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lesrollins
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Not the first.

Second is the most recommended.

Third has some merit. But is probably over complicated, The difficulty arises when wanting to disconnect a battery for individual testing, you have lots of live connectors to control without shorting.

 

I prefer 2 large busbars and separate near equal length cables to each battery.

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19 minutes ago, Mike the Boilerman said:

It doesn't matter a hoot which way you choose, back here in the real world. 

 

:)

 

 

Not very helpful was it?   Your "humour" is not helping the OP one little bit Mike, are you feeling a bit negative of late?

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Just now, Boater Sam said:

Not very helpful was it?   Your "humour" is not helping the OP one little bit Mike, are you feeling a bit negative of late?

 

Actually it wasn't humour, I was serious. It only matters which way you do it if you are using stupidly thin cables.

 

As the batteries approach fully charged, the charge current tends towards zero, so the asymmetrical volt drop caused by a poor wiring format tends towards zero too. Coupled with batteries being consumable items never fully recharged after every discharge in compliance with manufacturers instructions, I can't see that it matters a damn which way they are wired up if the cross links are substantial, say 50mm2 conductors.

 

 

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1 minute ago, Mike the Boilerman said:

 

Actually it wasn't humour, I was serious. It only matters which way you do it if you are using stupidly thin cables.

 

As the batteries approach fully charged, the charge current tends towards zero, so the asymmetrical volt drop caused by a poor wiring format tends towards zero too. Coupled with batteries being consumable items never fully recharged after every discharge in compliance with manufacturers instructions, I can't see that it matters a damn which way they are wired up if the cross links are substantial, say 50mm2 conductors.

 

 

We will have to agree to disagree, my experience suggests that incorrect wiring leads to unequal live spans. Seldom see cables bigger than 25mm as it is just too difficult to work and expensive. 25mm is not stupidly thin either.

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11 minutes ago, Boater Sam said:

We will have to agree to disagree, my experience suggests that incorrect wiring leads to unequal live spans. Seldom see cables bigger than 25mm as it is just too difficult to work and expensive. 25mm is not stupidly thin either.

 

I'm happy to learn and change my mind when a logical explanation arises from discussions. I'd say when you see 'unequal live spans', 25mm is too small for the interconnects, QED. 

 

Can you explain why my Post 12 explaining why it does not matter, is wrong in any way?

 

What is a "unequal live span" anyway?!

 

 

 

Edited by Mike the Boilerman
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The discharge and charge of the batteries will vary if the resistance of the connects is different, hence some batteries will last longer than other because they are effectively not all giving or receiving the same current. I have found this to make a difference to the battery life, small but seemingly positive.

This particularly applies when a large inverter is used. The very slight increase in resistance in the leads to one battery will significantly reduce the current drawn from that battery, but increase the current from the other/s

I get around this by as I said using seperate cables to each battery connected to a commoning busbar. And yes, they are 25mm cables, more than adequate in this installation. After the busbars the cables are short 90mm to the distribution and inverter.

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I would say minor variations in the resistance of the terminations as they grow older is far more significant than the differences in resistance caused by differing lengths of cable. Shall I post up some calculations to show how microscopic the differences are?

 

And even if the more distant battery is getting slightly less charge due to slightly longer cables, surely the opposite effect happens when it discharges. 

 

And I'd say 25mm interconnects with a "large" inverter (3kw perhaps?) are WAY too small!!

 

 

 

 

  • Greenie 1
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55 minutes ago, Mike the Boilerman said:

I would say minor variations in the resistance of the terminations as they grow older is far more significant than the differences in resistance caused by differing lengths of cable. Shall I post up some calculations to show how microscopic the differences are?

 

And even if the more distant battery is getting slightly less charge due to slightly longer cables, surely the opposite effect happens when it discharges. 

 

And I'd say 25mm interconnects with a "large" inverter (3kw perhaps?) are WAY too small!!

 

 

 

 

I have to agree with Mike on all his points.

Between 2005 and 2011, our lumpy water boat had the original 2 'lesiure' lead acids wired to the boat 12V system. I added 3 further lead acids forward of that position with about 6ft of 50mm cable between them. Those batteries were still fine 6 years later when we sold the boat. At least 70% of the original battery capacity. Any inbalance caused by the extra cable didnt show iteslf. We lived aboard for 3 of the 6 years. At that time, I didnt have a clue about the need to get them full every day or so, but did have a battery monitor so did get them back to 100% reasonably reguarly.

On our current boat, when we bought it, it had 3 *110AHr cheapo wet lead acids 6 months old. We put another 3 *110Ahr sealed LA's (dont ask!!!) (the boatyard put on the cheapest they could find). They were put on the opposite swim so again about 6ft of 50mm connecting cable - with no changes to try and balance the feed. At two years old, when we put the lithiums in the system, the 6 batteries were showing 90% of the original capacity (calculated from voltage at rest vs amp hours out - done a number of times at different levels of SoC). The 660Ahrs of capacity was never dropped below 75% and rarely below 80%.....and usually charged back to full (ie low tail current at 14.4V) at least every 48hrs.

