Wiring In Series (pro vs con)

[john61ct]

Originally Posted by ranger42c

The specific issue I was most concerned about has to do with the dual-purpose design of our main battery banks, each currently 3x Odyssey PC-2150s.

Each bank starts a main engine, runs approx half the house (one fridge each), and services a bridge function (electronics on one, electrics on the other).

Yes that is very unusual.

I am not quite as dogmatic about "no split banks" as the consensus here from those with much more experience and knowledge than me.

But taking that as given, my preference would be Bank A handles cranking/ignition, navigation electrics, everything essential to safety and propulsion.

Then Bank B is "auxiliary" domestic, House, entertainment convenience and comfort, nothing critical to life.

Sized not equally, but as needed for their respective loads, A a bit more conservatively so.

Perhaps all bought at once so cells remain as interchangeable as possible in a pinch.

Kept joined together while SoC is relatively high, get full advantage of Peukert most of the time, ideally can recharge when needed.

But when not possible, Propulsion bank A is isolated from sharing in House loads while SoC is still pretty high.

And it is obvious which bank is given priority, cared for more conservatively when needs must and perhaps replaced sooner, perhaps for a time donating to House for a while if space allows.

Purely my own thoughts, but to the extent TPTB object, I bet they object to your setup just as much, most strongly about the whole idea of a split bank itself.

[ramblinrod]

Originally Posted by s/v Jedi

Great choice; Lifeline takes a good position between affordability and quality. They even have that battery in the much better single-cell configuration for just a couple dollars more but you need space for six of them in that case

GPL-4CT-2V - Lifeline Batteries

Pros:

1. Lighter individual cells during transport.

Cons:

1. More cells to move when total replacement necessary.
2. Heavier in total.
3. Entire bank lost when one cell shorts.
4. Doesn't fit available space.
5. Replacements not easily acquired in most locations.
6. More terminal connections to fail.

[s/v Jedi]

Originally Posted by ramblinrod

Pros:

1. Lighter individual cells during transport.

Cons:

1. More cells to move when total replacement necessary.
2. Heavier in total.
3. Entire bank lost when one cell shorts.
4. Doesn't fit available space.
5. Replacements not easily acquired in most locations.
6. More terminal connections to fail.

You're in an endless and mostly false loop Rod, but I'll comment anyway:

1. a single 12V battery has just as many cells as two 6V batteries in series, as three 4V batteries in series or six single 2V cells in series.

2. you can't be serious?! do you really mean that 6 units that weigh 66lb each are heavier than 4 that weigh 66lb each?! Revelation!
Now the real issue that you keep sneaking around: it's about the weight per capacity unit. For AGM it means that more weight for the same capacity is better. That is completely opposite from your continued statements that lighter is better.

3. when you have a parallel setup with a battery that develops an internal short, you loose the bank as the other batteries discharge into that defect one. This is because you refuse to fuse the parallel strings. In a series setup you just continue with 5 cells unless you carry a spare. May be if your charger can't be programmed you need to keep an eye on the voltage and shut the charger down manually, but most boats can configure max voltage.

4. when you have space for 4, you can't fit 6 in there? Another revelation, wow, never thought of that!

5. 2 volt cells are the choice for industrial applications because it's the best option. It means you can get 2V cells wherever there is industry. If you go on expeditions far from civilization, like we do sometimes, then there is nothing so it doesn't matter what you need. In those cases you bring your own spares and a single 2V cell as spare restores full capacity.

6. Even that is false as well. When you have a multi-cell battery, even the sturdy 4V ones, they have cell interconnects as well but they are internal. There's all kinds of problems with that: it takes room that is lost for capacity or increased mechanical strength, they go through the cell walls and the seals can leak, you can not easily disconnect them without cutting the housing open, they are weaker etc. With external connections, a series setup with 6 cells has less problems than a setup with 6x a 6V battery. When you compare banks, then 6x the GPL-4CT has the same capacity as 6x the GPL-4CT-2V.

If you would study the 2V cells, you will find that the good ones have 2x a positive terminal and 2x a negative terminal. That is an engineers wet dream: you can have smaller cables, the current is much (MUCH) better spread over the plate surface, you have redundancy, you have less losses etc. etc.

