House burned down

[haraldt1]

hello, I came across you by chance while searching in a German forum, first of all, it's good that nothing happened to anyone. but from my point of view it's absolute nonsense what the fire expert here wants to have found as a fault.
if it happened at night with low currents, where did the high currents come from to blow the fuse? there must have been a short circuit on the inverter or the wiring. In addition, the BMS should have switched off. So if it was not a combination of several faults at the same time, then in my view the fuse can be ruled out. I would rather assume a short circuit due to the lack of insulation between the cells as far as I have seen. A fuse can never cause a fire without a significant load.

Sorry for my bad English ;-)

 

[upnorthandpersonal]

A fuse can never cause a fire without a significant load.

If there is a short due to a failing inverter for instance, and the fuse is not able to quench the arc, it most definitely can start a fire. Whether that is the case here or not is undetermined, but you can't rule it out.

 

[robby]

I'm glad these EG4 indoor batteries have integrated fire suppression.

I would like to actually see this work in a real situation. Has EG4 or anyone else ever demonstrated this being used to extinguish a fire inside a battery pack? I

 

[Mattb4]

If there is a short due to a failing inverter for instance, and the fuse is not able to quench the arc, it most definitely can start a fire. Whether that is the case here or not is undetermined, but you can't rule it out.

That's why I keep my fuses separate from the dynamite. Darn things are always causing a problem. Maybe the fuses need a special protective box?

Sorry about the humor.

 

[upnorthandpersonal]

Maybe the fuses need a special protective box?

You joke, but just look online to find images of melted/burnt fuse holders.

 

[Yurtdweller]

I have not read the entire thread. Apologies. My question is, do we know, did the arc start a fire that spread to the batteries? Or did incoming power overload the batteries somehow, and then the battery cells actually initiated the fire? I ask because I travel in a yurt, therefore I have my LiFePo4 cells inside my yurt with me. I cannot have an outbuilding for various reasons. Since the fire started at night, the solar was obviously not feeding excessive power into the system. This fault must have come from the battery outputting excessive power, for some reason, or from an incoming power source feeding massive amps into the system? I have four 12v packs of LiFePo4 cells (Lf280k). Each pack is individually mega-fused (125 amps) before connecting through a Lynx PowerIn bus. Each pack is BMS limited to 100 amps. I am curious as to how large of an arc can be initiated by 100 amps @ 12v, and whether it could arc across that fuse gap? I cannot conceive of any situation that could cause that battery to output enough power to jump such a gap, and since I have no incoming power besides 60 amps from my charge controller, I cannot see any chance of incoming power causing such a situation, either. But I want to try to understand what caused the situation of this fire, just in case I've overlooked something.

 

[upnorthandpersonal]

do we know, did the arc start a fire that spread to the batteries? Or did incoming power overload the batteries somehow, and then the battery cells actually initiated the fire?

We don't know anything, that's why we're 17 pages into speculation.

 

[Zwy]

hello, I came across you by chance while searching in a German forum, first of all, it's good that nothing happened to anyone. but from my point of view it's absolute nonsense what the fire expert here wants to have found as a fault.
if it happened at night with low currents, where did the high currents come from to blow the fuse? there must have been a short circuit on the inverter or the wiring. In addition, the BMS should have switched off. So if it was not a combination of several faults at the same time, then in my view the fuse can be ruled out. I would rather assume a short circuit due to the lack of insulation between the cells as far as I have seen. A fuse can never cause a fire without a significant load.

Sorry for my bad English ;-)

If a cell shorts internally, it will draw current from the other batteries in the bank. External loads can be non existent but the failed cell would cause a tremendous load.

 

[MattiFin]

If a cell shorts internally, it will draw current from the other batteries in the bank. External loads can be non existent but the failed cell would cause a tremendous load.

Also there are no quarantees that the cell shorts to solid zero ohms. It could as well short partially and draw only 200A.
Over time 6 parallel strings would dump nearly 1800Ah and 6kWh of energy to that poor cell. Enough energy to make the cell glow red.

Recommendation for String level contactor disconnect seem like smart move.

 

[SeaGal]

I cannot conceive of any situation that could cause that battery to output enough power to jump such a gap,

@Zwy's posting ^^^^ (post#333) explains a situation that could cause that battery to output enough power.

 

[Shimmy]

The OP did the right setup but used a fuse between batteries that was not a Class T. I'm quite certain this is the cause of the fire.

The fuse provided an ignition source for sure; it is also likely that it made the fire more difficult to put out.

