Battery packs - fire danger?

Discussion in 'Electric Propulsion' started by Bille Floyd, Nov 5, 2019.

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  1. Nov 5, 2019 #1

    Bille Floyd

    Bille Floyd

    Bille Floyd

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    I am Definitely going Electric, on my BKB-1 stand-off scale
    project ; but after seeing this , the battery's will be contained
    in a fire-proof box ; and i will have the ability to Eject the
    battery's on to a 10-foot SS steal cable, so i don't get burned
    alive in a glider. If the battery's are ejected ; the wire could
    keep my CG in the same spot.

    NO--- i will not be placing that battery pack, under my butt ; which
    is where my CG will be located.

    Bille
     
  2. Nov 6, 2019 #2

    rdj

    rdj

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    I imagine the drag and the flailing around of heavy batteries on a 10' cable will make CG issues the least of your problems. Unfortunately, just ejecting the batteries and starting a forest fire can also get expensive really fast.

    A better solution is to use a battery chemistry that isn't likely to explosively combust.
     
  3. Nov 6, 2019 #3

    stanislavz

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    Agree to @rdj. Just buy second generation leaf batteries. Much easier to pack. And safe..
     
  4. Nov 6, 2019 #4

    Derswede

    Derswede

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    Tesla is having a major problem with this. Some fire departments in areas with lots of Teslas are building sandpits in which to dump the car to extinguish the fires. LION is the problem, LIFE (Lithion Iron) are much safer and much less likely to burn in that manner. The battery tech is getting better, but the very low milage range of current battery tech keeps me from looking at it with much interest. 200-250 miles I do almost on a daily basis. And no long waits for recharging. My little Ford Ranger can even tow my ultralight! And 25-35 mpg.
     
  5. Nov 6, 2019 #5

    Mad MAC

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    Interesting thought: while there will be some scatter. while we use batteries are chemistry driven, higher energy density must result in increased fire potential (not all of which can be controlled by detailed battery design).

    So future proofing any electric aircraft will require a method of battery fire control.
     
  6. Nov 6, 2019 #6

    Topaz

    Topaz

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    Are they? I see at least 6-10 Teslas every day, of various models, here in SoCal. They're utterly commonplace here. I haven't seen any such "fire pits" anywhere in the area, and have never even heard of this idea before. I also have never seen a Tesla on fire. Oh, I've seen several Porsche 914's on fire, and several "tuner" Honda's, Subaru's, and such, but never a Tesla.

    I'm no fan-boy by any stretch. I'm just not seeing what you're reporting, and ought to have every opportunity to do so.
     
  7. Nov 6, 2019 #7

    Derswede

    Derswede

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    Am trying to find original article. Lots of info on the web about new ways needed to fight EV fires. We have had several here in NC. Local FD chief was the one who mentioned the sandpit as one Tesla here caught back on fire after initial fire. Lots of wrong comments as well, new tech resistance. Not to scare but just a thought as I have seen my share of fuel fires, esp. gasoline and static discharge. That is probably the most common cause of a car fire, esp. at a fuel station. EV fires get news time, same as airplane mishaps.
    Derswede
     
  8. Nov 7, 2019 #8

    TFF

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    Years and years ago , there was a karmann ghia on fire at an intersection. Fire department arrived to see it was a VW. There was a construction project near by, and a fireman went and got a dump truck full of sand and dumped it on the car. Instead of a ladder truck, they will come up with the fire dump truck for electric cars to smother the flames.
     
  9. Nov 7, 2019 #9

    Voidhawk9

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    Yeah, spraying water on an electrical fire probably isn't the way to go.
    The technology has changed, mitigations like putting out fires will need to adapt. Not just for cars, but battery storage on houses as well, etc.
     
  10. Nov 7, 2019 #10

    emir_82

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    Instead of having a mechanism to release the battery and having it hanging. With the problem that the power cables don't disconnect properly and tear the motor down the bulkhead.
    A better firewall and separation of the battery of critical systems is the solution.
    Lifepo4 is a extremely safe chemistry, but 2,5 times heavier.
    If you use Li Ion in the 18650 format each cell has less energy per unit that bigger Li poly pouch cell. So in case of failure the cascade effect is slower and with smaller fire ejections.
     
  11. Nov 7, 2019 #11

    Bille Floyd

    Bille Floyd

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    I can check for myself ; but have you done some weight
    analysis between leaf and Lipo battery's ? I can deal
    with discharge curves , not being as good , if they are safer.

