battery cable length?

[Graham Nash]

Im in the process of adding some bits and bobs to the electrics on my boat and one of the additions is a second battery. Ive fitted the switch and wired in the main battery to terminal "1," the engine and accessories to "common" and am intending on connecting the leisure battery to terminal "2". All pretty straight forward so far. 

 

The preferred location for the leisure battery is towards the front of the boat, in a small locker. This would require 5M of 16mm (110amp) cable between the switch and the battery (with very similar for the earth).

 

Once again, this (in my tiny mind) seems perfectly fine. However, reading electrical questions on other forums, there are lots of advisers saying that the voltage drop on 5M will be too much???? And it'll put a strain on the engine alternator or it'll not enable charging of the second battery due to the length of the cable! This is obviously Facebook replies, which we all know can range anything between truth and absolute rubbish ..... so, what do the REAL experts say? 

 

Over to you. (and thanks).  

 

Graham

[Alcyone]

20 hours ago, Graham Nash said:

Im in the process of adding some bits and bobs to the electrics on my boat and one of the additions is a second battery. Ive fitted the switch and wired in the main battery to terminal "1," the engine and accessories to "common" and am intending on connecting the leisure battery to terminal "2". All pretty straight forward so far. 

 

The preferred location for the leisure battery is towards the front of the boat, in a small locker. This would require 5M of 16mm (110amp) cable between the switch and the battery (with very similar for the earth).

 

Once again, this (in my tiny mind) seems perfectly fine. However, reading electrical questions on other forums, there are lots of advisers saying that the voltage drop on 5M will be too much???? And it'll put a strain on the engine alternator or it'll not enable charging of the second battery due to the length of the cable! This is obviously Facebook replies, which we all know can range anything between truth and absolute rubbish ..... so, what do the REAL experts say? 

 

Over to you. (and thanks).  

 

Graham

Hi Graham, go to 12 volt planet website who sell everything to do with 12v electrics and also specialise in marine. I’ve just ordered a marine 12v cigarette lighter for the new lamp I’m getting and needed cable, they have a cable size calculator on their site and also help information, you’ll be able to input load, length, voltage then you’ll select cable sqmm and you’ll see a cell going red into green as you select different cable sizes.. you’ll also need the tinned cable for marine but that won’t effect the size 

[Graham Nash]

Thank you Mark. 

Looking at their voltage drop calculator online and checking the alternator spec of my engine it would seem that a 12v 20A alterator charge over 5 met of 16mm cable should be well within tolerance. 

 

Unless anyone knows otherwise? 

[Rob]

I am not understanding what the reason is behind your setup.

Usually, 2 batteries which are designated as starter and leisure use multiple switches (3) with a cross over functionality.

The installation of a auto sensing split charge relay, allows for the leisure to be charged when underway.

Beauty of the above, allows the leisure to be drained when at anchor etc, and will leave you with a full charged starter battery when you head home.

The cross over option, allows you to start the engine via the leisure battery in a flat starter situation. Great redundancy.

The 16mm cable should be sized to allow starting of the engine from 5m away, not charging only.....
The model of outboard, will determine how big that cable really needs to be.

Happy to chat through if you'd like.

R

[Gummage]

The short answer from my engineers “Bolleaux, it’ll be fine!”