Adding 2 extra Trojan batteries to my bank

[Southeast Boater]

Hello all! 

 

Im planning on adding 2 extra Trojan batteries to my current battery bank. They’re 6v 240ah in the formation in the attached photo (currently I have 4). I installed them last month to replace the old leisure batteries. 

 

What would be the the best way to connect the next 2 batteries? I’d like them in another series parallel combination to essentially add another 12v 240ah battery to the bank if that makes sense? 

 

Many thanks!  

 

Edited May 9, 2018 by Southeast Boater

[Robbo]

Basically as long as the positive and negative are taken from the opposite batteries and all joining cables are of equal sizes.  If you have high amp loads don't stump on the size of the cables.  (if you had a large inverter like 3kw, I would 90mm2 cable)

 

 

Edited May 9, 2018 by Robbo

[Nickhlx]

To maintain balance between all the pairs, I think you need to have all 3 pairs going to a connecting bar with equal length tails from the positive and negative tails from each pair, then connect to this bank in the middle of this bar.  Gibbo makes reference to this and I will try to edit this post with the link

 

Nick

[Robbo]

9 minutes ago, Nickhlx said:

To maintain balance between all the pairs, I think you need to have all 3 pairs going to a connecting bar with equal length tails from the positive and negative tails from each pair, then connect to this bank in the middle of this bar.  Gibbo makes reference to this and I will try to edit this post with the link

 

Nick

The difference wouldn’t be noticeable in using a bus bar unless you were really anal or use under size cables.

[Nickhlx]

I agree, but a method of connecting 4 tails together mechanically and with adequate insulation whilst being able to carry the potential high levels of current would be needed to be used, and a "busbar" is one such way. There are of course others...

 

Nick

[Robbo]

3 minutes ago, Nickhlx said:

I agree, but a method of connecting 4 tails together mechanically and with adequate insulation whilst being able to carry the potential high levels of current would be needed to be used, and a "busbar" is one such way. There are of course others...

To be honest I think if you get into needing busbars due to the amount of batteries you have then using 2v batteries is the more appropriate way to go.

[MtB]

2 hours ago, Nickhlx said:

To maintain balance between all the pairs, I think you need to have all 3 pairs going to a connecting bar with equal length tails from the positive and negative tails from each pair, then connect to this bank in the middle of this bar.  Gibbo makes reference to this and I will try to edit this post with the link

 

Nick

 

I hold that out here in the Real World, the connection method doesn't make a blind bit of difference*.

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* Provided you use whopping fat cables. 

 

If however, you're planning to use grossly undersized cables, then the interconnect pattern makes a slight difference, but it will be the least of your worries. 

[Southeast Boater]

Thanks all for your responses! I am, and will be sure to use thick enough cables. 

 

I have a further question, what would be the effect of connecting the ground to say the middle set of batteries? 

 

Like so...

 

 

Edited May 9, 2018 by Southeast Boater

[MtB]

The sky will fall in, as any fule kno... 

 

I think it is more important to consider where on the boat the 'ground' connection is attached. Others will fill in the details. 

 

 

[WotEver]

1 hour ago, Southeast Boater said:

what would be the effect of connecting the ground to say the middle set of batteries? 

The consequence is that the current drawn from them would be less balanced. Whether the imbalance would be significant is a different matter but seeing as it’s so easy to connect them ‘correctly’ why bother?

32 minutes ago, Mike the Boilerman said:

I think it is more important to consider where on the boat the 'ground' connection is attached.

On the engine with a good bond to the hull or on the hull with a good bond to the engine. The electrons don’t care. 

[Southeast Boater]

Currently the ground cable is only long enough to reach the middle set of batteries shown on the diagram.

 

I was just trying to ascertain how much difference it would make. If it’s negligible then I don’t have to wire in a new ground cable that’s long enough to reach the other end of the bank. If it isn’t negligible then it’s a bit of extra work.

 

Just wanted to see whether it was a quicker job of connecting another 2 batteries or slightly longer job of also adding a new ground cable!  

[WotEver]

Your choice but if it was my boat I’d do it ‘properly’. It’s not like you’ll have to do it again at some point. 

[Southeast Boater]

Good advice, 2 new batteries and a new ground cable it is. Thanks for you help ?