LFP cells gone bad

[terrango]

These are battery cells from my coworker. My coworker is a licensed electrician and insisted he knew what to do.
He decided that a BMS was not needed and that the inverter would take care of regulating and protecting the cells.
So he left the power on in the middle of winter, the batteries drained 100%, froze, then at some point the inverter charged 9/16 cells as 9 are extremely bloated.
And now the entire pack of 16 cells shows 6V. (100amp cells) 3 cells are holding a voltage of 1.02V, 4 other cells are holding voltages of .034, .056, .0455 and so on...
We sometimes learn hard expensive lessons.
He bought a new set of LFP batteries and has decided that the bms is still not needed.
he will instead just disconnect the batteries when not in use.


Dont do this..... Buy a BMS!

 

[Steve_S]

Common Sense and a Grasp on Reality is OPTIONAL in the 21st century...
Stay away from this character, he'll burn the world (hopefully just his).
I'd seriously question any / all of his work if he is that diligent.... oivey

 

[rodrick]

You can’t fix stupid but you can learn from it

 

[Alkaline]

He bought a new set of LFP batteries and has decided that the bms is still not needed.

What a legend!?

 

[sunshine_eggo]

These are battery cells from my coworker. My coworker is a licensed electrician and insisted he knew what to do.
He decided that a BMS was not needed and that the inverter would take care of regulating and protecting the cells.
So he left the power on in the middle of winter, the batteries drained 100%, froze, then at some point the inverter charged 9/16 cells as 9 are extremely bloated.
And now the entire pack of 16 cells shows 6V. (100amp cells) 3 cells are holding a voltage of 1.02V, 4 other cells are holding voltages of .034, .056, .0455 and so on...
We sometimes learn hard expensive lessons.

Your coworker is excluded from that statement.

He's a moron.

 

[Zwy]

These are battery cells from my coworker. My coworker is a licensed electrician and insisted he knew what to do.
He decided that a BMS was not needed and that the inverter would take care of regulating and protecting the cells.
So he left the power on in the middle of winter, the batteries drained 100%, froze, then at some point the inverter charged 9/16 cells as 9 are extremely bloated.
And now the entire pack of 16 cells shows 6V. (100amp cells) 3 cells are holding a voltage of 1.02V, 4 other cells are holding voltages of .034, .056, .0455 and so on...
We sometimes learn hard expensive lessons.
He bought a new set of LFP batteries and has decided that the bms is still not needed.
he will instead just disconnect the batteries when not in use.


Dont do this..... Buy a BMS!

People like this are what cause the rest of us to have more regulation put upon us. The lobby for more regulation can point at cases like this fella that end up burning their house down.

 

[JJJJ]

Just when you think you have seen everything….

These are not AA batteries we are working with.

That is why I respect and appreciate this forum. Safe practices are taught and reinforced in our discussions.

 

[Magnetom]

Sounds like your co-worker may be a potential Darwin Award candidate.

 

[MarcoWasRight]

These are battery cells from my coworker. My coworker is a licensed electrician and insisted he knew what to do.
He decided that a BMS was not needed and that the inverter would take care of regulating and protecting the cells.
So he left the power on in the middle of winter, the batteries drained 100%, froze, then at some point the inverter charged 9/16 cells as 9 are extremely bloated.
And now the entire pack of 16 cells shows 6V. (100amp cells) 3 cells are holding a voltage of 1.02V, 4 other cells are holding voltages of .034, .056, .0455 and so on...
We sometimes learn hard expensive lessons.
He bought a new set of LFP batteries and has decided that the bms is still not needed.
he will instead just disconnect the batteries when not in use.


Dont do this..... Buy a BMS!

