Larger Battery Bank Wiring Configurations

[Blue Knight]

G'Day All,

I'm seeking some Funster wisdom on my potential battery set-ups for our boat. I won't post this on the boat forum as they are a fairly unforgiving lot to newbies and expect everyone to have a degree in electrical stuff - I don't so here goes:

Specifically to my charging set-up I have an onboard Mastervolt 80A EHU/Shoreline charger and a secondary 110A alternator for the 4 x 110Ah wet Leisure batteries. (The batteries may need replacing though).

My intention is to add a Victron Smart 100/50 MPPT Reg and c.700W of split panel mono solar to the top deck. The panels will be mounted on angled platforms to help maximise the solar efficiency (by 30% over flat panels).

My question relates to the following diagrams in terms of me achieving the best charging/equalization for the batteries etc (I'll be using 12v batteries for now although I may consider the use of 6v Trojans and linking them accordingly).

..........so chaps, which would you consider to be the best industry standard wiring application for the following 4 or 5 battery-sized banks please.

I'm also wondering if you could swap the load wires around a bit so that the two load wires were derived from the two outermost batteries in each of the diagrams below.

Any help/input would be much appreciated.

All the best,

Andrew

1. 5 x 12v battery bank (replace the starter battery with a 5th leisure batt).

2. 4 x 12v battery bank albeit the inverter and solar symbols are missing from this diagram:

 

[autorouter]

The idea is to make the total length of the wire to each battery equal.

The 4-battery diagram is fine. Imagine just the top pair of the 4-battery diagram. The lengths would be exactly equal. Wire the second pair in the same way. Now wire the pair of pairs in the same style. Again the wire length to each battery is about equal. This method works for 2, 4, 8 and so on.

Unfortunately it's not so good for other numbers, like 5 for example. One possibility is to run equal lengths from the isolator to each battery positive. If you are using a monitoring shunt in the negative wire, this can be wired as a common point for equal lengths on the negative side. If not, use a distribution post or busbar. This method works for any number of batteries.

Also it's best to connect loads, inverter and solar to the same points. If you've gone to the trouble of equalising the lengths, you can use those equal lengths for everything.

 

[Raul]

Why bother with four 12v blocks and four parallels when you could pick the capacity in L16’s cases and have a single string? Or at least two parallels of t105, or t125’s?. Less cables, less connection points and certainly less Cells to water.
Failing that, as autorouter says, The best option is equal lengths of interconnects to a buss bar or stud, and all loads and charging from that single point. Expect imbalance and frequent equalising at four parallels. Once SG( specific gravity) drifts over 0,015 between cells, needs equalising. I just watered and equalised my house bank, and it took 2hrs at 62v (48v nominal) to bring SG at 1,265. It drifted by 0,020 and is a single string of 6v L16 cases, 4,5years old. For longevity is important if you can do without paralleling.

 

[Blue Knight]

The idea is to make the total length of the wire to each battery equal.

The 4-battery diagram is fine. Imagine just the top pair of the 4-battery diagram. The lengths would be exactly equal. Wire the second pair in the same way. Now wire the pair of pairs in the same style. Again the wire length to each battery is about equal. This method works for 2, 4, 8 and so on.

Unfortunately it's not so good for other numbers, like 5 for example. One possibility is to run equal lengths from the isolator to each battery positive. If you are using a monitoring shunt in the negative wire, this can be wired as a common point for equal lengths on the negative side. If not, use a distribution post or busbar. This method works for any number of batteries.

Also it's best to connect loads, inverter and solar to the same points. If you've gone to the trouble of equalising the lengths, you can use those equal lengths for everything.

Nicely explained and incredibly useful. The busbar was an option to keep things simple but if I do opt for the 4 x 12v bank then your explanation nails it.

All the best,

Andrew

 

[Blue Knight]

Why bother with four 12v blocks and four parallels when you could pick the capacity in L16’s cases and have a single string? Or at least two parallels of t105, or t125’s?. Less cables, less connection points and certainly less Cells to water.
Failing that, as autorouter says, The best option is equal lengths of interconnects to a buss bar or stud, and all loads and charging from that single point. Expect imbalance and frequent equalising at four parallels. Once SG( specific gravity) drifts over 0,015 between cells, needs equalising. I just watered and equalised my house bank, and it took 2hrs at 62v (48v nominal) to bring SG at 1,265. It drifted by 0,020 and is a single string of 6v L16 cases, 4,5years old. For longevity is important if you can do without paralleling.

Funny you should say that Raul as the Trojan T-105 battery bank in two parallels sounds like an excellent option and one which seems to deliver excellent capacity for the £.

Tayna are doing good deals on 4 x T105s at the moment so definitely worth considering.

The only noticeable difference that I've seen for the T-105 and the T-125 is the 'C20' of 225Ah v 240Ah. The T-105's do seem to be a very popular choice though.

Many thanks for a great post-up.

All the best,

Andrew

^{_{Subscribers  do not see these advertisements}}

 

[Raul]

The T125 have thicker plates and better charge/discharge rates, also slight better water reserve. I fitted four at my brothers cabin, on a 24v system, over two years ago and they serve very well. If you got the space, I would go for the t125’s. Saying that the t105 are a legendary well tried and tested , with good to very good results.

 

[TheBig1]

One issue with a single (or wired as) battery bank, is one cell fails and takes out the entire bank of batteries. 2 matching banks would be better for redundancy after failure. Keeps the lights and heat on, even if one battery bank dies suddenly. Very important with boats

 

[Raul]

That will only be effective IF, each paralel is fused individually from the pos post to buss bar, or a blocking diode.

 

[Blue Knight]

The T125 have thicker plates and better charge/discharge rates, also slight better water reserve. I fitted four at my brothers cabin, on a 24v system, over two years ago and they serve very well. If you got the space, I would go for the t125’s. Saying that the t105 are a legendary well tried and tested , with good to very good results.

......and at an extra cost of just £40 for the four batteries (over the T-105's) then not bad value either.

Great info BTW - cheers ;-)

Andrew