Battery top mounted disconnect

Discussion in 'OnBoard Electronics & Controls' started by dskira, Aug 29, 2013.

  1. dskira

    dskira Previous Member

    I know it is not recommended for marine use. But I have no space beside finding a top mounted battery disconnect switch.
    Is some one has used this knife system?.
    What will be the worst case scenario if mounted on a boat battery?
    My battery is protected by a hatch and a plastic cover. But humidity of course creep in.
    Thank you for your feed back.


    [​IMG]
     
  2. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    Spark and KABOOMMM.

    I suppose that modern batteries are a bit safer.

    Dont use that switch with old fashion lead acid hydrogen gassers.
     
  3. dskira

    dskira Previous Member

    Good point Michael.
     
  4. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    I concur. This is not safe. Electrical equipment that could create a spark is not "ignition protected" which is the requirement especially in a space where hydrogen can accumulate or fuel vapors may be present.

    As Michael said, worst case? kaboom.

    And it doesn't matter whether it's lead acid or newer Gel or AGM. Those batteries don't outgas under normal operating conditions, but if overheated or over charged, they do outgas. They are required to be in a ventilated space just like lead acid batteries. And again, with that switch there is danger of explosion.
     
    1 person likes this.
  5. dskira

    dskira Previous Member

    This is the reason why the disconnect switch should be imperatively mounted outside the battery.
    Good reason. Kaboom:D
    Thanks
     
  6. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    The explosion will only take place in a confined space. If you take the lid off the battery case, all hydrogen has already left before your hand reaches the switch.

    No Kaboom, no matter how hard you try.

    As an engineering student I once had to do maintenance work in the emergency battery room in the basement of the main university building. Imagine a large room occupied by several 100's of large glass aquariums filled with acid, lead and copper strips interconnected the cells into 110 V arrays. No bolts and nuts, everything was soldered!

    To remove a bad cell, the solder joint was heated with a blowtorch. The safety instruction on the wall said to open the outside doors and wait for 5 minutes before using open fire. The only accident I know of was breaking the glass if the flame was pointed too low. Each cell held several gallons of sulfuric acid, so there was a fire hose in the room that was used to immediately soak the unfortunate student.
     
  7. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Kaboom...Ive seen it.

    When I was a kid..about a century ago..I had an after school, weekend job at the local yacht yard. The yard had a battery shed were they winterized clients batteries. The yard boss told me to go into the shed, disconnect mr Weewilly's battery and connect Mr Turdblossoms battery to the charger.
    I got right on it.

    Disconnected Weewilly's and began to hook up Turdblossoms....but I forgot to turn off the battery charger. As soon as the second clamp touched Turdblossom battery..spark..KABOOM... a Hydrogen bomb !!!! !!

    Turdblossoms battery was history, all my clothing dissolved and the Yard foreman gave me a bollocking ...TURN THE BATTERY CHARGER OFF BEFORE CONNECTING, you blockhead.
     
  8. dskira

    dskira Previous Member

    Michael, are you that old?
     
  9. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Yup....My back is almost two centuries old
     
  10. dskira

    dskira Previous Member

    I know exactly what you mean
     
  11. Ike
    Joined: Apr 2006
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    Ike Senior Member

    CDK is right that hydrogen will disperse very rapidly, but explosions have occurred in some very inexplicable ways. That is why spaces with batteries are required by law to be ventilated and electrical equipment is required to be ignition protected. This switch is not ignition protected.
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yep, the molecular vapor pressure of hydrogen is quite high, so it dissipates very quickly (epoxy has a similar trait). As Ike suggests, some gas can get trapped, but this would be an usual design and certainly not a certified one. A standard battery box will vent very rapidly. If you enclose this battery box, the enclosure need to be vented and this is often the problem with batteries. I have blown up batteries, though in hind sight, I should have known better and it wasn't an enclosure problem as much as an operator issue.
     
  13. dskira

    dskira Previous Member

    I liked the simplicity, but all your feedback make a lot of sense.
    Thanks
     

  14. Petros
    Joined: Oct 2007
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    Petros Senior Member

    when I was in high school one of my friends was in the news paper when a houseboat owner was nearly killed trying to change the battery in his houseboat. It exploded like a bomb, sinking the house boat and knocking the owner unconscious and into the water 30 ft away. My friend was fishing off the dock nearby and he dove in to bring the owner up out of the water and swam him to the dock where others were there to pull him out of the marina.

    I have heard similar storyies of people changing car batteries that have had them explod. there is a lot of stored engery in a battery, if ignited it will release it all at once.

    My favorite quick disconnect is this style, usually you mount it away from the battery:

    [​IMG]

    This type is also popular, not sure if it will cause a spark because clearly they are intended to be mounted on the battery terminal itself, they are popular however;

    [​IMG]
     
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