# Wiring twin leisure batteries



## Mark D (Apr 26, 2011)

When fitting twin batteries with a split charging system is there a correct way to wire them. Obviously they will be wired in parallel but should the charging wire and supply wire go to the same battery or should they be separated.


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## Lorry Ball (Apr 26, 2011)

If its 12volts negative earth
I would put charging wire to one battery + terminal then new red wire to other battery + terminal then to the supply.
I don't think it really matters so long as neat and tidy and that the wires are not chafing any holes they go through. use rubber grommets, I've even used lengths of plastic hose pipe for a tight fit and extra protection for the positive (red) wire.

The battery's negatives - (black/braided wire) , would probably be best to have their own separate connections to the body work (earth).

And make sure connections are clean and tight.

This is just my view of how I would do it  
I'm sure some one on here will reply with more knowledge if I'm completely wrong :goodluck:

(PS my bus is 24v,  2x12v in serial )


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## Neckender (Apr 26, 2011)

On my twin batteries I have the positive connected to 1 battery and the negative conected to the other battery, so you are drawing power from both, if you know what I mean.

John.


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## Mark D (Apr 26, 2011)

trikerman said:


> On my twin batteries I have the positive connected to 1 battery and the negative conected to the other battery, so you are drawing power from both, if you know what I mean.
> 
> John.


 
That would also make it 24v though or do you mean the 2 earths come through the 2nd battery


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## guyd (Apr 26, 2011)

Technically you should do this:-

two wires from both negatives to a single chassis point - NOT from battery to battery then to chassis

Two wires, again, from positives to a single point, then from there join in the charging wire. Sort of like a Y

This way you have even charging, with them in line, one gets charged more than the other (slightly). For the sake of it - do it properly.


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## Mark D (Apr 26, 2011)

Then I suppose you do the same Y arrangement for the fusebox feed, so that both drain equally as well.


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## Tony Lee (Apr 26, 2011)

There are several ways to do it properly but in practice, unless you are going to be drawing more than a few amps and or have stupidly-thin wiring, it isn't going to make a hell of a  lot of difference.

The way usually done is to
 hook battery 1 + to battery 2 +
Hook battery 1 - to Battery 2 -

Hook both incoming and outgoing positive leads to battery 1 +
Hook both incoming and outgoing negative leads to battery 2 -

The other simple method is as suggested by others - run leads exactly the same length from each of the terminal pairs to an external point and make all connections there.

This configuration will alter a bit when fuses are placed in the battery + leads and it is also very bad practice to bring two or three inputs (Solar, mains charger and engine charging) and lots of outputs (one for each circuit) all to the battery terminals because it ends up a rats nest with no proper fuseing or means of isolating the various circuits. Far better to take just one positive and one negative lead from the battery (meaning the battery formed by hooking two smaller batteries together) and make all necessary connections at another point.

As for connecting leisure batteries to chassis. Yes, there needs to be one connection at least to the engine battery negative and thence to chassis but ALL circuits in the habitation section MUST have both negative and positive leads run to each appliance or group of appliances.
Main reason for this is that most store-bought motorhomes don't have any metal anywhere in the house part - and in any case, we all know the hassles that poor earthing of vehicle lights causes and we can certainly do without similar problems in the house.

There is some info on battery connections on the net somewhere. For the peace of mind of any anal-retentives here, I'll see if I can dig it out.

Here it is  http://www.smartgauge.co.uk/batt_con.html    UK company so you can trust what they say.

They are messing around with several batteries connected in parallel and drawing currents of 100 amps to prove their point, but where there are only two in parallel they say "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. "


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## Mark D (Apr 26, 2011)

Mines a van conversion so no problems in running the negs to earth. I'm thinking with the live feeds I'll run a fused link from each pos terminal to a bus bar and then run individual feeds into the fuse box.

