exploded battery

Discussion in 'Electrical Systems' started by CDK, Apr 30, 2015.

  1. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    This almost happened in my boat. I had an old car battery in the house bank. Up to 50a of solar going into the bank and the car battery developed a short. What happens then is the other cells in that battery get more voltage. 6 cells at 14.5v is 2.4v each. 5 cells (one shorted) at 14.5 is 2.9v each. That would be like charging a 12v battery to 17.4v. The cells then go into thermal runaway and resistance goes down. Full charge current boils the acid away filling the area with explosive gasses. Eventually the level gets low enough and a spark lights the lot up. We noticed the issue by the smell of sulphuric acid and shut it off before it exploded. Individual battery temp monitoring can prevent these issues.
     
  2. owene
    Joined: Aug 2009
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    Location: Nelson, NZ

    owene Mr Owen Charles

    Wouldn't a thermal sensor piped back to the solar controller have covered that risk? I've installed literally thousands of solar controllers and refuse to even discuss with the customer an install without that.
     
  3. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    The thermal sensor is useful to determine the fully charged state of a battery because it is temperature dependent. It cannot prevent thermal runaway of one member in a battery bank.
    A sensor on each battery, connected to a small microprocessor and a loud alarm could provide an early warning system, but only when people are present.
    A completely fail safe installation requires some means to disconnect the hot battery in the bank.
     
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  4. Angélique
    Joined: Feb 2009
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    I don't see any means to automatically disconnect an individual hot battery in the below pic . . :oops:

    If so, it could be a fairly dangerous system I think, for the same reasons that started this thread . . :eek:
    [​IMG]
    We've had some electrical propulsion talks in between on the thread ‘What makes the best offshore cruising yacht’ from post #93 till #112 so far.​

    Ecolution's batteries as shown here came up in post #98 there.​
     
    Last edited: Dec 2, 2017
  5. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    One way to do this is putting a semiconductor switch (Mosfet) in the negative lead of each battery. They are cheap and normally do not spark.
    But I agree it is quite complicated because of all the wiring. Companies like Tesla use numerous microprocessors within the battery pack to prevent a chain reaction if one cell goes bad.
    My own solution is a star configuration with 20A fuses to each battery. The bank has 5 members and only has to provide power to one inverter that draws 60A average or 90A peak. There is a bit more wiring compared to the old daisy chain configuration but the cables are much lighter. The fuses are located is a box near the star point; in case one blows there are no gases nearby.
     
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  6. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Can you draw this circuit out and attach it. It sounds like an easy solution.
     
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  7. Dieselguy
    Joined: Apr 2018
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    Location: Scotland

    Dieselguy Junior Member

    Hello, bit of an old thread but I thought that I could posibly make a suggestion here.
    If each battery in parallel in the bank was individually fused then you could wire an LED with associated value of resistor across each fuse and you would have an instant view of which battery was down.
    Hth.
     
  8. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    There are many battery monitoring systems, some which fall under "critical system" requirements, but you need to be sure that you are not putting more "failure" points into the system. I was aboard a submarine that went from "drill" to "critical causality" in a few hundredths of a second. Being <cough> feet below the surface and the monitoring system takes the main battery offline (i.e. no power in the boat except the hydraulic accumulators) because of a sensed "fault" during the power cut-in was very...exciting.
     
  9. Barry
    Joined: Mar 2002
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    Barry Senior Member

    how would that work?
     
  10. Dieselguy
    Joined: Apr 2018
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    Dieselguy Junior Member

    You put an LED with a series resistor in parallel with the fuse, if the fuse is good then the voltage across it is millivolts but when/if the fuse blows there will be 12volts across it and illuminate the LED. This could be mounted in the fuse box or externally.
    jehardiman, did you ever visit the holy loch? Its across the river from me.
     
  11. jehardiman
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    jehardiman Senior Member

    My family was stationed there 1966/67. Took my 1st grade education at Gourock Primary. Yep, I've been to all the sub bases...part of what made me a Naval Architect.
     

  12. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    I dont see how you could protect a battery in a bank when its used for large load like cranking
    If the battery cca is 600amp what good is putting a fuse in rated to 601 amp?
    You would need some clever monitoring and switching to notice that the current is being consumed in a battery and the links then open
     
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