Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Buying 12v electrical wiring: amps?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by mattb, Nov 26, 2008.

  1. Hey All.

    When buying a spool of electrical wire to use on your bike, is there a standard ampage you should look for? I just got one with 5 amps, but there was also 7 and 10am options on the shelf. Is there a universal answer to my question (at least for modern Jap bikes, in this case the GR650)? What happens if it's too little? - I suppose I only blow a fuse... (The GR is notorious for electrical problems, so far mine has been fine, but now I'm messing with things...)

  2. If the wire is too small for the amount of power (current) you are trying to shove down it it will heat up and melt the insulation and if you really go overboard the wire could fail or the heat will set fire to something.
  3. Blowing a fuse wouldn't be the problem. The problem would be NOT blowing a fuse. Eg something drawing 15A with a 15/20A fuse but with 5A wiring, would melt the wiring before the fuse blew.

    That's an example, but you need to ensure that the wiring can handle the load you put through it. Some others could tell you specifics of what sort of loads bike gear pulls, I am used to dealing with car stuff when it comes to electrics :grin:

    Edit: Must have had the thread open for a while before replying...what he said ^ :)
  4. Depends on what you want to do with it...

    I have a couple of 50 amp wires going from my battery to the front for anything i decide i want to put on it...

    5 amps is good for anything that doesn't use more then 60 watts of power (i.e., you could use it for your highbeam, and nothing more, as long as it's a single 55/60W bulb...)
  5. A good rule of thumb is to use the heaviest wire available that will physically fit (within reason).

    Quite apart from potential melting/fire issues if you overload it, too light a wire can result in a fair bit of voltage drop at whatever you're trying to power. Even factory wiring can be a bit marginal sometimes. I've come across situations where a headlamp beam has been improved from a sort of dark brown to a cheerful orange simply by changing the feeble standard cables for something with a bit of cross sectional area. Still couldn't see where I was going worth a damn though :grin: .
  6. Good point, though I've heard that that sort of upgrade can be ineffective unless you upgrade your glasses at the same time :wink: :LOL:
  7. With some of the lamps I've ridden/driven behind, a diet of carrots would have been more use :LOL: .
  8. P=V X A. Where P=watts, V=volts and A =amps. You should have a pretty close idea of the watts being consumed by whatever you are trying to supply current to, the volts are fixed at 12, so quite simple to figure out the current required really
  9. not 12, closer to 14. But I'm just being a dick ;)
    There is not much a 20amp wire wont run on your bike, besides the starter.
    As said above, 5A will run your headlight, or anything with less watts, but if I was to pick a wire to do some spaghetti style wiring to make stuff better, it would be 10A. It is the inbetweener, that will do most things that you need it to, and carry ~15A before it gets cranky enough to melt :)
  10. Thanks for the replies. I took back the 5 amp spool and got a 10 amp one. Most commonly I use the stuff to cut and extend existing wires, whether when fitting a new part with too short a wire or, as in this case, cutting the wires from the bar switch assemblies to add six inches to their length to take higher bars. So I figure exceeding the existing wire's ampage will hurt nothing, while under-doing it might...
  11. Fixed it for you.

    I wouldn't run 15 Amp over a 10 Amp wire continuously, since while it can handle it (if it is a quality wire), that safety margin is there to cover voltage fluctuations or over voltages, like the 14 volts typical output from the alternator Joel mentioned.
  12. Spot on :)
  13. The amperage rating of wire is the MAXIMUM amount of amps recommended to be running through the wire... ie 50% safety factor is cool. Sounds a lot but it isnt.

    W/V=A... or Watts divided by Volts equals Amps. For example; an average automotive (motorcycle) tail light bulb is 5 watts and you can find that marked on the metal part of the bulb. So 5 watts divided by 12 volts equals a measely .42 of an amp. 5 amp wire will do the trick there.

    Many new bikes have LEDs for tail and brake lights(normaly 21watt) The LEDs draw far less current.

    Perhaps you want to put a 130watt bulb in your headlight 130/12=10.8amps If you use 15 amp wire the wire will be warm with the light on... use 20 or 30 amp wire for that application.

    BTW dont forget 2 21watt bulbes etc = 42watts.

    Final point here, make sure you do not exceed the output of your alternator. If you have a service manual for your bike you may be able to find that specification. Current of all electric circuits, including the ignition that run at the same time need to be added. If it exceeds the rated output of the alternator it will go up in smoke. Personaly on this point I would go for a 15% safety factor. You could fudge on the horn and flashers as they dont run all the time. If near the limmit of alternator output I would keep horn blasts short, they draw a lot of current.