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Richardcn

Battery rewiring help

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Hi All

Could you give us a bit of advice about re- wiring some batteries please.

My stepson needs new leisure batteries on his new (to him) boat as they are 5/6 year old cheapo's with very little capacity remaining. His current set up is considerably less than optimal and so with the new batteries needs to come a new layout. His current arrangement is:
- Beta JD3 with twin alternators
- 175W Solar (doubling to 350W soon)
- x4 Leisure batts (replacing with x3)
- Single starter battery
- 300W invertor (upgrading to 1600W)
- Continuous cruiser liveaboard

We aim to fit x3 new leisures where before there were x2 leisures and the starter batteries and then put the starter battery behind the side hatch ladder (where the other 2 leisures currently are). There will be all new 70mm2 wiring on the leisure batteries and I'm suggesting that he replaces his isolators with something newer and better.

Everything seems fairly straightforward to me apart from the negative paths. The main alternator -ve goes to a common point on the engine frame (along with the starter -ve) and then onto the starter battery. The additional alternator doesn't appear to have a dedicated -ve so I assume it's using the engine frame and, again, using the (sizeable) -ve cable going to the starter battery.  Thus (it appears that) both alternators and the starter motor use a common negative going solely to the starter battery. What is going to be the best way to deal with the -ve wiring with the proposed new arrangement (or maybe you can see a better alternative for the layout altogether).

Your help would be really appreciated
Hopefully the photos will help.

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Both battery bank negatives shoudl be linked and it looks like they are apart from an additional link cable. So the electricity from either alternator can "find its way back" to the correct bank. 

 

Linking the negatives and having a single negative hull bond ensures minimal danger of hull corrosion while ensuring an electrical fault on either will will cause the relevant fuse/circuit breaker to blow/open.

 

PS Looks like you have sundry supply cables on various positive battery posts. All positives would ideally go to one end of the bank and all negatives to the other.

Edited by Tony Brooks

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8 minutes ago, Tony Brooks said:

Both battery bank negatives shoudl be linked and it looks like they are apart from an additional link cable. So the electricity from either alternator can "find its way back" to the correct bank. 

 

Linking the negatives and having a single negative hull bond ensures minimal danger of hull corrosion while ensuring an electrical fault on either will will cause the relevant fuse/circuit breaker to blow/open.

 

PS Looks like you have sundry supply cables on various positive battery posts. All positives would ideally go to one end of the bank and all negatives to the other.

Thanks Tony. Yes the connections will be 'opposite corners' on the new layout, there was no point in worrying about it until then though given the long cable runs between the current leisures.

 

My problem will be that in putting the 3 leisures neatly together the starter battery will have to be positioned further away off to the side. I can't see how I can stick with a common -ve in that layout

, oh and something I forgot to mention, I have the battery monitor shunt to add into the equation. I need to split the negative somehow I imagine.

 

Richard

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14 minutes ago, Tony Brooks said:

Personally I would just run a long negative between both bank's negatives.

So retain the current arrangement in the proposed new layout by using a longer (common) negative from engine frame to starter battery and an extended link lead from starter to leisure bank. How would I link the shunt though?

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30 minutes ago, Tracy D'arth said:

2 seperate negs, cabin one with shunt in, both back to common hull neg? Too easy? Am i missing something?

Could I 'split' the negative from the engine via a busbar near the batteries (one lead going to starter battery and one to the shunt)? That would save adding another long -ve lead.

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The shunt goes between the domestic negative terminal and the negative lead. Any other domestic negative cables go to the lead end of the shunt.

 

How you deal with the common negative is up to you. Juts make sure the cables used are large enough and that you end up with just one hull negative bond that will serve both banks.

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4 minutes ago, Tony Brooks said:

The shunt goes between the domestic negative terminal and the negative lead. Any other domestic negative cables go to the lead end of the shunt.

 

How you deal with the common negative is up to you. Juts make sure the cables used are large enough and that you end up with just one hull negative bond that will serve both banks.

Okay thanks. I understand how to wire a shunt but given the need to reposition the batteries and also to add the domestic alternator negative to the shunt I wanted to find the 'easiest' way without unnecessary expense. I think I've got it straight in my head now. Take the common negative (I may need a longer lead though) to the starter battery, run a new lead from starter battery to the shunt and then from the shunt to domestic bank. Is that correct? Seems obvious now I say it!

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2 minutes ago, Richardcn said:

Okay thanks. I understand how to wire a shunt but given the need to reposition the batteries and also to add the domestic alternator negative to the shunt I wanted to find the 'easiest' way without unnecessary expense. I think I've got it straight in my head now. Take the common negative (I may need a longer lead though) to the starter battery, run a new lead from starter battery to the shunt and then from the shunt to domestic bank. Is that correct? Seems obvious now I say it!

