Domestic batteries connection protocol.

[greeny]

Looking at "new to her" boat for a friend and noted that on the Domestic battery setup she has 2 batteries under the quarter berths, one port and one starboard. These are paralleled with hefty battery cables to create the "bank". Ok so far so good. Then I see that the solar panel system is connected to the positive on the stb battery and the negative on the port battery. The 12v main distribution panel is fed from these batteries , positive from the strbd battery and negative from the port battery.
This wiring, like much of the other wiring, is very untidy and the routing of them could be much better. So plan is to do a wiring replacement on these wires and reroute them at the same time.
The question is, what is the perceived wisdom of splitting these feed/supply wiring this way? Is there a real advantage in doing it this way? We would prefer to just take the connections to the port battery as it cuts out a lot of re routing and cable length. With the large battery cable links that are used to parallel the bank I can see no difference electrically to where the feeds are connected. Or am I missing something?

 

[JumbleDuck]

Looking at "new to her" boat for a friend and noted that on the Domestic battery setup she has 2 batteries under the quarter berths, one port and one starboard. These are paralleled with hefty battery cables to create the "bank". Ok so far so good. Then I see that the solar panel system is connected to the positive on the stb battery and the negative on the port battery. The 12v main distribution panel is fed from these batteries , positive from the strbd battery and negative from the port battery.
This wiring, like much of the other wiring, is very untidy and the routing of them could be much better. So plan is to do a wiring replacement on these wires and reroute them at the same time.
The question is, what is the perceived wisdom of splitting these feed/supply wiring this way?

In theory it balances the load on the two batteries by balancing the connection resistances. In practice it makes absolutely stuff-all difference.

 

[VicS]

Looking at "new to her" boat for a friend and noted that on the Domestic battery setup she has 2 batteries under the quarter berths, one port and one starboard. These are paralleled with hefty battery cables to create the "bank". Ok so far so good. Then I see that the solar panel system is connected to the positive on the stb battery and the negative on the port battery. The 12v main distribution panel is fed from these batteries , positive from the strbd battery and negative from the port battery.
This wiring, like much of the other wiring, is very untidy and the routing of them could be much better. So plan is to do a wiring replacement on these wires and reroute them at the same time.
The question is, what is the perceived wisdom of splitting these feed/supply wiring this way? Is there a real advantage in doing it this way? We would prefer to just take the connections to the port battery as it cuts out a lot of re routing and cable length. With the large battery cable links that are used to parallel the bank I can see no difference electrically to where the feeds are connected. Or am I missing something?

As JD says in theory the positive connection ( loads as well as charging) should be made to one battery in the bank and the negative to the other in order to balance voltage drops in the cables

All explained here:
SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

But bear in mind that the author is a liveaboard on a boat with a very heavy duty electrical system. As JD also says it probably makes little difference in a small boat with a modest electrical system especially if the cables are heavy and short.

Info about the author, Chris "Gibbo" Gibson, and his boat here: SmartGauge Electronics - Gibbo's boat

 

[vyv_cox]

I followed the Smartgauge advice on this subject, 3 x 110Ah domestic bank. I really cannot say that it has made an appreciable difference to anything. I guess that it means all three will fail on the same day!

 

[greeny]

Thanks guys, pretty much as I thought. Good for the purist , but in practice will make little difference in this situation.

 

[RichardS]

Thanks guys, pretty much as I thought. Good for the purist , but in practice will make little difference in this situation.

Indeed so. Compared to the peak amps that the main battery cables have to carry in both directions, the amps going in from the solar panels are trivial and balancing is not going to be an issue.

Richard

 

[dankilb]

In practice it makes absolutely stuff-all difference.

it probably makes little difference in a small boat with a modest electrical system especially if the cables are heavy and shor

I really cannot say that it has made an appreciable difference to anything.

in practice will make little difference in this situation

Can I enquire - as it relates to our planned relocation and rewiring of 4 110AH house batts - would this still apply if they were in the same location (a single under-berth box), rather than on opposite sides of the boat as in this setup?

