24v Batteries.. Series or Parallel First?

[FlyingCloud1937]

In method 2, you depend on all connections to relay volt/amps to each pair. Which In my opinion will be more then sufficient, unless your series, and parallel cables are at different potentials.

In method three , you still depend on the series cables to be sufficient, but if the parallel cables are high resistance, then you only risk the bats that are in that group.

I typically do up-to 4 bats in parallel in method 2.

I do more then 4 in method 3.

But I start adding switches, and fuses in bats that exceed 3 in parallel.

It depends on the discharge loads, and the charge loads.

The higher the loads, the more likely I will add switches and fuses.

Lloyd

Originally Posted by Pelagic

Thanks Flying Cloud…What a wealth of real life knowledge CF offers, versus theoretical opinions.

So, back to Series First!... and decision to use either Method 2 or Method 3 depending on installation configuration issues

Understand that Method 3 is best and important to keep all branch cables the same length even if it means having longer than needed cables.

However if I can do with significantly less cable in Method 2, is it a better trade-off to accept the slight imbalance of this?

I am also wondering if the Series First connections between each pair would make that Method 2 inequality even less??

[FlyingCloud1937]

The rule of Law, in regarding bats.

Measure the longest series jumper between bats, then make all jumpers the exact same length.

Measure the longest parallel jumper between bats, then make all jumpers the exact same length.

The tails from the bats Pos/Neg to the bus bars can be of different lengths.

Lloyd

Originally Posted by FlyingCloud1937

In method 2, you depend on all connections to relay volt/amps to each pair. Which In my opinion will be more then sufficient, unless your series, and parallel cables are at different potentials.

In method three , you still depend on the series cables to be sufficient, but if the parallel cables are high resistance, then you only risk the bats that are in that group.

I typically do up-to 4 bats in parallel in method 2.

I do more then 4 in method 3.

But I start adding switches, and fuses in bats that exceed 3 in parallel.

It depends on the discharge loads, and the charge loads.

The higher the loads, the more likely I will add switches and fuses.

Lloyd

[Fuss]

Originally Posted by Pelagic

Thanks Flying Cloud…What a wealth of real life knowledge CF offers, versus theoretical opinions.

So, back to Series First!... and decision to use either Method 2 or Method 3 depending on installation configuration issues

Understand that Method 3 is best and important to keep all branch cables the same length even if it means having longer than needed cables.

However if I can do with significantly less cable in Method 2, is it a better trade-off to accept the slight imbalance of this?

I am also wondering if the Series First connections between each pair would make that Method 2 inequality even less??

Myself, I would not be changing anything. It is important to have the same sized (length and thickness) cables between the series connections and the same sized cables between the parallel connections, but that's standard.

The cabling in some of the above diagrams looked far too complicated and messy.

The method 2 diagram looks along the right lines to me.

I would not recommend the smartgauge ultimate solution as it is far too complicated as a realworld solution.

The whole thread came about as an electrical engineer talked about improved charging by changing interconnects from series first to parallel first.....

What is your absorbtion voltage set to and for how long and what is the recommendation of the battery manufacturer?

[Andina Marie]

In real life, as opposed to theoretical hypothesizing, and in contrast to many published authorities, it matters very little what path the connections take. It is more important to use an adequate wire gauge.

If you calculate voltage drop of the cables under normal loads the voltage differentials due to lead length work out to be a few millivolts which is insignificant compared to normal battery to battery internal impedance variations resulting from manufacturing, age, electrolyte level, etc. Even brand new batteries from the same batch can have variations exceeding 1% so you don't need to be worried about a voltage differential even as high as 10 millivolts = 0.1% difference in the load on the battery.

During starting loads which last for an extremely low percentage of total battery time, those voltage differentials may eventually exceed normal battery to battery differences but it has virtually no effect on battery life because within a fraction of a second after ceasing engine cranking, battery to battery current will equalize the voltages.