 

Why? If its all acommon negative the domestic alternator negative is already joined to the cable end of the shunt.

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2 hours ago, Tony Brooks said:

 

Why? If its all acommon negative the domestic alternator negative is already joined to the cable end of the shunt.

The shunt is a recent addition and the domestic alternator does not yet pass through it. The common negative from the engine frame currently goes directly to the starter battery and the domestic bank is linked in at that point. Once the batteries are rearranged that link will no longer exist and, as I see it, I can't take the current common negative to the shunt as it is also the (reverse) path for the starter motor. I'm probably not seeing the obvious or not explaining myself very well so apologises for that, it's been a very busy week so very tired.

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That link in that form will no longer exist if you  remove it and that would not be the correct thing to do.

 

The engine and domestic negatives must be linked, how you do it is up to you. Tracy gives you one way, that is take the engine battery negative and domestic battery negative to the same hull  bond stud so in effect its just one long cable with a join in the middle. I suggested keeping the wiring scheme more or less as it is now but with a single long cable linking the two bank's negatives.

 

You suggested another way that involved a bus bar but as I can not completely understand what you intend I can not comment.

 

The shunt fits between the domestic battery negative and the cable.

 

You must ensure that you have a common negative with a  single bond to the hull although you may have two, one being on the engine and one on the engine bed. That's fine. Lets assume that you maintain the common negative between the two batteries so:

 

The engine alternator sends it charge down the positive charging cable to the engine battery, it flows through the battery and then back via the common negative to the engine alternator negative or the case completing the circuit.

 

The domestic alternator sends its charge down  its positive to the domestic bank positive. Then through the bank and shunt to the common negative cable and then to the domestic alternator negative or case completing the circuit.

 

You may well have current from both alternators passing through one negative cable at a point in the circuit but that is fine so forget about it. Electrons leaving one alternator can only flow back to tat one and no other and likewise for the other one.

 

Why do you not draw it out and work out what goes on.

Edited by Tony Brooks

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Tony, would it be worth drawing a diagram? Often easier to understand than words, especially to non-experts.

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1 minute ago, Graham Davis said:

Tony, would it be worth drawing a diagram? Often easier to understand than words, especially to non-experts.

It would, but to do it satisfactorily takes time and as I am not paid for help on the forum I am not willing to do it. If the OP wants to email me directly and accept the terms and conditions on my website or if he emails Canal Boat or asks on the Canal Boat Forum I will do it happily because I will be paid by the magazine for my time.

  • Greenie 1

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9 minutes ago, Graham Davis said:

Tony, would it be worth drawing a diagram? Often easier to understand than words, especially to non-experts.

I just knocked this up, please check it

Battery connections.jpg

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22 minutes ago, Tony Brooks said:

That link in that form will no longer exist if you  remove it and that would not be the correct thing to do.

 

The engine and domestic negatives must be linked, how you do it is up to you. Tracy gives you one way, that is take the engine battery negative and domestic battery negative to the same hull  bond stud so in effect its just one long cable with a join in the middle. I suggested keeping the wiring scheme more or less as it is now but with a single long cable linking the two bank's negatives.

 

You suggested another way that involved a bus bar but as I can not completely understand what you intend I can not comment.

 

The shunt fits between the domestic battery negative and the cable.

 

You must ensure that you have a common negative with a  single bond to the hull although you may have two, one being on the engine and one on the engine bed. That's fine. Lets assume that you maintain the common negative between the two batteries so:

 

The engine alternator sends it charge down the positive charging cable to the engine battery, it flows through the battery and then back via the common negative to the engine alternator negative or the case completing the circuit.

 

The domestic alternator sends its charge down  its positive to the domestic bank positive. Then through the bank and shunt to the common negative cable and then to the domestic alternator negative or case completing the circuit.

 

You may well have current from both alternators passing through one negative cable at a point in the circuit but that is fine so forget about it. Electrons leaving one alternator can only flow back to tat one and no other and likewise for the other one.

 

Why do you not draw it out and work out what goes on.

Thank you for sticking with me on this Tony. I have it now, it clicked after this more detailed explanation although a diagram probably would have helped earlier on. I'll remember that next time.

 

Many thanks

Richard

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10 minutes ago, ditchcrawler said:

I just knocked this up, please check it

Battery connections.jpg

It is correct but the way the OP was going I think he would have needed the complete charging circuits with alternators and arrows sowing what electrons flowed where. Anyway the important thing is that he seems to have understood now.

  • Greenie 1

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