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Old 10-03-2013, 22:10   #2281
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

There is no bolt in the battery case near the protrusion in cell 5. And the report noted that the arcing between cell 5 and the battery case occurred after expansion of cell 5 [Pg 21].

My guess is that cell 5 bulged for some reason, and as a result, developed an internal short. It then exhibited localized "blowtorch venting" of volatile electrolyte gas, that penetrated its case (from within), pushing its exposed cathode into electrical contact with the battery case. High current then flowed through the battery case to the cable shield at the J1 signal connector---shorting out the BMS and then shorting other cells, via their balancing lines.
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Old 10-03-2013, 23:06   #2282
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

It may have been a different outcome if there was no ground connection from the battery case to A/C ground which seemed to cascade the whole event. As stated before we all may yet learn from this event & the yet to be reported air return in Japan with the other battery. The resultant damage sounds the same. I am recommend the use of basalt fibre in the form of fireproofing & will be putting it on my boat.
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Old 10-03-2013, 23:09   #2283
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

On second thought, my "BMS shorting out" theory simply doesn't hold water. Those balancing lines cannot possibly carry enough current to short out eight cells. And if they did, the lines would be totally fried---and they aren't.

So how DID the other cells short out? Look at the photo of the compartment after the battery had been removed. To me, it looks like the localized chassis short in cell 5 caused enough heat to melt its plastic bottom, gravity then bringing its anode and cathode in direct contact with the metal battery case, shorting them. This released even more heat, melting the bottom of one or more adjacent cells in a progressive catastrophic failure.

The bottom of the battery case definitely needs some kind of very fireproof electrical insulator.
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Old 10-03-2013, 23:33   #2284
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Ferrocement battery box? Like tile backing board?
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Old 10-03-2013, 23:54   #2285
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

From what this thread this taught me with regard to the cells we are using is that it's important to strap the batteries to contain expansion.

From what i can make out their design held the batteries together but then in the void at one end they mounted various electrical components, ie BMU.

Didn't that place charged components inside the 'crush' zone?

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Old 11-03-2013, 00:14   #2286
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Diugo, It does hold water!! The wires used is able to take direct flame & heat to a very high temp. The wires used would take 20A + for a few minutes but look at the wires at the outlet & they were passed through a stainless shield which was earth to the case & that end is a mess.(see fire damage in this area & flames were were reported by the LAME). So approx half of the battery shorted in the middle of the series string is busy with the case shorting & the other half is being subjected to over voltage because of the leakage to the case effectively reducing this battery to two batteries. Every cell except one was shorted when tested ie 7shorted!! If it makes you feel better the plastic used on the cells we are using will be gone at 200 degs C. The cement sheet is brittle but it is avail. everywhere. The basalt fibre without resin is good for 1450 degs C. It is used for fireproofing. The above is only what may have happened IMO which counts for nothing!! Result & not what caused it.
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Old 11-03-2013, 02:32   #2287
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I have considered the value of placing a 300amp ANL fuse as the centre link between cell groups 2 and 3. The though is, if a serious external short, like something falling across the positive terminal to an earthed frame etc was to occur, the fuse would seperate the pack reducing the voltage and current to nil. It should have the same effect if a cell was to go short circuit internally for what ever reason.
If the max current draw was greater than 300 amps for a particular event, a high current relay could be closed to create a parallel path to the fuse.
I know one member here has isolated all the cells using ANL fuses, maybe over kill, but better to be sure nothing could create that dead short without a safety fuse.
What are other members thought on this?

T1 Terry
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Old 11-03-2013, 06:16   #2288
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Originally Posted by T1 Terry View Post
I have considered the value of placing a 300amp ANL fuse as the centre link between cell groups 2 and 3. The though is, if a serious external short, like something falling across the positive terminal to an earthed frame etc was to occur, the fuse would seperate the pack reducing the voltage and current to nil. It should have the same effect if a cell was to go short circuit internally for what ever reason.
If the max current draw was greater than 300 amps for a particular event, a high current relay could be closed to create a parallel path to the fuse.
I know one member here has isolated all the cells using ANL fuses, maybe over kill, but better to be sure nothing could create that dead short without a safety fuse.
What are other members thought on this?

T1 Terry
Genasun does just that. See the ANL in this picture.

