Zwy
Emperor Of Solar
Did you have web integration enabled?
House burned down
- Thread starter Jejochen
- Start date
Daddy Tanuki
Solar Wizard
you know Hedges, that is one of the best theories to date on why the Fire Inspector would call out the fuse.... Never occurred to me that the Fire Inspector might be a good Dude.
Sverige
A Brit in Sweden
Respect to the OP for putting this thread up for everyone’s benefit, I’m always impressed when people risk being questioned/ criticised for the greater good of us all maybe becoming a little safer by understanding why things can go wrong.
Lots of discussion of fuses on this thread but I didn’t see any ask about the cell compression used. The OP has said the system was put together a few years ago when cell compression was just becoming a thing and separators were not being discussed. So I’m wondering how much compression was applied and could it have been too much and contributed to the previously leaking cell and maybe even an internal short developing in another cell later, leading to this event?
Lots of discussion of fuses on this thread but I didn’t see any ask about the cell compression used. The OP has said the system was put together a few years ago when cell compression was just becoming a thing and separators were not being discussed. So I’m wondering how much compression was applied and could it have been too much and contributed to the previously leaking cell and maybe even an internal short developing in another cell later, leading to this event?
He did have compression. The typical threaded rods and end plates.
Sverige
A Brit in Sweden
Yes I know he had compression, I’m suggesting the amount of compression might be an important factor. Perhaps if the cells were over compressed, the cracking and leaking of one cell early on and the possible internal short circuit and fire later might be a result of this.
Brucey
Solar Wizard
Yeah this doesn't seem like suitable material for battery shelves. Look at how the material has basically disappeared in the fire. One wonders how things would have faired with his original steel shelving unit prior to his expansion. Other shelves and strings collapsing/pancaking down to strings below wouldn't have helped.
Brucey
Solar Wizard
I did find this regarding flammability:
Seems to indicate certain versions won't sag under fire up to 400 degrees but I don't think they tested with hundred of pounds of batteries on top as a shelving unit, moreso for floors, walls and ceilings.
Seems to indicate certain versions won't sag under fire up to 400 degrees but I don't think they tested with hundred of pounds of batteries on top as a shelving unit, moreso for floors, walls and ceilings.
Guys, please, yall looking at things way too far. The shelves were fine, the fire fighters have torn everything apart to drag all the cells outside. I dont even know what is being discussed here.
_voltmeter_
New Member
- Joined
- Apr 24, 2022
- Messages
- 65
this would be much better for fire protection
Tulex
Solar Wizard
What is being discussed is how to not have this happen to us. There are many variables in adding batteries to a system. We all just want to eliminate the variables that could lead to what happened to you.
seneysolar
Solar Addict
Because this^
Composite shelves simply do not hold that much weight for extended periods of time. They can/will/do sag over time.
That style shelving does not support the center and whatever material used is too thin for span/weight.
Periodic maintenance is recommended for other items such as automobiles.
Currently planning a tear down, detailed inspection and reassembly in a battery case with dividers and a redundant fuse on each case. This was already planned. This thread reinforces need for me to follow through with this plan. Batteries already have dividers.
Currently planning a tear down, detailed inspection and reassembly in a battery case with dividers and a redundant fuse on each case. This was already planned. This thread reinforces need for me to follow through with this plan. Batteries already have dividers.
The rack itself was steel and rated for 300 kg/shelf if i remember correct. There was little to no sagging. The hpl i just added as divider between the system and metal rack.
HalfBaked
Ever the student
I read the entire thread and have an uneducated question:
I currently have 5 sok lifepo4 51.2 100ah units paralleled to a busbar, then a 125a class T fuse before the inverter. It seems a better practice is to have 5 class T fuses between each battery and the busbar.
Assuming I'm correct so far, if I were to perform this upgrade, would I leave the current fuse in place and add the other 5, or would the current fuse become unnecessary or even counterproductive?
Thanks everyone for what you do and for OP sharing his nightmare so that it may help others.
I currently have 5 sok lifepo4 51.2 100ah units paralleled to a busbar, then a 125a class T fuse before the inverter. It seems a better practice is to have 5 class T fuses between each battery and the busbar.
Assuming I'm correct so far, if I were to perform this upgrade, would I leave the current fuse in place and add the other 5, or would the current fuse become unnecessary or even counterproductive?
Thanks everyone for what you do and for OP sharing his nightmare so that it may help others.
Ideally you would fuse everything, but the SOK does have a circuit breaker that should be able to isolate the unit from the system automatically so the string-level fuse becomes supplemental protection.
I like adding the fuse because I don't trust the circuit breakers to reliably interrupt a dead short.
seneysolar
Solar Addict
Ok, so it was metal beams with a metal sheet for the shelf (not particle board or any other material) with the HPL on top of/in addition to the original metal shelf?
My apologies if I misunderstood what you have. I see a ton of people using shelves where the beams only go around the outside and a board lay in the middle, nothing supporting the center of the load. There is another post on the forum where a shelf like that likely collapsed.
