Author Topic: Desulphation (Mad Science!) Experiments  (Read 439 times)

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thunderhead

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Desulphation (Mad Science!) Experiments
« on: September 17, 2017, 10:11:25 AM »
It's been a long time since I last posted, but in the meantime (7 years off-grid in rural Ireland) I have learned a lot.

I have a theory that the process of desulphation is only a problem on one electrode.

The textbooks say that the process of charging a lead-acid battery is like this:-

+ve: PbSO4 + 2H2O -> PbO2 + H2SO4 + 2H+ + 2e-

-ve: PbSO4 + 2H+ + 2e- -> Pb + H2SO4

Now the problem is that the lead sulphate is supposed to form a non-conductive form which cannot easily be broken down.  My theory was that it might be easy to break down on one plate but not the other: for example, lead sulphate could become lead at the -ve plate but not become lead oxide at the positive plate.

The test for this is to try charging the battery in reverse.  If sulphation is equally a problem on both plates then it won't matter: they'll still not take charge.

Now, before we go any further, I should point out that I am a mad scientist by hobby.  I have been fooling around with things that corrode (including concentrated sulphuric acid) and things that go bang (including hydrogen) since I was thirteen -- over forty years ago!  If you don't know what risks are associated with abusing batteries, (and, to give you a better idea, try googling "acid burn face",) please take it from me that this is not something to try.  As they say in all those jackass TV programmes: DO NOT TRY THIS AT HOME!

Nevertheless, I tried it to see if my theory was true.  I had four old deep-cycle batteries that I bought from Halfords many years ago: they said 85Ah on them but, after I had abandoned them as too worn and then left them in the back of the shed for two years, they showed between  5Ah and 7Ah capacity.   I connected a bulb across each and discharged them flat.  I left the battery connected to the bulb for about a week each, and then connected each -- in reverse -- to a 40W solar panel and gave them about a week of Ireland's finest summer.

All ended up reverse polarity.  What is more, each could then be charged up to about 40Ah to 50Ah!  So each went back on the bulb to discharge flat, and then slowly charged up to correct polarity again.

Summer has gone here in Ireland, so I am charging them as I have spare electricity (through a 12v bulb in series with my dumpload) but one is already back up to 60Ah (and has been added to my battery bank,) and the other three should be added in a month or so.

Now, since you are not going to repeat my crazy experiments, why is this interesting?   The reason is that I believe I have demonstrated that sulphation is only a problem on one plate, and suggested how these desulphation gadgets are supposed to work.  The active part of the desulphation pulse must be the part where current flows in reverse direction.  That should help with desulphation circuit design.

I'm not going to have much electricity to spare until next summer, so I won't be doing any more mad science until then, but I hope that this knowledge might be useful to someone.
« Last Edit: September 17, 2017, 12:49:04 PM by thunderhead »

joestue

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Re: Desulphation (Mad Science!) Experiments
« Reply #1 on: September 17, 2017, 01:03:35 PM »
I believe it. I might try this with my truck battery which seems to be down to less than 10 amp hours capacity, but still works fine.

charging in reverse is going to turn pbso4 and pb02 back into lead, which is a good thing. the lead is what holds the entire positive plate together. if you can charge it slow enough to get that lead deep into the posititive plate, you've permanently increased the capacity of the battery when you charge it "forwards" and that lead is retained, holding the active material (pb02) together.


in my experience the positive plate expands and corrodes and litterally crumbles apart, well before the battery should have reached end of life.


the risk you would be taking would be permanent damage to the negative plate, as it expands and fills with lead oxide.

george65

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Re: Desulphation (Mad Science!) Experiments
« Reply #2 on: September 17, 2017, 05:24:02 PM »

in my experience the positive plate expands and corrodes and litterally crumbles apart, well before the battery should have reached end of life.

This is always why I took these " Restore a dead battery " products/ devices/ gimmicks as hogwash.  You can't just add powder or a devise to a battery to restore physical Damage...... Or so I thought.
The other things is the lead that comes off eventually piles up on the bottom of the cells and the thing self shorts.
I guess it depends on the individual case but I have to wonder how much of the lead can be Re-deposited back on the plates? 
The other question would be how long is the restored battery life? Will you get another year out of it before having to do it again or will you get closer to original life?


Quote
  The risk you would be taking would be permanent damage to the negative plate, as it expands and fills with lead oxide.

