Solar panel connections

[Cloudinspector]

Should positive and negative solar panel connections be at opposite ends of the battery bank or does it not matter?

[Ex- Member]

I'm assuming you're not connecting direct from a solar panel to the battery bank, and are using a controller?

 

Opposite ends of a bank is ok with 2/3 or 4 batteries. When you get to 5 batteries you can come in one each end. so battery 2 and battery 4 There is an excellent guide to battery connecting from Smartgauge

 

here http://www.smartgauge.co.uk/batt_con.html

 

We use the post method with same length cable from battery terms to posts, but only because we fitted a completely new installation. This way is tricky and expensive and the end method you enquired about is only slightly less efficient but much easier to fit.

Edited November 2, 2013 by Julynian

[Paul C]

There's typically 3 ways to connect solar panels:

 

- via an MPPT controller

- via a PWM controller

- directly to the batteries

 

There is a good reason to use a solar controller (first two options), eg efficiency, not overcharging battery, cuts off reverse current at night.

 

With all of these connection styles, the final connection to the battery must be done via at least a fuse or circuit breaker (its in the BSS), but you could put a switch in there too if you wanted. The sensible position for the connection is the battery side of the isolation switch, so that it continues to charge even if your isolation switch is off - depends on how you use your isolation switch though.

[Cloudinspector]

Sorry should have given more info. The panels are connected via an mppt controller and I have connected the leads from that to one end of a bank of 4 batteries. I wasn't sure if they had to be at opposite ends.

[matty40s]

It spreads the charge more evenly across the bank if wired at opposite ends.

take offs and alternator charging cables should also be balanced across the bank.

[Justme]

Every thing you connect to the bats should connect at the same points.

 

Every thing, no exceptions.

 

Where those points are depends on the number of bats in your bank.

[bottle]

First two lines I agree with.

 

Last line I am not sure.

Should positive and negative solar panel connections be at opposite ends of the battery bank or does it not matter?

 

Yes and it does matter.

[Justme]

 

 

Last line I am not sure.

 

 

 

 

Check out the Smartgauge battery FAQ re wiring banks.

 

Opposite ends only works up to I think 4 bats. After that coming in one bat on each end is better but better yet is to bring all the +'s to one master point & all the -'s to another master point & then connect everything from those points.

[bottle]

but the interconnects have to be correct.

 

Just coming in from the end is not the full answer.

 

Yes, connecting to one master point is better/best but even then all cable lengths need to be the same.

[nicknorman]

Diagonal across the battery? Probably doesn't matter. (Shock horror!)

 

If you have inadequate battery interconnect leads / poor connections, and a high current appliance such as a big inverter or alternator, then it does matter.

 

If you have good interconnections and a relatively low current appliance such as a modest solar installation, it doesn't matter.

 

If you have good interconnections and you could connect either way without too much difficulty, you might as well connect diagonally if only to stop those who don't quite understand, from hassling you!

Edited November 3, 2013 by nicknorman

[trackman]

Read Gibbo's website, the Smartgauge one quoted earlier. It shows why it does matter. Even good cables and connections have some resistance , and when high currents are involved even a tiny resistance matters.

With 12V electrical systems it doesn't take that much power demand to give rise to high currents. This is why 24V systems are popular for the DC on larger vessels and commercial craft.

[nicknorman]

Read Gibbo's website, the Smartgauge one quoted earlier. It shows why it does matter. Even good cables and connections have some resistance , and when high currents are involved even a tiny resistance matters.

With 12V electrical systems it doesn't take that much power demand to give rise to high currents. This is why 24V systems are popular for the DC on larger vessels and commercial craft.

Yes I'm familiar with the relevant bits of Gibbo's website. However if I recall correctly it wasn't written following a vision whilst he was atop a mountain many thousands of years a go!

 

As you and I both said, when high currents are involved, tiny resistances matter. However a typical modest solar installation doesn't have what would be called high currents in this context, hence my point that it doesn't matter.

 

Our own installation of 4 x110 batteries, 2.5kw inverter charger and 175A alternator was not wired diagonally at build. It did however have 70mm^2 interconnects with properly crimped connectors. With >100A charging or discharging currents, I was unable to measure any imbalance in the interconnect leads within the resolution of the clamp meter. I was unable to measure any voltage drop between the battery posts using a DVM, that was greater than the noise floor of the DVM - a few millivolts.

 

When challenged on the matter, Gibbo, who is not prone to conceding any points, did admit that it was primarily a problem due to the prevalence of inadequate interconnects on real-world battery banks.

 

Personally I would prefer to expend my energies on having and maintaining adequate interconnects rather than having to make up a longer 70mm cable to achieve the diagonality. Of course, if its easy to wire a new installation diagonally then why not?

 

But giving diagonality an almost mandatory status is a bit like demanding strict obedience to the "not below 50% SoC" mantra. They are good rules of thumb for use in the absence of more specific info, but neither posses god-like qualities!

[Paul C]

There is no reason not to try install battery connection cables as efficiently as possible.

 

However, one would have to make a judgement if their boat already had battery connections which were in good condition but sub-optimal layout, especially with the price of copper. When I added 50mm2 cabling for an inverter to our boat, I used the opportunity to revisit the battery interconnects and go for the diagonal setup, but I shuddered at the cost of the cable (about £90 for 10m of 50mm2, 5m of red & black each).

[Ex- Member]

There is no reason not to try install battery connection cables as efficiently as possible.

 

 

 

Agreed

 

Having completely botched the first B/B I installed resulting in a lead acid battery exploding, " the one I attached both neg and pos charge leads to" I decided to start again and do the job right.

 

A few members including smileypete Nicknorman helped me along with our new set up. So now all the battery terminal connections go to posts made using Brass studding using the same length cables, I recall all these both pos & neg were 16inches or 40cm using 70mm s cable. Nothing else what so ever is connected to the batteries, all connections go to the 10mm posts via battery isolator switch and shunt.

 

The B/B has been in over a year now, 11 months on dry land mains and now approaching 3 months on the water. We really have had no issues at all, I regularly check cables and battery water levels. They've only needed just over a litre of replacement distilled water in over a year and about the ame amount of water per cell, which I reckon is pretty good and hopefully denotes the batteries are balanced, if that's the correct term. With the 740 watt of solar panels giving a good regular charge I'm sure is keeping them happy. even though the sun is now very low in the sky we're keeping the batteries between 50% and 75% and as long as the sun is out still getting up to 40 amps around mid day to 2pm.

 

Also we've only needed to run the engine a total of 13 hours in over 10 weeks. A new 12v diesel generator will be fitted soon as well which will put in a lot more amps into low battery levels than the engine alternator. So our B/B size seems to work well for us too which is another important thing to try and calculate.

 

I would strongly advise anyone building/fitting out a boat to pay particular attention to Batteries and charging regimes and not to skimp on battery quality or installation. It's very easy to be tempted to order cheaper thinner cable & batteries, don't though as it will definitely cost you long term.

 

 

 

 

 

 

 

 

 

 

[smileypete]

With 4 batts they can also be connected with this 'recursive' method:

 

 

Though it means 3 connections to a batt post which isn't as easy as the 'classic ladder'.

 

Or if there's loadsa batts, they could be done like this:

 

The total length of each pair of batt cables being the same.

 

 

With a bank of open batts it can be worth comparing the cell SGs between batts, if all over the place then a carefully and safely done equalisation charge should help.

 

cheers, Pete.

~smpt~

Edited November 3, 2013 by smileypete