I was planning to follow Graham Mills’ recommendation for a four-battery (plus starter) bank, with the double-length loops connecting the outer batteries: wiring batteries - CanalsOnline Magazine
I know his wiring diagrams are well thought-of, so that was all the research I did and just assumed I had to do it that way!

They’ll be installed all sitting in a row, so short leads from each terminal to its next-door neighbour could simplify things a bit (and I don’t love the idea of battery cables running over/around other terminals if it can be avoided).

sorry to hi jack...!

 

[pvb]

Can I enquire - as it relates to our planned relocation and rewiring of 4 110AH house batts - would this still apply if they were in the same location (a single under-berth box), rather than on opposite sides of the boat as in this setup?

I was planning to follow Graham Mills’ recommendation for a four-battery (plus starter) bank, with the double-length loops connecting the outer batteries: wiring batteries - CanalsOnline Magazine
I know his wiring diagrams are well thought-of, so that was all the research I did and just assumed I had to do it that way!

They’ll be installed all sitting in a row, so short leads from each terminal to its next-door neighbour could simplify things a bit (and I don’t love the idea of battery cables running over/around other terminals if it can be avoided).

sorry to hi jack...!

It's massive complication for minimal benefit. In the real world, you won't see any difference. However, with 4 batteries in parallel in a bank, it is worth making the main positive and negative connections at opposite ends of the bank.

 

[dankilb]

It's massive complication for minimal benefit. In the real world, you won't see any difference. However, with 4 batteries in parallel in a bank, it is worth making the main positive and negative connections at opposite ends of the bank.

Thanks, that’s good to know and makes my life a bit easier, then! In my ignorance it looks like I’ve greatly exaggerated the need for ‘balance’?

Incidentally I had also assumed the main connections would have to be in the middle somewhere (again so it would be balanced). At opposite ends would mean a clear run out of the box - so potentially simpler and even a bit safer.

 

[JumbleDuck]

Can I enquire - as it relates to our planned relocation and rewiring of 4 110AH house batts - would this still apply if they were in the same location (a single under-berth box), rather than on opposite sides of the boat as in this setup?

If you connect the batteries like a ladder, with both connections at one end, the one nearest that end in theory will discharge a wee bit more than those progressively further away, with those at the furthest end doing least. As VicS says, though, it's only an issue with very heavy loads and even then, if you are worried about it, you can always swap the batteries round from time to time in the same way that serious men with pipes and cardigans used to rotate the wheels on their car, just as the Haynes manual said to.

I'd take that canal boat stuff with a pinch of salt. Anyone who refers to links as "loops", introduces voltage drops without explaining them and, apparently, gets them the wrong way round is maybe not a wholly reliable source of advice.

So basically, wire them in whichever way is most physically convenient unless you intend to thrash them with an inverter or electric propulsion.

 

[TernVI]

Battery manufacturers are very clear that batteries in a bank should be treated identically.
Batteries are among those devices that don't naturally 'share'.
If you charge two batteries in parallel, then if one gets a little more current, it warms up and the tempco exaggerates the difference.

Whether it matters in reality probably depends whether you a permanent off-grid animal or a weekend yotty whose batteries will die of old age rather than use.

It gets more interesting if any pulses of current flow and you start to consider inductance.

 

[pvb]

If you charge two batteries in parallel, then if one gets a little more current, it warms up and the tempco exaggerates the difference.

Batteries can only accept current according to their charge state and the voltage applied.

 

[dankilb]

All very interesting stuff. Good to know.

I can see how a canal boat or an off grid setup might lend itself to this level of ‘tinkering’. Higher power demand vs. fewer physical stresses of sailing!

We do run the inverter and it’s not a small one (1500w), but most of the time the batteries are rarely working hard. We inherited a bigger setup than we really need with the boat.

 

[TernVI]

Batteries can only accept current according to their charge state and the voltage applied.

Meaningless wibble.

 

[PaulRainbow]

Meaningless wibble.

On the contrary, your post #11 is just nonsense.

 

[lw395]

On the contrary, your post #11 is just nonsense.

Maybe it's nonsense to someone not very technically qualified, but design engineers would probably understand it.

 

[PaulRainbow]

Maybe it's nonsense to someone not very technically qualified, but design engineers would probably understand it.

rubbish