Setting them up with different length cables does not seem to have affected them. Very surprised they are still 90%+ given the mix of wet and sealed.

All my batteries and now my lithiums have 50mm cable.

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2 hours ago, Mike the Boilerman said:

 

Actually it wasn't humour, I was serious. It only matters which way you do it if you are using stupidly thin cables.

 

As the batteries approach fully charged, the charge current tends towards zero, so the asymmetrical volt drop caused by a poor wiring format tends towards zero too. Coupled with batteries being consumable items never fully recharged after every discharge in compliance with manufacturers instructions, I can't see that it matters a damn which way they are wired up if the cross links are substantial, say 50mm2 conductors.

 

 

 

I think the symmetrical balanced connection methods are probably more theoretically efficient than real world efficient. But on the other hand why not? Everything has an effect however small and those small effects might accumulate over time. So if you're using expensive batteries rather than 2 year consumables I think it's probably worth doing.

 

Anyway, Gibbo used to talk about the importance of 'balancing' batteries on this forum. I don't know who's right, but I don't see any harm in making the effort.

Edited by blackrose
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Reading different things today and have found that the second option of connection is best as it charges and discharges the batteries equally. Rather than the first option which seems to work the first battery differently because it's the first on the connection. I'm no electrician but just trying to get my head around things and learn what I can before tackling and making changes so all advice is appreciated 

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3 hours ago, Mike the Boilerman said:

I would say minor variations in the resistance of the terminations as they grow older is far more significant than the differences in resistance caused by differing lengths of cable. Shall I post up some calculations to show how microscopic the differences are?

 

And even if the more distant battery is getting slightly less charge due to slightly longer cables, surely the opposite effect happens when it discharges. 

 

And I'd say 25mm interconnects with a "large" inverter (3kw perhaps?) are WAY too small!!

 

 

 

 

Read again Mike, 25mm per battery.

Not arguing the point, its anal anyway.

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5 hours ago, blackrose said:

 

I think the symmetrical balanced connection methods are probably more theoretically efficient than real world efficient. But on the other hand why not? Everything has an effect however small and those small effects might accumulate over time. So if you're using expensive batteries rather than 2 year consumables I think it's probably worth doing.

 

Anyway, Gibbo used to talk about the importance of 'balancing' batteries on this forum. I don't know who's right, but I don't see any harm in making the effort.

Agreed. It’s easy enough to do it to the best standard, so why not?  Chris’s musings on the subject are here btw:

http://www.smartgauge.co.uk/batt_con.html

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4 minutes ago, WotEver said:

Agreed. It’s easy enough to do it to the best standard, so why not?

 

Particularly if you have the gear set up for making cables. Why on earth not make the interlinks out of the same cable as the longer runs? Switching to a smaller CSA means buying a separate batch of smaller cable and terminations, and swapping jaws in the hydraulic crimper. FAR easier and simpler to just press on and make the interlinks out of the same big stuff.

 

 

  

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7 hours ago, Boater Sam said:

... they are 25mm cables, more than adequate in this installation.

Not what one would call ‘large’ or ‘heavy duty’ though. 25mm2 is the minimum size acceptable for the BSS. 

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26 minutes ago, Mike the Boilerman said:

 

Particularly if you have the gear set up for making cables. Why on earth not make the interlinks out of the same cable as the longer runs? Switching to a smaller CSA means buying a separate batch of smaller cable and terminations, and swapping jaws in the hydraulic crimper. FAR easier and simpler to just press on and make the interlinks out of the same big stuff.

 

 

  

I was surprised at how cheap the hydraulic crimpers are. I think I paid £40 and it worked great for the 20 or so crimps I did when sorting out my Lithiums on 50mm cable. The cost of 50mm cable is not cheap though. I think I paid 80 squid (may have been 60) on fleabay for 10M.

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11 hours ago, Dr Bob said:

I was surprised at how cheap the hydraulic crimpers are. I think I paid £40 and it worked great for the 20 or so crimps I did when sorting out my Lithiums on 50mm cable. The cost of 50mm cable is not cheap though. I think I paid 80 squid (may have been 60) on fleabay for 10M.

Looking at Fleabay, there are some very cheap hydraulic ones now. Worthwhile for the occasional use. I bought the sort you hit with a hammer. Seems to work OK.

Incidentally, for those that don't know, the way to get an superscript 2 as in 25mm2 is to use BBCode, which the forum supports. Superscript uses square brackets around the superscript tags each side of the bit you want to format. Very useful when discussing cable sizes and avoids confusion. Like this:

 

 

Screenshot_2019-04-29_10-21-20.png

Edited by Jen-in-Wellies
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