Wiring In Series (pro vs con)

[Tasso]

Originally Posted by ramblinrod

...
Configuring a 6 battery house bank such that there is no redundancy, and a single battery failure renders the entire house bank useless, is a serious design flaw in my opinion.

All batteries will fail some day. Many will decrease in capacity; some will shed plate material causing a short between plates and instant total failure.

You can do what you please on your boat, but what you suggest, in my opinion, is a very, very bad idea.

Where are you getting your information? Can you cite one instance where a vessel has been lost because a 12 Vdc battery developed a shorted cell?

No one is advocating leaving shore without at least two fully redundant banks. But individual cells within a 12v or 6v battery can and do occasionally short. Given that a 12v battery is just six 2v cells in a single package - the mean time to failure is no different with six 2v batteries or one 12v battery. A cell failure - open or shorted - is what kills a battery in either case.

As an electrical engineer - please advise what happens when two 12v batteries are in parallel and one gets a shorted internal cell.

[thomm225]

Originally Posted by Tasso

No one is advocating leaving shore without at least two fully redundant banks. But individual cells within a 12v or 6v battery can and do occasionally short. Given that a 12v battery is just six 2v cells in a single package - the mean time to failure is no different with six 2v batteries or one 12v battery. A cell failure - open or shorted - is what kills a battery in either case.

As an electrical engineer - please advise what happens when two 12v batteries are in parallel and one gets a shorted internal cell.

Looks like he's an Engineering Tech, not an engineer.

There is quite a bit of difference between the two, and there are many variation of each and their knowledge. level

[Tasso]

Originally Posted by thomm225

If you have your batteries in parallel and they are fused, I'm thinking they are as safe as batteries in series.

My batteries are now fused to the load and to each other.

I don't have a starter battery. Well, I do but it's now in the house bank. It's one of my two 12 volt batteries in parallel. My engine is pull start.

The batteries are charged with solar.

Agreed - ABYC recommends each battery bank be protected by a fuse or breaker. I have 200 amp breakers.

I have been entertained by the battle on this tread - but find it odd that people can be so passionate when a 12v batter is just six 2v batteries connected in series internally. The argument is basically mute. But purpose-built "deep-cycle" batteries are a must for any serious cruiser.

Form factor - by and large - determines what battery we install. I simply do not like to see any batteries connected in parallel. You have been the first to recommend fuses to protect from melt-down. It is my opinion this is essential for safety.

Also note the the type cruising one does is a huge factor. If you are on the hook for days at a time - don't run your engine or gen-set daily - this has a massive effect on battery choice and longevity.

I think that the passions expressed above have to do more with the difference in the cruising experience of the posters than science.

I noticed one prolific poster is based on the great lakes. This is the cruising domain of marina folks. They have very different battery needs than someone crossing the Pacific...

[Tasso]

Originally Posted by thomm225

Looks like he's an Engineering Tech, not an engineer.

There is quite a bit of difference between the two, and there are many variation of each and their knowledge. level

I don't want to get into a piss fest - but it's interesting than an article that I wrote for Good Old Boat was turned down because they no longer want to publish advice on battery configuration because they are afraid of lawsuits...

I would advise anyone configuring a battery bank to do substantive research. An electrical fire at sea can kill you. It's a simple as that.

[Pete7]

Originally Posted by TeddyDiver

To mention the most dangerous one is the accumulation of shedded lead in the bottom of the cells. If this silt reaches the plates the cell shorts and the battery as it is now only 10v starts to drain the other paralled batteries in the bank. That is more likely to happen with old well served batteries than with abused and sulfated ones.
Despite Rod hates the frase, "true" deep cycle batteries have more reserve space below the plates to avoid such issues. That's on reason why they are higher..

BR Teddy

Is that it well since I have 2 x 12v house batteries then it shouldn't be problem as I can disconnect one then carry on and buy any old cheapo replacement next time I reach land. What would you do with a bank of 6v batteries?

[Pete7]

Originally Posted by ka4wja

Pete....these batteries are only an inch to 1.25" taller (including the HydraCaps) than the 8D's they replaced....I think almost any production yacht or battery box will fit them....(they are not the "tall" L-16's)....the Rolls battery boxes would ad another inch in height, but if you don't need their boxes, as most of us have battery boxes already, then they're about one inch taller than an 8D) Fair winds.. John

John, sadly still too tall so likely to cause a lumpy bed and can't go down as the battery boxes sit on the hull. Out of curiosity how much was one of those 2v batteries?

