Lithium batteries - cell failure.

[nicholsong]

Lead/acid batteries can suffer a single cell failure, so it is wise to have two batteries, in order to disconnect said battery.

Does the same apply to LiFePo4 batteries?

 

[Just smiffy]

 

[bigtwin]

Does the same apply to LiFePo4 batteries?

It’s possible but I can’t say how likely it is.

However, in the event that it did happen it would be very evident as the BMS monitors each individual cell.

Ian

 

[Derbyshire wanderer]

Sort of……..
Any battery can fail but the reality is that it is rare unless it’s either old or abused.
Ultimately you are rarely going to be more than an hour or so away from a garage or motor factor that could sell you an ordinary lead acid replacement if you were stuck for power and of course you can always use the changeover to the vehicle battery for emergency power.
Edit to say that lithium batteries are monitored by the BMS so usually can be fixed by charging them as the shutdown is often due to cell imbalance rather than failure.

 

[LithiumConvert]

and of course you can always use the changeover to the vehicle battery for emergency power.

Not on a nice new German A class motorhome.

But we do carry torches.

We also carry a bank of LiFePO4 batteries.

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[RogerIvy]

Although possible I’d say it’s very unlikely based on the track record of all the reputable LiFePO4 battery producers. Very low failure rate, and most of the modern BMS’s are really good at protecting the cells.

 

[Guigsy]

If you have twice as many batteries, you're twice as likely to see one fail.

For most things like lighting and the pump, it would give you a bit of redundancy.

Smaller batteries tend to have less current capacity. So if you need both the smaller batteries to drive your beefy inverter, you've actually put yourself in a worse position.

Two batteries will also take up more room, more weight and cost more than a single unit with the same capacity.

 

[funflair]

You can of course have multiple LiFePO4 batteries and depending how these are connected if one detects a problem and shuts down the other/others would still function.

 

[funflair]

If you have twice as many batteries, you're twice as likely to see one fail.

For most things like lighting and the pump, it would give you a bit of redundancy.

Smaller batteries tend to have less current capacity. So if you need both the smaller batteries to drive your beefy inverter, you've actually put yourself in a worse position.

Two batteries will also take up more room, more weight and cost more than a single unit with the same capacity.

I must be so predictable that you knew what I was going to say before I said it

 

[Pausim]

Lead/acid batteries can suffer a single cell failure, so it is wise to have two batteries, in order to disconnect said battery.

Does the same apply to LiFePo4 batteries?

The answer depends partly on what type of cells are used. If you have four large series connected prismatic cells in your battery then in the unlikely event that one cell fails the whole battery would fail. However if you have multiple cylindrical cells then a single cell failure will only take out a proportion of the capacity. A typical 100Ah 12.8V cylindrical cell battery will have 80 cells, 20 parallel rows of 4 series connected cells, if one cell fails it will take out only one row of 4 cells. So one cell failure would reduce the capacity by 5Ah.

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[Raul]

The answer depends partly on what type of cells are used. If you have four large series connected prismatic cells in your battery then in the unlikely event that one cell fails the whole battery would fail. However if you have multiple cylindrical cells then a single cell failure will only take out a proportion of the capacity. A typical 100Ah 12.8V cylindrical cell battery will have 80 cells, 20 parallel rows of 4 series connected cells, if one cell fails it will take out only one row of 4 cells. So one cell failure would reduce the capacity by 5Ah.

Only if they are fused inside by a small wire to separate the failed ones by the rest, most cylindrical's are put together with flat metal tabs spot welded and work as a single cell, and also as seen by the bms as a single cell.

The only way sure to separate failed cells of the good ones is fuse. So multiple banks with separate bms needs separation with fuse to isolate the pack. The one failed cell will receive all the energy available from neighbouring cells and go into thermal runway. A transistor based bms will not have the capability to shut down/ isolate under major fault condition, only bms with external controlled relay can work on such fault, or class T fuse. LiFePo4 failures are very very rare, and starts with abnormal swelling, and major leakage if it opens the valve. If it does open, in contact with oxygen will heat up rapidly. You will not spot this until too late. At this point you want the pack dragged outside immediately. Fire extinguisher will not work, as the exothermic reaction happens inside the cell's aluminium casing.

 

[Pausim]

Only if they are fused inside by a small wire to separate the failed ones by the rest, most cylindrical's are put together with flat metal tabs spot welded and work as a single cell, and also as seen by the bms as a single cell.

