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Cause of Battery Fire

Good insulation is the essential part here. Also solid compression on the cells laterally to stop any movement in this mobile environment. Ive heard the cells dont like being compressed from the top, so unsure if that will cause problems in the long run.
 
Good insulation is the essential part here. Also solid compression on the cells laterally to stop any movement in this mobile environment. Ive heard the cells dont like being compressed from the top, so unsure if that will cause problems in the long run.
it would cause problems. for one of the same reasons compression is needed when using solid (not flexible) bus bars, it will harm the terminals. There's a thread floating around here about a fire caused from having put too much pressure on top of the battery. plywood was laid over the top (laying across the battery studs) and was used as a seat. It didn't take long. IIRC, less than a day.
 
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I'm no fan of those serrated lock nuts. I would put a dap of silicon/lock tight/etc on the stud threads after you tighten the nut down so it can't shake loose and come off the stud.
 
I'm going to add my advice, mount between the rear axle and the front axle. Anything behind the rear axle is going to bounce a lot more and harder than the rest of the rig

As a kid the rear most seat of the school bus was a premium seat to get the bounce on speed bumps, good fun for a kid, but not for batteries.

This is actually very useful information to those in mobile applications.
 
I built my battery box out of aluminum and found an interesting thing while I was assembling it. The bottom of my cells (i dont know about others) are open to the elements, as the blue sleeve doesn't wrap the entire battery. As some know as well, there is a positive charge on the case if you check it between the terminals. When I set the cells down onto my aluminum box, I was getting ~18v from the case to the negative terminal. After setting down a sheet of UHMW and ensuring no metal was making contact, all was well.

Pics for reference:
20210424_115349.jpg

20210424_120000.jpg

I cant tell in your picture, but if your cells are resting directly onto the unistrut, then you are probably causing a dead short right there.
 
Nice box LtDan! ... welding aluminum is not easy. Is the square hole for a monitor?
 
Nice box LtDan! ... welding aluminum is not easy. Is the square hole for a monitor?
Thanks! I actually bolted it entirely together so I could set the batteries onto a bottom tray, and then put the sides up around them, rather than trying to set the batteries into a box that my hands couldn't fit into. And no, they are for handles that I got on McMasterCarr, they are spring loaded and are flush with the exterior of the box.
 
I built my battery box out of aluminum and found an interesting thing while I was assembling it. The bottom of my cells (i dont know about others) are open to the elements, as the blue sleeve doesn't wrap the entire battery. As some know as well, there is a positive charge on the case if you check it between the terminals. When I set the cells down onto my aluminum box, I was getting ~18v from the case to the negative terminal. After setting down a sheet of UHMW and ensuring no metal was making contact, all was well.

Pics for reference:
View attachment 62920

View attachment 62921

I cant tell in your picture, but if your cells are resting directly onto the unistrut, then you are probably causing a dead short right there.
omg that's what, 3.5, 4mm thick? holy **** your batteries are SAFE
 
Ok, I may not be able to see it from the pic, but I assume you also used electrical insulation between each cell. Please say yes.
And along the sides of the box. The cells should be completely isolated from the aluminum frame.
 
Ok, I may not be able to see it from the pic, but I assume you also used electrical insulation between each cell. Please say yes.
Absolutely, there is 1/16" HDPE sheets inbetween every cell, and the threaded rods are also heat shrinked to prevent shorting.

EDIT: Sorry for the thread jacking lol
 
I cant tell in your picture, but if your cells are resting directly onto the unistrut, then you are probably causing a dead short right there.

Those did look like pressure points to me. Insulation should be used.

Maybe a dead short between cases, but not between cell terminals, I don't think.

We're heard of some cells leaking out the vent when laid on their sides. I think there is a jelly roll inside with separator material, but excess electrolyte sloshing around. That would make an electrochemical cell between electrodes and cell case, producing some voltage and current. I don't think the current flow would be enough to cause catastrophic damage when connected between cells or between cells and chassis (and negative terminal of pack.) At positive end, fairly large voltage to chassis which would force current and etch or electroplate materials.

Such current flow might etch a hole in the case. It would cause some draining of the cell's charge, probably limited by "capacity" of the electrode/case "cell". Depending on materials, it could dissolve chemicals from case into electrolyte, adding contamination that could diffuse into cells.

I would want to insulate cases from each other and from enclosure, but I don't think failing to do so would cause fireworks. At least, not unless it drove a cell to over/under-charge conditions.
 
Thank you for the detailed post and photos, you experienced one of my RV nightmares when thinking about changing over the battery bank. So glad you caught it before you lost the bus, imagine if this happened while you were asleep. . .

I am really struggling around how to best build my packs and if I should use these aluminum thin walled cells. They just do not seen robust enough to handle the harsh vibrations for over the road applications without a very well thought out and constructed case. The PVC cased units like the Fortune cells, seem like a much more robust and applicable form factor to start with, but you still need the right mount and enclosure.

Based on your fire, I think a metal enclosure is just required. I can't imagine plywood protecting from a blown tire, running over a ladder at 60 MPH, etc. Our RV is running a full active air suspension but there are still times where we hit a road transition that launches me out of the air seat (Looking at you I-24 in Chattanooga). Adding a flammable material to the box doesn't seem like the best option either, you could create a smoldering fire that goes on for a long time before finally igniting.

Not sure the best way to alert on a potential fire like this. The operating environment rules out a typical smoke detector, VESDA, etc so I think you'd have to use a heat detector but that's only going to tell you when it's actually on fire, it's not going to work for smoldering. I can't imagine a way to keep diesel soot out of the box well enough to use anything else unless you completely air seal the box.

Thanks again for posting, and please continue to let us know how decide to tackle this on round 2, looking forward to learning from your journey!
 