Nor am I convinced that we would gain anything. If I explain that the lowest our 220AH house bank (2 x type 31s) has been is about 160AH or 12.4v over the last 6 years then expensive battery configurations are unlikely to pay for themselves. With redundancy in that only one of the batteries is required and the option of easy replacement what is there to gain? so I agree with some of the ideas Ramblinrod is putting forward.

Interesting discussion though.

Pete

[TeddyDiver]

Originally Posted by Pete7

Is that it well since I have 2 x 12v house batteries then it shouldn't be problem as I can disconnect one then carry on and buy any old cheapo replacement next time I reach land. What would you do with a bank of 6v batteries?

Well, personally I would choose batteries according the bank size. Say a bank of 2400wh one 12v/200Ah battery would do fine. A bit bigger bb with two 6v batteries in series up to 4800wh (12v 400Ah). After that size there are two ways, either with 6v batteries 4 in series up to 9600wh (24v/400Ah) or with 2v batteries, where there's no practical upper limit. Whether it's 12 or 24v depends of other factors.
All of these configurations are in series only. For backup a separate starting battery.

I've seen a battery explosion so I never go to paralled batteries. Of course fuses could be used but they have their issues like increased resistance with higher current and how well that resistance is balanced with separate fuses. Fuses nor prevent a faulty battery draining the bank totally if the short has still some resistance.

BR Teddy

[camel2012]

Originally Posted by john61ct

Yes a lot of fork trucks use 12V as the foundation, but I do think a minority.

Bringing AGM into the argument may well change things too, definitely a higher price point, to me not worth the extra unless needing to mount sideways. Especially losing the cheap and easy hydrometer SoC benchmarking to optimize charging/use patterns.

But one nice thing about getting the install space standardized on paralleled G31s, is the ability to go to Firefly Oasis to handle PSOC without having to go up to LFP before you're ready.

Very few fork lifts are 12V... maybe walk behinds walkies... but lift equipment that gets serious duty are 99% 24, 36, or 48 V... and the industry is moving to higher voltages...
... they use 2v cells in series, no redundancy but little need. Typical battery bank life is 3k to 5k hours which in warehouses is 400 to 600 days / cycles... not impressive life but then again they are treated like cordless drills and drained completely quite often.

[GrowleyMonster]

Originally Posted by jamesdavis

Comment: when batteries are connected in series you add terminal voltages, but can only draw as much current as a single battery in the series can offer by itself.

Example:Three 4V batteries connected in series at 450A capacity each will yield 12V, but the series string can only produce 450A.

Just to keep everybody straight, I would like to point out the obvious, for the benefit of any relative newbies reading this thread, that the above post is confusing current with capacity. AmpHours is capacity. Amps is current. The current in a circuit depands on voltage and resistance (or impedance) and capacity is how long at what current it takes to completely discharge a battery.

A 450AH battery can source 1000A of current, or more, briefly. Very briefly. Not something you would want to happen, though!

Yes, when you connect in series, you add the voltages, and the total AH capacity is the same as a single battery. NOT CURRENT; CAPACITY. When you wire them in parallel, you add the capacities, and the system voltage is the voltage of one battery.

[GrowleyMonster]

Having an electric boat puts things in a different perspective. When your 12v house loads come from a 48v, 60v, 72v, whatever size series bank, via a DC/DC converter, it doesn't matter if you lose one 6v battery in the string, or one 2v cell. You remove the faulty one, jumper across where it was in the string, and life goes on. Just sayin. I used to keep a pair of my old 12v batteries for house loads and use the 48v bank just for propulsion, but when the group 31s started getting a bit soft, I switched to a DC/DC converter rather than replacing the 12v batteries. If I lose a 6v battery I am down to 42v nominal, and my motor controller will still run, and my lights will still burn. There are also inverters that are not overly picky about input voltage, too.

There is no particular reason why a series bank of batteries cannot be individually charged. That eliminates the worry about overcharging with a full bank charger. Currently I have a 4 bank 12v charger and each pair of leads charges two 6v batteries. If I had to do it all over again, I would simply have 8 individual 6v chargers. Same idea if I had a higher voltage bank. Even if you are not using electric propulsion, going above 12v for storage has its advantages.

