Conductors for intermittent duty

[Philrock]

I need to select conductors for a small starter motor. 12 vdc, 125 amps, intermittent duty - same duty cycle as a car starter. Each conductor about 8 feet long. Flexibility and resistance to sunlight desirable. I know the conductors don't need to be rated for continuous duty, but I don't know how they should be sized for intermittent duty. I imagine two separate conductors or two side-by-side conductors, like in a jumper cable, would be better than a cable with an overall jacket, due to heat dissipation considerations. Any suggestions?

 

[VEBill]

I've seen some people crank their car starter continuously until the battery was flat. 20 minutes On followed by 180 minutes Off (awaiting someone to give them a boost) is also '10% duty cycle', but it doesn't offer much in the way of thermal derating. Then again, the stock battery cables survived the abuse just fine...

Sounds like you should follow normal automotive standards.

 

[nbucska]

It may heat up until the plastic can tolerate it
The voltage drop is defined by the motor's and
the battery's min. voltages.

A few simple experiments should help you to decide.
The only thing difficult to calculate is the heat
loss in air vs. wire diameter.


<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032