If a couple of G31 batteries that don't even deserve the label deep-cycle (I would only call the Firefly that, not even my Odyssey 2150's which are beasts but more for starting service than deep cycle) would be as good as the 2V cells, then all the Contests, Oysters etc. would have them... but they don't. They use the long life gel cells like these: https://www.victronenergy.com/upload...tteries-EN.pdf that have a designed lifespan of 20 years as where one can make a happy dance when a G31 manages 6 years.

[john61ct]

http://www.newyorker.com/magazine/20...ange-our-minds

[ramblinrod]

Originally Posted by s/v Jedi

1. a single 12V battery has just as many cells as two 6V batteries in series, as three 4V batteries in series or six single 2V cells in series.

I never claimed it doesn't?

So what?

2. you can't be serious?! do you really mean that 6 units that weigh 66lb each are heavier than 4 that weigh 66lb each?! Revelation!

Well, despite this nonchalant dismissal, unnecessary excess weight and capacity can be very undesirable.

Now the real issue that you keep sneaking around: it's about the weight per capacity unit. For AGM it means that more weight for the same capacity is better. That is completely opposite from your continued statements that lighter is better.

Error # 1.

Almost all of my posts have been in reference to standard FLA batteries.

Error # 2.

Please show me one statement of mine, where I have indicated "lighter is better" as it relates to battery performance. Can't do it? Didn't think so. I never stated that at all.

That said, weight is an important consideration, unit weight as it pertains to battery handling, and total weight as it relates to the vessel performance.

3. when you have a parallel setup with a battery that develops an internal short, you loose the bank as the other batteries discharge into that defect one.

Actually, if you have 6 x 2Vdc in series, and one develops a short, the bank voltage instantly drops to 10.75 Vdc (at no load, if fully charged other wise).

Some voltage sensitive devices may drop out immediately. As the load increases and charge decreases, more devices will drop out, until nothing works.

This is because you refuse to fuse the parallel strings.

Because, with standard FLA batteries there is no need.

Some science for ya...

If a Grp 27 battery, suddenly develops a shorted cell, it will draw approximately 20A from the batteries connected in parallel, regardless of number.

As the other batteries discharge, the current through the defective battery decreases.

Regardless how many batteries, the bank will eventually reach a steady state of 10.75 Vdc.

No fire, no explosion, no significant safety risk.

In this case, the boater has usable voltage longer (as compared to a series string only which instantly drops) so that he has time to isolate the defective battery, at which point, all other batteries (if healthy to begin with) are fine, nothing more to be done, than replace the defective battery when convenient.

In a series setup you just continue with 5 cells unless you carry a spare.

False.

More science for you.

In a 6 x 2 Vdc series set-up, the voltage instantly drops to 10.75 Vdc when a cell shorts, at which point voltage sensitive devices may fail, and that voltage decreases as the load and discharge increases on the remaining cells until everything quits.

May be if your charger can't be programmed you need to keep an eye on the voltage and shut the charger down manually, but most boats can configure max voltage.

Incorrect.

Your "maybe" should be "absolutely".

If you do not change the charge voltage, you will hurt the remaining 5 cells.

Note that when this occurs to a cell in a parallel bank, isolate the defective battery, and nothing else needs to be done; everything works fine.

4. when you have space for 4, you can't fit 6 in there? Another revelation, wow, never thought of that!

You suggested 6 where the boater indicated space was limited.

Perhaps you should consider available space more seriously before making suggestions.

5. 2 volt cells are the choice for industrial applications because it's the best option.

So what?

Storing spare cells, and keeping them charged, in a warehouse is a wee bit different than storing spare cells, and keeping them charged on a boat.

Because something is preferred for one application, does not make it the preferred for another.

Else there would be only one type of battery, and for that matter, one type of boat for all applications.

It means you can get 2V cells wherever there is industry. If you go on expeditions far from civilization, like we do sometimes, then there is nothing so it doesn't matter what you need. In those cases you bring your own spares and a single 2V cell as spare restores full capacity.

