Noobie fitted a relay to my air horns today

[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.

[emjaybee]

I say again, "vehicle electrics", rather than ancillary tow-alongs.

[russell.huffer]

Wireing from the battery to the relay my unfused wire touched the chassis.

You should always wire to wards the power source not away, last thing you do is connect the power.

I love following your stories Alex but pray to god you never end up as my next door neighbour.

Kind regards

Russell.