Arcing is not possible in the senerio. The voltages are WAY to low. You would need hundreds of volts or even thousands to jump even a small amount.
http://en.wikipedia.org/wiki/Paschen's_law
This was current runaway. These chips are most likely a "chained" design used to obtain maximum efficiency. If one chip in the series "chain" shorts internally, it can
cause a great increase in current through the other chips in the chain thus causing the temperature to rise suddenly and dramatically. This would literally set them on fire!
Somewhere on here I have seen a picture of a heavily burned "one string miner" that used Bitfury chips. These use 14 chips and run directly off the 12Vdc feed in series.
So if one ship shorts, it starts an overcurrent condition that very quickly pops all of the others.
http://en.wikipedia.org/wiki/Paschen's_law
This was current runaway. These chips are most likely a "chained" design used to obtain maximum efficiency. If one chip in the series "chain" shorts internally, it can
cause a great increase in current through the other chips in the chain thus causing the temperature to rise suddenly and dramatically. This would literally set them on fire!
Somewhere on here I have seen a picture of a heavily burned "one string miner" that used Bitfury chips. These use 14 chips and run directly off the 12Vdc feed in series.
So if one ship shorts, it starts an overcurrent condition that very quickly pops all of the others.
Thank you for taking the time to explain the concept -- I was familiar with "thermal runaway" and "runaway brides" but not "current runaway." So this was very educational for me, so thanks for posting it.
That said, the explanation (above) strikes me so far as the most likely cause...in both fires. I'm basing this not just on "looks" but also on the fact that I recall Asicminer informing shareholders (last week maybe?) of a "Chip Popping" problem that had plagued the BE200 chip, causing failures for various OEMs -- so please correct me if I'm way off base, but is it possible this "chip popping" could trigger the current runaway you described?
And if that *is* true, then (not trying to cause a panic, just asking the question) -- if there's no known way to identify chips with this defect, and they can run for several days/weeks before they "pop" -- is there any way a regular user (without access to absurdly advanced tools etc) could detect or otherwise know if their unit is at risk? Wouldn't that mean (to some degree) that all Prismas are at risk for this kind of behavior?
BTW: Please note, I am not trying to push an agenda -- my 2 RMA Prismas are arriving today, and I still have one running (the one that wasn't damaged by the fire) so I'm not trying to worry people or discourage new sales or otherwise hurt ASICMiner. I honestly just don't know the answer to the questions above, and they seem significant, so I thought I'd ask. Not a fanboy, not a hater. Just a miner.
EDIT: One other question: I had all my miners connected via the USB/UART connectors. But I realize I could have "daisy chained" them together... This is probably a dumb question but -- when you daisy chain boards, is it kind of like "extending the one string" ... meaning, could a chip pop on one board and then just follow that "string" back from one board to another and another, damaging more than one board (or more than one Prisma)? That's my main question -- because if daisy chaining makes it possible for ONE popped chip to potentially damage everything that's connected to it, it seems to me like it might be safer to just connect each prisma to a USB hub (rather than chain them together and the connect the last one via USB). Or is that just such an unlikely scenario that it's not worth worrying about?