    I have had , Lipo batterys blow up near me, in the past ; i use
    them a Lot in RC helicopters , and Yea it's kinda Ugly when they
    start shooting flames. Over the years , there have bin several
    houses burnt down ; the usual cause was improper use of Lipo
    chargers or shorting out a fully charged Lipo.

    Bille
     
    Last edited: Nov 7, 2019
  12. Nov 7, 2019 #12

    stanislavz

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    Minor difference, teslas are lighter (~10% ), but it saves on connectors and no cooling
     
  13. Nov 8, 2019 #13

    12notes

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    Leaf batteries are LiPo (specifically, common LiPos are lithium cobalt), same as a Tesla.
     
  14. Nov 11, 2019 at 3:58 AM #14

    Tiger Tim

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    As battery fires become more common they will become less newsworthy and thus less scary. Problem solved.
     
    stanislavz, Voidhawk9 and Bille Floyd like this.
  15. Nov 11, 2019 at 5:02 AM #15

    Bille Floyd

    Bille Floyd

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    I,m fine with that ---- unless those battery's, that just burst into
    flames ; yea -- as long as there not in MY , E-glider !

    If i go cheap , on the batterys , with a higher risk of fire; then
    i'll also have a way to eject the flames, onto a 10-ft SS cable.
    Pull it up before landing ; and the CG stays, near the same.

    Bille
     
    Last edited: Nov 11, 2019 at 5:07 AM
  16. Nov 11, 2019 at 5:33 AM #16

    Hephaestus

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    bmcj likes this.
  17. Nov 11, 2019 at 10:37 AM #17

    litespeed

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    We have discussed this issue at length in a previous thread about battery safety.

    The proposed battery tether is not a good approach. The moving mass will do aweful things in flight. And it is now on fire which will very quickly become intense now it's in the airstream.

    You do not want that flaming box swaying around below the aircraft.
    I hate to think of trying to land that way. Assuming no structural damage results as well. The idea of retracting it back in to the aircraft to land?
    Can't see that happening.

    The only insurance you can have is the best battery chemistry. Charge and discharge correctly. Design your wiring correctly and have proper cooling.

    And you need to be able to dump the battery before it kills you in flight or in the rush to land.

    It must leave the aircraft, pure and simple. Have it around the c of g and a way of it dumping in its enclosure. It must completely leave and plummet to earth so you do not.

    No concern for a potential ground fire should stop you. Only don't dump it on a person or house.
    If you can dump in water that would be great.
    That flaming battery is going down the only choice is, are you going with it. You get to choose where you dump it.

    The time for the battery to go from thermal overload to intense fire is seconds and will spread to other cells very fast.

    I really doubt you would ever have enough time to land before been fatally overcome or structural failure in its many potential forms.

    No parachute for the aircraft can help in a big fire and a personal one still means a flying, burning and now unmanned aircraft coming down.

    So the solution is dump and live. You can think this a strange strategy but it will work in a emergency. It is the only method with the highest potential to work every time.

    In a mere second that deadly load can be gone.

    Until unburnable batteries arrive, this is the engineering solution .
     
  18. Nov 11, 2019 at 10:55 AM #18

    litespeed

    litespeed

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    I know my solution seems extreme, it is, to a extreme situation of burning to death in the air.

    The issue of fire on the ground is a big one. But no matter what happens once the huge,heavy and very high energy pack starts to burn- it is going to burn.

    Stopping it hitting somewhere it can burn means water burial. Bar that it is going to burn something. Just like a flaming gas powered plane will. Unless your next to the airport when trouble strikes at circuit height.

    It will burn, the choice is do we dump it like the incendiary it is or ride it down like Slim Pickins?
     
  19. Nov 11, 2019 at 11:03 AM #19

    stanislavz

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    I think i will just repeat myself. Just move batteries to a wingtips. And let it burn . As is. OF course not for wooden wing entirely, but just a kind of 30cm section of stainless steel will do it.
     
  20. Nov 11, 2019 at 11:19 AM #20

    litespeed

    litespeed

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    Putting all the weight of the batteries, a big mass fraction at each tip may sound good in theory but does create a lot of problems handling and strength wise.

    The spar would have to be many times stronger than normal. The leverage effect would be huge.
    It is not like doing wing tip tanks on a military design unless you want a military style spar. And all the big weight elsewhere, so the aircraft hardly notices the relatively small weight at the tips.


    I just can't think of a current design that would even come close to been able to take such a heavy load at the tips. The mass fraction of the batteries compared to the AUW, is just too great in any small electric design with any range beyond takeoff. Also requires heavy cables the length of the wings- a lot of weight.

    Unless you have something in mind designed to do it?
     

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