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Discussion Starter #1 (Edited)
Last month Top Fuel Tim reported that he saw a small spark, a plume of smoke from the pack, and measured current flowing when he had an open pack of bare sticks on his bench when the test fuse was put across the main switch points. After a lot of test we could not determine where that current was flowing, or why smoke came out of the pack?

Last week, I got a scary photo from Rufus, a charger user that went much further, it burned his pack down.
The common component was that the sticks were bare with no heat shrink.
Luckily Rufus was also using the datalogger to record the reconditioning, and we saw an unusual trace. during the charge at 1A, the voltage rose to the 166V plateau as normal, but after the current dropped to 350ma, the voltage dropped instead of rising, and it now seems that this was due to the leakage through the rubber drawing more than 350ma and depleting the pack during this low current topping.
Tim had measured ~ 500-800ma, which would be right in line with the traces.
Unfortunately, Rufus got so freaked out with the smoke and flames that he just wheeled it out doors and swore as it burned to a crisp.

Tim reported that there was some charring on his rubber and the cells that were contacting that part, so between Eli, Peter, Tim, and I we deduced that the rubber was conductive.
A few simple test confirmed this. A HV test showed high conductivity

And finally a simple test with a 150V pack, and a couple of aligator clips and a meter, showed that the rubber will burn at the 150V potential.


Bottom line, don't play with sticks that do not have heat shrink on them in an empty pack, the rubber is highly conductive and can burn, charging or not, connected to a circuit or not.
Not a good idea to even leave them in a pack with out heat shrink on them.
We learn something new every day. be careful.
 

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Well written

This was an interesting experience, tracking down and then finally determining the cause with help from Mike and Eli. Lesson learned and taken to heart.

My 0.02 worth,
Tim Glover
 

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This was initially very worrying as we had a few theories none of which was comfortable reading, including rogue sticks, bad charger, reverse discharging etc etc etc.

Now the mystery is solved we can put those to bed and breathe a sigh of relief.
As has been said though we are still learning so it pays to be very careful.

Interestingly as the rubber carbonises when effected it might becomes more conductive and a runaway then ensues, aided by heat causing cells to fail and add to the conflagration.
 

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Years ago, we built a "relay circuit tester" for measuring air flow on a production line at work. Inside the unit was rubber hose and 120 VAC for the relays. A portion of the rubber hose made contact with a section of bare wire. The unit did not start on fire, but did leave a trace of smoke and carbon.

As Peter mentioned, in our case the rubber got hot enough to char and turn to highly conductive carbon.

On a side note: I would not have guessed that the pack case is rubber ??? To me it seems like hard plastic, but then in this case, you never know.

Jim.
 

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Discussion Starter #5
The case is plastic, but the rubber is a spacer that supports the sticks as it passes through the holes, and seems to be both an abrasion preventive, and an air flow director.
The rubber conducts as is, the meter lead had just touched the rubber and it smoked immediately. In Hondas defense, when you buy black rubber, the black is usually carbon black. They did not ever expect crazy Insight owners to put bare sticks into a pack without the heatshrink.
A good lesson in when you change something from the original design, don't make assumptions, as assumptions are where Mr Murphy lives, as Poor Rufus has learned.
He has bought 2 junkyard packs as donors, so he is in good shape to continue with his rebuilding.
So hopefully Tims keen observations and the IC tech teams analysis and conclusions,has prevented any more pack meltdowns.
 

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Yeah, this was a very interesting learning experience! We may have never figured it out without Tim's keen detective work, just would have had a string of burned packs! The rubber would have been the last thing on my list of suspects, if I didn't see the correlation with my own eyes.

When I ran out and hit the rubber with the Fluke 87IV, it was very hard to get a reading - but I was getting 1-10 megaohms just with the tiny tips of the DMM probes, depending on how close together they were. That was good enough for me to know that the rubber was definitely conductive, and I suspected surface area and obviously voltage had something to do with it.

I will be including a note to this effect with the boxes of bare sticks people purchase from me.
 

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Great detective work.
I appreciate Top Fuel Tim coming forward with this.

Sometimes when errors are made people are afraid to come forward. But without this kind of open discussion I'm not sure we could have gotten this helpful safety info.

Thank you to everyone who helped figure this out!
 

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Scary thought. What is the melting point of the shrink wrap? Just thinking about the possibility of heating the sticks too high during charging, melting the shrinkwrap, and causing a short.
 

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Me too. Ill never forget the time someone painted the spark plugs on an engine and it wouldnt fire or develop any spark. Turned out the paint was conductive and the spark just went down the outside edge to the block and grounded out.

I had a smart comment to make about stripped cells and putting them in the case together, but think Ill save it for another time. :D
 

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Scary thought. What is the melting point of the shrink wrap? Just thinking about the possibility of heating the sticks too high during charging, melting the shrinkwrap, and causing a short.
Pretty high.. Certainly much hotter than the sticks would get under any semblance of normal use. I'd say 250F minimum. If you have sticks that hot, there are probably other things to worry about.. lol.
 

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Discussion Starter #12 (Edited)
If the shrink was burned through, the rubber would have likely burned as well.
The photos that tipped us off :

Just to be clear for the not so tech savy.
The rubber acted as a resistor, like a mild short circuit. because of the conductive carbon black in the rubber.

Each rubber piece had every stick in the pack passing through it, so each had the full pack voltage across it. The sticks that burned just happened to press against the rubber deep enough to get a good connection, a current started flowing between the sticks, through the rubber, which got hot and melted, eventually causing an arc that ignited the gasses, and poof a fire was started. After that, the whole thing was like a blast furnace with the fan drawing in new fresh air and fanning the flames.
As Peter pointed out, the rubber probably gets even more conductive when it burns.
The 4 mill heat shrink on each stick is the main protection.
Scary indeed.


I charge packs at the full 1A all the time, and see maybe a 5-7 degree in to out temp rise, so unless your charging at 2+ A, or your fan dies when topping at 1 A, the cells are unlikely to get hot enough to melt anything.
A superbrain with 10A, could do some serious damage if un regulated
 

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After that, the whole thing was like a blast furnace with the fan drawing in new fresh air and fanning the flames.
Oh yeah. Forgot about the fan.
That would definitely speed up the fire.
Yipes!
 

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Yes, it definitely needs to be stickied - Done.

Edited title to draw more attention as well.
 

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Wow that is a bit scary. It looks like I am going to be buying some narrow Kapton tape for the effected areas. Could something like this have caused the fire in California in2009? It does look similar (burned battery).
 

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Which fire?

We, (Californians) had a few.
 

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Is the construction of the pack the same for the gen 2, HCH, accord etc? If so, perhaps a edited sticky for them as well? (if its there already dis regard then, I just glanced at that part of the forum)
 

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No, this would only affect the 1st gen Insight and 1st gen Civic battery cases.
 

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Discussion Starter #20 (Edited)
IMHO, this is only an issue when the pack sticks have no heatshrink, and this is not how their built, all sticks have a shrink wrap covering unless it has been removed like Tim and Rufus had done.
The 4mills of heatshrink on each stick, provide plenty of electrical insulation, and to have sufficient voltage for a level of conduction through the rubber, one would have to also have cells that were at greater than 60-80V difference, each have a bare spot that aligned with the small raised areas on the rubber spacers.
The HCHII packs have no rubber spacers, but instead have nylon spacers on the 12 cell dual sticks, so the sticks are just stacked one on the other. The HCHII pack is much more likely to break apart and have a hard short between cells in the advent of a serious accident, compared to the insight or the gen 1 civics, because of the less robust construction.

But there is little danger unless the pack has been modified and the shrink removed.
 
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