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Epsom salt in lead-acid battery

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Red Squirrel:

--- Quote from: G7PSK on December 18, 2020, 03:50:31 pm ---A few days ago I tried one of those pulse battery chargers on a deep cycle battery that had never been used but had sulphated trough age. There was a very loud noise from the garage late at night and the alarm went off.
When i went to investigate the garage reeked of sulphuric acid with everything covered in the acid and the battery was completely demolished.
I have never seen a battery blow up so completely and I have seen a few over the years.
The charger had also been thrown across the garage with the plug being ripped out of the wall and the casing Brocken. I have tried other remedies for sulphated batteries in the past without much success and this pulse charger is the worst one I have ever tried.
In future I will just recycle the batteries it is cheaper in the long rub.

--- End quote ---


Woah that's pretty crazy.   I do wonder as well if this was a hydrogen explosion, though I would not have thought a single battery would produce enough at a fast enough rate to get that catastrophic.     But yeah if the charger failed in some way where it was delivering line voltage to the battery or something, I could see it.  The hydrogen would build up inside the cells and escape out slowly, then some source of spark ignited it.

floobydust:
A common lead-acid battery charging tragedy is a shorted cell. If you originally read open-circuit voltage under 10V, you have to be careful.
Chargers will act as if the battery is dead and pile on the current, bulk-charging. Then after a while, the remaining cells get overcharged and gas, end-of-charge is never reached.
It also frequently happens in UPS as the gel-cells age and a cell shorts and then the remaining cells are overcharged and roast, the case bloats out, until cells dry out and the battery goes open-circuit to protect the server room from blowing up lol.

A smart charger will start off applying low charging current until the battery voltage comes up to nominal 1.94Vpc (11.6V) before going into high current bulk-charging. Even DIN 41773-6 etc. miss this important test. A battery with a shorted cell rarely will make it to that high a voltage. A good charger also keeps track of coulombs because putting in say double the Ah rating into a battery indicates trouble, more-so after the battery was already charged up like in a UPS.

Hydrogen requires the smallest ignition energy,  pretty much the easiest gas to light up as well as acetylene. At 12VDC it's about 3A. But at 24V only 0.15A, and 50V 60mA so a pulse-charger might be a dangerous idea with a really old battery.
I would say the battery may have originally had a shorted cell or badly sulphated, so it's just a hydrogen generator. Some pulse chargers dump as a boost-converter into the battery and high ESR would let high voltage spikes into the battery, then any spark will ignite inside. Or later it must have developed a new short and a lead flake made a hot spot to light up the gas.
Anyhow, really bad to have the battery ignite, super dangerous :scared:

james_s:
It has to be hydrogen, there's nothing else flammable in a battery. I'm actually not all that surprised, I've put electrodes in soapy water and held a flame to the little bubbles of hydrogen and oxygen that form and a bubble about the size of a pea makes a bang that will spray water in your face if you're not careful. It's not just hydrogen you get when you put electricity through water, it's hydrogen and oxygen in a perfect stoichiometric mix. I doubt the charger was malfunctioning, it just gradually created hydrogen and over the course of a few hours it was enough to fill the space. What set it off I don't know, but the result is not surprising.

Red Squirrel:
I've had several of my Crappy Tire batteries die to a shorted cell.  Normally what happens is I start getting hydrogen alarms (still at a safe threshold at that point) so I go investigate by touching all the battery cells and will find one that is warm.  That is usually the culprit. 

I'm down to 3 batteries now as I stopped replacing them, when I'm down to just 2 or even 1 I will probably look at replacing with Surette golf cart batteries instead of marine, hopefully those will be better.

Basically when a cell is shorted, it's like if the battery is now a 10v battery instead of a 12v as it will have 5 working cells instead of 6.  You could in theory use it normally if you had equipment that is 10v such as a 10v charger and other things that can run on 10v.  Not that you can really buy stuff like that off the shelf.   The shorted cell itself will be a write off and you'd probably want to find a way to jumper it to create a higher amp rated path but if you caught it fast enough the other cells should be ok.  If you did not catch it fast enough then the other cells will have been overcharged and probably be dead too.   The overcharging part is what will be generating so much hydrogen.  Though the shorted cell will probably generate a ton too until it goes flat.

james_s:
Years ago I drove my car with a shorted cell in the battery for about 3 months before I got around to replacing it, never occurred to me at the time that it would be dangerous, glad nothing happened.

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