Noobie fitted a relay to my air horns today

[AlexD333]

So after installing my air horns and blowing through two fuses in 2 beeps of the horn I was left with little choice than to fit the relay, not having done Anyang like this before it was a bit daunting. It actually turned out to be ok, hardest part was my crappy 6.99 halfords crimping tool that crimps on the piss

Had a few head scratching moments as to which wire where but all wired up (just)


Oh yeah and wiring in the positive off the battery and then running it through the body holes and touching the chassis.... Whoops.... Lol...


And most importantly, all working, it's loud and comical

Pat on the back for myself

[rustic]

I hope you have fused it correctly, and used cable with a current carrying capacity greater than the fuse rating, or you will be looking at a possible vehicle fire should there be a fault, which could happen at any time, with or without people in the car, or you could drain the battery, and be unable to start it again.

Just because it is only 12 volts, there is enough energy in the battery to melt and set fire to every loom in the car and then more.


So please share you calculations...
What size wire are you using, also type, ie No. of strands etc
What is the fuse rating?
What is the maximum power of the horns hence the maximum current drawn?
What rating is the relay you have used?
On long cable runs, the voltage drop needs to be calculated, have you considered this and used thicker cables?
It's not just the positive feed cable that you need to consider, but also the return wire

[AlexD333]

All wires are reasonably short, the 10a standard fuae is still in place, the cable I think was all 17a, the relay was rated at 30a and the relay and the compressor both have individual earth's.

Longest wire is probably positive to relay, still not long.

[Fez_uk]

Originally Posted by AlexD333

All wires are reasonably short, the 10a standard fuae is still in place, the cable I think was all 17a, the relay was rated at 30a and the relay and the compressor both have individual earth's.

Longest wire is probably positive to relay, still not long.

Is that 10a fuse for the standard horn, If so that means just your trigger wire is fused and not the main supply wire

[AlexD333]

Originally Posted by Fez_uk

Is that 10a fuse for the standard horn, If so that means just your trigger wire is fused and not the main supply wire

There is only one fuse, are you suggesting I need a second on the relay positive?

[emjaybee]

ABSOLUTELY, YES

[rustic]

Originally Posted by AlexD333

There is only one fuse, are you suggesting I need a second on the relay positive?

For goodness sake ...
This is what my post was all about...
You have installed wiring direct to the battery without a protection fuse...

Insurance should be null and void if this is found to be the cause of a total loss.

I don't know about "putting a spanner in your hands and bad things happen"... it looks like any form of tool.

Talking of tools...

And the other thing, those cheap plier type crimp tools should be banned, try pulling the wire from the crimp with a reasonable force, it might just pull out.
I have the ratchet crimp tools that require a minimum crimping force, before the crimp can be released.

Most Auto electricians have been trained in how to use and install the correct cables. Domestic and Commercial electricians also, and they have the kit to test what they have done, do you have a multimeter, if so do you know how to use it? (Properly)...

My first career was an Electronic Engineer, and that involved studying at University and passing exams etc, ok the current carrying capacity of cables was a small part of three years study, but it was essential for calculating PCB design and track size etc. Also component selection, plus a lot more.

You have to ask yourself... are you competent in vehicle wiring, and the answer is clearly no.

[emjaybee]

As an electrician, and someone who has fitted airhorns to most vehicles I have owned, you should ALWAYS fit aftermarket horns via a relay, even electric, even if you are just sticking another original equipment horn along side.

As Rustic said, cables size must be correct and you MUST fuse the air-horn circuit seperately, the standard circuit fuse covers the other piece of wire leading from fusebox-steering wheel-horn, section. Vehicle fire is worse case scenario, also you could slowly destroy your horn push as the higher current will burn out the contacts.

As an aside, when you buy a vehicle don't assume all the fuse are correct rating in the fusebox, my last vehicle T2 '01, nearly went up in smoke as some previous bar-steward had replaced a fuse incorrectly, he had put a 40A in a 10A circuit, had smoke coming out of the dash!

When I buy a vehicle now, first job is to check all circuits are fused correctly.

Lecture over, now, down to business, Dixie? or La-Cucharacha?