Anywhere there is an automobile, (virtually within 20 km of land, anywhere in the world), a 12Vdc battery can be found in a pinch.

But the most beautiful thing about parallel 12 Vdc batteries is that there is no pinch. One fails, isolate it, and continue as normal.

Not so with the series string, where considerable system alteration is required, before normal operation resumes.

[ranger58sb]

Originally Posted by john61ct

Yes that is very unusual.

I am not quite as dogmatic about "no split banks" as the consensus here from those with much more experience and knowledge than me.

But taking that as given, my preference would be Bank A handles cranking/ignition, navigation electrics, everything essential to safety and propulsion.

Then Bank B is "auxiliary" domestic, House, entertainment convenience and comfort, nothing critical to life.

Sized not equally, but as needed for their respective loads, A a bit more conservatively so.

Yes, I think our setup wouldn't have been my first choice, but it has turned out to work surprisingly well -- or at least very well enough for our purposes -- over the last 12 years or so.

And I've only had to use the parallel switch a few times over those years, at first when the oldest bank was on the verge of crapping out just after we bought the boat (replaced with those now-old PC-2150s)... and then a couple times over the last few years when I've seriously depleted that bank by trolling on the other engine for 7-8 hours, with electronics full on. And its comforting to know the genset has it's own separate battery, so there's another slightly "slower" level of redundancy available using the battery chargers.

FWIW, I'm gathering from elsewhere it's actually not a totally uncommon scheme in medium size powerboats such as ours, especially those very probably imagined by the manufacturer as a marina hopper, or for day use or maybe light overnight use (as in fishing and general sightseeing)... and not really imagined as a likely candidate for liveaboard or long-distance cruising in the "never close to shorepower" sense.

Our last boat battery setup, slightly smaller boat, different manufacturer, was identical in design, only differing in the number of batteries on each main/dual-purpose bank.

-Chris

[john61ct]

Yes, stinkpots and close to shore whole 'nother kettle of fish.

12 years a nice run though 8-)

[TeddyDiver]

Originally Posted by ramblinrod

Because, with standard FLA batteries there is no need.

Some science for ya...

If a Grp 27 battery, suddenly develops a shorted cell, it will draw approximately 20A from the batteries connected in parallel, regardless of number.

As the other batteries discharge, the current through the defective battery decreases.

Regardless how many batteries, the bank will eventually reach a steady state of 10.75 Vdc.

No fire, no explosion, no significant safety risk.

False.

More science for you.

In a 6 x 2 Vdc series set-up, the voltage instantly drops to 10.75 Vdc when a cell shorts, at which point voltage sensitive devices may fail, and that voltage decreases as the load and discharge increases on the remaining cells until everything quits.
.

You are living in the Laalaa land? First there's difference between shorts in a cell. Normally once short develops it will start with high resistance and is very hard to notice. If the boat is left unattended for a while it will drain all the batteries down or if connected to charger the short develops and starts to drain more until the charger can't keep up and all the other batteries start to feed the defected one aswell. Now in this case the resistance might be low enough the heat will build up and melt is unevitable by the current of both charger and other batteries. And of course a there's a possibility for a sudden low resistance short. And I'm not going into possible battery explosions here..

And tell me how can a depleted 10,75v bank be better than a fully charged 10,75v bank (which pretty much is only academic scenario since nobody have heard of a shorted 2Vdc battery)

BR Teddy

[ramblinrod]

Originally Posted by TeddyDiver

Normally once short develops it will start with high resistance and is very hard to notice.

With no charger connected, when a cell shorts (high or low impedance) it draws current from parallel connected batteries. If it is a high impedance short, it draws very little current, if it is a low impedance short, it draws max current of about 15 A for a Grp 27. In either case, the battery voltage will drop to 10.75 vdc, at a rate proportional to the impedance. Very easy to detect. Look at the panel meter.

If the boat is left unattended for a while it will drain all the batteries down

As I stated in the previous post, but more accurately, only those batteries connected in parallel, and more specifically, to 10.75 vdc and then stabilize, if no load is present.

or if connected to charger the short develops and starts to drain more until the charger can't keep up and all the other batteries start to feed the defected one aswell.

