# Quick Q, battery wiring



## subfiver (Oct 15, 2011)

OK, two leisure batteries, wired in parallel to give 12v.

(1) Should the load/charging circuits be connected to the +ve and -ve of one battery, with the second battery's poles connected to the first battery

OR

(2) Should the load/charging circuits be connected to the +ve pole of one battery and the -ve pole of the second battery, with the other two poles connected to each other. IE the load/charge circuit is connected across the entire battery bank.

Reason I ask is that one of my two leisure batteries failed (6 months old, negligible prior use) during recent three week trip to Outer Hebrides, and they were wired ( by the dealer) as per (1) whereas my I believe my boat's 10 batteries are wired as per (2)

I'm about to replace both batteries, prior to our 5 month winter trip ....


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## Mrplodd (Mar 4, 2008)

I dont think it makes any difference, the wriggly amps will find their way into both batteries whichever way they are wired !

Before I had a van where the solar panel charged both batteries I used to link the leisures to the starter battery with a fly lead and crocdile clips, worked a treat (as per Clive MGTB's diagram)
Andy


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## dolcefarniente (Jan 2, 2012)

No. Strictly plus to plus and neg to neg to achieve 12v parallel. Then connect consumers to plus and neg of one battery. Load will be shared by both. DO NOT series the batteries. you will have 24v.


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## Fatalhud (Mar 3, 2006)

Ive done mine as per option 2

it charges and discharges evenly across the bank and i find the voltage maintains a higher level for longer

option 1 in my opinion has the effect of a master and slave battery and the voltage drop of is a lot quicker

Alan H


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## knothobber (Oct 17, 2006)

Hi, You may find this website informative. http://www.smartgauge.co.uk/batt_con.html
Regards,
Trevor.


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## rayc (Jun 3, 2008)

Fatalhud said:


> Ive done mine as per option 2
> 
> it charges and discharges evenly across the bank and i find the voltage maintains a higher level for longer
> 
> ...


I am not questioning your experience of option 1 but I am trying to understand why. If the connecting links are proper battery linking cables then the resistance and volts drop would be negligible. Both positive poles would be electrically the same place as would both negative terminals.

If the batteries are wired as option 2 if one battery is faulty it will show up as the supply will fail. If they are wired as option 1 then one battery may be failing or failed which will be masked by the other one.


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## Fatalhud (Mar 3, 2006)

Thanks for the link Trevor, Not often i'm barking up the right tree

quoting from article
"Finally, if you only have 2 batteries, then simply linking them together and taking the main feeds from diagonally opposite corners cannot be improved upon"

trial and error got me to connect mine using this method
I originally had my batteries connected with the tap offs coming from just one of the batteries but with the Blow heating on, it would cut out very quickly with the voltage dropping below 10.5v

by taking the terminals to opposite sides it lasts for ages

Alan H


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## HarleyDave (Jul 1, 2007)

In your quoted article, are they talking about 2x batteries linked in series with a single wire from +ve on one to -ve on the other?

If so this would give you 24v across the "diagonal" terminals (assuming a pair of 12v batteries of course...)

If both batteries are linked with 2 wires (+ve to +ve and -ve to -ve) then, as previously advised, they are effectively one large capacity battery and the charging (and take off) should (conventionally) be from the +ve and -ve of the same battery.

Having said that it shouldn't actually make any difference so I don't understand how you found such a difference in capacity??

:? :? 

Cheers

Dave


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## subfiver (Oct 15, 2011)

Thanks, Trevor, for the link to the Smartguage page - I should've looked there myself - I have Smartgauges fitted to both m/h and boat!

I shall follow their advice, viz opt (2) !!


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## dolcefarniente (Jan 2, 2012)

Leave the drugs alone guys...........Option 2 will give 24v and will pop anything connected. Trust me I've been doing this since 1973.


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## dolcefarniente (Jan 2, 2012)

Aha , checked link to see why peeps had said they followed option 2 in the original post. The original post is totally incorrect in it's description of option 2 on the website. As described in the start of the thread it will produce 24v, go to the link and view the diagrams.


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## subfiver (Oct 15, 2011)

dolcefarniente said:


> .........Option 2 will give 24v and will pop anything connected..


No, it won't. The batteries are still wired in parallel. Take a look at the pretty pictures on the smartguage link Trevor posted.

Got thro' a lot of fuses since 1974, have you


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## dolcefarniente (Jan 2, 2012)

Subfiver....... Your original post was incorrect in it's description of option 2. Your description will give 24v. I hope nobody followed it. The diagrams in the link are correct but either way of doing it will not increase reserves if the cable links are heavy enough. I wasn't winding anybody up, I was trying to stop anybody dropping a clanger. :wink:


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## HarleyDave (Jul 1, 2007)

The Smart Gauge info is comprehensive (to put it mildly) but, to my mind, overly complicated for the average MH with 2 or 3 leisure batteries on board.

How often do you anticipate pulling 100A from your leisure batteries?

Cheers

Dave


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## dolcefarniente (Jan 2, 2012)

Hallelujah Dave :roll:


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## HarleyDave (Jul 1, 2007)

8)


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## subfiver (Oct 15, 2011)

dolcefarniente said:


> Subfiver....... Your original post was incorrect in it's description of option 2.:


Poor explanation on my part; I knew what I meant 

The reason I asked the question was because one of an identical pair of batteries has failed - and it was the one that the load/charger is connected to. 
It has had negligible use, but both batteries have been completely flattened, once, by the residual drain that remains even when the circuits are all "off" (I now know to unplug the Schaudt controller too)
The remaining battery appears fine, still, tho' the only means I have of verifying that is a voltmeter atm.

I'm trying to come up with an explanation, and I think that the dealer's wiring was at least part of it.

The vehicle has a (600w, 1500w transient) factory fitted inverter which we have regularly used to power a small hoover. I can't do the sums to convert 230Vac 500w to current draw from the battery - and my Schaudt control unit is a mickey-mouse version that doesn't incorporate an ammeter. A stand-alone ammeter will be installed with the new batteries.


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## selstrom (May 23, 2005)

Your 500w hover will draw approx 40a from your batteries.

The difference between the 2 wiring methods is very small when only 2 batteries are connected and would not cause 1 battery to fail in such a short time.

Chances are the failure is due to a manufacturing fault.


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## dolcefarniente (Jan 2, 2012)

Agree with selstrom but one battery will suffer under that kind of load if the cables linking the batteries aren't heavy enough to allow proper load sharing. 25mm squared cable should cover it (not 25mm diameter). Option 2 diagram still won't overcome the problem of underweight cabling at the links. Hope it makes sense. 8O


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## subfiver (Oct 15, 2011)

dolcefarniente said:


> Agree with selstrom but one battery will suffer under that kind of load if the cables linking the batteries aren't heavy enough to allow proper load sharing. 25mm squared cable should cover it (not 25mm diameter). Option 2 diagram still won't overcome the problem of underweight cabling at the links. Hope it makes sense. 8O


It does.
The cables linking the batteries were substantially smaller than the cables to the inverter and the main fuses. I'll be replacing the clip-on battery connectors with traditional ones so that I can properly terminate appropriately sized cables...


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