Battery cable sizing

[JoyceP]

Hello,
Would anybody electrically minded be able to help me size battery cables. I removed everything including the engines and now have two second-hand Perkins 4108 engines with I assume Lucas LSR00189 starter motors. I have new batteries, both Exide ER550 760 CCA and 115Ah. The maximum run from the battery to the engine (via the switch panel) is 8m.
Thanking you in advance.
Perry

 

[David2452]

Assuming a current draw of 200a, 16m round trip (8m x 2) and a voltage drop of around 10% then 50mm2 should cover you.

 

[Nick_H]

Assuming a current draw of 200a, 16m round trip (8m x 2) and a voltage drop of around 10% then 50mm2 should cover you.

10% drop is quite high isn't it, I thought normal target was less than half that?

 

[Solitaire]

Hello,
Would anybody electrically minded be able to help me size battery cables. I removed everything including the engines and now have two second-hand Perkins 4108 engines with I assume Lucas LSR00189 starter motors. I have new batteries, both Exide ER550 760 CCA and 115Ah. The maximum run from the battery to the engine (via the switch panel) is 8m.
Thanking you in advance.
Perry

You don't say where you are based, but call Paul Lawson at MarineTech. 07530 045193. He is a proper marine electrician!

 

[JoyceP]

Thanks, I'm in Yalding, Kent. I've checked ASAP tinned cable and 35mm2 manages 240A, or is that a bit on the limit.

 

[Spi D]

Do you need to run full capacity via the switch panel?

It is common practice to run the heavy wire directly from battery to a relay near the consumer and then control the relay by a (much) lighter dimension wire from the switch panel.

Just a thought.

 

[David2452]

10% drop is quite high isn't it, I thought normal target was less than half that?

No not really, 0400 standards allow 10% drop for things like lighting circuits, motorised kit and the like. 3% for electronics, charging and comms. A very important factor in the equation is a well specified and maintained power bank with a good charging regime.

 

[Trundlebug]

10% drop is quite high isn't it, I thought normal target was less than half that?

Maybe, but it's important to put in a safety factor to allow for age, corrosion, wear and tear, etc etc.
That's what increases reliability.

If everything is designed to run on the limit, the slightest defect means it won't work.
And as we all know, defects are rather common in a marine environment.

FWIW (although I haven't worked it out) 50mm2 sounds right for this application & length.