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Old 11-15-2012, 02:58 PM   #21
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Originally Posted by Midpack View Post
No surprise, but Fisker has reported:
  • fires in 16 2012 Fisker Karmas during Hurricane Sandy were caused by a short circuit in one car that resulted in a fire that was spread to other cars by high winds.
  • Salt damage caused the short circuit
  • "There were no explosions as had been inaccurately reported," said Fisker.
  • "The Karma's lithium-ion batteries were ruled out as a cause or contributing factor."
  • Fisker noted that "several electric hybrid and non-hybrid cars from a variety of manufacturers caught fire and were damaged in separate incidents after flood waters receded at Port Newark" in New Jersey.
  • "After a thorough inspection witnessed by (National Highway Traffic Safety Administration) representatives, Fisker engineers determined that the damage to the Karmas was the result of the cars being submerged under 5-8 feet of seawater for several hours that left corrosive salt in a low-voltage Vehicle Control Unit in one Karma," the company said.
  • "The Vehicle Control Unit is a standard component found in many types of vehicles and is powered by a typical 12V car battery.
  • According to Roger Ormisher, a Fisker spokesperson, 320 Karmas parked on a New Jersey port were destroyed during Hurricane Sandy last week. This meant a $32 million loss for the company. Of the 320 Karmas, one had a short circuit that caught fire and due to high winds, 15 other Karmas caught fire as well. The rest of the Fisker plug-ins parked along the port were damaged by floodwaters.
Simply FWIW...

In fairness to Fisker (re: spin), I did not see where any of the sources that initially sensationalized reported the incident (without knowing anything about cause) - filed follow up reports. Again, I have no horse in this race whatsoever...

Fisker Reveals Cause of Karma Fires During Hurricane Sandy - Edmunds.com

DailyTech - Fisker Loses 320 Karmas to Hurricane Sandy
Well, that sure takes the fun out of this thread
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Old 11-15-2012, 03:18 PM   #22
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Seems Edmunds accepts the conclusions as well. Good to know.

"Edmunds says: Fisker Automotive nails down the root cause of fires in several Karmas during Hurricane Sandy, which should be reassuring to consumers."
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Old 11-16-2012, 07:54 PM   #23
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Quote:
Originally Posted by Midpack View Post
No surprise, but Fisker has reported:
  • "After a thorough inspection witnessed by (National Highway Traffic Safety Administration) representatives, Fisker engineers determined that the damage to the Karmas was the result of the cars being submerged under 5-8 feet of seawater for several hours that left corrosive salt in a low-voltage Vehicle Control Unit in one Karma," the company said.
  • "The Vehicle Control Unit is a standard component found in many types of vehicles and is powered by a typical 12V car battery.
There is still something peculiar about the design of this vehicle control unit. All modern cars have an Engine Control Unit that runs off a 12V battery, and thousands get flooded every year, many right in the same Sandy hurricane, yet they do not burn up.

However, this may be an item of interest to a car electronic designer more than to the average car driver. After all, only one car got on fire, and no matter whether a flooded car burns up or not, it's still toast (pun intended) and declared a total loss.

By the way, because I am not a car enthusiast, I first read of this Fisker car on this thread. So, I went to the Web and looked at its picture. Nice car!
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Old 11-17-2012, 11:49 AM   #24
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There is still something peculiar about the design of this vehicle control unit. All modern cars have an Engine Control Unit that runs off a 12V battery, and thousands get flooded every year, many right in the same Sandy hurricane, yet they do not burn up.

However, this may be an item of interest to a car electronic designer more than to the average car driver. After all, only one car got on fire, and no matter whether a flooded car burns up or not, it's still toast (pun intended) and declared a total loss.

By the way, because I am not a car enthusiast, I first read of this Fisker car on this thread. So, I went to the Web and looked at its picture. Nice car!
Well, as an engineer I'd have to say "It depends..." :-)

I'm pretty sure that seawater immersion is not considered a normal operating condition for consumer grade automobiles, so any consideration of how a vehicle handles immersion is off in the "infrequent or abnormal operating conditions" realm. There are a number of ways that the ECU can be packaged, some of which may have an effect on what happens under these conditions.

The ECU could be a simple circuit board in a plastic housing, with electrical lines connected by ordinary pressed on double sided edge connectors. That would be OK for normal under the hood moisture conditions, but would fail with seawater immersion. The board could be conformal coated, which would help, but the edge connectors would be exposed for immersion risks. The board could be potted (cast inside a block of something like resin) with connectors molded into the housing. That's even better, and could handle spraying with fresh water. Immersion in salt water would still penetrate and short the connectors.

You'll really need to go with potting and watertight connector plugs, along with an immersion-resistant wiring harness. This will raise the cost a little bit. Something like this... (Note the exposed DB-19 diagnostics port. A shield with rubber gasket and silicone grease covers this when installed.)
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Old 11-17-2012, 02:01 PM   #25
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Even aerospace products, where very expensive Mil-spec'ed parts are used, cannot stand immersion in salt water, unless specifically designed to do so. And there is no point in putting something like that in a car, which if submerged is a total loss any way. A car is not a submarine!

