Vehicle & Technical > Discovery

Can I use a spair switch?

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Big Rich:
Hi

Is this the sort of relay you mean Tim?

Designed with automotive applications in mind, this high power relay is capable of switching loads up to 40A at 12V. Suitable for controlling spotlights, heater systems, wiper motors, compressor driven air horns, tailgate lifts etc. Electrical contact is made with push on 635mm (1/4in.) blade conne...

Or is it too big? What's the best cable to use as well?

Thanks.

Rich

Wanderer:
That'll do you Rich.
All you are after is protecting the wiring and switch when you switch the lights on.
The relay handles the high current without it going through the switch itself and can also cope with any arcing that may take place (or stop it happening) which would burn out your standard switch.

Ed

Wanderer:
Big is usually better by the way. Unless you star talking 600 amp relays :)

Ed

Big Rich:
a.... So that could be why if I use my air horns for more than a min it blows the fuse cus we didn't use the relay's. Thought my mate at the time knew all about it.
 :?
Rich

Wanderer:
The basic idea behind a relay is that you can have it near the battery or the "appliance" so as short a run of cable as possible is possible. Which keeps down volt drop.
Also you can run thinner wires and/or less capable switches. All of the work is done at the relay end. All the switches and wiring for the switch has to do is switch the relay. This needs minimal current.

Early Disco wiring (don't know about later stuff) just isn't capable of running much more than sandard lamps. So even higher rating bulbs in the headlights should have relays used to protect the wiring harness and the lighting switch.

Without a relay you will draw all of the current across the contaacts of the switch and soon wear it out.

Ed.

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