All other batteries in parallel deliver current to a lower impedance battery with no charger connected.

If there is a charger connected to a parallel bank, the charge voltage will supply current to the shorted cell while the others remain fully charged.

If the charger supplies sufficient current (about 20 A for a Grp 27) all other batteries remain fully charged. If one has an unusually small charger on the bank (less than 20 A), a small amount of current will be drawn, distributed between each parallel battery, to the total of 20 A.

The condition will manifest itself, as the apparent presence of a load (the charger will never go to float and the panel meter will read high current) despite no load being connected.

Time to load test the batteries, isolate the defective one, and replace it if the rest are good, or all if they to are at end-of-life.

Note that if a charger is connected to a series string that develops a shorted cell, exactly the same thing happens, except there is no battery(s) in parallel, so the charger supplies all of the current the defective cell will draw.

Now in this case the resistance might be low enough the heat will build up and melt is unevitable by the current of both charger and other batteries.

Incorrect, a standard FLA grp 27 battery with a shorted cell will draw 30 A max. Under normal charge conditions, at 50% SOC, it will draw about 20 A max. not a significant difference in heat build-up whether shorted cell or just hungry.

If the charger is left on for a long, long time, and nobody is paying any attention whatsoever, eventually the battery will boil dry, more cells may short, and the current will increase. Thermal runaway is possible.

If a series string of high acceptance rate batteries are supplied with a high output charger, the same thing is likely to happen.

And of course a there's a possibility for a sudden low resistance short. And I'm not going into possible battery explosions here..

Because it really never happens with a FLA grp 27? OK.

And tell me how can a depleted 10,75v bank be better than a fully charged 10,75v bank

There is no such thing as a fully charged 12 Vdc nominal bank at 10.75 Vdc.

(which pretty much is only academic scenario since nobody have heard of a shorted 2Vdc battery)

Nonsense, those who use 2 Vdc cells in those industrial applications that were being referenced, experience shorted cells, likely about as frequently as the average boater. It is the nature of FLA batteries. When one attempts to use a battery beyond it's normal service life, and after it shows signs of failing, any battery can develop a shorted cell. Few boaters ever hear of 2 Vdc cells shorting, because so few boaters use 2 Vdc cells (for the many reasons against it as I've stated).

In contrast, millions and millions of boaters use grp 27s in parallel. How many battery explosions due to cell shorts happen? Almost none. More likely to be hit by space junk.

Most claims of "self exploding" FLA Grp 27 batteries are because some fool put batteries in an unventilated space, never checks them, leaves a charger on all the time, and made a spark, like dropping a ratchet across the terminals, connecting an auto battery charger on the terminals while plugged in, or disconnecting a terminal before disconnecting loads. Same thing will happen with a series string if you treat them the same way.

So you can raise all of the bogus arguments you wish, but the science AND real world experience proves that a parallel bank of grp 27 FLAs with a properly sized charger, is a safe, dependable, viable solution for most marine house banks. If it weren't, marine electrical standards, such as ABYC, would prohibit their use. They don't. It's as simple as that.

[ranger58sb]

Originally Posted by john61ct

Yes that is very unusual.

I am not quite as dogmatic about "no split banks" as the consensus here from those with much more experience and knowledge than me.

Et cetera...

Purely my own thoughts, but to the extent TPTB object, I bet they object to your setup just as much, most strongly about the whole idea of a split bank itself.

Originally Posted by ranger42c

Yes, I think our setup wouldn't have been my first choice, but it has turned out to work surprisingly well -- or at least very well enough for our purposes -- over the last 12 years or so.

Originally Posted by john61ct

Yes, stinkpots and close to shore whole 'nother kettle of fish.

12 years a nice run though 8-)

A couple more thoughts, in case useful for the wider readership...

Our split dual-purpose banks also each have their own set of house loads. One fridge each, electrics on one and electronics on the other, freshwater pump on one and electric toilet on the other, etc.

If we use ~60 amps/day total, that can work out to 10%/day from each bank if loads are evenly split (i.e., 30 amps from each of our 300-Ah banks).

If we had a single 600-Ah bank, and all house loads on that bank... usage would still be about the same, ~10%/day (60 amps from a 600-Ah bank).

