And even then the damn bridge suitcase won't work after you go to test depth and then later surface the submarine...
Hybrid cars, submerged
- Thread starter ls99
- Start date
M Paquette
Moderator Emeritus
Nords said:
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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NW-Bound
Give me a museum and I'll fill it. (Picasso) Give me a forum ...
- Joined
- Jul 3, 2008
- Messages
- 35,712
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.
Good times, good times. Gosh I miss being the surfacing OOD.
NOT.
"Survivor bias"...
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.
(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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