300kg is not a lot. Even some of the particle board ones from U-Line are rated at 800lbs. They are also rating it in "Uniform Distributed Load" assuming the max weight is the exact footprint of the shelf. It's important that people don't make this mistake, this is the reason for my post.
I'm definitely not trying to be critical of your build, I'd say it's likely in the top 10 for cleanest install, but... sh*t happens. You seemingly had a cascade of failures, and all these bits of information are critical to system design and safety. Let's get it out there for others to learn.
Brucey
Solar Wizard
So I would leave the class t in place (on the positive between the bus bar and the inverter?) that will protect that wire in case something fails badly in the inverter.
Unfortunately the OP does not seem to have photos of his final configuration before the fire. Photos of several years ago from his old threads are not informative if major changes were made. The 1 photo posted of after the fire is insufficient to establish much. His description of things can be a bit easy to misinterpret. He never stated there was metal shelves only that it was a steel rack. Rack is the frame and may not be a shelf.
Dagoth Ur Does Solar
Solar Enthusiast
I gotta say, this thread has been the exception out of all the fire threads on here I've read. OP's installation looked very professional, to my untrained eye, nothing immediately stuck out as bad. The other threads have had stuff like alligator clips everywhere, cells sitting on particleboard, etc.
Glad OP had insurance and that no one was hurt.
I remember one of Will's recent videos was showing some of the modern powerwall-style batteries seemed to have some kind of fire suppression system built in? If those work at all, I could see the value in paying extra for that.
I am not in any way implying OP did anything wrong here, because I'm too uneducated to be able to tell, but I do notice that these fire threads often have the in-common factor of a DIY battery build as opposed to a prebuilt. Just makes me further shy away from trying it.
Glad OP had insurance and that no one was hurt.
I remember one of Will's recent videos was showing some of the modern powerwall-style batteries seemed to have some kind of fire suppression system built in? If those work at all, I could see the value in paying extra for that.
I am not in any way implying OP did anything wrong here, because I'm too uneducated to be able to tell, but I do notice that these fire threads often have the in-common factor of a DIY battery build as opposed to a prebuilt. Just makes me further shy away from trying it.
Brucey
Solar Wizard
I think the last big fire that was discussed (Germany, Poland?) ended up being a basen green commercial rack style battery
robbob2112
Doing more research, mosty harmless
Looks to most of us that the OP did everything correctly at the time he did them. Several things in the realm of DIY battery build have changed over the years. Namely separators between cells and compression methods.
And I agree, the attention to detail in this was amazing. Very professional looking and in all cases. He followed the vendor recommendations on the design and fusing.
The type fuse used probably shouldn't have been even though the vendor recommends it - i.e. the AIC was low and the plastic it was made from could catch fire along with the flame resistant fuse holder. Flame resistant doesn't mean it can't catch, just that it won't in expected operating conditions for running and failure.
What IMO caused the fire is a combination of a cell in one bank shorting and the fuse blowing and igniting into flames because of the resistance of it when faced with full amps from all other banks. i.e. 125a x 6 = 750amps. Math shows the fuse/wire was hot enough to at the minimum melt the fuse and wire sheath to the max of instant flames. That high temp would have happened between 0.01s and 0.1s. High enough to spontaniously ignite hydrogen from a vent or catch anything flamable in contact with the wire between the bus bar and battery. That combined or instead of a vent could have started the fire.
In the Navy they would call this and all fires a failure of imagination. Failure to imagine all ways the system could possibly catch fire.
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I've done a back of a napkin calculation with a colleague today while discussing this incident. We assumed an internal resistance per cell of 0.3mR, a 16s bank and 7 banks in parallel. We also assumed one cell failed in a pack with a 0 Ohm/0V resulting short link of that one cell (not sure if this is realistic to assume, but I guess it's worst case). In this case, there would be a potential 5kA current flowing into that battery from the others, or 830A per battery.
While I'm pretty sure the aforementioned mega 48v 300A Mega fuse can break that 830A, that 5kA is likely above the AIC rating (didn't look it up). That said, even if the fuse can't handle the 5kA, the other packs should have blown their fuses and the current dumping should have stopped. With the other packs disconnected, there should now be no more issue in the faulty pack, except that once cell if e.g. internally shorted.
But then, internally shorted cells due to dendrites are not low resistance shorts and they can't sustain large currents and tend to be fragile and not sustained...
While I'm pretty sure the aforementioned mega 48v 300A Mega fuse can break that 830A, that 5kA is likely above the AIC rating (didn't look it up). That said, even if the fuse can't handle the 5kA, the other packs should have blown their fuses and the current dumping should have stopped. With the other packs disconnected, there should now be no more issue in the faulty pack, except that once cell if e.g. internally shorted.
But then, internally shorted cells due to dendrites are not low resistance shorts and they can't sustain large currents and tend to be fragile and not sustained...
robbob2112
Doing more research, mosty harmless
Tulex
Solar Wizard
No, we only know that the fuse blew and arced, and that the fire inspector said that was the cause.
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