A BMS is not needed. But some common sense is. If your system is running without a human present to check on it at least twice a day and has the capability of recharging the cells in cold weather then you've set yourself up for failure.
If you have cells that could be exposed to freezing temps you need to either get a BMS that has low temp protection/built in heating, install your own heating system with external temperature controllers or have a way to disable the charger/prevent the cells from receiving charging current if the temperature drops below a certain point.
I'd like to know how his cells dropped below 2 volts. What inverter was he using? Did he have it correctly programmed with a low voltage setting? I'm going to bet the answer to that is no.
More importantly, what drained his cells beyond the low voltage threshold of the inverter? What was drawing a load after the voltage in the pack was too low to power any kind of AC load? I'm assuming his inverter had completely powered off and there was no idle current draw from it...so??

 

[sunshine_eggo]

A BMS is not needed. But some common sense is.

You literally just expressed your lack of common sense.

A human BMS has a 100% failure rate.

Everything else you said is irrelevant.

 

[richard cabesa]

I know someone doing the no bms thing.
I just keep telling him I hope no one dies in the fire

 

[Horsefly]

There's a guy on another forum who built his own 8-cell LFP battery and despite my warnings he was set on not using a BMS. Instead he just hooked up a Heltec capacitive balancer. He's been using it for about 8 months now in his camp trailer, and posts updates on how it is doing. I guess it can be done successfully, at least for 8 months.

I'm not sure I get why someone would specifically choose not to use a BMS. Except for some of the crazy expensive ones (Batrium, REC, etc.), they are not a significant cost relative to the whole system.

 

[sunshine_eggo]

There's a guy on another forum who built his own 8-cell LFP battery and despite my warnings he was set on not using a BMS. Instead he just hooked up a Heltec capacitive balancer. He's been using it for about 8 months now in his camp trailer, and posts updates on how it is doing. I guess it can be done successfully, at least for 8 months.

I'm not sure I get why someone would specifically choose not to use a BMS. Except for some of the crazy expensive ones (Batrium, REC, etc.), they are not a significant cost relative to the whole system.

I know someone using NMC without a BMS (same PHEV cells I'm using with the Batrium). He is EXTREMELY knowledgeable, and is a bonafide inventor of some pretty impressive stuff. He has his own custom monitoring system in place, is using active balancers, and he doesn't go anywhere near 4.20V when charging (3.92V). He does have a pack voltage based cutoff relay system in place at 4.0V/cell average.

Each of his cells is capable of 150A (about 6C), and there are 21 cells in parallel. They are also internally fused (built into the Panasonic cell).

So, it's the next best thing to a BMS, but he's aware of the risks, is intimately familiar with the cells, and has made a conscious decision to not deploy an off-the-shelf BMS because he sees little added value over his own custom solution.

It's a little nuts, but he's the only human on the planet that I personally know, who I think is probably going to be fine.

 

[JoeHam]

BMS or

BE A MESS !

 

[time2roll]

He bought a new set of LFP batteries and has decided that the bms is still not needed.
he will instead just disconnect the batteries when not in use.

Please keep us updated on the results over the next year.
Should be interesting if it can be held together.

Often third time is the charm

 

[MarcoWasRight]

You literally just expressed your lack of common sense.

A human BMS has a 100% failure rate.

Everything else you said is irrelevant.

A human BMS has a 100% failure rate? So the packs made in the early days of LiFeP04 for RV's that had no BMS and are just now being taken out of service in some cases (usually to upgrade to 304's or something similar) that never had a BMS on them and survived a decade or so are................
Like I said, if you have low/high voltage cutoff in your system (ie inverter and SCC) and you trust them because you know as long as you don't push them hard they have an extremely low failure rate you can run a pack for thousands of cycles without a BMS.
I have a small A123 12V 20Ah pack with no BMS and she's still chugging right along. Rarely ever take it below 12.8V and normally I'm using a Lipo balance charger to bring it back up to 13.6-14.0V. I'll let you know when it dies but don't hold your breath.

