even went a step further and not only put my passing lights on a relay, but I put in a second relay for my headlight. This gets more load off of the ignition switch.

Now being safety minded and lacking night vision ability, I wired a toggle switch parallel to the headlight relay, just in the event of a relay failure, I can still have

[BuddyRich]

The higher the current the hotter the contacts get. Best to burn out a relay than an expensive switch. Relays are cheap and that's their job.

[Guest tx2sturgis]

My additional comment is that by using a relay, you divert all that excess current draw around the ignition switch, instead of thru it.

 

The ignition switch is not designed to handle a lot of extra amperage, and by using a relay that sources current directly from the battery, but is triggered by the headlight switch and/or a separate switch, you help to prolong the life of an item that tends to be pain to replace if you burn it out.

 

 

 

[Carbon_One]

Just my

I even went a step further and not only put my passing lights on a relay, but I put in a second relay for my headlight. This gets more load off of the ignition switch.

Now being safety minded and lacking night vision ability, I wired a toggle switch parallel to the headlight relay, just in the event of a relay failure, I can still have

 

I've done the same thing on my bike as well. No secondary bypass switch thou bcause the high beam being on a seperate part of the circut is still operable. Plus I still have driving lights if both should fail.

Larry

[OB-1]

My additional comment is that by using a relay, you divert all that excess current draw around the ignition switch, instead of thru it.

 

The ignition switch is not designed to handle a lot of extra amperage, and by using a relay that sources current directly from the battery, but is triggered by the headlight switch and/or a separate switch, you help to prolong the life of an item that tends to be pain to replace if you burn it out.

 

 

 

 

This is a VERY GOOD REASON to use a relay!

[twigg]

OK I'm sure you are going to get varied opinionson you're question but here's the facts in a nutshell. The main reason to use a relay is to protect the switch that controls the lights. Relays aren't needed for low power lights such as LED's but are a good idea for heavier current drain. Any switch contact is not a perfect zero ohm connection but has a small amount of resistance. The more the current, the more voltage drop occurs across the switch contacts resulting in heat being developed at the contact point. The more the heat, the more the damage to the contacts, the more the voltage drop across the contacts, the more the heat. It's like a snowball efect. Also, as more current goes thru the contacts, the contacts begin to pit because it sort of acts like a mini welder on itself.

 

So, to answer your question, although not necessarily needed. it may be a good idea. Also, it's generally a good idea to run the hot connection directly to the relay coil and switch the ground on and off to prevent the remote chance of 12 volts being shorted to ground thru the switch or the wires...

 

Good post.

 

Add to that ... The extra wiring doesn't help either. The shorter the better and if the switch only has to carry relay switching current, it all helps.

[Guest]

I was thinking of doing a mod to my driving lights anyway. What im planning to do is install a wireless router in the trunk with a WiFi connection at the driving light bracket, then add the "Clapper" on/off switch making it a two clapper on/off light.....no more switches and relays to burn out. It will all be wireless.............

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[V7Goose]

snip

 

I bought the Kuryakyn Master Cylinder switch and have the hot connected to the Red wire with yellow strip (power on all the time when key is turned on). One of the switch wires I connected to the driving lights.

 

The hot wire to the switch has a 30 amp fuse and the wire going to the lights has a 10 amp fuse.

 

snip

Melvin

Lesson 1: A fuse is designed to protect the WIRE, so it should always be smaller than the maximum safe current for everything in the circuit. That way it will blow before the wire or switch overheats and starts a fire.

 

I have never personally seen that specific switch you have, but I'd bet that the wires to it are very small - probably 20 or 22 AWG. Depending on how LONG the total circuit is, those wires should probably not handle more than 5 amps, or 10 amps MAX, so fuse the input wire accordingly. This is the same reason why the aux power plugs on your bike only come with 5 amp fuses from the factory.

 

Lesson 2: By using a relay to switch the lights on and off, you can safely route much larger wire from the power source to the lights and control them with a small wire and switch mounted on the handlebars.

 

Lesson 3: An electrical circuit is only as safe as the smallest/weakest part of the circuit. So when running a high-amp circuit to power something like driving lights or horn, make sure you tap into the power supply at a safe place that can handle the total current, this includes the current that was ALREADY being drawn by the bike PLUS the new load you are adding. In general, this means you never tap into the existing wires.

Goose

[djh3]

Something I learned on my other bike when running "new" circuits and extra powered wires. When you put the fuse in, get as close to the power source. I ran a circuit on my other bike and it was fused, but I had the fuse up by the handlebars and the wire got a short and melted the insulation before it blew the fuse. It was ugly and took alot of time to repair.

[BuddyRich]

Lesson 1: A fuse is designed to protect the WIRE, so it should always be smaller than the maximum safe current for everything in the circuit. That way it will blow before the wire or switch overheats and starts a fire.

 

 

You may want to rephrase that. The fuse is designed to protect the ENTIRE CIRCUIT . It should be the same size as the weakest component in the circuit. So if you have wire capable of 30 amps but the relay is only a 20 amp relay then use a 20 amp fuse. Quite often the wire can carry more than the components of the circuit.

[dacheedah]

All this talk about limited power makes me want to throw a cooler rack on the back ( one beer required for this task) , then a generator with an auto start function( six pack required for this task), then wire it up to accept enough lights to make any venetian night look lame ( bust out a pony keg). Once completed head to the Venetian Night Lighted Bike Parade and maintenance day party, is that in Oberlin this year ? ? ?

[twigg]

You may want to rephrase that. The fuse is designed to protect the ENTIRE CIRCUIT . It should be the same size as the weakest component in the circuit. So if you have wire capable of 30 amps but the relay is only a 20 amp relay then use a 20 amp fuse. Quite often the wire can carry more than the components of the circuit.

 

He was correct.

 

The fuse is there principally to prevent the wire from melting and causing a fire.

 

Secondary protection is incidental. If individual components require protection, they would normally contain their own fuse.

 

The reason that we use fuses rated lower than the wire capacity is simply that a higher current draw than required by the item is a fault, and the fuse blows .... No need to stress the wire to the max.

[BuddyRich]

I Have been in electronics for 37 years. The purpose of a fuse is to protect the ENTIRE CIRCUIT. Not just the wire.