Heat detectors come in two general forms, one uses a fusible link which melts at a predetermined temperature, then there are dual function type, which use a chamber with a small pinhole to activate on rate of temperature, they too incorporate a fusible link, making them dual purpose, the application depends on environmental conditions.

Smoke detectors also fall into two categories, photo electric and ionization, both can detect smoke, but one may be more sensitive to the particular type of smoke generated, as for the smoke generated for from a LiFePo4 fire, I can't, ar this time definitively answer that question, without further research.

Basically what I'm alluding to is, don't assume because there are protections installed, they will work as intended.

BTW, I am qualified in fire alarm inspection and testing.
 
I don't see any way to use a smoke detector for an externally mounted battery box on a diesel. It would need to be incredibly well sealed to keep out all of the water and particulates. Otherwise it would trigger all the time or foul the sensor.
Single stage heat detector is all I think might work, too much heat rise on a hot interstate drive to use a standard heat rise at 135 degrees. My tires are regularly over that on a long daytime drive in the west.
 
My biggest fear with lifepo4 in the RV... :oops:

I'm surprised HDPE 'starboard' isn't used more often. Impervious to everything and non-conductive. It's used a lot on boats and I suspect that many are unaware of its existence due to that.

I liked this build so much I'm copying its overall design parameters with a few modifications.

Thread link:

20211216_200841-jpg.76040
 
My biggest fear with lifepo4 in the RV... :oops:

I'm surprised HDPE 'starboard' isn't used more often. Impervious to everything and non-conductive. It's used a lot on boats and I suspect that many are unaware of its existence due to that.

I liked this build so much I'm copying its overall design parameters with a few modifications.

Thread link:

20211216_200841-jpg.76040
I’m afraid that HDPE melts at 235 degrees while lithium burns closer to 2000 degrees. I love starboard, and have used it a lot on my boat, but it won’t save you from a fire I’m afraid.
 
My biggest fear with lifepo4 in the RV... :oops:

I'm surprised HDPE 'starboard' isn't used more often. Impervious to everything and non-conductive. It's used a lot on boats and I suspect that many are unaware of its existence due to that.

I liked this build so much I'm copying its overall design parameters with a few modifications.

Thread link:

20211216_200841-jpg.76040

LDPE/UHMW are not dimensionally stable. Over time both of the end of this box will bend in 1/8"-3/16"and the Lexan/Plexigalss will sag.

The wires on he edge of the Lexan/Plaxi is not a great feature.

Tin plated lugs and bus bars aren't used?

Hope the crimps with 3 wires are done properly.

HDPE is stable but to have any rigidity it needs to be a min 3/4". Even 3/4 HDPE will sag if used over the battery. I'd use 1/4"-1/2" HDPE with a 1/2" or 3/4" x 3/4" HDPE bar screwed along the center.

At 1250F it takes 15min to burn through 3/4" plywood.

Ceramic fiber board will prevent plywood or HDPE from burning.....costs about the same as plywood these days.
 
Heat detectors come in two general forms, one uses a fusible link which melts at a predetermined temperature, then there are dual function type, which use a chamber with a small pinhole to activate on rate of temperature, they too incorporate a fusible link, making them dual purpose, the application depends on environmental conditions.

Smoke detectors also fall into two categories, photo electric and ionization, both can detect smoke, but one may be more sensitive to the particular type of smoke generated, as for the smoke generated for from a LiFePo4 fire, I can't, ar this time definitively answer that question, without further research.

Basically what I'm alluding to is, don't assume because there are protections installed, they will work as intended.

BTW, I am qualified in fire alarm inspection and testing.
I like to use fenwal thermostats for rugged environments and positive operation. They are rate compensated and at the lowest temp (140f?) should be good. They come in many flavors including different coatings for different environments. Strictly heat detection but reliable.
 
LDPE/UHMW are not dimensionally stable. Over time both of the end of this box will bend in 1/8"-3/16"and the Lexan/Plexigalss will sag.

The wires on he edge of the Lexan/Plaxi is not a great feature.

Tin plated lugs and bus bars aren't used?

Hope the crimps with 3 wires are done properly.

HDPE is stable but to have any rigidity it needs to be a min 3/4". Even 3/4 HDPE will sag if used over the battery. I'd use 1/4"-1/2" HDPE with a 1/2" or 3/4" x 3/4" HDPE bar screwed along the center.

At 1250F it takes 15min to burn through 3/4" plywood.

Ceramic fiber board will prevent plywood or HDPE from burning.....costs about the same as plywood these days.
Agreed. Mine won't have those features. My T fuse and shunt will be on the base with the bms in a vertical position.

But 'dimensionally stable'? You mean from flex and sag. Emkay, maybe.
Why didn't you post on the guy's thread and tell HIM his build was crap? Seriously. Why?
 
I could tell you stories about voltage leaking from batteries, battery switches and fuse blocks to metal cases. When I make a marine battery boxes it has to be non conductive.
In my own boat ~1993-ish I put two bolts through the helm support plywood of my closed-bow 14’ boat - one for a positive terminal post, one for negative. About 4” apart iirc

A few years later I was having some mild battery drain issues and was looking under the foredeck when I saw wetness running along the plywood. I touched it, it wasn’t wet!???
Got a flashlight and examined closely only to discover that a silvery gray metallic something was ‘plating’ the plywood along late growth grain of the wood. While it wasn’t wet or water stained, apparently there was enough moisture to facilitate electrolytic migration of tin or zinc or electrical solder from the electrical connections of one bolt to the other bolt, heavier nearer the negative side. Not even close to a “peelable” thickness but visually it was there. Blew my mind.

That completely changed my thinking on a lot of things.

I’d probably not use plywood without a substantial plastic liner for any battery box and a cover over the conductors LOL
 

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