Does anyone know what it means to desulfate a lead-acid battery? What does It do? Thanks :)
I have had a problem with this with a number of batteries and asked a question about it a few years ago. It was a pretty good discussion.
I bought one of those desulfater units. It didn't really work. One of my battery chargers even has a special cycle for desulfating. I use it be truthfully don't know if it does anything. The batteries in battery backup units will get sulfated if they are not charged and left for a few months. I had a customer who had a brand new one, never opened, and he had it for a couple of years on a shelf. When he finally got around to plugging it in the battery was bad because it had sulfated.
If you keep a battery charged it will not form much in the way of sulfate. If you leave it sit with only a partial charge or no charge it will sulfate to the point of being no good. I have not had very good results in trying to bring them back.
I have been able to add water to "sealed" batteries like those in the APC units and get them working again but other than that not much success.
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I have a dangerous homemade desulfater that basically sends 230V pulses to the battery. It is not able to make every battery work, but it does work on some of them. Best example - a tiny scooter battery, drained and left so for months, connected to regular charger the charging current was 4 milliamps. I connected it to that crazy desulfater for 5 minutes, then back to normal charger - now the current was 400 milliamps. So it took the ruined battery back to somewhat rechargeable state. Second example - I found two normal car batteries at once, both of them at about 4.5 volts (different manufacturers). I got one of them working with the help of desulfater but not the other one. The better one has been my "drill battery" for 3 years already, I charge it couple of times a year.
I've heard (but not verified) that the desulfating process mechanically kicks the foreign compounds off from the lead plates and the stuff sinks to the bottom. And that is supposed to be a reason why desulfating works on liquid lead-acid batteries but not on the SLA ones - because they are filled with "wool" the stuff can't move. My experience with my dangerous homemade desulfater so far agrees with this theory - I have successfully revived few car and scooter batteries but it made no difference on any of the UPS batteries I have tried (maybe there were 5).Sorry for this being a little rumor based...
Disolve the lead sulfate crystals, which build up on the lead plates, back into the acid electrolyte, usually using a frequency component overlaid on the dc charge.
When stored discharged or badly maintained or from old age the lead plates in a SLA battery will develop a lead sulfate layer on the surface, This is non conductive and inhibits the battery working. It's the biggest reason for SLA batteries failing.
The process can be reversed with some special charging equipment and techniques. there is an instructable for building a de-sulfater.