 

[MarcoWasRight]

I know someone using NMC without a BMS (same PHEV cells I'm using with the Batrium). He is EXTREMELY knowledgeable, and is a bonafide inventor of some pretty impressive stuff. He has his own custom monitoring system in place, is using active balancers, and he doesn't go anywhere near 4.20V when charging (3.92V). He does have a pack voltage based cutoff relay system in place at 4.0V/cell average.

Each of his cells is capable of 150A (about 6C), and there are 21 cells in parallel. They are also internally fused (built into the Panasonic cell).

So, it's the next best thing to a BMS, but he's aware of the risks, is intimately familiar with the cells, and has made a conscious decision to not deploy an off-the-shelf BMS because he sees little added value over his own custom solution.

It's a little nuts, but he's the only human on the planet that I personally know, who I think is probably going to be fine.

Quite the contradiction....in such a short span of time.

 

[TomC4306]

A human BMS has a 100% failure rate? So the packs made in the early days of LiFeP04 for RV's that had no BMS and are just now being taken out of service in some cases (usually to upgrade to 304's or something similar) that never had a BMS on them and survived a decade or so are................
Like I said, if you have low/high voltage cutoff in your system (ie inverter and SCC) and you trust them because you know as long as you don't push them hard they have an extremely low failure rate you can run a pack for thousands of cycles without a BMS.
I have a small A123 12V 20Ah pack with no BMS and she's still chugging right along. Rarely ever take it below 12.8V and normally I'm using a Lipo balance charger to bring it back up to 13.6-14.0V. I'll let you know when it dies but don't hold your breath.

The point of the BMS is not the pack voltage, it's the cell voltages...
In your 20 amp hour pack, what are the cell voltages when the pack is at 14 volts? Any of the individual cells over 3.6 or 3.7 volts? it's the individual cell safety and health that is the point of using a BMS.

 

[Zwy]

I have seen instances where a cells in a pack become unbalanced and the pack voltage of a 48V 16S pack, for example, might be 56.0V however you will see a cell at 3.6V and some at 3.4V. Moving from 3.6V to a higher voltage that can be cell damaging takes just a few seconds or less with enough charging amperage.

One could run without a BMS in theory, if you were to work very conservatively inside the knee areas of the LFP cells. However, over time, the imbalance between cells will increase, some cells might be at less than 3.0V while others at 3.6V and higher. An active cell balancer might help keep a loose balance. But there is nothing in place for a safeguard.

 

[sunshine_eggo]

A human BMS has a 100% failure rate? So the packs made in the early days of LiFeP04 for RV's that had no BMS and are just now being taken out of service in some cases (usually to upgrade to 304's or something similar) that never had a BMS on them and survived a decade or so are................

You'll have to provide evidence of this claim.

Like I said, if you have low/high voltage cutoff in your system (ie inverter and SCC) and you trust them because you know as long as you don't push them hard they have an extremely low failure rate you can run a pack for thousands of cycles without a BMS.
I have a small A123 12V 20Ah pack with no BMS and she's still chugging right along. Rarely ever take it below 12.8V and normally I'm using a Lipo balance charger to bring it back up to 13.6-14.0V. I'll let you know when it dies but don't hold your breath.

The only thing I'll grant you an exception for is the use of a balance charger as you indicate. That essentially eliminates the risk of cell over-volt during charge, and it minimizes risk on the downside as at least you know the battery is top balanced with max potential capacity at every charge.

Quite the contradiction....in such a short span of time.

Not in the least. I responded to your, "A BMS is not needed," which remains an absolutely absurd statement vs. me summarizing a custom monitoring system by someone with high technical knowledge and understanding of the consequences. These are also a chemistry with voltage to SoC correlation unlike LFP.

It's likely you've not been around long enough, and/or you've not paid enough attention to see the many instances of destroyed cells from folks deciding to run without a BMS. One guy completely trashed a Tesla module from overcharge and is lucky to not have experienced a fire.

So it's probably best to keep your BS statements to yourself. A BMS is needed.