Monitoring pack pressure for safety

fafrd

Solar Addict
I’m concerned enough about the 2-3 reported fires here on the forum that I’m considering adding a pressure sensor to my 16-cell LiFePO4 battery pack.

I’ve already got my single-line of cells in a 300kgf clamping fixture which I’m setting to ~12psi @ 50% by counting turns on my 8 calibrated springs so adding a pressure sensor should be straightforward and inexpensive: https://www.amazon.com/dp/B07S9YJH8C

I’ll probably just do this and monitor the pressure range I measure under ‘normal’ operation before deciding what I want to do with this pressure signal and how to use it for an extra level of protection.

Has anyone else done anything like this?

Once I know what the max pressure is at 100% SOC, I’m thinking I’ll run the pressure signal into a threshold circuit controlling an alarm and perhaps eventually a fire extinguisher / preventer.

Any thoughts & advice appreciated…
 
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HighTechLab

Small Business Owner
Would not recommend triggering a fire extinguisher based on pressure alone. Sounds like a nightmare to clean up on the first false trip.
 

Bob B

Photon Sorcerer
I’m concerned enough about the 2-3 reported fires here on the forum that I’m considering adding a pressure sensor to my 16-cell LiFePO4 battery pack.

I’ve already got my single-line of cells in a 300kgf clamping fixture which I’m setting to ~12psi @ 50% by counting turns on my 8 calibrated springs so adding a pressure sensor should be straightforward and inexpensive: https://www.amazon.com/gp/aw/d/B07S...rd_i=B07S9YJH8Cp13NParams&smid=A3KMW5XZ660KGT

I’ll probably just do this and monitor the pressure range I measure under ‘normal’ operation before deciding what I want to do with this pressure signal and how to use it for an extra level of protection.

Has anyone else done anything like this?

Once I know what the max pressure is at 100% SOC, I’m thinking I’ll run the pressure signal into a threshold circuit controlling an alarm and perhaps eventually a fire extinguisher / preventer.

Any thoughts & advice appreciated…

Good luck with that.
 

fafrd

Solar Addict
Would not recommend triggering a fire extinguisher based on pressure alone. Sounds like a nightmare to clean up on the first false trip.
Appreciate the thought, but first, if I can trade off the (small but catastrophic) risk of burning down my house go the hassle of cleaning up after a false alarm, I think that’ll be a good trade-off.

And second, since I won’t do anything until I’ve got months if not a full year’s worth of ‘normal’ pressure data, the risk of a false alarm can be reduced close to zero by setting the threshold high enough (>2X normal maximum pressure, for example).

But more importantly, what would you suggest as the best use of a early warning of a possible combustion event?

I can shut down the whole system, but that’s not going to do anything to stop an internally-shorted cell from continuing to heat up…
 

Bob B

Photon Sorcerer
Can’t tell if you mean this is a stupid / impossible / impractical idea (in which case I’d appreciate details) or if you’re wishing me well in thus new initiative…
I'm pretty much in agreement with @HighTechLab.

If you want to do a fire protection system, I think a more conventional Heat / smoke detector system would be more reliable.
Do we have any data to indicate there is a risk of a cell going bad in such a way that it first increases pressure and then starts a fire?
 

fafrd

Solar Addict
I'm pretty much in agreement with @HighTechLab.

If you want to do a fire protection system, I think a more conventional Heat / smoke detector system would be more reliable.
Do we have any data to indicate there is a risk of a cell going bad in such a way that it first increases pressure and then starts a fire?
Gotcha, thanks.

If there are any threads on the conventional Heat / smoke detector system I’d appreciate a pointer.

That’s always an option and I’ll probably add it in any case, though by the time you detect smoke it’s certainly ‘too late’ and while heat at the individual cell level should be a much earlier indicator, heat at y try he battery level may not be.

I’ve not seen any data regarding excess pressure being a reliable precursor of a failure resulting in combustion - that’s why I’ve decided to be the guinea pig ;).

Looks easy and inexpensive to start collecting / monitoring pressure data from my 300kgf fixture which I think will be interesting in any case.

What would be fantastic would be if anyone has heated up cells while monitoring pressure. If heated cells bloat and increase pack pressure, as several suspect, that would make pressure a reliable proxy for increased cell temperature.

I’ve got a couple spare cells and I suspect one or two are failing, so I may resurrect my temperature-controlled chamber, add my new pressure sensor to it, and sacrifice one of my spare cells for science to see what happens to bloat / pressure when temps increase beyond normal operating range (eventually, other priorities for now).
 

RCinFLA

Photon Sorcerer
You are many many many more times likely to start a fire from a bad electrical connection than an overpressure burst of a LFP cell.

An LFP burst spits out electrolyte surrounded by CO2 gas. Solvent in electrolyte is about as flammable as fuel oil. The most likely way to get it to ignite is to put an open flame about 2 feet away from the direction of burst port to give enough distance for the CO2 envelope to disperse leaving just the misted electrolyte solvent to hit the open flame.

A fire around a battery pack is likely started by a bad electrical connection that starts the fire which overheats the cells to bursting point.
Cell pressure would likely be a lagging indicator of a fire already started.
 
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Bob B

Photon Sorcerer
Gotcha, thanks.

If there are any threads on the conventional Heat / smoke detector system I’d appreciate a pointer.