But in terms of a roof-cause analysis you either need to say cell failures are inevitable, and the lack of BMS string isolation was the root cause, or you say that the cell failure was an extraordinary event and the root cause.

Moreover, with cell failure you have what I understand to be an anomaly in a cell failing shorted to the point that other cells enter thermal runaway. For a cell to fail shorted are we looking at things like dendrites that escalate a small, high-resistance short into a dead short, or some catastrophic event that creates a dead short?

 

[ScropusGobbleBottom]

Also there are no quarantees that the cell shorts to solid zero ohms. It could as well short partially and draw only 200A.
Over time 6 parallel strings would dump nearly 1800Ah and 6kWh of energy to that poor cell. Enough energy to make the cell glow red.

Recommendation for String level contactor disconnect seem like smart move.

It would only be a 3. 2v drop and the other 15 cells would soak that up in mere seconds across the 15s . We are talking about 0.225v gain across the 15s remaining.... if the other cells were at rest, fully charged, at 3.45 they might not even be high cell voltage disconnect.
I seriously doubt we are talking about more than 100 amps for less than a minute. Certainly nothing to blow a fuse over.

 

[MattiFin]

It would only be a 3. 2v drop and the other 15 cells would soak that up in mere seconds across the 15s . We are talking about 0.225v gain across the 15s remaining.... if the other cells were at rest, fully charged, at 3.45 they might not even be high cell voltage disconnect.

Very good point. Current dumping from other cells would be a major problem only on battery banks with cells in parallel.
Also fuses should have no problem disconnecting the string with one battery failed to zero ohms as currents involved are only about 1/15 of invidual cell short circuit current. (3.3v voltage difference between the strings but ~15x series resistance of invidual cell)
Fuse also needs to break only 3 volt potential, again very easy task for even something less capable than class-T.

 

[Shimmy]

It would only be a 3. 2v drop and the other 15 cells would soak that up in mere seconds across the 15s . We are talking about 0.225v gain across the 15s remaining.... if the other cells were at rest, fully charged, at 3.45 they might not even be high cell voltage disconnect.
I seriously doubt we are talking about more than 100 amps for less than a minute. Certainly nothing to blow a fuse over.

So in an inverter short scenario how does the battery not get disconnected from the inverter... and why is the fuse considered the ignition source? The fuses are significantly less likely to see currents in excess of their interrupting rating as currents are shared and external resistance comes into play.

For an unmaintained system I get how there could he multiple failures that went unnoticed, but that doesn't seem to be the case here.

 

[ScropusGobbleBottom]

I Got a 6s 20Ah lipo battery with one cell at 0. Should I charge it?
Or should I put it in parallel with a 6s and see what happens? Kidding. 6s is very different than 15-16s

 

[ScropusGobbleBottom]

Fuse also needs to break only 3 volt potential, again very easy task for even something less capable than class-T.

Good point here as well 3v doesn't like to arc

 

[ScropusGobbleBottom]

So in an inverter short scenario how does the battery not get disconnected from the inverter... and why is the fuse considered the ignition source? The fuses are significantly less likely to see currents in excess of their interrupting rating as currents are shared and external resistance comes into play.

For an unmaintained system I get how there could he multiple failures that went unnoticed, but that doesn't seem to be the case here.

why is the fuse considered the ignition source?

Because fire dept. Guy thinks that was the hottest spot. And that is usually where the fire originates. There is probably some truth to the location, tho, not necessarily the fuse.

 

[Solar254]

The OP did the right setup but used a fuse between batteries that was not a Class T. I'm quite certain this is the cause of the fire.

I don't think the fuse is to blame. The OP reported that some of the cells had leaked and he had to replace them. Most likely some cells shorted.

 

[hogback]

3V could pull a lot of current with the primary resistance being the thick cables we all tend to use. I don't know if it is enough to maintain a plasma across the distance of the gap in these non-T fuses though. Seems like there needed to be some sort of flammable material already present when the fuse might have arced.

 

[Ampster]

I don't think the fuse is to blame.

I look at it this way, if the fuse had not melted and not created and arc, there would not have been a combustion source. I have had leaking LFP batteries before, but they did not self ignite. Yes the cells shorted, and that was what caused the fuse to melt. Shorts themselves cause current to flow but do not necessarily create combustion if a fuse does its job. I may be splitting hairs but from a risk management viewpoint I came to the conclusion a Class T fuse would have mitigated the risk of a short.

 

[Brett V]

Contactor needs to be in umm contact in order to function. If the fuse blows, then the contactor is pointless. REC manuals and my (former) industrial electrician are in agreement on placement.