The only way sure to separate failed cells of the good ones is fuse. So multiple banks with separate bms needs separation with fuse to isolate the pack. The one failed cell will receive all the energy available from neighbouring cells and go into thermal runway. A transistor based bms will not have the capability to shut down/ isolate under major fault condition, only bms with external controlled relay can work on such fault, or class T fuse. LiFePo4 failures are very very rare, and starts with abnormal swelling, and major leakage if it opens the valve. If it does open, in contact with oxygen will heat up rapidly. You will not spot this until too late. At this point you want the pack dragged outside immediately. Fire extinguisher will not work, as the exothermic reaction happens inside the cell's aluminium casing.

This is how Relion explain cell failure.

 

[Guigsy]

The answer depends partly on what type of cells are used. If you have four large series connected prismatic cells in your battery then in the unlikely event that one cell fails the whole battery would fail. However if you have multiple cylindrical cells then a single cell failure will only take out a proportion of the capacity. A typical 100Ah 12.8V cylindrical cell battery will have 80 cells, 20 parallel rows of 4 series connected cells, if one cell fails it will take out only one row of 4 cells. So one cell failure would reduce the capacity by 5Ah.

The counter argument is lots of cylindrical cells mean lots of small soldered connections. So more likely to get a failure. Compared to only a few prism cells that are often held with bolted studs.

 

[Raul]

This is how Relion explain cell failure.
View attachment 975442

Exactly, as I mentioned above "fused inside". That is for Relion, fused on pcb, not the rest, i have seen cylindrical open welded with tabs

 

[Raul]

The counter argument is lots of cylindrical cells mean lots of small soldered connections. So more likely to get a failure. Compared to only a few prism cells that are often held with bolted studs.

They are spot welded not soldered, solder only on pcb not on cell directly.

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[Raul]

Lead/acid batteries can suffer a single cell failure, so it is wise to have two batteries, in order to disconnect said battery.

Does the same apply to LiFePo4 batteries?

Yes.

 

[AdrianChen]

The counter argument is lots of cylindrical cells mean lots of small soldered connections. So more likely to get a failure. Compared to only a few prism cells that are often held with bolted studs.

Gosh - I'd be in a constant state of anxiety with a Tesla

 

[MisterB]

Cells can be replaced in a lithium battery if you know how to do it......

Though I understand that most BMS's have inbuilt protection to prevent the damage in the first place.

 

[enark]

Not sure, but Boeing may know??

That said never had a lead acid battery knowingly suffer a single cell failure. They do fail when life expired, and length of life (like most things) depends how they are used and maintained, same will be said for Lithium etc

 

[AdrianChen]

Lead/acid batteries can suffer a single cell failure, so it is wise to have two batteries, in order to disconnect said battery.

Does the same apply to LiFePo4 batteries?

We chose two smaller batteries, mainly because of the physical constraints but there were ways round that.

In the past I have had failed LA batteries in large battery banks both flooded and AGM, and one 2*5500wh lithium bank with an issue where the BMS had activated the latching relays. The issue came up on a sale survey so I never actually saw them myself.

So with the van I was aware that it was a possibility and more inclined to choose two, because I might be able to continue the journey with the remaining battery. The chance of an getting an issue is reportedly very low with quality lithium LiFeP04 cells, but I would still focus more on safe installation as the priority over the number of units

Ours (cylindrical) can cope with 100A charging each, and 200A continuous discharge each, so no trouble with either of those in our case with 3000va inverter and 120amp charger. One would require a little more care with the inverter load.

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[AdrianChen]

Cells can be replaced in a lithium battery if you know how to do it......

Though I understand that most BMS's have inbuilt protection to prevent the damage in the first place.

That's the purpose of the BMS, to protect the cells it's 100% a safety device, reporting SOC etc is just a convenience. Having seen a few exploded lead acid batteries, and the mess they can make, it would be good if they had a BMS as well!

 

[nicholsong]

Thank you all.

In my innocence I had expected a yes/no answer.

I shall have to re-read them And try to distil them to make.a decision on what I would need to fit.

 

[bigtwin]

Thank you all.

In my innocence I had expected a yes/no answer.

I shall have to re-read them And try to distil them to make.a decision on what I would need to fit.

The question that you asked should not really be a factor in your decision making process.

However, noting your concern you would be better off with a pair of LiFePO4 batteries as, in the event of a problem with one battery, the BMS would isolate it leaving you with a good LiFePO4 connected.

In the case of a lead bank, a failed cell would result in the good battery trying to feed the bad battery with a likely net result of both batteries becoming kn*ckered.

Ian