What to do when a FLA 2v cell fails.

[Fuss]

There seems to be some confusion on here when a 2v flooded lead acid cells fails. It is really not a major disaster with which you lose the whole bank.

Unlike 6v or 12v batteries, you do not really lose capacity. You just lose 2 volts.

Take the failed cell out of the bank.

You now have a 23v or 11.5v bank
Check state of charge calcs to know 100,75 and 50% eg 23v, 22.5v, 22.1v

Check the water on the remaining cells and check every day until the failed cell is replaced.
carry on as usual using your engine alternator to make up the volt shortfall.

Check the alternator is handling the constant bulk charge mode ok.

dont go over 29v (14.5v)
dont go over 28v (14v) for more than 2 hours a week.

aim for 27v (13.5v) maximum when running the engine

At this stage the only downside is that the engine and alternator are working longer hours each week.

Try to get yourself an replacement cell as soon as possible.
Don't forget to check the water and alternator until you get a feeling for how they are coping.

[a64pilot]

Yes, but you lose 2V. Now when you hit 50% SOC, your at 10V instead of 12V. How much of your stuff is happy at 10V?
OK I know it's not exactly 2V, but it's real close, I think it's actually 2.33V?

[Fuss]

Originally Posted by a64pilot

Yes, but you lose 2V. Now when you hit 50% SOC, your at 10V instead of 12V. How much of your stuff is happy at 10V?
OK I know it's not exactly 2V, but it's real close, I think it's actually 2.33V?

It works better for 24 than 12 as you effectively have 1 more 2v cell.

It still works for 12, run the engine and the voltage at 50% charge will come up to 11 almost instantly and then try not doing a 50% depth of discharge.

We are talking an emergency and a 2v cell failure in a 12 volt system still does not disable the whole bank.

[a64pilot]

Understood, still how do most things electrical work on 10V? Bulbs would be dimmer but other than that I'm pretty sure fine, fridge compressor I think would have a tendency to overheat and would shorten it's life, maybe even slug and not start? Some electronics would be fine, some Garmin I think is OK with anything from 6 to 36V for example, quite a few others I think won't even work at 10V, remember most 12V things are actually designed to be run on 14. Bilge pumps maybe OK, but decreased pumping output? I don't think an inverter will even come online, I know mine wouldn't low voltage shutdown is around 11V, I think.
So in short, You'd still have a bank of course, just how much stuff wouldn't work is a question and for how long when the charge drops.

[a64pilot]

There are current stabalizers or some similar name, devices that will keep a steady 14V or so whenever the voltage increases or drops. I don't know their capacity amps or watts wise, nor the range of voltage they will operate at, but it's an idea how to keep going if you lose one 2V cell, if one will work to say 10V or so.

[phorvati]

you are forgetting that current has to flow through that "lost" cell, there is an internal resistance associated with that cell, and there is heating and loss which is now substantially greater in the battery. Not to mention that other cells are likely on their way. Onboard systems are so sensitive that i would not run anything unless its an emergency or I went through datasheets for each of the systems and looked up the rated specs and knew exactly if it could handle the extra drop and increased current. Then think of all the fusing, wire sizing, wire length. In the AC world its easy to get away with a drop like that but in a DC world especially 12V, its a lot more sensitive.

[a64pilot]

I believe his point is if a 2V cell goes bad, you remove it from the battery and operate at a lower voltage.

[ontherocks83]

Originally Posted by Fuss

There seems to be some confusion on here when a 2v flooded lead acid cells fails. It is really not a major disaster with which you lose the whole bank.

Unlike 6v or 12v batteries, you do not really lose capacity. You just lose 2 volts.

Take the failed cell out of the bank.

You now have a 23v or 11.5v bank
Check state of charge calcs to know 100,75 and 50% eg 23v, 22.5v, 22.1v

Check the water on the remaining cells and check every day until the failed cell is replaced.
carry on as usual using your engine alternator to make up the volt shortfall.

Check the alternator is handling the constant bulk charge mode ok.

dont go over 29v (14.5v)
dont go over 28v (14v) for more than 2 hours a week.

aim for 27v (13.5v) maximum when running the engine

At this stage the only downside is that the engine and alternator are working longer hours each week.

Try to get yourself an replacement cell as soon as possible.
Don't forget to check the water and alternator until you get a feeling for how they are coping.

I understand and see your point but let me play devils advocate just for poops and giggles.

Now this is my personal take on how I look at it, right wrong or indifferent.