I'm also not pulling a lot of power, all I have is 2 strip lights, a 40w tv, a playstation converted to 12v that we use as a DVD player and 2 power sockets for phone charging etc.


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## guyd (Apr 29, 2011)

Tony is right - I was remembering from when I had 4 batteries on my last camper - not really thinking about 2 batteries.

So just take the + from battery A and the - from battery B is good. Worth the discussion to highlight this for anyone in the future tho'.


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## Mark D (May 4, 2011)

guyd said:


> Tony is right - I was remembering from when I had 4 batteries on my last camper - not really thinking about 2 batteries.
> 
> So just take the + from battery A and the - from battery B is good. Worth the discussion to highlight this for anyone in the future tho'.


 
You mention you had four batteries. To complicate things I've just added a third to my setup. Slightly different question now, I'm using a 30amp split charging relay but have a 120amp alternator. Will the single relay now be sufficient with 3 batteries or should I fit a 2nd??


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## Tony Lee (May 4, 2011)

Mark D said:


> You mention you had four batteries. To complicate things I've just added a third to my setup. Slightly different question now, I'm using a 30amp split charging relay but have a 120amp alternator. Will the single relay now be sufficient with 3 batteries or should I fit a 2nd??


 
Unless you are going to be using a 1kWinverter for long periods, no need to worry to much about how they are connected, although using the diagonal method will reduce any imbalance to a reasonable level

Depends on the relay rating mainly and you haven't given us any details so no possible answer. Most stand-alone mechanical relays will be able to handle the extra current but electronics ones may not so best check markings on the relay and/or specification sheet or look them up on the internet. If the relay is incorporated in your power management box then it could well be undersize for more than two batteries.


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## Mark D (May 5, 2011)

The relay is a 30amp electrical smart type that connects to the 2 + terminals and the batteries are 85ah x 3.  I've done a bit of googling and i've found it suggested that they will charge at approx a 10th of their AH rating.  That means it should be around the 25amp area.  In the supply wire from the van battery i'm running 2x25amp fuses (1 at each end) so i suppose the real test will be to see if it blows the fuses.  If it does i think i should be able to use a conventional 60 amp relay and use the feed from the smart relay to energize it, does that sound logical??


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## Bigpeetee (May 6, 2011)

Sounds good, usually the resistance of the cable feeding the leisure batteries result in a current limit unless you use really heavy cable. Best to not let the batts get too low as they can then take an age to charge (the batts try to take a large current, the cable and inline fuse are a resistance so a voltage drop occurs meaning that the voltage at the leisure batts is much lower that at the starter batt so slower charge!!)

If you drive regularly with just an overnight or so then it's not an issue.

To join the leisure batts together, I use the cable sold for meter tails (The thick cable going from the mains input to your house consumer/fuse unit from the meter) Screwfix etc sell this by the metre.

I get a couple of lugs from the local battery shop ans solder them to make sure of a good connection.

I use a dainty cooks blowlamp for this, gives a pencil thin flame to heat the lug and cable and is very portable.

I always put additional insulation on the + cable if it goes near any metalwork. In my case under the seat frame, although the meter tail is a very rigid beast I don't want to risk any short to earth caused by a cable vibrating against an edge. Molten metal and a massive flash is the result!!

Central heating pipe wrap is easily cut, it's already split so will fit over the cable, the rest of it put on your exposed pipes!! if they're underneath the body and exposed to the outside world, use cable ties to restrain.


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## appo (Mar 3, 2016)

Hope you can help guys, 


Looking at putting a second leisure battery in our camper, now i get confused, OK, i can find wiring diagrams, but here is where the confusion begins.

Some people say the same Ah is needed, some even say the same brand of battery is needed and now i also read that both batteries need to be new ??

Confused .

any help would be great.