[firebobby]

Originally Posted by rustic

I hope you have fused it correctly, and used cable with a current carrying capacity greater than the fuse rating, or you will be looking at a possible vehicle fire should there be a fault, which could happen at any time, with or without people in the car, or you could drain the battery, and be unable to start it again.

Just because it is only 12 volts, there is enough energy in the battery to melt and set fire to every loom in the car and then more.


So please share you calculations...
What size wire are you using, also type, ie No. of strands etc
What is the fuse rating?
What is the maximum power of the horns hence the maximum current drawn?
What rating is the relay you have used?
On long cable runs, the voltage drop needs to be calculated, have you considered this and used thicker cables?
It's not just the positive feed cable that you need to consider, but also the return wire

I had a vision of Alex sat at his desk, studiously raking through volumes of "wire weekly", desperately searching for the information that uncle Rustic was demanding

[Lazy-Ferret]

Originally Posted by firebobby

I had a vision of Alex sat at his desk, studiously raking through volumes of "wire weekly", desperately searching for the information that uncle Rustic was demanding

Hmmm.. did you really use "Alex" and "Studiously" in the same sentence??

That must be up there as one of the best examples of an oxymoron in use ever.

[rustic]

Originally Posted by firebobby

I had a vision of Alex sat at his desk, studiously raking through volumes of "wire weekly", desperately searching for the information that uncle Rustic was demanding

If you know what you are doing, it's fairly basic stuff, I am installing an anchor winch to our boat, and the cable length could be as much as 7m each way, depending on the cable size, I have to calculate the voltage drop, and see if the voltage at the winch is enough to prevent it stalling, having a low voltage can be more damaging than having a high voltage, depending on the application.

(For example, an inverter will have to work harder for the same load, when the supply voltage is lower, as the current in will have to be much greater.
Motors, if on low voltage can stall, or burn out because they are not rotating fast enough, which can also affect the cooling effect.)

I will then compare the actual voltage drop to the calculated value, dependant on the load.

If you want things to be reliable, and not "just" work, then that is what you have to do.

[emjaybee]

I don't think you need worry too much about voltage drop on vehicle electrics, you'd need to do a couple of laps of the vehicle before you had much drop. Cable capacity, relay capacity and correct fuse rating and the main concerns.

[Lazy-Ferret]

Originally Posted by emjaybee

I don't think you need worry too much about voltage drop on vehicle electrics, you'd need to do a couple of laps of the vehicle before you had much drop. Cable capacity, relay capacity and correct fuse rating and the main concerns.

It all depends on how many terminals and connectors there are in the cct as well as the actual wire size and current being drawn.

I know when we were trying to get a decent feed from the car to the caravan I was amazed at just how much voltage drop there was on the "fitted" wiring, which was why I ran some decent sized cables straight from the front of the car to the back and also up rated the cables in the caravan.

When you workout the minimum amount of connections needed to get a cable to a Caravan it was scary, as each one introduces a minute resistance, and at the currents drawn by the fridge and battery charge, they mount up. I think I worked it out that the original wiring ended up with about 50 connections in it.

If you think about it, just from the battery to the output of the first fuse can have 7 joints.

e.g,
Join between Terminal on Battery to Battery terminal clamp
Join from Battery terminal clamp to the terminal on your cable (Assuming you run straight to the battery terminal)
Join from your wire Terminal via the crimp attaching it to the cable
Short length of cable
Join for Cable back to terminal crimp
Join between Terminal pushed onto fuse holder
join between Fuse holder to fuse
The Fuse has a resistance as well
Join from Fuse back to fuse holder output terminal.

Then add in some cheap terminals and crimp tools, making it worse.

With the original wiring, where it went via the cars loom, fuses, plug and sockets, then add in the relays at the back, plus all the joins it goes through between the car and caravan, by the time it got to the fridge, I only had 9.5volts with the engine running. Now I have 3 x 60 amp cable front to rear on the car, separating the fridge, battery and 12v, so get 13.5volts in the caravan.

[Sweety]

Originally Posted by AlexD333

So after installing my air horns and blowing through two fuses in 2 beeps of the horn I was left with little choice than to fit the relay

Told you that from the start & told you which wire went to which pin on a relay