The point is that most ECUs, although they will fail due to water penetration, do not erupt in flames. This particular unit did. There's something different about its circuit design. For example, all cars have fuses or fusible links to protect the wiring harnesses against a dead short.

So, I am afraid that you missed my point. Again, it hardly matters anyway. Any submerged car is still toast. There is no need to spend a lot of money on water-tight connectors and enclosures, if a simple fuse would work.
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Old 11-17-2012, 02:02 PM   #26
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You'll really need to go with potting and watertight connector plugs, along with an immersion-resistant wiring harness. This will raise the cost a little bit. Something like this... (Note the exposed DB-19 diagnostics port. A shield with rubber gasket and silicone grease covers this when installed.)
And even then the damn bridge suitcase won't work after you go to test depth and then later surface the submarine...
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Old 11-17-2012, 02:14 PM   #27
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And even then the damn bridge suitcase won't work after you go to test depth and then later surface the submarine...
Always fun to spin off the electrical caps and have seawater dribble OUT. Or rig out the running lights and notice the great fishbowl imitation...

Actual exchange between Electrical Operator and EOOW:

"Sir. Ground detected on starboard bus."

"Oh. Um... Keep the button pressed for a little while and see if it burns off..."


On that fire... With sufficient seawater in the wrong place, and enough electricity (like a fresh 12 volt car battery), I could set pretty much anything on fire, even if I had to wait for enough hydrogen to be electrolysed... Most of the really interesting (non-obvious) placement of fuses or fusible links in wiring harnesses comes after incidents like this.
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Old 11-17-2012, 02:28 PM   #28
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Most of the really interesting (non-obvious) placement of fuses or fusible links in wiring harnesses comes after incidents like this.
Yes, there we go!

One thing about aerospace products is that they evolve fairly slowly compared to consumer products. For critical systems where reliability is of utmost importance, designers are very cautious to adopt "new" and "exciting" things. The risk and cost of unforeseen failure modes or side effects are just too great.
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Old 11-17-2012, 03:11 PM   #29
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Always fun to spin off the electrical caps and have seawater dribble OUT. Or rig out the running lights and notice the great fishbowl imitation...
Actual exchange between Electrical Operator and EOOW:
"Sir. Ground detected on starboard bus."
"Oh. Um... Keep the button pressed for a little while and see if it burns off..."
Good times, good times. Gosh I miss being the surfacing OOD.

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One thing about aerospace products is that they evolve fairly slowly compared to consumer products. For critical systems where reliability is of utmost importance, designers are very cautious to adopt "new" and "exciting" things. The risk and cost of unforeseen failure modes or side effects are just too great.
"Survivor bias"...
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Old 11-17-2012, 03:38 PM   #30
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A couple of (long and boring) battery technical comments:

(1) Under normal conditions Li-ion batteries do not contain Li metal. The exception is abusive charge conditions when Li metal can be deposited on the negative electrode.
(2) Instead, the "charged Li" is in the form of LiC6, a carbon intercalation compound. This is what enabled Li based rechargeable batteries, e.g. Li-ion batteries. Rechargeable batteries with Li metal do not cycle very well and become less and less safe as they age whereas Li-ion generally become safer as they age and have good cycle life when properly designed.
(3) However, the voltage of LiC6 is very close to that of Li metal (about 50 mV difference) so it has about the same potential (pun intended) to react with water as Li metal.
(4) However Li-ion cells are hermetic so unless they leak the LiC6 should never come into direct contact with water even when the batteries are submerged.
(5) However the external negative terminal is at the negative electrode potential and can catalyze reaction of water to release flammable hydrogen gas at the negative and O2 gas at the positive.
(6) But since voltage is the driving force for this reaction a 30 V Li-ion battery would not be much different than say a 30 V nickel metal hydride battery of the same capacity.
(7) Cell phones battery typically have a single Li-ion cell with a max voltage of 4.2 V and a much smaller capacity so the potential for evolving H2 gas is much, much smaller.
(8) But apparently the Karma fire was a result of a short circuit that did not involve the Li-ion battery.
(9) Most Li-ion cells will go into thermal runaway if they are short circuited from a charged condition. This is chemistry and design dependent. The main, but not only, "chemisty issue" is that the metal oxide positive electrode material reacts exothermically at the high temperatures resulting from the short, causing even higher temperatures, venting, combution of the flammable solvents, etc, etc.
(11) Designers "engineer" safety into these batteries in a couple of ways but they are not inherently safe under all conditions.
(10) Fiskar reportedly used A123 batteries. I don't know if they switched to some other type of Li-ion batteries after A123 got into trouble.
(11) A123 batteries have a positive material based on iron phosphate rather than an oxide. Iron phosphate does not react in the same way as the oxide materials mentioned above so they are much more inherently safe with respect to short circuit simply because the "bad" reaction doesn't occur. I would hesitate to call them 100% inherently safe because you can force them into thermal runaway if you know what you are doing but you have to work at it.
(12) However as mentioned above this is all rather academic since the Fiskar fire appears to have a different root cause.
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