Thanks


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## oldish hippy (Mar 3, 2016)

Clive`s   here the diagrams


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## trevskoda (Mar 3, 2016)

Bigpeetee said:


> Sounds good, usually the resistance of the cable feeding the leisure batteries result in a current limit unless you use really heavy cable. Best to not let the batts get too low as they can then take an age to charge (the batts try to take a large current, the cable and inline fuse are a resistance so a voltage drop occurs meaning that the voltage at the leisure batts is much lower that at the starter batt so slower charge!!)
> 
> If you drive regularly with just an overnight or so then it's not an issue.
> 
> ...



Would it not be more simple to use these marine clamps at £3.14 ebay


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## Deleted member 56601 (Mar 3, 2016)

trevskoda said:


> Would it not be more simple to use these marine clamps at £3.14 ebay



'orrible flimsy things, threw ours away after one collapsed. Use decent battery terminals with 8mm post.


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## ivecotrucker (Mar 3, 2016)

Appo :

ANY 2 x 12v batteries can be connected in parallel, they don't have to be the same Ah, Make, age or anything else.

But, an older battery will tend to drag down a newer battery due to it's higher internal discharge rate. Also, if the batteries are different in internal resistance, one will always take more charging current than the other, which will always 'piggy-back' & let the better (or lower resistance) battery do more than it's fair share of the work.

So the preferable solution is 2 batteries of similar age & Ah rating. They should of course both be the same TYPE of battery, i.e. wet lead, gel or whatever because they require different charging regimes.

Regards,  Ivecotrucker


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## trevskoda (Mar 3, 2016)

Edina said:


> 'orrible flimsy things, threw ours away after one collapsed. Use decent battery terminals with 8mm post.



Never had any bother with them but there is always a first time.


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## Deleted member 56601 (Mar 3, 2016)

trevskoda said:


> Never had any bother with them but there is always a first time.



They were fitted to a boat we bought and one was not connecting properly, when I pressed down to tighten it, it literally fell to bits. I'd rather have an 8mm post with nut.


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## trevskoda (Mar 3, 2016)

Edina said:


> They were fitted to a boat we bought and one was not connecting properly, when I pressed down to tighten it, it literally fell to bits. I'd rather have an 8mm post with nut.



Thats because you did not put vasoline on it,but never use these on a large outboard with engine management as if they flip of mid flight the electronics will be bu--ered.
There ok for vans & i would not use them if i thought them dodgy.:angel:


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## appo (Mar 3, 2016)

thank you 


ivecotrucker said:


> Appo :
> 
> ANY 2 x 12v batteries can be connected in parallel, they don't have to be the same Ah, Make, age or anything else.
> 
> ...


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## Polar Bear (Mar 4, 2016)

I would not put any pipe insulation around any battery cables as they may get too hot. 

Only need to fit grommets when going through a sharp hole in metal. 

I have a two battery set up in my Hymer and it has three 60 amp fuses protecting them. Each battery has a fuse where it goes into the distribution block and the out lying one has a fuse where it leaves that battery.


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## 1 Cup (Mar 4, 2016)

*while fitting*

Why not make a good jumper lead now. So its good for life. While you have access!
ive put solar pannel connector on them !
You could also do this

 make a ring main so it doubles the ampage of the wire?
Less heat, less waste 

Take good photos so when you sell,  they go with home .


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## 1 Cup (Mar 4, 2016)

*fuses thats act like the wife.*

What will a 60 amp fuse protect?  
I use 5 ,10 ,15 ,  mostly 5 amp?
Am i missing something?  
They don't blow.


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## Chris356 (Mar 4, 2016)

band driver said:


> What will a 60 amp fuse protect?
> I use 5 ,10 ,15 ,  mostly 5 amp?
> Am i missing something?
> They don't blow.


it protects the connection between both of the batteries


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## Polar Bear (Mar 4, 2016)

band driver said:


> What will a 60 amp fuse protect?
> I use 5 ,10 ,15 ,  mostly 5 amp?
> Am i missing something?
> They don't blow.



Just fitted two new batteries and trust me they do blow. I keep spares in the van now.


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