what diameter cable for headlights?
blakep82 - 15/3/09 at 03:27 PM
not sure what current they draw. 33amps cable maybe?
are they ok to run one cable (33amp - 3mm sq) up to one light, then jump over to the other, in parallel of course.
dinosaurjuice - 15/3/09 at 03:41 PM
3mm cable is plenty big enough for both.
some people prefer to wire L&R independantly in case of a fuse/wiring failure at night.
blakep82 - 15/3/09 at 03:43 PM
quote:
Originally posted by dinosaurjuice
3mm cable is plenty big enough for both.
some people prefer to wire L&R independantly in case of a fuse/wiring failure at night.
ooh thats a good call! seperate relays too?
what sort of current will they draw though?
and sorry i didn't mean 3mm diamter, i mean 3mm sq
dhutch - 15/3/09 at 04:16 PM
Standard h4 headlights are 60/55w. Which is around 5 amps.
- Assuming that they dont come on dipped/main together thats 10amps for the front too.
The thing your battleing is not over all current limit (before the cable melts) but the voltage drop before its gets to the lights (how dim the lights
are).
- Unlike mains wiring in a house, one or two volts drop is a decent chunk, and with filliment bulbs, the results in a disproportionate loss in
brighness.
So it also depends on the lenght of the total cable run (cheap it short) and how much driving at night you have planned (how much you care!)
Daniel
blakep82 - 15/3/09 at 07:38 PM
10 amps for main lamps? the hella lights i've got at the type where you have a H7 bulb on all the time, it does both main and dip, and a little
flap is what switches it over.
sooo, 2mm sq (25amp) should be fine then? could go to 1mm (16 amp) but seems a bit small)
What affects voltage drop? cable length? or can a diameter too big?
[Edited on 15/3/09 by blakep82]
[Edited on 15/3/09 by blakep82]
dhutch - 15/3/09 at 09:37 PM
quote:
Originally posted by blakep82
10 amps for main lamps? the hella lights i've got at the type where you have a H7 bulb on all the time, it does both main and dip, and a little
flap is what switches it over.
sooo, 2mm sq (25amp) should be fine then? could go to 1mm (16 amp) but seems a bit small)
What affects voltage drop? cable length? or can a diameter too big?
According to wiki the H7 is 55w.
Voltage drop is a factor of cable lenght, and cross section.
- Twice as long, twice the drop.
- Twice the size, half the drop. Etc.
What is an acceptable drop is open to debate but to be honest, to cut a long story short i would have said 2mm^2 was sufficent. And you would
proberbly at that point loose more through the connectors than the wire.
However i would be interested in what others do, and the brightness of my lights in something i keep meaning to look at.
Im geting around a volt lost on the earth, and a 2-3 on the live feed. Resulting in a terminal voltage closer to 10 than 12, or the 14.8 the
alternator is belting out.
Daniel
blakep82 - 15/3/09 at 10:13 PM
cool 
thank for that daniel!
so, just to clarify in my head, ideally the cable should be thick and short?
if i'm looking around 10 amps for my lights (which are essentially always running main beam) 2mm^2 is good for double the current, should be give
less of a voltage drop than 1mm^2 cable?
2mm cable sounds like its up to the job. think i'll probably go for that, and like you say, the connections in the plugs look smaller than 1mm ^1
anyway
so am i good to have 1 relay, splitting to 2 fuses then seperate cables to each light?
or one fuse, as long as i have spares with me? ideally i want to have a compartment in the car with some essential spares anyway. fuses, some spare
relays maybe etc
dhutch - 15/3/09 at 10:56 PM
Again i dont know whats common practice, and have never wired a car from scratch.
Mine appears not to be wired two sided.
- Just sides, dipped, main, paired as you say.
- Actually, run up the right, and onto the left daisychained out of the back of the loom conector to the right side.
I guess again it all depends what your planning to do. Although i dont want to no be able to, im never going to do many miles in the dark, and if the
shit hits the fan im just going to call for my breakdown cover!
Production cars have the right and left tails independly i think, or did, certainly trailers do.
- But certainly on the 306 the two headlamps are wired to the one fuse.
Anyone else any thoughts on this?
Daniel
blakep82 - 15/3/09 at 11:25 PM
i guess i don't plan to do much night driving with it, an i guess in all the 10 years i've been driving, and all the cars i've had (all
older cars) i've only ever had 2 fuses blow. 1 was the radio/clock, not a problem, the other was electric windows, because i tried closing them
both at the same time i think. i often do so was a freak one.
if a keep a box somewhere with a handful of fuses IF i have a fuse go, i can replac it, if it does it again, i call the RAC i guess. then i can rewire
if i decide it blew unreasonably
i've tried searching the internet for wiring examples. the ones i've found, all american, have been wired like yours Daniel. and haynes ones
are a bit too confusing lol
Thank you very much Daniel you've helped a lot. not only helping me with what i didn't know (the current draw on headlights) but also
what i thought i knew (if wiring paired was acceptable or not)
[Edited on 15/3/09 by blakep82]