And Im the one with ANL fuses in my 12P by 4S pack, but mine are between the parallel cells, so far, not between the series cells. So in a 12P string, a cell short wont take out the other 11. But it will then pull that one 4S group to the pack voltage, about 13.2, forcing the remaining 3 cells to 4.4V as the scheme is currently designed. It limits, but does completely solve the problem. I attached the fusing scheme, and plan to try and resolve this when I get back to easy access to parts. Maybe someone has some ideas? The yellow marks are existing 80A ANL fuses.

The advantage of having 40 100Ah cells instead of 4 1000Ah cells, is there are ways to minimize the energy released in certain failure conditions.
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Old 11-03-2013, 09:24   #2289
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Just because seven of the eight cells showed shorted, doesn't necessarily mean they shorted first, then caught fire. Because I would imagine that if one were to expose a good cell to extreme heat, at some point, the electrolyte/separator would ignite, and then even slight thermal deformation would short one or more electrodes.

As far as fusing goes... First of all, an ANL fuse is only rated to interrupt 2700 amperes DC. LFPs can easily exceed this. Second, a tool accidentally grounding a terminal is likely enough that it is prudent to place the catastrophe fuse on the battery negative terminal---between the battery and ground. That way, if any cell terminal is shorted to ground, the fuse will blow. Third, fuses do have nonzero resistance, each of which will add to the total voltage drop under high current. So battery performance may be impacted by excessive fusing.
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Old 11-03-2013, 09:51   #2290

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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

eb-
The problem with your "bolt" theory is that so far no one has reported the presence of any "bolt" near that location.

I would suspect that every bolt and screw on that aircraft has been treated with a thread-lock and assembled with a torque tool of some kind. That doesn't make it impossible for one to come out and generate enough force puncture something, but it becomes extremely unlikely when there's no bolt observed in the area and no bolt location.

So far, at least.

For anyone using lithium combustible batteries, it might be worth noting that the USN uses special extinguishers for combustible metals. Apparently they spray salt, copper, or graphite, all of which melt to form a hard shell over the battery, excluding air while the remains works its way down to China.

I see a market for ceramic battery boxes here. :-)
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Old 11-03-2013, 13:43   #2291
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Given the small difference in micro volts between cells in parallel in the normal cell operations, would it not be better to use very low valued fuses for the parallel & the high value for the series current limit? The parallel will keep balance between the parallel cells. I opt to solder a single fuse wire between the parallel cells with no trouble so far.

Diugo The sequence commenced with one failure, the rest is result of that one cell failure & unexpected reaction not designed to happen. Why that cell failed is not clear yet but the specs of that cell calls for CC/CV & as yet only a CV charge is stated.
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Old 11-03-2013, 15:52   #2292
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Quote:
First of all, an ANL fuse is only rated to interrupt 2700 amperes DC.
According to the Blue Sea catalog, ANL fuses are rated at 6000 AIC. That said, AIC rating is a function of being able to open (including arc quenching) during a fault and, in the case of a fuse, not disintegrating and spreading molten metal around the area.
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Old 11-03-2013, 16:50   #2293
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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According to the Blue Sea catalog, ANL fuses are rated at 6000 AIC.
Is Blue Sea a fuse manufacturer? The Bussmann spec sheet http://www.bdfuses.com/anl.pdf shows interrupt rating of 6000A AC---but only 2700A DC.
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Old 11-03-2013, 17:44   #2294
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Is Blue Sea a fuse manufacturer? The Bussmann spec sheet http://www.bdfuses.com/anl.pdf shows interrupt rating of 6000A AC---but only 2700A DC.
Blue Sea shows 6000AIC@32VDC, and this datasheet direct from the Cooper website has removed the distinction, but still lists the ANLs for up to 80VDC:

http://www.cooperindustries.com/cont...NL_Limiter.pdf

The BDFuses datasheet says it is from '04 (the Cooper one is not dated), so looks like Cooper changed the specs.
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Old 11-03-2013, 17:48   #2295
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by diugo View Post
Is Blue Sea a fuse manufacturer? The Bussmann spec sheet http://www.bdfuses.com/anl.pdf shows interrupt rating of 6000A AC---but only 2700A DC.
The Copper Bussmann made ANL's are rated at 2700 AIC for 80Vdc and 6000 AIC at 32Vdc... Blue Sea uses the 32Vdc AIC spec for marine use.

FWIW I just popped a number of MRBF and ANL fuses, on purpose, using my Li bank..

None failed to pop and none disintegrated. I even popped a 300A MRBF using 15' of 8GA wire and my 400Ah Li bank... Just curious and wanted to see how these fuses handled the Li current into a dead short.
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