Cause of Battery Fire

limey44460

New Member
Joined
Feb 18, 2020
Messages
28
First, everyone was fine and I was able to stop the fire before it spread to other parts of the RV.



With that out the way I had an unexpected fire in one of my two battery packs(photos attached). Each one of them is a “48” volt system with 16 of the Basen 280 AH LiFePo4 cells. Each pack has a Chargery BMS and DCC relay, in addition to a 300 amp class T fuse and 250 amp DC rated breaker with 265 amp conductors. The negative is bonded to the chassis of the RV. Each pack is installed in a metal cage and then covered with a metal box. This setup worked for about 3-4 weeks before one battery pack developed a hard short between the positive cabling and the vehicle chassis, thus destroying the fuse as intended. I tried to switch to the secondary battery pack and screwed up on turned on both at one and destroyed both fuses. Yes I forgot to check the time constants on the breakers, so I just have expensive switches. At this point I am about a week from home and both battery packs done. Both are mostly charge ~54 volts.

Since the fuses are hard to replace, I decided to limp home and stop at RV parks one the way home vs a field replacement of the fuses. I plug this RV every night for 6 or 7 days. I have not issue with the 50 amp connections but have some trouble with ground faults when I had 15 amp connections. Then on my last stop I plug in the 50 amp connection, start up the AC (1500 watts) and water heater (2300 watts) and walk back out to see smoke coming from the battery box. I was able to get the fire extinguished with the fire extinguisher and water hose. The power at the RV park looked good, roughly 240 L1-L2 and 120 L1-N and L2-N, but I did not write it down.

So not I am trying to figure out what happened so I can fix it. The fires destroyed the most positive cell of the 16, while the other 15 are still holding a charge. I bought the LiFeP04 chemistry because it was not supposed to be fire prone. A little reading and what I could find says they will catch fire because of: 1) manufacturing defects, 2) excess charge rate, 3) excess discharge rate. Since the fuse was blown there was no intentional charge or discharge.

After I removed the battery pack I found two cells had continuity to the metal case (which was not the case when it was installed. The cell that burned (Most positive, #16) had continuity from positive and negative to the case. Cell #14 also had continuity from the negative terminal only. I do not know if this was caused by the fire. This battery pack had three previous shorting incidents. Once during assembly the main fuse went. I never noticed this but suspect I bummed one of the fuse terminals with the RV chassis. I went to replace this fuse and dropped the hex nut from the positive terminal creating an arc and welding the nut. Then trying to solder the BMS back on the solder shorted out and melted. While discharging during these shorts, cell 16 is survived all these insults without catching fire before my 3 week trip.

I inspect my DC wiring, in particular the bonding between the 48 volt negative terminal and the RV chassis and found no damaged wiring. I am not sure quite what happened but am looking for ideas. The suspected cause of battery 16 making contact with the chassis ( before the fuse allowing for uncontrolled discharge) doesn’t seem to make sense since it happened while stopped and just after I plugged it into an 50 amp RV plug. Lack of a clear cause also makes it hard to decide to rebuild with metal for fire protection or wood for isolation.View attachment 58887
WHY METAL CASE JUST ASKING FOR TROUBLE.
 

koobs

Solar Enthusiast
Joined
Nov 19, 2020
Messages
64
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.
 

DerpsyDoodler

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Jan 10, 2021
Messages
1,635
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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jtvt

Solar Enthusiast
Joined
Feb 11, 2021
Messages
148
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.
 

Mcgivor

Solar Addict
Joined
Jul 24, 2021
Messages
187
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.
 

Lt.Dan

Photon Sorcerer
Joined
Dec 25, 2020
Messages
1,152
Location
Visalia, Ca
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.
 

Sanwizard

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Feb 2, 2021
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1,302
Nice box LtDan! ... welding aluminum is not easy. Is the square hole for a monitor?
 

Lt.Dan

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Dec 25, 2020
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Visalia, Ca
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.
 

curiouscarbon

Science Penguin
Joined
Jun 29, 2020
Messages
1,585
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
 

Sanwizard

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Feb 2, 2021
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1,302
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.
 

Lt.Dan

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Dec 25, 2020
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Visalia, Ca
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
 

Hedges

I See Electromagnetic Fields!
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Mar 28, 2020
Messages
8,434
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.
 

jberger

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Joined
Jun 1, 2021
Messages
14
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!
 
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