Different ways to wire multiple batteries

Very informative web site SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank



Cable lengths voltage loss etc


top choice (you can double each if using 6V)

I just have 2 house batteries and one starter battery.
My 2 house batts I run to a 3 way switch, can select combinations that way.
1 house battery to a 3 way switch can also be joined to the other 3 way switch.

Keeps house and starter separate, I keep both house connected always. i then join starter to house with a solenoid and manual switch in series with that. Solenoid comes on with either engines ignition turning on, so really gives me a boost from house to start up. Yet when engines are off isolates the 2 banks. Solenoid allows both alternators to charge all 3 batteries at same time. Been working great for me. I dont need a huge house bank. I do have a 6500 watt generator.
I can sit for hours on the house running the fridge by inverter, and no troubles starting up again.

My philosophy, batteries are all going to fail, and more batteries just means more wasted money. I have lots of cars too, I have bought lots of batteries over a few decades. So I get by with least number that will do the job. All my boat batteries are 12v.

If question is how to connect multiple batteries into a single large house bank, see diagram below - middle option keeps the lengths equa-distant and each battery will undergo similar/same charge (NOTE - battery switches not shown). If goal is how to charge multiple battery banks with multiple sources (alternator, battery charger, solar, etc.), diagram is much more custom.

I would argue that with the close proximity of batteries to one another and the use of adequate sized cable that there are really no measurable losses across the wire, and therefore no real differences between wiring techniques.

ksanders said:

I would argue that with the close proximity of batteries to one another and the use of adequate sized cable that there are really no measurable losses across the wire, and therefore no real differences between wiring techniques.

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According to the SmartGauge website, even the short cables interconnecting the batteries create resistance contributing to inconsistent charging of some of the batteries in the bank.

And a few other things that affect bank performance....


Many discussions about boats dwell on unrealistic "perfect" situations rather than easy and what is good enough....possibly cost effective.

There is some merit to correctly wiring batteries.

If I can get one more season out of a battery bank that lasts 5 to 6 years and cost $600, it would be cost effective. The battery cables get reconfigured once and get the benefit forever. And reconfiguring battery cables is not expensive if you have a crimper and odd lengths of cable.

Assuming it is another year and not another 5 minutes.


Do we have any data for my setup let alone the tens of thousands of different wires, connectors, batteries, switches, etc, etc.?


Sure there "might" be a best set up, but unless the batteries are all in a perfect location, then wire lengths are gonna be different.


Strive for perfection ....I get it.... but I know most boats fall short of that in many ways and they are safe and efficient enough to cmeet standards and carry their owners happily ever after.


Owners should look to see if improvement is an easy, dollar wise task....but not get too excited about it until they really know what they have or don't have in terms of a safe, efficient, cost effective system.

After your battery bank is fully charged, disconnect the interconnecting cables and let sit over night.

Check individual battery voltages and PH the next day and you can see the variations between batteries based on their location in the bank.

I did the test on new batteries. Your results may vary depending on your batteries age.

There may not be a huge difference on charging voltage between "Best" (spoke) vs "Better" (modified daisy-chain) setup. But that's not the only benefit: Use a 5-6 terminal 600 amp bus bar to terminate the cable ends and there is plenty of room to attach additional cables for inverter/charger, battery isolation relay, bilge pump, parallel switches, etc. Its a clean setup and minimizes cable connections on battery posts. All good things.

mvweebles said:

If question is how to connect multiple batteries into a single large house bank, see diagram below - middle option keeps the lengths equa-distant and each battery will undergo similar/same charge (NOTE - battery switches not shown). If goal is how to charge multiple battery banks with multiple sources (alternator, battery charger, solar, etc.), diagram is much more custom.

View attachment 92302

Click to expand...

The central example is excellent and doesn't have the advantage of having two terminal bars that can be used. However, the initial example given by lipets serves the same purpose of keeping all the current paths for each batter equal. This will result in equal charging and equal discharging, just s your central example does.

Nervous folks may chose to simply move the batts to a different position in the string every year or two , while cleaning cable ends,

The middle 'best' diagram doesn't indicate that you also make each cable to each battery the same length. Farthest battery sets the length and the closer batteries just have a little extra cable. This ensures that the connections from bus bar to battery are all the same voltage drop under load and during charging, giving the best possible balance between batteries.

syjos said:

After your battery bank is fully charged, disconnect the interconnecting cables and let sit over night.

Check individual battery voltages and PH the next day and you can see the variations between batteries based on their location in the bank.

I did the test on new batteries. Your results may vary depending on your batteries age.

Click to expand...

As a point of reference:
I recently did this on my 8 year old 4 6V battery bank.
It's wired similar to the "good" diagram above.
There was less than .1 v difference between the 4 batteries.

jleonard said:

As a point of reference:
I recently did this on my 8 year old 4 6V battery bank.
It's wired similar to the "good" diagram above.
There was less than .1 v difference between the 4 batteries.

Click to expand...

That's why your batteries are still good after 8 years.

mvweebles said:

If question is how to connect multiple batteries into a single large house bank, see diagram below - middle option keeps the lengths equa-distant and each battery will undergo similar/same charge (NOTE - battery switches not shown). If goal is how to charge multiple battery banks with multiple sources (alternator, battery charger, solar, etc.), diagram is much more custom.