That’s always an option and I’ll probably add it in any case, though by the time you detect smoke it’s certainly ‘too late’ and while heat at the individual cell level should be a much earlier indicator, heat at y try he battery level may not be.

I’ve not seen any data regarding excess pressure being a reliable precursor of a failure resulting in combustion - that’s why I’ve decided to be the guinea pig ;).

Looks easy and inexpensive to start collecting / monitoring pressure data from my 300kgf fixture which I think will be interesting in any case.

What would be fantastic would be if anyone has heated up cells while monitoring pressure. If heated cells bloat and increase pack pressure, as several suspect, that would make pressure a reliable proxy for increased cell temperature.

I’ve got a couple spare cells and I suspect one or two are failing, so I may resurrect my temperature-controlled chamber, add my new pressure sensor to it, and sacrifice one of my spare cells for science to see what happens to bloat / pressure when temps increase beyond normal operating range (eventually, other priorities for now).

I would be interested in seeing how you do the pressure monitoring .... and some of the data about how it tracks with SOC, temperature, etc
I think an easy to implement pressure monitor would be nice to have to experiment with.
Especially since you have a spring fixture.
 

fafrd

Solar Addict
You are many many many more times likely to start a fire from a bad electrical connection than an overpressure burst of a LFP cell.

An LFP burst spits out electrolyte surrounded by CO2 gas. Solvent in electrolyte is about as flammable as fuel oil. The most likely way to get it to ignite is to put an open flame about 2 feet away from the direction of burst port to give enough distance for the CO2 envelope to disperse leaving just the misted electrolyte solvent to hit the open flame.

A fire around a battery pack is likely started by a bad electrical connection that starts the fire which overheats the cells to bursting point.
Cell pressure would likely be a lagging indicator of a fire already started.
Appreciate all of this insight (and it’s exactly what I was hoping for when I started the thread).

As far as a bad electrical connection being a far higher risk of starting a fire than a shorted cell, we are in total agreement.

As far as a fire starting from a bursting cell, that’s not really the failure I was worried about.

I’ll lay out my working hypotheses and would appreciate your insight:

1/ a cell shorts (possibly from wiring failure, possibly from internal terminal failure due to mechanical stress, possibly due to some other mechanism such as dendrite formation possibly combined with a manufacturing defect (Chevy-Bolt-like, and yes, I understand the chemistry is different).

2/ high inter-cell discharge generates a excess heating of the generator me shorted cell.

3/ as the shorted cell heats up, it heats up the adjacent cells above normal operating temps.

4/ as the adjacent cells heat up above normal operating temps, they bloat beyond normal operating levels, resulting in pack pressure exceeding normal operating ranges.

So it was pack pressure exceeding normal operating range that I was interested in, in the hope that the pack pressure might increase from that effect before the primary shorted cell can reach the temps needed to start combustion.

I have no idea whether cell pressure/bloat even increases with increasing temps, let alone whether any such effect would be ‘fast enough’ to be an early indication of a shorted cell heating up y to k the point it could start a fire.

But it was not the risk of a bursting cell I was going after as much as the risk of an individual cell which becomes shorted (for whatever reason).
 

fafrd

Solar Addict
I would be interested in seeing how you do the pressure monitoring .... and some of the data about how it tracks.
Cool - you’ve given me extra motivation to follow through and I’m going to go ahead and invest $10 in one of those Amazon sensors…
 

fafrd

Solar Addict
Treat the box like a fireplace, so it's not touching combustibles and its vented to the outside
Interesting, so metal box on brick or ceramic with a vent….

Couldn’t you even build a complete enclosure out of brick / pavers? (With vent, if needed).

What is the purpose of the vent? To assure the gasses emitting from any bursting cells get vented to the outside rather rust reaching the living space?
 

RCinFLA

Photon Sorcerer
Thermally blocking between cells will help prevent a cascading meltdown. Durock board (shower wall material) may be good enough.
 

Skinny76

Solar Enthusiast
Treat the box like a fireplace, so it's not touching combustibles and its vented to the outside
I'm building a separate enclosure that is not inside my shop. Should something happen, I lose my batteries and Growatt, not my shed and all that is in it. I have 16 more batteries on the way. Once I build them, (no matter how awesome I think I have wiring, fuses, breakers, etc..) I'll at least have that piece of mind. The compression should not be an issue at low C-rates and good quality cells. I do compress mine and have had no issues thus far.
 

Skinny76

Solar Enthusiast
I'm building a separate enclosure that is not inside my shop. Should something happen, I lose my batteries and Growatt, not my shed and all that is in it. I have 16 more batteries on the way. Once I build them, (no matter how awesome I think I have wiring, fuses, breakers, etc..) I'll at least have that piece of mind. The compression should not be an issue at low C-rates and good quality cells. I do compress mine and have had no issues thus far.
Pretty sure I replied to the wrong person!!!
 

Professor Farnsworth

𝕃𝕠𝕘𝕚𝕔𝕒𝕝 ℂ𝕠𝕟𝕤𝕖𝕢𝕦𝕖𝕟𝕔𝕖
Interesting, so metal box on brick or ceramic with a vent….

Couldn’t you even build a complete enclosure out of brick / pavers? (With vent, if needed).

What is the purpose of the vent? To assure the gasses emitting from any bursting cells get vented to the outside rather rust reaching the living space?
I wouldn't trust a brick enclosure, If things go sideways it will produce gases and you want that to go outside.
 
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