Of course the loads aren't actually equal, not perfectly evenly split... but they're close enough for quick estimation... and the outcome is that we've experienced no practical penalty with the set-up we have.

I mentioned earlier the heavy electronics load on one battery bank during our routine of trolling on the other engine. Even that is more of a regional/fishboat thing. Folks running our kind of boat on the ocean and trolling for tuna (or anything out there) would be moving at much higher speeds, both engines running all the time, and the electronics load would be serviced completely by engine alternators (if they're on a starting bank). Our trolling here is more like 2.5 kts plus/minus (we're often passed by almost-becalmed sailboats), and I can't even run that slowly on one engine without using trolling valves. IOW, this would be a non-factor for most users elsewhere.

Bottom line is that our factory setup doesn't fit the normal mold folks here would usually expect or recommend, but it's turned out to be a very satisfactory installation.

-Chris


-Chris

[s/v Jedi]

I just checked my Victron Quattro and I can set my absorption voltage to 12V which is perfect for 5 cells in series just like 6 cells have 14.4V. This means that I am right and can run a battery made up from 5x 2V cells in series with automatic, unattended recharging and use it until I can replace a defective cell.

I would still carry a spare, or have a second bank of the same cells (I had 2 of those of 900Ah each as oem setup).

Also, there has never been a boat with 2V gel or AGM cells that had one that shorted out. They never short out because construction is much more solid that multiple cells in one housing, plus they are made better to start with. 20 years service life, may be LFP can beat it but did not prove that yet

BTW, I just decided to go with LFP if I can source the cells

[Tasso]

Originally Posted by ramblinrod

With no charger connected, when a cell shorts (high or low impedance) it draws current from parallel connected batteries. If it is a high impedance short, it draws very little current, if it is a low impedance short, it draws max current of about 15 A for a Grp 27. ...

All other batteries in parallel deliver current to a lower impedance battery with no charger connected.

This would suggest an internal impedance of about 130 milli-ohm over the remaining 5 internal cells - which is ridiculously high. While the failed battery would be in rapid charge mode and internal impedance is dynamic - the current draw would be much higher initially - and this would put additional stress on the failed battery. The duration of the high current spike would depend on the size of the remaining parallel bank.

Originally Posted by ramblinrod

If there is a charger connected to a parallel bank, the charge voltage will supply current to the shorted cell while the others remain fully charged.

This is another gross oversimplification of what will happen. Actual current is failed battery will certainly increase and the increase will depend on the capacity of the charger. Some alternators can put out 200 amps or more - with such a system there may not even be an indication of battery failure until a temperature sensor trips.

Originally Posted by ramblinrod

If the charger supplies sufficient current (about 20 A for a Grp 27) all other batteries remain fully charged. If one has an unusually small charger on the bank (less than 20 A), a small amount of current will be drawn, distributed between each parallel battery, to the total of 20 A.

The condition will manifest itself, as the apparent presence of a load (the charger will never go to float and the panel meter will read high current) despite no load being connected.

Your estimate of 20 amps is low and the actual current would depend on multiple factors. When providing this sort of advice - deliberately underestimating current may put others at risk. Also - the point that several of us have been making is that a single cell failure in a large parallel bank could go unnoticed for some time. As you say it just appears as a high current load - but many would miss this until some sort of alarm would go off.

With a series bank - there would be an immediate voltage drop. this would be very noticeable as you have pointed out. Also - most modern chargers would automatically cut-out (unless the charge voltage was modified as suggested by others).

Originally Posted by ramblinrod

Note that if a charger is connected to a series string that develops a shorted cell, exactly the same thing happens, except there is no battery(s) in parallel, so the charger supplies all of the current the defective cell will draw.

The current is the same in every cell in the series chain. That is the point. A charging circuit with no low-voltage cut-out will attempt to increase the voltage across the remaining non-shorted cells in series. This could cause increased gassing off - but would be distributed more evenly across cells than for a parallel bank.

Originally Posted by ramblinrod

Incorrect, a standard FLA grp 27 battery with a shorted cell will draw 30 A max. Under normal charge conditions, at 50% SOC, it will draw about 20 A max. not a significant difference in heat build-up whether shorted cell or just hungry.

