Starting Current and Cable Gauge

Discussion in 'Outboards' started by CarbonFootprint, Apr 2, 2016.

  1. CarbonFootprint
    Joined: Nov 2009
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    Location: Northern Scotland

    CarbonFootprint Ill-Advised Boat Modifier

    Hello,

    I'm currently plumbing in a Johnson v4 115hp 2-stroke outboard and need to replace the starter cables.

    At present, they're about 9mm/(approx 11/32") diameter including the insulation - the conductors are about 7mm/(approx 9/32") diameter, so I reckon that makes them about AWG 1 and good for about 110A - does this sound likely?

    The current cables are so old, the insulation has started breaking down, so they need replacing, but is the same again the best choice? I need quite a run of cable from the starter batteries to the motor, too - about 5m/16'6" once all the wiggles and bends are taken into account. Does anybody know what the typical starting current of this outboard is?

    Thanks for any guidance :)
     
  2. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

  3. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    The typical starting current is approx. 70 Amps: small starter motors are usually 700 Watts, 10 V arriving at the motor terminals.
    5m is very long for starter cables. If there is no alternative I would use a heavy cable from the battery to a junction box near the engine and a lighter one from there to the engine.
     
  4. CarbonFootprint
    Joined: Nov 2009
    Posts: 60
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    Location: Northern Scotland

    CarbonFootprint Ill-Advised Boat Modifier

    Hello both,

    thanks very much for your advice.

    Based on this calculator, I reckon AWG 3 would result in about a 0.5V drop at the starter at 70A, which sounds reasonable to me. I guess the battery voltage drops from 12V when the starter's connected, though - do you know what a typical cranking voltage would be?

    Thanks :)
     

  5. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    what year is the engine?
     
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