Definitely not epsom salt


[Follow Ups] [Post Followup] [Dodge Power Wagon Forum]


Posted by Sherman in Idaho [108.162.245.181] on Sunday, January 15, 2017 at 16:40:29 :

In Reply to: Battery (automobile) reconditioning. Anybody ever done it? posted by bucky [173.245.50.147] on Sunday, January 15, 2017 at 15:00:43 :

Here's the real deal, with honest chemistry:
Yes, you can recondition batteries. No, it's not a matter of just pouring some magic goop in. You need to have a good (preferably adjustable) battery charger, a real hydrometer, a volt meter, and be willing to get a little bit technical.

The first step is to try to just give it a proper charge. A totally dead battery that measures zero volts CAN be brought back to life, at least somewhat. The problem is that when the battery is totally dead, the electrolyte is pure water, which is non-conductive. An ordinary battery charger will never charge it. In reality, it's always at least a little bit conductive, tough, and if you put enough voltage on it, it will eventually start to charge. I have had batteries where I had to crank the voltage up to 40 volts to get them to start charging. Once they start, the current will go up quickly, so you have to watch closely over the first half hour or so and keep turning the voltage down so as to keep the current around 5 amps. Once you're down to around 14.5 volts, you can let it set at that voltage for a couple of days for an "equalizing" charge. Some cells will probably be off-gassing, so keep them topped up with enough distilled water that the plates are never exposed to the air. If the plates are exposed to the air, it ruins them. The idea here is that over the course of many ordinary charge/discharge cycles, the cells became unevenly charged. If one cell goes "dead" while the others still have charge in them, it essentially breaks the circuit and makes it look like the whole battery is dead. Ideally, with enough charging at 14.5 volts, all the cells will come up to full strength, as indicated by the fact that they're bubbling. If the battery continues to draw too much current at 14.5 volts or there's one cell that just never bubbles, you may have a shorted cell, but don't conclude that yet. Over-charging will not hurt a flooded lead-acid battery so long as you don't overheat it and you keep the electrolyte topped off with distilled water. That's one of the beauties of a flooded cell compared to a "gel" or "dry" battery.

Top off the electrolyte and then let the battery sit for a day, or at least for several hours. Next check the voltage. It should be very close to 12.6 volts at room temperature, for a fully charged, resting battery. It won't be higher than that. If it's lower, either it isn't fully charging, due to too much sulfation (more later) or it has a shorted cell. Each cell puts out 2.1 volts resting, if fully charged, so one shorted cell will generally drop the open-circuit voltage down to 10.5, two shorted cells will drop it to 8.4, etc. If you have a shorted cell, the battery is scrap.

Next check all the cells with the hydrometer. In the old days, this was the ONLY way mechanics tested batteries. A fully charged cell at room temperature, that's had time to "rest", should have a "gravity" of 1.260. A totally dead cell is 1.000 (pure water). On old batteries, you'll generally find one or more cells that won't come up to 1.260 no matter how much you charge (and over-charge) them. This is where the "magic goop" comes in.

When a lead-acid battery discharges, the acid reacts with the lead to form lead sulfate. The acid gets weaker and the lead sulfate builds up on the plates. When you charge it, the electricity turns the lead sulfate back into lead and sulfuric acid, which is why the "gravity" goes up when it's charged. This is all normal and good, except that over time, some of the lead sulfate falls off the plates and accumulates in the bottom of the cells. When you charge the battery, it remains inert since it's not in contact with the plate any more, and it can no longer be converted back into acid by charging. This is what you're detecting when you're measuring a "gravity" of less than 1.260 in a cell that ought to be fully charged. Some of the acid has been permanently lost to the sulfate crystals sitting at the bottom of the cell doing nothing.

At this point, you can still salvage some extra life out of the battery by adding more acid. This works because there is always a surplus of lead, relative to acid, in the cell. In theory, you could keep adding acid until all the lead is used up. In reality, at some point the lead sulfate will accumulate so deep in the bottom of the cell that it will short out the plates. Also, when the plates get too thin, they will fall apart and short the cell that way. But you can always "doctor" a battery at least one time to restore its life.

The "purest" way to increase the gravity of a weak cell is to suck out as much of the weak electrolyte as you can with the hydrometer and then add some concentrated sulfuric acid and distilled water as needed to fill the cell to the right level and to get the gravity to 1.260. There's no advantage in going above that. For a final test, you'll need to over-charge the cell for a little while so that the bubbling action will mix the fresh acid with the old electrolyte and you'll get an accurate reading. You can buy straight concentrated sulfuric acid off ebay or amazon these days, but I've even had success with the "drain cleaner" acid they sell in hardware stores.

A slightly more convenient and safer source of acid is sodium bisulfate. It's a dry chemical, and isn't as strong as concentrated sulfuric acid, so it's less like to spill and burn holes in things. Some of the "magic potion" battery rejuvenation stuff is just sodium bisulfate. Similar-sounding chemicals like sodium bisulfite and sodium sulfate won't work. Epsom salt (magnesium sulfate) probably works because the sulfate part becomes sulfuric acid and the magnesium part becomes magnesium hydroxide (milk of magnesia) which is insoluble and settles to the bottom of the cell. But why add more sludge to a cell that's already getting sludged up with lead sulfate?

Another popular rejuvenation chemical is cadmium sulfate. I see a lot of people selling it on ebay. The claim there is that the cadmium goes into the lead on the plate and helps it in some way, while the sulfate part makes the electrolyte stronger. The chemistry is sound enough, but I haven't tried it. If anyone wants to try it, I'll send you some to play with because I happen to have gotten a large amount of premium lab-grade cadmium sulfate. Personally, I prefer to just add straight sulfuric acid.

In short, first charge the p**s out of the battery, using an adjustable charger, as I described. Most of the time, that's all it takes. If that doesn't work, and you have no shorted cells, there are several ways to replenish the acid, which will probably get you another couple years' life out of the battery.



Follow Ups:



Post a Followup

Name:
E-Mail:
Subject:
Message:
Optional Link
URL:
Title:
Optional Image Link
URL:


This board is powered by the Mr. Fong Device from Cyberarmy.com