Switch amp ratings

[GeorgeHurst]

Hi,

I am adding a few things to my car; reversing light, fog lights etc. and need to wire them up to switches with a warning light for each.

I intend to use a on/off SPST toggle switch, could anyone tell me what amp rating I should be looking for? I have been looking on eBay and have found some that are rated 1.5amps at 250VAC, will this be ok?

Many thanks,
George

[Packedup]

Just run them through relays - All you need to do is spec a relay up to the job and use thick enough wire then

You might also be able to use shorter runs wire to the lamps that way too.

[alex_holden]

I think fog lights are 55W each, so that's about 10A for a pair, and the surge current when you first switch them on is a fair bit higher. A 20A or higher automotive relay would probably be your best bet.

[GeorgeHurst]

Thanks for that.
If I were to get a 20A switch would that remove the need for a relay? The cost would probably work out the same... buying a low amp switch and a relay vs. buying a higher amp switch

[polo2k]

the easy way to do it is using ohms law:
V x A = W (voltage x Ampage = wattage)
which is the same as :
W divided by V = A
-so-
55Watts divided by 12Volts = 4.583...
so there fore if you use 5A rating equipment then i will run 1 spotlight of 55W
double it for 2 meaning 10A

The relay isnt just to save on expensive switching.
If you run 10 Amps into the back of your dash and there is a fault you run the risk of doing a lot of damage. If you use a 0.5A switch and wire, to run a 0.5A relay under the bonnet, then in the case of a fault the damage is lessened. The coil (attached to the switch) and the contacts (connected to highload item e.g. spotlights) are totally independent.
The last benefit is that you can run thinner wire in inhabited areas (the cockpit) making it more discrete
If you want an inexpensive relay & switch then try to get ones like the ones supplied in the kind of air horn kits at halfrauds.
Dont forget that all new wireing directly from the battery (non earthed terminal) must be fused appropriatly. Also any wireing added must not, in any situation, be capeable of overloading the existing fuse (even if you fit a bigger fuse, can the wireing cope?)

Happy wireing let me know if there is anything else i can help with


::EDIT::
(WooHoo 100th post)
::EDIT::

[Packedup]

^^^^^
What he said

[polo2k]

hehe

[Alec]

Hello George,

yes you can use a suitably rated switch and omit the relay. In some ways this is better from a reliability point of view.
I don't agree with Ash that this is more hazardous, as long as the circuit is correctly fused. However a Minor is rather short of fuses so it really will require an additional fuse block.

Have a look at this website:- /www.vehicle-wiring-products.eu/VWP-onli ... mepage.php

You can buy cable with the correct colour coding and rating for whatever you wish to install, switches, relays, fuses and looming tape (non adhesive PVC tape) to make a neat job of any wiring.

Incidentally ohms law is the relationship between current, voltage and resistance. (I=V/R)

Alec

[GeorgeHurst]

Thanks to you all, most helpful.