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What size battery cables?


Psycloud

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Having just re-done my battery bank...

 

Get the biggest you can afford that will fit on your terminals. make them as short as you can get away with without stretching, but, always make sure that matching cables are exactly the same length. I went to a specialist and got all my cables made to measure, expensive, but well worth it.

 

The science is basically, the bigger the cable the lower the resistance therefore reducing losses around the system. Keeping cables the same length balances resistances around the system which helps to balance the loads. ((or something like that)).

 

HTH

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These guys did me proud - excellent service, good advice over the phone, highly recommended.

 

http://www.barden-uk.com/

 

(No connection, just recommending a company that gets it right)

 

ETA - not entirely sure they do mail order, but I'm sure they would arrange something for you if you asked nicely :)

Edited by lockedout
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PS forgot to add, I think under 25mm2 is a BSS fail but not 100% sure on that.....but you'll be using bigger than that......won't you?

 

That is correct. I looked it up only last week.

 

N

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Consider what you will be using off the batteries! A 3KW inverter will want more cable than a few LED lights left on all day. Any of the above cable sizes will do but check that you can get the connections properly made bad connections waste all the money you spend on heavy copper.

 

Do make sure that the person who is making up the cables is using decent kit. The dies that form the crimped connection should plastically deform the connector and the individual strands into hexagons. This means that each strand is in full contact with its neighbours. I have been in boatyards and asked to borrow crimping tools which I refused to use. One just pressed a spike into the connector and effectively spread all of the strands out.

 

If you are using a crimping tool yourself make sure that you get the right connectors to go with that tool.

 

N

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Do make sure that the person who is making up the cables is using decent kit. The dies that form the crimped connection should plastically deform the connector and the individual strands into hexagons. This means that each strand is in full contact with its neighbours. I have been in boatyards and asked to borrow crimping tools which I refused to use. One just pressed a spike into the connector and effectively spread all of the strands out.

 

If you are using a crimping tool yourself make sure that you get the right connectors to go with that tool.

 

N

 

Belt and Braces...

 

If you have any doubts about the quality of the crimp, you could, carefully fill the crimp with solder. Has the effect of tinning the individual strands as well which helps prevent corrosion in the marine environment, but if the crimp is good and tight (mine all were) and then heatshrink wrapped, probably no point.

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Consider what you will be using off the batteries! A 3KW inverter will want more cable than a few LED lights left on all day. Any of the above cable sizes will do but check that you can get the connections properly made bad connections waste all the money you spend on heavy copper.

That's a fair point about inverters. I did have an inverter connected up to the entire system but recently I removed it. I'm now going back to the traditional D.C. alternator charge system and should be using fairly low wattage loads. For example, last night I was trying to get some idea of the usual wattages on D.C. and find there are bilge pumps that are about 40 watts. Add shower and water pump to that but we're still on far less wattage that an inverter might create (more so on a family boat).

 

As you said, in such a case very large cable isn't necessary so long as it can comfortably handle 100 amps.

 

I think it's a good idea to clean up all the battery clamps as well as make sure the crimping is good. Inner parts of a clamp are known to get grubby and create a lot of resistance.

 

 

 

 

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You are going to be using so little material that cost diferential should not be a consideration as there will be a real trade off in efficiency and longevity, I use only tinned high flex cables for battery and invertor leads and say a 70mm2 1m lead with hydraulicly crimped tinned lugs, heat shrink insulation and insulator caps comes out at less than £25, against probably £15 for plain copper.

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Belt and Braces...

 

If you have any doubts about the quality of the crimp, you could, carefully fill the crimp with solder. Has the effect of tinning the individual strands as well which helps prevent corrosion in the marine environment, but if the crimp is good and tight (mine all were) and then heatshrink wrapped, probably no point.

 

Soldering crimped joints is not acceptable. A fact which was not at all obvious to me when I was first told. The solder wicks up the cable beyond the crimped joint and makes it brittle. In this case the belt works against the braces.

 

N

Edited by Theo
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Soldering crimped joints is not acceptable. A fact which was not at all obvious to me when I was first told. The solder wicks up the cable beyond the crimped joint and makes it brittle. In this case the belt works against the braces.

 

N

Not just unacceptable but on a properly crimped battery cable it should be all but impossible, there should be nowhere for solder to go as the strands are effectively fused. Of corse on a poorly crimped termination it would be possible but as you say, unacceptable. I am no longer allowed to use solder under ISO 13297 issued december 2014, I know that applies to low voltage AC but is just as valid for extra low voltage DC.

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Not just unacceptable but on a properly crimped battery cable it should be all but impossible, there should be nowhere for solder to go as the strands are effectively fused. Of corse on a poorly crimped termination it would be possible but as you say, unacceptable. I am no longer allowed to use solder under ISO 13297 issued december 2014, I know that applies to low voltage AC but is just as valid for extra low voltage DC.

 

I can't remember where I saw the whole soldering a crimped joint thing, it was when I was researching my recent rewire and contemplating making up all of the cable myself, it was probably on youtube somewhere...

 

As it happens I decided against doing it all myself and got a professional to do it for me, you are right the quality of the crimp was so good I probably couldn't have got any solder to wick into the crimp anyway.

 

Certainly worth remembering for the future though.

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I currently have 2 Trojan T105 batteries 6v batteries in a single bank 12v but have 2 more to add to the system. What size cables should I use to join the 2 banks together? They will need to be about 60cm long.

 

Thanks :)

You haven't given the necessary information which is what the maximum charge and discharge current will be. In the absence of knowing that, the short answer is probably 70mm sq since, as said, the cable runs are so short that the cost of the copper is not really that significant.

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