If you are playing with an already dead and rejected battery, in my book there is no risk. Nothing to loose, something to gain.

I have played with a lot of batterys as well. Boiled them up, had them gassing wildy and of course blown them up. 3 times now and I have had the acid to the face.
Every single time I have blown a battery, it was NOT doing anything I should not have been, just charging them ( or not) normally.  First one that went off I was about 20.  Had taken the battery out of the car and sat it under the workbench.  I dropped a shifter which landed right across the terminals. Must have been some gas venting because the entire top of the thing went straight up followed but a rush of acid. I had looked down to see the shifter fall but managed to close my eyes maybe in reaction to the sound before the acid got me.  Run for the garden hose, Clothes ruined like a swiss cheese, I was OK.

Next one was charging a battery with the caps off and again managed to drop something that hit one of the clamps on the  terminal and knocked it off. Must have sparked and whooshka. Blew the thing to pieces. Saw the bit of metal falling and turned away before it hit but was nearly deaf for about 3 days.

Last one was about 2 years ago. Had a battery from my 4WD which was a very large and quite new one on charge as I replaced the alternator.  I'm pretty sure that must have been faulty. Was no where near charged and only on a 2.5A charger.  I had it sitting on the ground down from where I was standing, ( had just walked up to the bench with something) when the thing again blew apart like a bomb.  Scared the crap out of me because I had not touched the thing or come within about 3 ft of it.  Daughter was sitting on the back verandah and looked up in time to see me throw myself into the swimming pool in the middle of winter fully clothed and stay down a long time.

I caught a piece of plastic in my leg which I didn't even feel till my daughter pointed out as I was trying to get my jacket off. The blood was running down my leg  quite well. Pulled the plastic out and then it hurt like a bitch.  It slowed bleeding in the shower but was a nice deep 2" gash. Bandaged it up and it was fine apart from the pain. Don't like stitches.

Just annoys the crap out of me that every time I get hurt, it's innocent. I do all manner of stupid $#|+ where I am expecting to get my butt smacked by the hand of the " You should not have been doing something so stupid or dangerous" god but nothing EVER happens.  Come out the shower in the lounge room where mrs throws me a t Shirt from the washing she is sorting and nearly loose a thumb as I pull it over my head and stick my hand in the ceiling fan. Play with an induction generator doing 500V+ and work on live terminals, nothing.  Finish up and walk out the shed looking at something and knock myself out on the roller door I didn't push up far enough and wake up 5 min later looking at the sky and wondering how I got flat on my back on the floor?

If I got hurt Boiling batterys or playing with DIY burners doing 600KW and throwing 8ft flames I'd say Fair enough, serves myself right but it's always something like slipping on wet grass and doing my knee a month ago ( that still hurts like hell) where I has hobbling for a week that is what gets me.

I just moved here and cashed in a heap of dead batterys. I'll have to give this a go next time I get one. Think the battery in the ute is getting a bit ordinary so that may be the first test.
Question I have though is how can you tell a battery is sulphated or when it's died from other causes and what apart from internal shorting and breaks in the connections can there be?

I think I'll charge the batterys in a wooden crate on it's side with the open side facing a wall or into the yard. The crate would then be completely ventilated and act like a blast shield should another want to become a firework on me. Of course the fact I would be doing something risky would also mean nothing will happen to it at all.  ::)

joestue

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Re: Desulphation (Mad Science!) Experiments
« Reply #3 on: September 18, 2017, 02:05:10 PM »
A sulphated batter will have low specific gravity. A low capacity battery will have a lot of lead oxide that is electrically disconnected( mostly) from the positive plate.

George your experience with exploding batteries can be partly explained by the internal spark hazard from the broken plates reconnecting...

thunderhead

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Re: Desulphation (Mad Science!) Experiments
« Reply #4 on: September 18, 2017, 02:29:21 PM »
Question I have though is how can you tell a battery is sulphated or when it's died from other causes and what apart from internal shorting and breaks in the connections can there be?

The obvious way to tell is that a sulphated battery shows a normal voltage (e.g. 11.8v - 12.8v or so) but only a tiny capacity.

Batteries that have shorted cells will show a lower voltage, because one cell is shorted out.

The batteries I tried this on were not starter batteries, but leisure (deep cycle) batteries.  These are constructed more solidly inside, and might well deteriorate in different ways.  In all four cases, though, they showed full voltage -- just hardly any capacity.

How long they will last ... I'll know by springtime.  :)