[ramblinrod]

Originally Posted by Tasso

No one is advocating leaving shore without at least two fully redundant banks. But individual cells within a 12v or 6v battery can and do occasionally short. Given that a 12v battery is just six 2v cells in a single package - the mean time to failure is no different with six 2v batteries or one 12v battery. A cell failure - open or shorted - is what kills a battery in either case.

As an electrical engineer - please advise what happens when two 12v batteries are in parallel and one gets a shorted internal cell.

I am not an electrical engineer.

I am an electronic engineering technician, from an accredited Canadian college program.

Here is what happens when a battery cell shorts.

1. A small amount of material from the lead plates within the battery can fall off and settle to the bottom.

2. This tends to increase with battery age. Perhaps near or beyond normal end-of-life, but possibly sooner.

3. If enough material falls off, it can short the plates within a cell.

4. An otherwise fully charged battery will immediately drop by the voltage produced in a cell (around 2.15 Vdc). For a 2 Vdc nomimal cell, it drops to 0Vdc. For a 6Vdc battery, it drops to 4.3 Vdc, for a 12 V battery, it drops to 10.75 Vdc.

5. If other batteries are connected in series to make 12 Vdc nominal (12.8 Vdc when fully charged), electrically, to the connected circuit, it looks like one battery. If the bank 1 x 12Vdc, 2 x 6Vdc batteries, 3 x 4 Vdc batteries, or 6 a 2 Vdc batteries, the output voltage is now 10.75 Vdc.

6. At 10.75 Vdc, some devices will not work well, some not at all. AS load increases on the battery and it sags, more devices will drop out. As the battery discharges, even more devices will drop out, until few or no devices work at all.

7. When a cell shorts, the charger connected in parallel, will now be supplying to high a charge voltage to the battery. If it should be 14.4 Vdc for a 12 V battery (2.4 Vdc per cell), now it should only be 12.0 Vdc.

8. If the normal charge voltage is applied to a battery with a shorted cell, the battery will lose water rapidly and gas an extreme amount. The area around the battery will have a strong pungent odour.

This gas (that comes from the battery whenever it is charged, but moreso when overcharged) is comprised of hydrogen, and if contained in sufficient concentration in a non-ventilated space can explode.

If left for a long period, it is possible that all of the water will boil off, the battery may overheat, and melt down.

9. If someone is aboard the boat, they will most likely notice things not working correctly, the low battery voltage, the strong smell, and investigate. So the most likely occurrence of a cell failure and battery melt down, is if nobody is aboard.

10. There are millions and millions of boats on the water around the planet.

Very, very rarely, an explosion may occur when the off-gassed hydrogen is ignited by a spark.

The most likely culprits for causing this are:
a) Improper battery handling procedures.
b) Improper battery compartment ventilation.
c) Bad wiring.

Remember, all FLA batteries off-gas hydrogen when being charged, so this could occur whether a cell is shorted or not.

Note that this can happen to any configuration of cells. Any battery of how ever many cells, even a single series string, that suffers a cell short, will do exactly the same thing.

Just as a guess, maybe one in 100 batteries suffers a cell short. Maybe 1 in a million boats suffers an explosion from a battery off-gassing. Maybe 1 in 10 million were directly related to a cell short.

11. If there is another battery (remember a series string is still considered one battery electrically) in parallel, it will discharge into the battery with a shorted cell, until it attains the shorted battery voltage (10.75 Vdc for a 12 Vdc nominal battery).

12. This discharge, being deeper than the 50% target maximum discharge (around 12.2 Vdc resting voltage) that most advocate for maximum life output, will reduce battery life expectancy, the longer it is left in that condition. If immediately detected and repaired, the impact on life expectancy will be negligible, due to the one time, temporary event.

13. Because the parallel battery voltage is much less than normal charger voltage (also connected in parallel) and drops to the shorted cell battery voltage, the risk of an over-voltage condition, boiling dry, and thermal run-away is negligible. (If a battery charger is connected and on, that risk still exists, and there is very little difference if a parallel bank exists or not.)

14. If there are 12 Vdc batteries in parallel, the battery or string with the shorted cell can be isolated, and the remaining batteries (not in the shorted string) will work normally, as will the charging system.

