hey all,

i'm not sure what size of fuse to use with my aftermarket driving and fog lights . . .

i have 2 relays - (1 per pair of lights), so one relay powers 2 lights. each light is 100w each.

i have an inline ATO fuse-holder between positive power and each relay.

i think that should be enough info - what size fuse should i be running in the fuse-holders?

 

10 amps should suffice, 20 if you want to be overly cautious

 

did you guess those numbers? or calculate them?

fuse size calculation is wattage / voltage, correct? so do i take 200w or just 100w?

also, i think you have it backwards pind - 20 should be suffice and the 10 would mean being overly cautious . . . (would blow sooner)

 

you should use a 20amp fuse or technically you are using 16.6amps, keep in mind you need wiring to support 20amps but wiring guage is not too critical for 2-100watt bulbs, 14g should be fine.

watts / volts = amps
amps x volts = watts

you have...
200w / 12v = 16.6A

other examples below
10amp x 12v = 120watts
20amp x 12v = 240watts.

 

sounds like 20 it is then, thanx guys.

BTW - i am using 12g wire for my power and grounds - and 16g to trigger the relays (i'm sure 18g for relays is fine, but smallest i had was 16g)

 

I am trying to recall the calculations for series circuits vs parallel circuits here, and having trouble with it.

That said, all my 100 watt light sets, wired in parallel, as they normally are, use 10 amp fuses. I've been running them that way for 20+ years, and haven't had any trouble so far.

I guess I'm really lucky, or God looks out for drunks and fools... Take your pick.

Good luck with the lighting, anything is better than stock.