If you are going to agonize over what sequence path to wire the batteries you should first do extensive measurements on battery capacity and internal impedance so their position in the series/parallel chain matches their characteristics, then repeat this and rewire once a month as they age differently.

Get REAL, use the connection that is the simplest and minimizes total length and the number of terminal junctions

[goboatingnow]

+1 advice from a real life engineer


Dave

[Pelagic]

Originally Posted by Fuss

The whole thread came about as an electrical engineer talked about improved charging by changing interconnects from series first to parallel first.....

What is your absorbtion voltage set to and for how long and what is the recommendation of the battery manufacturer?

Here are the tech specs for my Fullriver Batteries.

From correspondence with their technical dept.:

780AH @ 24V is correct.
Our engineer confirmed that it is OK to use the 29.4v Absorption Voltage setting
156A @ 24V is our recommend charging current but you also apply 195A @ 24V.
Puekerts Exponent for our DC260-12 is 1.18.

On the smart meter I just put in the battery data and its Peukert rating.
On the Victron Chargers I set absorption voltage as 19.4V

[Pelagic]

Originally Posted by FlyingCloud1937

The rule of Law, in regarding bats.

Measure the longest series jumper between bats, then make all jumpers the exact same length.

Measure the longest parallel jumper between bats, then make all jumpers the exact same length.

The tails from the bats Pos/Neg to the bus bars can be of different lengths.

Lloyd

Thank Lloyd and Adina Marie for simplifying and putting the issues in perspective.

It is funny when you know you are weak on experience with something, you tend to over obsess on getting it perfect!... or maybe that’s just me!

The physical challenge I have is that the 2 banks of 4 are in two separate vented spaces one directly above the other and separated by about 16 inches in height.
I show the 2 levels side by side on Sketch

I can tie them together a number of ways.before going to the electrical locker where all the distribution points are.
I will put the main 450amp FUSE in the upper bank (1-4)

2nd sketch shows a solution which keeps all the purple series connections the same length, but to simplify runs I positive paralleled EACH Upper and Lower sets separately at equal length to combine at the FUSE.

For negative parallel I combined All Upper and Lower sets together before going to negative Bus.
Is that ok?

Alternatively, in sketch 3 I linked all Positive parallel sets together first before going to FUSE.
Which is better?

[Pelagic]

Still playing with connections (ever obsessive)
This looks the cleanest for a Method 2 solution

[sailinglegend]

Originally Posted by Andina Marie

If you are going to agonize over what sequence path to wire the batteries you should first do extensive measurements on battery capacity and internal impedance so their position in the series/parallel chain matches their characteristics.....

If you search these forums you will find that Maine Sail has done just this and proved that the cable connection position does matter. I guess he hasn't responded because he has got bored arguing with you and goboatingnow.

As he and others repeatedly post ALL manufacturers recommend connecting the cables in such a way as to balance the loads on each battery.

[sailinglegend]

Originally Posted by Pelagic

...The physical challenge I have is that the 2 banks of 4 are in two separate vented spaces one directly above the other and separated by about 16 inches in height......

I will put the main 450amp FUSE in the upper bank (1-4)...

Put a fuse on the lower bank as well to protect the connecting cables.

[Pelagic]

Originally Posted by sailinglegend

Put a fuse on the lower bank as well to protect the connecting cables.

Don’t quite understand need for 2nd Fuse as my 450A Fuse is rated max load for the whole 8 batteries, which are all in parallel together.

I put arrows on my sketch to show the flow

Pos. 2>1>6>8> Fuse> Master Switch

Neg. 5>7>4>3> Neg Bus and Ground

Am I missing something here?

[Fuss]

Originally Posted by Pelagic

Here are the tech specs for my Fullriver Batteries.

From correspondence with their technical dept.:

780AH @ 24V is correct.
Our engineer confirmed that it is OK to use the 29.4v Absorption Voltage setting
156A @ 24V is our recommend charging current but you also apply 195A @ 24V.
Puekerts Exponent for our DC260-12 is 1.18.