It's a relay. Doesn't matter where in the circuit it is to operate. You shouldn't have anything between the positive of the battery and a class-t but as short as physically possible cable that's sized large enough to carry the current surge that will open the fuse.

 

[Tulex]

I look at it this way, if the fuse had not melted and not created and arc, there would not have been a combustion source. I have had leaking LFP batteries before, but they did not self ignite. Yes the cells shorted, and that was what caused the fuse to melt. Shorts themselves cause current to flow but do not necessarily create combustion if a fuse does its job.

I believe it's a chicken/egg thing. We don't know that the fuse was the combustion source. The fuse could have blown because wires melted from the fire and shorted.

 

[SilverbackMP]

It's a relay. Doesn't matter where in the circuit it is to operate. You shouldn't have anything between the positive of the battery and a class-t but as short as physically possible cable that's sized large enough to carry the current surge that will open the fuse.

Meh, argue with REC. There’s verbiage besides the schematics but I can’t be arsed to look for it.

 

[ScropusGobbleBottom]

So are we really saying that a previously happy and functioning cell just randomly, without abnormal load, shorted itself to an ohm value low enough to raise temp and vent? and after this, the parallel strings fed into this shorted cell and blew the fuse causing a spark?

Im as interested as any in this but, I have dealt with MANY Li Cobalt, Lipo with internal cell shorts. Hundreds of them. I use to go thru old laptop batteries and find the good cells after testing 500 (I charged every one that arrived over 1.5v) cells I took the best in mAh and put them in strings. ALL internal shorts, start very small, almost unnoticeable. The only early indication in my experience is slightly warmer than normal while charging.

Also I was using a Lipo every day for 2-3 years on an ebike and only when I let the battery sit for 2 YEARS UNUSED, did I find out it had a bad cell.

I am not sold on any of these hypothesis

​

.

 

[robbob2112]

I have not read the entire thread. Apologies. My question is, do we know, did the arc start a fire that spread to the batteries? Or did incoming power overload the batteries somehow, and then the battery cells actually initiated the fire? I ask because I travel in a yurt, therefore I have my LiFePo4 cells inside my yurt with me. I cannot have an outbuilding for various reasons. Since the fire started at night, the solar was obviously not feeding excessive power into the system. This fault must have come from the battery outputting excessive power, for some reason, or from an incoming power source feeding massive amps into the system? I have four 12v packs of LiFePo4 cells (Lf280k). Each pack is individually mega-fused (125 amps) before connecting through a Lynx PowerIn bus. Each pack is BMS limited to 100 amps. I am curious as to how large of an arc can be initiated by 100 amps @ 12v, and whether it could arc across that fuse gap? I cannot conceive of any situation that could cause that battery to output enough power to jump such a gap, and since I have no incoming power besides 60 amps from my charge controller, I cannot see any chance of incoming power causing such a situation, either. But I want to try to understand what caused the situation of this fire, just in case I've overlooked something.

One big difference between your setup and the OP is he was working at 48v verse 12v.

Doing the math -
each battery has internal resistance of 2.72mΩ before a short cell.

Put all of those in parallel and you get 0.388mΩ

Now assume the batteries are at 55.2v (16 * 3.45)

If we just do ohms law and delete one cell from one battery and figure what is left .... Either the figure is 750amps from the other 6 strings or somewhere in the neighborhood of 9000amps for an instant.

If it is 9000amps there is really nothing going to stop instant combustion.



Now - there are some assmptions here

But this brings to mind recent discussion of where to put fuses in parallel configuration .... i.e. at the bus bar or the battery or both.

In this case he had quit long cables and the fuse closer the bus bar

At any rate if the fuse blew at 0.1 seconds and the wire was 2/0 welding wire and 2 meters long - this makes the wire temp 94c... not to bad, hot but not bad.

Now - add in a megafuse (0.0004ohms) - two bolt on connections of 0.0004 ohms.

This recalculates as 119c or 246f

NOW - the mega fuse 58v data sheet says at 600% of rated amps it will blow between 0.1 sec and 1.0 sec.

Recalculate with time of 1.0 sec

The wire and fuse will be at 966c or 1769f

So the wire was probably someplace in between those numbers

and the fuse plastic if a form of ABS which ignites 349c, if it is a form of PET it ignites around 275c

Wire rated at 105c presumably.



I think this brings us back to the fuse as the hotest point in the wire and the fuse is the fuse itself.

I think I agree with the fire investigator now. The ultimate cause could have been just an out of balance cell verse an actual vent/short.