Lets compare 1 bank of 6 x 2v cells producing 1100 ah and another bank of 8 x 6v cells putting out approx. 1000 ah (lets leave space the banks take up for another discussion) (ah are ball parks from batteries I previously looked up but don't have the motivation to put links to right now)

If I were to be on a crossing or far away from land for an extended time I like the idea that if one of my 6v's dies I can disconnect 2 of the 6v batteries bringing my bank from 1000 ah to 750 ah with just a few minutes of disconnecting and reconnecting battery cables and be done. My charging system would stay the same and I wouldn't have to monitor charging voltage. The worse thing about it is reaching 50% SOC sooner and having to recharge the batteries.

Now if I were close to land then the 2v's and the process you described would seem reasonable, but personally too much of a headache for me to constantly be worrying about charging voltage and such as you described.

Thank you for the information though it did clear up some info about 2v's for me.

Happy sailing

[TeddyDiver]

Originally Posted by ontherocks83

I understand and see your point but let me play devils advocate just for poops and giggles.

Now this is my personal take on how I look at it, right wrong or indifferent.

Lets compare 1 bank of 6 x 2v cells producing 1100 ah and another bank of 8 x 6v cells putting out approx. 1000 ah (lets leave space the banks take up for another discussion) (ah are ball parks from batteries I previously looked up but don't have the motivation to put links to right now)

If I were to be on a crossing or far away from land for an extended time I like the idea that if one of my 6v's dies I can disconnect 2 of the 6v batteries bringing my bank from 1000 ah to 750 ah with just a few minutes of disconnecting and reconnecting battery cables and be done. My charging system would stay the same and I wouldn't have to monitor charging voltage. The worse thing about it is reaching 50% SOC sooner and having to recharge the batteries.

Now if I were close to land then the 2v's and the process you described would seem reasonable, but personally too much of a headache for me to constantly be worrying about charging voltage and such as you described.

Thank you for the information though it did clear up some info about 2v's for me.

Happy sailing

If..
Having 4 parelled banks means you are about 30 times moro prone to loose one of them compared to 6 of 2v in series. After loosing one of your 2 of 6v's you are 10 times more prone to loose next one and after that 3 times to loose second last. Now we have even chance to loose a cell in 2v set..
Happy sailing

[ontherocks83]

Originally Posted by TeddyDiver

If..
Having 4 parelled banks means you are about 30 times moro prone to loose one of them compared to 6 of 2v in series. After loosing one of your 2 of 6v's you are 10 times more prone to loose next one and after that 3 times to loose second last. Now we have even chance to loose a cell in 2v set..
Happy sailing

You're really going to have to spell out the math on that one for me. Not following your logic at all.

Maybe talk slower I dont read too good

[TeddyDiver]

Originally Posted by a64pilot

I believe his point is if a 2V cell goes bad, you remove it from the battery and operate at a lower voltage.

Or running only vital systems and have enough voltage. Internal resistance lowers voltage in every battery.
They are considered empty when the voltage drops to 1.75 to 1.85 per cell which means for the 6 cell bank 10.5 volts. Fully charged 5 of 2v bank lightly loaded has 11v.

[TeddyDiver]

Originally Posted by ontherocks83

You're really going to have to spell out the math on that one for me. Not following your logic at all.

Maybe talk slower I dont read too good

It's the nature of paralled battery banks. Check my posts, had a link in the other battery thread to 6page article about battery banks.

[a64pilot]

I'll take another guess, but I bet his math is based on a 6V battery having three cells and therefore is three times more likely to have an issue than a 2V battery which really isn't a battery at all as it's one cell.

[ontherocks83]

I just searched found and read the link you are referring to and I still don't see your math anywhere in it. It does say that multiple parallel banks require more maintenance (i.e as stated in the article there are more connections that could corrode, not really a big deal) and all the cables need to be the same length, and should go to a bus bar to parallel the banks to make sure they all share the load equally, and should be fused between banks but i am not seeing how it is SO much more likely to fail. And again my point of if one bank fails I still have a very functional working slightly smaller bank.

Maybe I am missing something but could you please educate me/us on what you are talking about.

The article states many times that "multiple banks are bad" but doesn't seem to give any hard evidence, examples, or detailed explanations of who what where when and why this is true.

Here's the link by the way in case anyone else is curious but doesn't want to have to go searching for it.

High-Capacity Battery Banks | SolarPro Magazine

[nimblemotors]

If a 2v cell fails, then install the spare..
if a 6v cells fails, install the spare..

One would need to understand just what fails to engineer the best way to avoid it. Wiring connections are a source of trouble in my experience.
More likely than a cell failure itself? I would think so.