Lead Acid Battery Desulfation? Does it really work?

Yes, it works.

The machines you can buy in the stores or the internet are nearly all useless.

To desulphate effectively within a reasonable length of time you must have strong pulses with straight-up leaking edges to the spikes.

Say for example you've got a 60A/h battery from a car that's been sitting for five years.

The voltage is a few volts with the connections pulled. You try to charge it using a normal charger overnight and the next day it is still useless.

You do another charge and leave it charging for a full day, and it's still not going to crank even a motorcycle. - That's what a sulphated battery gets like.

Lead/acid batteries must be kept charged or they will sulphate. (alleged) maintenance free batteries that are valve regulated and are not flooded are able to be left for longer periods between charges than regular (with caps) batteries, but they don't last long for a few other reasons, and in the end still get sulphated.

Here's what to do:-

1. Open the caps and check the electrolyte's specific gravity. If it's sulphated then the SG will be so low the balls won't float, or the float sticks at the bottom. With this battery, the sulphur in the acid has left to form lead-sulphate on the plates. Over time this has hardened and what you have now is an insulating layer of lead sulphate (crystals) which won't give its sulphur back to the acid, and forms an impenetrable layer so it won't charge or discharge much if at all.

* Sometimes these lead sulphates form a colony so big that parts of it push the plates next to it and can short some or all of the plates. If this has occured then your voltage from a nominally 12V battery will settle at around 10.5V. If this is the case then it's a doorstop. Even if you've got a use for a 10V battery then the chances are if one cell has shorted then the rest aren't far behind.

2. First of all put enough distilled water in each cell to cover the plates. DON'T fill the cells to the max-mark. The reason for this is that the level will rise as a charge is taken in, and if you fill it to the max then it will become over-filled, which means the electrolyte is too diluted and/or you get (highly destructive) sulphuric acid everywhere.

3. Now here's where most won't be able to go. - Have a 20V DC supply pulsed into the battery. Have the duty cycle as 1% to 10% and pulse it with a square wave, or any wave providing the leading edge is pretty much vertical. The trailing edge isn't so important, but that should be a vertical line as well if possible (I'm poor and scavenge parts so the devices I make aren't so great so the trailing edges aren't straight).

* You have to keep your eye on the battery and keep the battery between fifteen volts and sixteen for about two or three days - with the pulses, not a straight charge.

* You'll need to add distilled water to one or more of the cells as you go, so look at them occasionally.

If you smell hydrogen sulphine (bad eggs) then that's a good indication of a shorted cell - if so then the battery's stuffed.

After a few hours of this "punching" by (relatively) high voltage, high current (1 - 200A variable) you should see the SG rising in all cells. After three days they should all be in the green if the battery isn't physically broken. If the battery's plates or internal connections are shot then there is no practical way to fix it.

After three days the battery is ready for a test - it might even do for your car at this stage. When the pulsing is done, then add distilled water to the high mark and test.

If, when discharged slowly, the battery seems to be OK but when under heavy load such as cranking, it goes dead then an internal connection is loose. The battery is junk. - & risky because an internal spark from a poor connection could ignite the hydrogen and oxygen gas given off during charging. (Very big bang).

If the (60A/h) battery's capacity is tested to be more like 10, then it m-i-g-h-t start a small car, but what's happened is the positive plates have rotted over time and are now so effectively small that the battery is acting like a very-much smaller one. The battery is as good as junk, or to mess with low-power stuff on your bench or something.

If one or two cells are bubbling a lot then that's a short. The battery is toast.

If one or two cells' SG is far different from the rest then it indicates the plates of those cells are either disconnected and are just hanging there by the insulating layers or that the plates are extremely corroded. The battery is not much use, but might get you out of a fix.

What desulphating by electronics does is to get the battery to the best condition it can be in depending on its physical condition. It won't fix a battery with plates that are corroded or broken.

I make my desulphators with the transformer of (for example) a mini-arc welder and the pulses exit the transistor blocks I find in the control circuits of inverter air conditioners. I make a simple asymetrical multivibrator with two transistors and vary each side's 'clock' duration with resistors and capacitors. I deliver the signal to the output transistors with a relay, and my pulsers tend to operate at about 10 - 100pp/s. I think low speed high current works better than lower current pulses. I use a relay because they give me a perfect sharp leading edge to the spikes... The residual capacitance in the semiconductors is what causes the trailing edges of my machines to linger - I'm poor so I can't buy a proper driver circuit and make mine from bits here and there.

So yeah, desulphators work - but they work on the sulphates only and won't fix a battery that is basically broken.

I get ten years at least from starting batteries. Deep cycle batteries last me twenty years, and marine batteries somewhere between the two. I fix batteries for friends, and pick them up from junkpiles - nearly all the ones I find I get to cranking again.

* The bought ones are crap. You have to make your own and the spikes should deliver a real whack or it won't work.

The true death of a battery is when the positive plates decompose to the point where it won't hold a useful charge. There's no getting around a rotted positive plate, and today's car batteries are crap and are getting worse. - Well made batteries have thicker plates and can last decades. - still! with care, you can get three or four times the usual use from a cheapo car battery if you know what to do.

I'd advise against the (alleged) maintenance-free batteries, but it's true that they are reliable for at least a year and likely two. MF batteries are fine for women or lazy men. Get the old type with caps you can remove. There is no such thing as a maintenance free lead acid battery - they need maintenance or they will die.

Also - find which company makes good batteries and pay the extra because they'll last much longer than the cheap shit creeping in on the shelves of automotive stores - and finally, put in the biggest battery you practically can for your car. The bigger battery will last longer.

* Sorry about typos.