15. If there are no batteries in parallel, the reduced voltage in the string with the shorted cell will be problematic as indicated above. The battery will not produce sufficient voltage to operate DC appliances. The charge voltage will be too high. The battery must be disconnected, and all house bank devices will not function. Repairs must be made to get the boat working again. Repairs could include:

a) Replacing the shorted cell battery with a good one. This may be one that that has been carried around, as dead weight or a loose cannon, consuming prime storage space, and somehow kept fully charged (remember off-gassing) despite self discharge. In most cases, nobody does this, they stop in the next port and wait for a new one to be delivered. The more exotic the battery, the more it will cost for the battery, the farther it will likely have to come from (and hazardous shipping, especially to remote places can be extremely expensive) and the longer one has to wait, most likely incurring unexpected marina fees.

b) Bypass the shorted cell, reprogram the DC to DC converter and all charging systems. If the boat is equipped (very uncommon) with a DC-DC converter, it can be reprogrammed so that the 10.75 Vdc nominal of the bank with the shorted cell, can be output at 12 Vdc nominal. The converter may or may not have a high enough output to run all DC loads. The higher the output, the more expensive the converter. Some chargers can be programmed to a reduced charge voltage, some not.

[ramblinrod]

Originally Posted by GrowleyMonster

Having an electric boat puts things in a different perspective.

Actually, I believe you mean a boat having electric propulsion. ;-)

And yes, this changes the vessel storage and charging capacity needs dramatically.

Because this represents such a small percentage of boats on the water, it really does need to be considered in isolation.

This is a case where expensive DC - DC converters, monitoring, and charging equipment may be warranted (if one can justify electric propulsion to begin with).

[ramblinrod]

Originally Posted by camel2012

Very few fork lifts are 12V... maybe walk behinds walkies... but lift equipment that gets serious duty are 99% 24, 36, or 48 V... and the industry is moving to higher voltages...
... they use 2v cells in series, no redundancy but little need. Typical battery bank life is 3k to 5k hours which in warehouses is 400 to 600 days / cycles... not impressive life but then again they are treated like cordless drills and drained completely quite often.

Almost all fork lifts with infernal combustion engines have 12 Vdc batteries.

[ramblinrod]

Originally Posted by TeddyDiver

Well, personally I would choose batteries according the bank size. Say a bank of 2400wh one 12v/200Ah battery would do fine. A bit bigger bb with two 6v batteries in series up to 4800wh (12v 400Ah). After that size there are two ways, either with 6v batteries 4 in series up to 9600wh (24v/400Ah) or with 2v batteries, where there's no practical upper limit. Whether it's 12 or 24v depends of other factors.
All of these configurations are in series only. For backup a separate starting battery.

I've seen a battery explosion so I never go to paralled batteries. Of course fuses could be used but they have their issues like increased resistance with higher current and how well that resistance is balanced with separate fuses. Fuses nor prevent a faulty battery draining the bank totally if the short has still some resistance.

BR Teddy

This is ridiculous.

A battery is no more likely to explode in a parallel bank as it is in a series string.

A 2400wh house bank is perfect solution for 2 x Grp 27 "Deep Cycle" in parallel.

There are literally millions of boats configured this way.

1. Can be found anywhere. (Even a car start battery will work in a pinch).
2. Natural redundancy. One fails, just disconnect it, still got 12 Vdc.

For this bank, a single 12 Vdc x 200 A-hr battery would not be wise.

If the house battery dies, one would be forced to run everything off the start battery. If they kill that, they're dead in the water.

I can think of no valid reason not to configure a house bank connected in parallel, and have listed many for doing so.

[Tasso]

Originally Posted by ramblinrod

This is ridiculous.

A battery is no more likely to explode in a parallel bank as it is in a series string. ...

This statement is false.

The biggest risk of melt-down, explosion or potential fire, occur from rapid discharge. Rapid discharge is more likely when batteries are connected in parallel.

Originally Posted by ramblinrod

There are literally millions of boats configured this way. <batteries in parallel>

..

This is true. But mine is not one of them. According to ABYC - each branch in a parallel configuration should have fuse or breaker protection.

You should realize when posting electrical advice that you may be putting others at risk.

To understand the amount of potential energy in a battery - you can google "car battery arc welder"...

1. Rapid discharge is dangerous.

3. Configurations that make it more likely should be avoided.