Wiring size guide

[Bevan-L]

Hey could anyone give me some advice on wiring in terms of wire gauge/thickness.

What gauge/thickness would you use for the following:
Headlights
Taillights
Stoplights
Indicators
Alternator wiring.

[R59]

Is this for road going for for racing - the difference being that roadgoing will be for reliability, where racing will be for "it works"

What are the headlights (wattage) and what are the tail lights/stop lights/indicators (bulb/LED?)

What's the alternator rated at, and more importantly - what is the battery capacity (Ah)

[ian_w]

The wire size will depend on the current flow.

Headlights are around 60W, so approx 5 amps each ( at 12V )
Stop / Indicators are 21W, approx 1.75 amps
Taillights are 5W, approx 0.4 amps
Alternator, can be anything from around 40 - 100+ amps.

The current capacity of a wire is very much dependant on its design and the quality of the insulation - its a heat build-up effect. Top spec 'MIL-spec' wire can carry several times the current of cheap wire. Choose the type of wire you want to use and then pick the required size based on the current capacity.

A good source for wire and general automotive wiring bits and bods is: www.vehicle-wiring-products.eu

[phoenix]

Further to what ian_w has said, Vehicle Wiring Products off thinwall insulation cables which have a higher current capacity than cables with thickwall insulation:

http://www.vehicle-wiring-products.e...e/thinwall.php

So, without going to MIL spec, this is probably the best choice cabling for weight/performance. Plus you get multiple coloured wiring - which makes wiring up the car a lot simpler than with the four or five colours available in MIL spec (red, black, white, grey and pink, last time I looked). The insulation on these thinwall cables is 'tougher' than the softer PVC found on the thickwall insulated type.

If you have an electric fan, or an electric HP fuel pump, they will require fairly high current handling - I would use Ref 25. Wiring from the starter switch/button/relay to the starter solenoid also needs this gauge of wire. If you run a windscreen wiper, they can be pretty juicy too (i.e. draw a fairly high current) so unless you know the actual current it draws (and it will draw more as the screen dries than when it is wet or running un-loaded on the bench) use Ref 25 to be on the safe side. Heated rear/front screens also draw a lot of current, so use the appropriate gauge wire if you have one fitted.

For everything else you have listed, including your headlamps but excluding the alternator, the Ref 11 wire is absolutely fine.

For the alternator you will probably need Ref 39, or Ref 50 at the most, as unless you are rallying, or 24 hour racing, I doubt you will draw more than 50 amps from the alternator, whatever it is capable of delivering.

Hope that helps.

[Notso Swift]

Unless he wants to run those "FULLY SIK" subwoofers

[MIdsm]

http://www.rallylights.com/hella/SensibleWiring.aspx

[R59]

When the OP comes back with the answers to the questions that he asked, I can give him my recommendations based on it being either a road car, rally car, or race car.

Personally, I use Wurth's thinwall wire. It's rating is higher than the stuff supplied by VWP (who I do use from time to time). The Wurth product is lighter too, and offered in more choices of colours/colour combinations.

If I were building from scratch, I'd choose LED lights wherever possible. They are much more resilient, as well as being lower power.

The battery to alternator wire - you also need to take the capacity of the battery into account. When a battery is low, it will take a big kick of a charge to start with. Plus it'll also affect the amount of time that the battery takes to charge, and thus how much heat will be generated in the charging lead.

In a commercial application (such as an emergency services vehicle), I'd use the biggest practical csa of wire to minimise volts drop, and to be able to cope with considerable heating.

In a race car situation, a 45A alternator with a 44Ah battery, I'd use 84/030 as a bare minimum, which is rated at 50A. If it were a rally car, I'd go for 126/040, rated at 110A, it'll be as cool as a cucumber, and ensure that the battery is charged well.

14/030 would be suitable for most of the lighting - if you use bulbs. If you use LED's you can drop that to 16/020 (also known as 0.5mm). That goes for race/rally and road.

The headlights - I'd use 14/030 for a race car used in daylight hours only (ie: so they work!), for a rally car or road car, I'd use 28/030 (one run for each lamp) which is rated at 25A. This is mostly to reduce volts-drop over longer runs. The longer the run, the more resistance, the lower the voltage at the lamp = dim bulbs!

And I'd be using HID headlamps too - conversions are pretty cheap now.

