Thursday, February 16, 2012

Mysterious Liquid

While lugging the cells around for their initial charge, I noticed something odd about them.  Three of them had free liquid electrolyte sloshing around in them, while the other five appeared to be free of the free liquid (if that makes sense).  That is, some cells appeared totally solid when you picked them up and tilted them, while others made a sloshing noise of liquid running from one end of the cell to the other.

Two of the ones I'd already charged had this liquid, but one that was waiting to be charged also had some liquid, so they came out of the crate like that...

So I weighed all the cells to see if the "wet" ones were any heavier than the "dry" ones.  Maybe they'd been overfilled?  But no, they were all the same weight to within 100g and some of the dry ones were heavier than the wet ones.

I mailed GWL, and asked them about the liquid and whether it meant that I should use the cells only in an upright attitude.  I know lots of people have mounted them on their sides in cars and the cells are often promoted as being "sealed" and suitable for mounting in any orientation except upside down.

The reply came back that some free liquid is normal in new cells.  It may have been evolved during the pre-charge at the factory or in pre-delivery "testing".  But the liquid should all be absorbed back into the cell plates and the cell become "dry" over a number of charge and discharge cycles.  Over charging or over discharging the cells will lead to lots of liquid and gas being evolved, which would cause the cell to swell up and vent. If the cell is on its side, it could spray the liquid out of the vent.  If it's upside down, it will almost certainly spray any liquid inside, out.

So... Nothing to worry about and the recommended installation position is "right way up", to allow emergency venting without loss of liquid in the event of serious fault or abuse of the cells.

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