Saturday, December 24, 2011

Have a VRLA Merry Christmas!

Ok, it wasn't the best pun in the world.

But for your Christmas entertainment, I present the dissection of a dead VRLA 7Ah battery :D

Been wondering what exactly the "Valve Regulated" bit of a Valve Regulated Lead Acid battery is?  Wait no more...

Here's a dead battery I've been using as a door stop for a while...
The lid is spot glued down so levering it off breaks these. It could be super-glued back down afterwards but this little guy is destined for the recycling centre so no worries there.

Under that "sealed for life" exterior we have the cell tops with their "valves"...
Which turn out to be nothing more than rubber caps that are pressed on the cell tops with a bit of grease to make a gas tight seal.  The cells have gone to vacuum a bit and you can see the rubber caps sucked in a bit.  When I prised this fella off, it made a little hissing noise (but sucking air in, not blowing gas out).
The top of the cell vent has some slots in it to allow gas out and above some random pressure below 6psi, the grease and rubber combo lets the gas out and then re-seals to stop air getting in (the oxygen would poison the cell).  The gas can then escape along the shallow channels to the gaps in the lid (which, at first sight, looked to be just a gap for jamming my screwdriver into, in order to get this guy opened up... silly me :D ).
In the final picture, you can see the top cover was pressing lightly on the rubber caps, to stop them popping off under pressure.  You can also see where cells 2, 3, 4 and 6 had vented under overcharge and left some acid residue on the lid.

Well, I'm off to see the family, watch bad TV, and eat too much for a few days :D.  See you on the other side!

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