Cable size

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single

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Today i found the copper core of the cables running from the xsplit charger to batteries has a black tarnish. This doesn't look good so i'm replacing them.They are about 10mm2 at the moment, but what size should they be? (4m from xsplit to batteries)
 
I'm not sure how many amps without testing. The alternator is rated 50A so I assumed it just went straight through the X split to whichever battery bank needed it?
 
Hmmm. The website says X split can handle up to 120A, but if the only input is your alternator at 50A then I think you should be looking roughly at 14.5V, 50A, distance 8m. That comes out at 50 mmsq.

Something funny going on, bcs that is about the size of medium jump cables, yet you have been using 10mmsq.


What are the cables like from the alternator to the X Split, pls ? Have they, or the XSplit to batteries, ever got hot to your knowledge ?
 
sarabande said:
Hmmm. The website says X split can handle up to 120A, but if the only input is your alternator at 50A then I think you should be looking roughly at 14.5V, 50A, distance 8m. That comes out at 50 mmsq.

Something funny going on, bcs that is about the size of medium jump cables, yet you have been using 10mmsq.


What are the cables like from the alternator to the X Split, pls ? Have they, or the XSplit to batteries, ever got hot to your knowledge ?
Click to expand...

I agree 50 amps for 8m there and 8m back again works at at something like 50mm²

In reality not often going to get 50amps for long unless battery bank is vast and well discharged so perhaps not unduly worried about some volts drop at 50 amps. 10mm² Ok for 12or 13 amps

10mm² has adequate safety margin for 50 amps as far as max safe current capacity is concerned but up grade to something between 10 and 50 mm² to reduce vols drop would be sensible
20mm² would give no volts drop concerns up to 25 amps.
 
Any volt drop in the feed line to batteries for charging will not be as significant as you ,might think. A volt drop will limit the max charge current into the batteries but not the voltage becuase the resistance means less volts so less current so less volt drop. As soon as the batteries start to reduce their current take in the volt drop resistance thing matters even less. So sure use a decent sized wire but no need to get carried a way with 50 amp stuff. As said tinned copper wire will last longer. However the tarnishing of the wire is only a real problem when you try to solder or reconnect the wire. It does not increase the resitance of the wire itself. good luck olewill
 
sarabande said:
...here's a calculator. Don't forget the distance is there and back.
http://www.solar-wind.co.uk/cable-sizing-DC-cables.html....
Click to expand...
On most on-line calculators like this one the distance is NOT there and back it is only the length from the battery to the load. Most chart based tables use the distance there and back - and they tell you that clearly. If you use this calculator your cable size will be much bigger than you need - but most of these come from battery cable sellers so they win each time, or are they just playing safe!

That is the trouble with this industry, which is why we need Forums like this.

The best calculator I've found is - http://circuitwizard.bluesea.com/ - they make it clear the cable length is there and back, and they do a much better APP that allows you to set feet ot metres etc..

The reason you need to calculate there and back is because there is a voltage drop on both the positive and negative cables. So a one volt drop from a 12.8v battery to a load means there is only 10.8v at the load. And of course voltage drop is important, some systems won't work at 10.8 volts, and charging times will certainly be affected.
 
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Thats why i asked on here really. Depending on which calculator i use, it gives different suggested cable size which always seem massive compared to what you see in reality in most boats. I reckon i would be ok with 16mm2 but i might go for 25mm2 if i'm feeling generous!!
The existing stuff seems to be about 10mm2.
More worrying it the cable running from batteries to EVERYTHING on the boat is only 2.5mm domestic T&E so i'm changing that straight away!
 
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