parallel batteries

[hisw]

Hi, after some wiring advice. Does it matter if the + and - that go to the system come off the same battery or should it be at either end of the bank?

Also if I connect a mains charger can this go on to one battery, be it at the end of the bank or the middle or should it go at either end of the bank?

I hope that makes sense

Thanks in advance

 

[VicS]

The with two batteries in parallel the positive connection should really be made to one and the negative connection to the other.
As shown here:

For small loads it would be unlikely to matter. For big loads like engine starting, bowthrusters, winches perhaps more important. Likewise for charging currents ...but possibly even less important.

 

[Bosun Higgs]

Assuming the links between batteries are shortish and of decent wire - in other words of low resistance - it doesnt matter at all. If they are long connections or poor wire then take the feed off one battery and parallel the others to it.

 

[vyv_cox]

Hi, after some wiring advice. Does it matter if the + and - that go to the system come off the same battery or should it be at either end of the bank?

Also if I connect a mains charger can this go on to one battery, be it at the end of the bank or the middle or should it go at either end of the bank?

I hope that makes sense

Thanks in advance

A website was posted earlier in the year giving good information about this topic. Unfortunately I forgot to save it but I remember the details as I was about to change my installation.

For two batteries, just as VicS has shown. For more than two, let's say three in parallel, take + and - from the central one and connect the other two using shortest wire possible. The website said that if you took the connections from the end battery it would see a disproportionate amount of work whereas the far end one would see very little. Same applies to your charger connections.

 

[VARNE]

All clear at www.smartguage.co.uk under "tech info."

 

[VARNE]

Sorry ---Can't spell !
Try www.smartgauge.co.uk
Then "Tech. info." then "Interconnecting batteries"

 

[philip_stevens]

Try www.smartgauge.co.uk
Then "Tech. info." then "Interconnecting batteries"

(in page 2)


Couldn't be more specific

That answers all questions on connecting, with facts and figures.

 

[VicS]

Thanks Philip and lizdu, I could not remember where I got the info from.

Direct link to the relevant bit http://www.smartgauge.co.uk/batt_con.html

 

[vyv_cox]

Sorry ---Can't spell !
Try www.smartgauge.co.uk
Then "Tech. info." then "Interconnecting batteries"

That's the one, thanks. I have saved it this time.

 

[Bosun Higgs]

Anyone tried to work out the maths of this? It doesnt sound right to me but the brain wont work this evening and I get hopelessly lost.

Way I see it, the initial larger draw on battery 1 would cause a voltage drop but as soon as that battery gets to 12.63 v and the second battery to 12.66v then the draw from all three is equal.

 

[NealB]

Anyone tried to work out the maths of this? It doesnt sound right to me but the brain wont work this evening and I get hopelessly lost.

Hi Bosun,

Did you look at the smartgauge link? They explain the effect there.

 

[Bosun Higgs]

Yes , it's the link that I'm referring to. He doesnt give the maths and my guess was that the figures he quoted ( which were too high a current for a boat anyway) were initial numbers. So I tried to do the maths myself and failed miserably.

Will try again in the morning when the brain might work - or most likely wont.

Bloody sad - times were when I would have cruised through this sort of question. Now I have trouble with the fingers on one hand.

 

[Fekosa]

You may find these links useful..

Two pdf documents covering 12v and 24v bank wiring. For a very well balanced connection.
http://www.solar-wind.co.uk/solar-pv-battery-wiring-diagrams.html

Additionally, this also may be useful to some. Cable sizing for low voltage DC systems to minimise voltage losses.
http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

 

[hisw]

Thanks for the help. Option 4 looks like a brain teaser. Just trying to workout how to use the method for 6 battreys!

 

[gavin_lacey]

VicS diagram is spot on. If there are more batteries then same principle applies. Wired any other way then the batteries will not share load or charge equally. They will as a result age unequally and the most loaded and charged will fail prematurly. VYV your suggestion will cause the centre battery to die long before the others.

 

[vyv_cox]

VicS diagram is spot on. If there are more batteries then same principle applies. Wired any other way then the batteries will not share load or charge equally. They will as a result age unequally and the most loaded and charged will fail prematurly. VYV your suggestion will cause the centre battery to die long before the others.

Not according to the link given above. Not my suggestion anyway, just regurgitating theirs.

 

[VicS]

VicS diagram is spot on

Not according to the link given above.

My diagram is not particularly well drawn. I'll replace it with a better one one day.

It is intended to show that with just two batteries in parallel the positive supply cable is connected to one of them and the negative to the other.

That is perfectly correct for just two batteries, Once you go to more than two the situation becomes more complex as illustrated on the Smartgauge website.

 

[vyv_cox]

My diagram is not particularly well drawn. I'll replace it with a better one one day.

It is intended to show that with just two batteries in parallel the positive supply cable is connected to one of them and the negative to the other.

That is perfectly correct for just two batteries, Once you go to more than two the situation becomes more complex as illustrated on the Smartgauge website.

Not criticising your diagram or information, just the statement that connecting three in the way described by Smartgauge would lead to excessive loading of the centre one.