View attachment 92302

Click to expand...

syjos said:

That's why your batteries are still good after 8 years.

Click to expand...

Is that not contrary to what you expected. Only 0.1 V difference wired as the good diagram is neglible for improvement. What am I missing.

I may pour some gasoline on fire but do you really think that 2 or 3 inches difference of oversized high quality wire will make any difference on battery life?
Don't misunderstand me, this is not bashing on anybody just that some things may be a bit overthought.

L

Lou_tribal said:

I may pour some gasoline on fire but do you really think that 2 or 3 inches difference of oversized high quality wire will make any difference on battery life?
Don't misunderstand me, this is not bashing on anybody just that some things may be a bit overthought.

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My guess is that it would be negligible. However, that is nothing but an ignorant guess. Given my track record, I’d not trust my guesses.

Here is another link to support the previous
https://www.iotaengineering.com/pplib/balancedcharging.pdf

syjos said:

According to the SmartGauge website, even the short cables interconnecting the batteries create resistance contributing to inconsistent charging of some of the batteries in the bank.

Click to expand...

I’m sorry, but here is the math behind it.

4/0 wire has a resistance of .049 ohms per 1000 feet. That means it has a resistance of .000049 ohms per foot.

if you have a 100 amp charging current then the voltage drop per foot is .0049 volts per foot.

If you wire your boat house batteries using a daisy chain technique you are adding maybe a foot or two of cable. Maybe even 5 feet total, but that is a stretch.

That is a tiny difference in voltage drop.

You will get more variation in voltage drop due to differences in torque on the bolts on your battery connectors.

so... Based on my 40 years of hands on experience in the electrical field, including many years of professionally maintaining stationary batteries, and the two week long classes I have attended on the subject...

I respectfully call BS on the whole wiring issue.

It’s not that the folks back at the lab’s intentions are not good, they just do not reflect the reality of boat systems.

Even the photo (see attached) they used is flawed. Their photo represents a four deep parallel battery bank, which is really pretty unusual in a boat.

Generally in a boats house bank we use 6 volt batteries and generally two in series for 12 volts, and two in parallel for capacity. A four battery bank in series and parallel is probably the most common.

Then we have wire sizes. The articles do not indicate voltage drop based on wire size, and almost every house bank I have seen on a boat is wired with 4/0 cable.

I’m not saying the engineers are wrong, I’m saying that their testing criteria does not accurately reflect real world installations in boats.

Most of the battery makers are delighted with a slight overcharge after use. .

If this is done all the batts will be 100% charged , regardless of cable length or position in the string.

The wiring diagrams are for 4 batteries.

Any diagrams for a balanced 3 battery bank?

syjos said:

The wiring diagrams are for 4 batteries.

Any diagrams for a balanced 3 battery bank?

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since I have 6-6volt batteries in 3 sets of 12V I too began to ask that question.
It appears while it can be done physically, no one recommends doing it. In fact in all the balancing info there is always 4-12 volt batteries. (or 8-6V)
This suggests that to balance a system you need an even number of batteries.

Not really...the suggestions are probably just recommending that all batteries see the same charge and discharge voltages/amperages.

ksanders said:

I’m sorry, but here is the math behind it.

It’s not that the folks back at the lab’s intentions are not good, they just do not reflect the reality of boat systems.

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Kevin! Why ruin a good debate with something as silly as Maths!

Your post immediately brought psneed to mind. He often reminds us that there are many ways to do things; bad, perfect, and good enough. (I’m paraphrasing here).

For me, if “good enough” is significantly easier and less work than “perfect”, I’m usually quite happy with it. My two battery thruster bank was wired by the PO in a daisy chain fashion with both. + and - coming off the same battery. Since I haven’t had to mess with those batteries, I haven’t even bothered to do the simple and easy fix to improve it. I’m too lazy. It is good enough for now.

Soo-Valley said:

since I have 6-6volt batteries in 3 sets of 12V I too began to ask that question.
It appears while it can be done physically, no one recommends doing it. In fact in all the balancing info there is always 4-12 volt batteries. (or 8-6V)
This suggests that to balance a system you need an even number of batteries.

Click to expand...

The Best approach works for all configurations - even or odd # battys.

Everything I read to date says even # of batts

Yep..... Make sure you follow that rainbow to the pot of gold where batteries last forever...

Usually because for house 6V GC recommended so always pairs.
Start rarely needs more than 2 if sized properly.

lipets said:

Everything I read to date says even # of batts

Click to expand...

dhays said:

Kevin! Why ruin a good debate with something as silly as Maths!

Your post immediately brought psneed to mind. He often reminds us that there are many ways to do things; bad, perfect, and good enough. (I’m paraphrasing here).

For me, if “good enough” is significantly easier and less work than “perfect”, I’m usually quite happy with it. My two battery thruster bank was wired by the PO in a daisy chain fashion with both. + and - coming off the same battery. Since I haven’t had to mess with those batteries, I haven’t even bothered to do the simple and easy fix to improve it. I’m too lazy. It is good enough for now.

Click to expand...

Thanks!

We seem to debate the minute details of things here on TF. I am not sure why, but I suspect that people are trying to do things that they are unfamiliar with, so they google the issue.

I think that is Wonderful, but we always need to remind ourselves that there a lot of different and very valid ways to do things, and that the difference between “good” and “perfect” is often immeasurable in practical applications.