On the smart meter I just put in the battery data and its Peukert rating.
On the Victron Chargers I set absorption voltage as 19.4V

Thanks for the settings. From what I can see the charging settings seem to be fine and so I would not change anything at all.
It all looks good to me and if the cabling was all professionally done, then I would leave it as it is.
As to the fuses... I guess its a matter of personal preference.

On the original subject of improving the charging... I see some room for improvement after looking at your diagrams.
I assume that your 65ft boat has a generator and that it is more than 6kw and that you use it to charge your batteries when not on shore power. If not, ignore the following...

The batteries are 1040a or 780a at 24v not sure which from info sofar in this thread. I'll assume 780 as thats what you wrote above.
A 70a and a 50a charger gives a maximum of 120a to charge a 780a/hr bank. This is not optimised when using a generator.
You need at least 230a worth of AC charging to optimise the generator run time. When you run the generator, you want to do all your generator tasks as well a significantly stuff tons of amps back into the batteries.
You also need 230a worth of alternator charging.

Back to the AC chargers.... I would install another 3000/70 multiplus charger. It can be paralleled to the other multiplus using an ethernet cable. To do this all multiplus models must be identical and the software must also be identical. This would bring you up to 190a which is still not perfect.
I assume you have long generator run times to recharge the bank or that you do it mostly from shore power (which is ok aslong as you do it once a week fully).

I don't want to create a thread drift, but the thread is about charging improvements and I assume that the electrical engineer is charging for his time. For an electrical engineer to replace all the cables as suggested would probably cost the same a victron multiplus. Something to be considered.

What I wrote above may at first glance sound crazy, but it does show the importance of having the bank size matched to the dc charging and ac charging sizes.

[sailinglegend]

Originally Posted by Pelagic

Don’t quite understand need for 2nd Fuse as my 450A Fuse is rated max load for the whole 8 batteries, which are all in parallel together....

As I said - you are protecting the connecting cables from the bottom bank to the top bank - via I don't know what - but if that cable gets damaged and shorts to earth the 450 amp fuse you have on the top bank will do nothing to stop the bottom bank discharging huge currents to earth.

Fuses protect cables not batteries.

[Pelagic]

Thanks sailinglegend, I understand your concern.

The pos cable from #8 Battery to FUSE is only 32” long and goes thru a wooden floor penetration which will have thick rubber chafe protection. All heavy cables are new and will be well clamped.

[Pelagic]

Originally Posted by Fuss

What I wrote above may at first glance sound crazy, but it does show the importance of having the bank size matched to the dc charging and ac charging sizes.

Thanks for your well thought out post Fuss

To clarify… it is a 24v system at 780a.

I already have a charging profile on this set since it was first installed about 3 years ago, when I upgraded from the original 400a (4 x 12v) truck batteries.

What I am doing now during a major refit is to reposition the 2 banks much closer together to offset the weight of the generator on opposite side and to substantially reduce the length of the wiring runs.

The battery cables are like new, heavier than needed for my new shorter runs and I just need to hydraulically crimp on the new cable ends for the AGMs

With the whole boat empty it is a perfect balance.

My calculated approach was a little different than yours as I focused on matching battery capacity with my average 24 hr. consumption.

My goal was to only consume about 10% of my capacity, so that I was never forced to put the batteries in a less than 60% SOC

It also gave me the option to only charge up to 80% (start of the Absorption Phase) when the smart chargers automatically start limiting the charge current they will put in.

So if I do not need to run the Gen for other things like Air Cons, dive compressor or making water, I just let the SOC live between 80% and 70% at anchor.

Then it takes me less than 2 hours of Gen time with present chargers running at bulk to gain 10% in that range.

I of course fully charge on passages by motor sailing for a while (230amp 24v alternators) when the autopilot loads are heavy.

I am now installing 4 x 327W Sunpower Panels and switching the many original halogen and incandescent reading and engine room lights to LED, so it will be interesting to see what my new consumption levels are.

Thanks all for your advice on sorting this out.