Spot light wiring/relay question

[Alex Laidlaw]

I am wiring up spots onto a road car. In order to have them coming on with the main beam only is it OK to put the cars standard main beam wire (with full current for standard 55W headlights) through the low current/switching side of a standard 30A automotive relay or will it create a large voltage drop/blow up the relay?

I don't need to put the normal headlights on relays because I don't like being stuck with over bright dipped beams that are rather anti-social and attract plod.

I have tried to show a wiring diagram of what I want to do.

[VIVA GT]

Hi Alex, I'm not sure about your diagram (or your description), but this is how I wired the Super Oscars up when I fitted them to my Viva GT in the 70's:

As you suggest, using a relay with (fused) power directly from the battery, and one side of the switching section of the relay was earthed. I then took a signal wire from the main beam circuit (by adding an extra wire), through a switch, to trigger the switching side of the relay.
(Putting the whole power supply for the main beam headlams as you suggest would not be a good idea in my opinion).
Good luck with it mate.

[Alex Laidlaw]

On second thoughts I think it is an exceptionally bad idea to try and put all that current through a thin coil inside the relay, even if it doesn't burn out I think my normal headlights would have an unacceptable voltage drop. I think I might put the main beams onto relays with direct power as well and use the normal main beam power wire as my signal wire, not terribly neat but at least it gets the job done quickly. I'm rallying on Friday and I had scarily hopeless lighting on the last rally I did!

[oneofapair]

I am no expert on this type of thing but I would of thought that the "Signal" from your Main beam wire will energise the coil in your solenoid/relay to enable the switch part of the solenoid to make contact.The power to your spots will then be supplied direct from battery throught the switch part onto spot lights.

[GORDON STREETER]

Just powering the coil side in a normal relay from the HL wires will cause no problems.
Using relays on normal headlamps improves them no end if they are fitted close to the lamps and stops dip switches buning out.

[AlexH]

Originally Posted by Alex Laidlaw

I am wiring up spots onto a road car. In order to have them coming on with the main beam only is it OK to put the cars standard main beam wire (with full current for standard 55W headlights) through the low current/switching side of a standard 30A automotive relay or will it create a large voltage drop/blow up the relay?

I don't need to put the normal headlights on relays because I don't like being stuck with over bright dipped beams that are rather anti-social and attract plod.

I have tried to show a wiring diagram of what I want to do.

Hi Alex,

If you send me your Email address I will draw a circuit that will work fine with the relay supplying power to the spot lights on full beam. All the best, Alex.

[R59]

OK, standard automotive relay - note the terminal numbers:
Connect 85 to the main beam on your car (via a dash switch if you want),
Connect 86 to ground.
Connect 30 to battery +ve via a 20A fuse (at the battery end).
Connect 87 to your spot lanterns (with the -ve terminal on the spots to battery negative)

Use 4mm wire from the battery to the relay, and from the relay to your spots (and for the ground wire.

You can use 1mm wire for the "signal" wire from the main beam via your switch to the relay.

Use good quality crimp connectors (DO NOT SOLDER!) with a proper ratchet crimp tool.

Any questions?

[terence]

As above but with a Hella relay,they do one with a pullout 20amp Blade Fuse in the body.

[R59]

No no no! ALWAYS fuse at the battery for things like this. If it goes belly up between the battery and the relay, then the fuse blows, rather than the wire burning out (and the car catching fire). I've seen far too many "amateur" wiring jobs go up in flames.

Vehicle manufacturers have cottoned on to much of this these days, take most VAG cars that have a power distribution unit on the battery positive terminal with a bunch of fuses.

[GORDON STREETER]

Originally Posted by R59

I've seen far too many "amateur" wiring jobs go up in flames.

.

The best one I saw was a customer that was trying to fit a child seat belt in an estate car that had a double skinned rear floor. He drilled through it to put in the mounting eye and drilled right through the rear loom and even tightened the eye up
Depending on the application I tend to run the earth to a relay on the coil side via the switch inside. Its easy to do as you don't have to find a suitable + feed. Also if the wire chafes through it doesn't cause any grief.

[thebear]

Originally Posted by Alex Laidlaw

On second thoughts I think it is an exceptionally bad idea to try and put all that current through a thin coil inside the relay, even if it doesn't burn out I think my normal headlights would have an unacceptable voltage drop. I think I might put the main beams onto relays with direct power as well and use the normal main beam power wire as my signal wire, not terribly neat but at least it gets the job done quickly. I'm rallying on Friday and I had scarily hopeless lighting on the last rally I did!

You are mistaken. The voltage/current for the lights goes thru the contacts of the relay, not the coil. The coil only `operates' the contacts.

The wire's route(s) should be as follows:

Battery -> fuse -> lamp -> relay contact(s) - > earth

and

Battery - fuse (1 or 2 amp) or switched side of existing high beam source -> relay coil -> new switch -> earth.

This will allow the new lamp to operate only when the high beams are on as well as when the new switch is operated.

You are `grounding' a device in order to operate it which is contrary to the way residential and industrial wiring is done. However, it is common practice in the automotive world.

- ZOTCH -

[terence]

Originally Posted by R59

No no no! ALWAYS fuse at the battery for things like this. If it goes belly up between the battery and the relay, then the fuse blows, rather than the wire burning out (and the car catching fire). I've seen far too many "amateur" wiring jobs go up in flames.

Vehicle manufacturers have cottoned on to much of this these days, take most VAG cars that have a power distribution unit on the battery positive terminal with a bunch of fuses.

So why do Hella obviously think them to be a good idea?

[R59]

They are a good idea. Don't get me wrong.

My day to day work is emergency services vehicles, and we always switch the positive, with the supplies fused at source (the battery), then split via a distribution & relays to the destination (blue lights, siren, etc...). The relays are controlled by low current switching, whether that's microprocessor controlled, or simple switches on a dash panel.

The Hella fused relays are useful when you have a short supply run, and running a single circuit without the need for a separate fuse box. I'd still feel "safer" with a fused supply (at the battery), or very near to it - smoking wiring ain't no fun!

[terence]

Fairynuf,The Hella version is fused on the live feed side though,thats the only way I would use it,so far,never been a problem.