This is not true and it is irresponsible to make such a statement.

Originally Posted by ramblinrod

If the charger is left on for a long, long time, and nobody is paying any attention whatsoever, eventually the battery will boil dry, more cells may short, and the current will increase. Thermal runaway is possible.

This is exactly the scenario I am concerned with. With a high capacity bank - particularly when connected to a high current charge system - I would expect that most boaters would not notice until a high temperature alarm when off. This could be too late to prevent meltdown or worse.

Originally Posted by ramblinrod

If a series string of high acceptance rate batteries are supplied with a high output charger, the same thing is likely to happen.

First a "high output charger" should be able to detect a failed cell in a series bank. Second the energy from rapid charging would be better distributed over ALL CELLS in a series bank.

Originally Posted by ramblinrod

Because it really never happens with a FLA grp 27? OK.

This is the logic that gets people hurt and is the sort of thing that makes many of us wonder of you ever spend extended time away from the dock.

Originally Posted by ramblinrod

In contrast, millions and millions of boaters use grp 27s in parallel. How many battery explosions due to cell shorts happen? Almost none. More likely to be hit by space junk.

Explosions are infrequent - but more likely than being hit by "space-junk". Melt-downs are not that uncommon and can be equally dangerous depending on situation.

Originally Posted by ramblinrod

So you can raise all of the bogus arguments you wish, but the science AND real world experience proves that a parallel bank of grp 27 FLAs with a properly sized charger, is a safe, dependable, viable solution for most marine house banks. If it weren't, marine electrical standards, such as ABYC, would prohibit their use. They don't. It's as simple as that.

I won't disagree - but for some of us there are several advantages to a series configuration. The strongest are that failures are more obvious and monitoring of the life-cycle state of individual cells is simpler. For this and other reasons many find the series configuration is less wasteful and more advantageous economically. I would also point out again - that while a catastrophic failure is unlikely with either configuration - I believe that series configuration is safer.

[ramblinrod]

Originally Posted by s/v Jedi

I just checked my Victron Quattro and I can set my absorption voltage to 12V which is perfect for 5 cells in series just like 6 cells have 14.4V. This means that I am right and can run a battery made up from 5x 2V cells in series with automatic, unattended recharging and use it until I can replace a defective cell.

????? Did anyone say your charger couldn't be programmed this way?

Regardless, it won't do it automatically, so your remaining series cells will be over-charged and seriously hurt if you aren't around to reprogram your charger. Man that would hurt financially. And where the heck are gonna find replacement cells for the whole bank in the middle of nowhere?

I would still carry a spare, or have a second bank of the same cells (I had 2 of those of 900Ah each as oem setup).

OK, well if you have two 900 A-hr banks in parallel, that is the redundancy I was talking about.

Also, there has never been a boat with 2V gel or AGM cells that had one that shorted out. They never short out because construction is much more solid that multiple cells in one housing, plus they are made better to start with.

Sorry, I don't believe that no 2Vdc cell on a vessel has ever shorted. Citation please.

[TeddyDiver]

Originally Posted by ramblinrod

????? Did anyone say your charger couldn't be programmed this way?

Regardless, it won't do it automatically, so your remaining series cells will be over-charged and seriously hurt if you aren't around to reprogram your charger. Man that would hurt financially. And where the heck are gonna find replacement cells for the whole bank in the middle of nowhere?

So you are basicly claiming it's impossible to notice a voltage drop (series setup) but instanly be aware of amps drain to a shorted cell (parallel)


[/QUOTE=ramblinrod;2387123]
Sorry, I don't believe that no 2Vdc cell on a vessel has ever shorted. Citation please.[/QUOTE]
The architecture of 2Vdc battery is to prevent such incident. To put such thing into right scale by propability it's more common to have total "open circuit" ie break welded connection between the pole/bar and plates.

BR Teddy

[ramblinrod]

Originally Posted by TeddyDiver

So you are basicly claiming it's impossible to notice a voltage drop (series setup) but instantly be aware of amps drain to a shorted cell (parallel).

No. That is not what I stated.