If it were a rally car, I'd be running 84/030 to the front panel, direct from the battery, and then have relay's right up there with the headlights to reduce volts drop and to ensure maximum bright lights - especially if you're fitting an occasional light pod.

Just a few pointers.

Then again, I know nothing. I only do it for a living (with things that have blue flashing lights and go neee naaarrr!)

[GORDON STREETER]

Originally Posted by R59

If it were a rally car, I'd be running 84/030 to the front panel, direct from the battery, and then have relay's right up there with the headlights to reduce volts drop and to ensure maximum bright lights - especially if you're fitting an occasional light pod.

Quite right, the times I've seen people putting in high wattage bulbs that just melt dip switches fittings and wiring, when all that is needed is a couple of £5 relays with a decent feed. Amazing difference and legal.

[phoenix]

I thought we were talking about a race car with a couple of 60 watt bulbs here?

I could easily expand on what I have written above - just trying to keep my response relevent to the question posed at the top of the thread....

[Bevan-L]

Originally Posted by R59

Is this for road going for for racing - the difference being that roadgoing will be for reliability, where racing will be for "it works"

What are the headlights (wattage) and what are the tail lights/stop lights/indicators (bulb/LED?)

What's the alternator rated at, and more importantly - what is the battery capacity (Ah)

Sorry been away,

Car is for track racing only, trailered to the track and back
Headlamps are 60w, all lights are bulbs
Alternator is 75A and Battery is a Odyssey PC680 which is 68Ah i believe then??

Cheers

[R59]

OK, so follow the recommendations for the race car wiring, however, you have a 75A alternator, and a 68Ah battery, so I'd go for the (as per rally car) larger rating on the charge cable.

You can go for the "hefty" feed to relays for the headlights, as a pair of relays weigh less than the typical length of 3mm wire you "need" for your headlanterns. If you get clever, you can do it with three relays - one to turn it all on/off, the other to switch between dip and main beam (for flashing slower cars when you're racing in the rain).

Where you can, change filament bulbs for LED units, as you can reduce the wire rating dramatically - and thus save weight.

Always use automotive grade thinwall wire. It's flame retardant to a different (better) standard to normal "switch wire". I definitely recommend you try to find someone to supply you with Wurth's brand, it's soooo much better quality.

[phoenix]

Originally Posted by Bevan-L

Sorry been away,

Car is for track racing only, trailered to the track and back
Headlamps are 60w, all lights are bulbs
Alternator is 75A and Battery is a Odyssey PC680 which is 68Ah i believe then??

Cheers

The Odyssey PC680 can supply 680 amps for cranking but is only rated at 16Ah, so it will re-charge to 'full' pretty quickly.

You could save some more weight by running a smaller alternator. 75 amps is much more than you need, judging by the little electric equipment you run with. A 40-45 amp alternator would be plenty big enough. I commonly fitted amp meters to my rally cars, and I have never seen a battery draw a charging current of more than 30 amps even from flat. I hope that you keep the Odyssey fully topped up with a proper charger between races, so the battery will only ever draw a heavy current for a short while after cranking the engine. And if you use a 'slave' battery to start the car, the drain on the Odyssey will be only 50%, so the re-charging time (and initial current) will also be substantially less, so less load on the alternator which will save a little engine power - which is always a good thing.

[R59]

I agree with the slave & out of use charging bit- if you can, fit an Anderson connector somewhere handy so you can easily plug your slave battery in for "cold" starting. it also gives you an easy point to plug in the charger.

[Bevan-L]

thanks heaps for all the advice. will be using a slave battery for starting etc.


now the question.... where can i obtain thinwall cable in Australia.... anyone from down under know???

B

[R59]

I'm sure that Notso Swift will point you in a better direction......

[Notso Swift]

Actually I think you would be best serverd by EfiOz, I do not know him but I think it is part of his business, www.compsystems.com.au
They are in Melbourne, if he can't help directly he may point you in the right direction.
Other than that the links above, after all with the state of the GBP (Great Brittish Peso) you now get 25% better value (too bad we are backwards against the Euro, though)
There can be a lot of value buying local with the initial direction and follow up information, what seems to be a lttile dearer may save you lots of money and time

[racerkart]

Other option get in touch with Anixter and ask about aviation spec 18AWG wire or just plain 18AWG copper wire (as used by companies such as Leoni and CMR).