a few quick questions on wire thickness
omega0684 - 27/10/10 at 06:38 PM
evening all,
i am looking to add in an FIA cut off switch in the car, from my understanding of the wiring diagram i need a cable to run from the battery to one
side of the switch and from the opposite side i need to run 1) a cable to the starter motor, 2)a cable to the ignition barrel and 3) anything else
that i want to run with a perminant 12v. e.g horn.
now im not sure what size cable i need to run for either of the sides of the switch, so can anyone shed any light.
the switch is a 1000amp FIA Approved cut off switch (but im sure the starter won't be using in excess of 1000 amps
)
so what currents should i expect to see in the following wires.
1)from Battery to Cut off switch (During and not during cranking)
2)from the switch to the starter motor (current during cranking, (at a guess 200-300amps???))
3)the size of the cable needed from the switch to the igntion barrel (i would hazard a guess and say 16amp should be fine?)
thanks in advance for any help
Alex
Mr Whippy - 27/10/10 at 06:44 PM
won't be any higher than what's written on the battery
at a guess 350 - 400 amps would be as high as you'd normally expect
sebastiaan - 27/10/10 at 07:04 PM
As a (very) rough guide, you need around 1mm^2 of wire cross-section per 5-10A. No idea how much that is in SWG.
Use 1mm^2 per 5A for continuous loads (lights, etc.) and 1mm^2 per 10A for intermittent loads (horn)
Strontium Dog - 27/10/10 at 07:38 PM
quote:
Originally posted by omega0684
evening all,
i am looking to add in an FIA cut off switch in the car, from my understanding of the wiring diagram i need a cable to run from the battery to one
side of the switch and from the opposite side i need to run 1) a cable to the starter motor, 2)a cable to the ignition barrel and 3) anything else
that i want to run with a perminant 12v. e.g horn.
now im not sure what size cable i need to run for either of the sides of the switch, so can anyone shed any light.
the switch is a 1000amp FIA Approved cut off switch (but im sure the starter won't be using in excess of 1000 amps)
so what currents should i expect to see in the following wires.
1)from Battery to Cut off switch (During and not during cranking)
2)from the switch to the starter motor (current during cranking, (at a guess 200-300amps???))
3)the size of the cable needed from the switch to the igntion barrel (i would hazard a guess and say 16amp should be fine?)
thanks in advance for any help
Alex
You will be fine with 16mm cable from battery and 10mm to alternator IIRC as long as it is not a long run ie. battery in boot, I use welding cable as
it is cheaply available and super flexi for ease of routing!
You may find there is more to it than you have described as the alternator may well back feed and keep the engine running even with the battery
disconnected!
The cranking amps is dependant on the starters rating. The alternator upon it's rated output. Volts/Resistance=Watts and Watts/Volts=amps
You are only cranking for a short time (hopefully) and don't need a cable that is rated to the max current as the duty cycle is so low.
I fuse the battery in my boot at 150A and then a fuse in the bay at 100A. Works fine unless you try to start it in gear! I carry a spare fuse
Many edits as I have a woolly head!
[Edited on 27/10/10 by Strontium Dog]
[Edited on 27/10/10 by Strontium Dog]
Chippy - 27/10/10 at 10:39 PM
Don't know if it's allowed, but the easiest way is to fit the switch in the earth lead, that shuts everything down and it's just one
wire. HTH Ray