I too have spent a lot of time charging batteries using different methods on various chemistries. Once upon a time, I build a number of suitcase battery chargers for the US Army that allowed them to charge every portable secondary battery type that they had in inventory... SLA, AgO, NiCD, NIMH, LiIon... I proved a concept, and someone else got to make all of the money off of it when the ARMY shopped my prototypes around... but I digress.
When you try to charge a sulfated lead acid cell, you can think of the cell as being a bunch of little parallel lead acid microcells (uCell). Each is in some state of charge/discharge. So imagine this: +--+--+--+--+--+--+.....+--+---Plus terminal S..S..S.[B].S..S..S.....S..S +--+--+--+--+--+--+.....+--+---Minus terminal In this case, all of the "S"s represent a microcell (uCell) that is highly sulfated, and the "[B]" represents a microcell that is in perfect condition, and is taking a charge normally. If you try to put current into this lead acid cell, the sulfated uCells will appear as open circuits (due to the sulfate's insulating properties), and the good uCell will take all of the current, and will keep the voltage down to a low enough value that the sulfated uCells will not see any significant electrolysis action. So you say, "Pooh, I want the sulfated uCells to charge too!" and up the voltage across the lead acid cell, and poof! The good uCell dies from over heating, revealing a new uCell that wants to charge, and poof, it dies, revealing another uCell that wants to take a charge, and poof... You get into a situation where your success causes your failure. If, instead, you apply high voltage pulses to the lead acid cell, you can sometimes beat the system. The good uCells will take a hit, but it is short enough that they don't have time to burn up, and the sulfated uCells will get to draw enough current during the pulse that a little electrolysis will happen, and convert some of their sulfate back into oxide and acid... Sometimes you can win by using a pulse charge system. However, there is a little physical problem that has to be understood. Part of the way the lead acid batteries get their high current handling densities is because the lead plates are made to have high surface area. They are kind of like sponges on the surface. And, lead sulfate takes up significantly more room than lead oxide. Sorry, that is the way it just is. So, when a cell gets all sulfated up, the lead sulfate that forms in the deep nooks in the mossy lead electrodes fills the nook up so full that it breaks it apart, and damages the cell plate. This happens, albeit slowly, even when you treat the battery nicely. You can't win. Long term everything heads towards entropy. -Chuck Harris Brooke Clarke wrote:
Hi Robert: I've spent a lot of time charging batteries using different methods and on various chemistries. When the charge is in the form of a pulse, ideally including a reverse polarity pulse, the charge is more effective. This is also a way to sometimes, but not always, will recover a battery that otherwise will not take a charge from a DC source. I think this works because it takes some time for chemical reactions to work and by using a pulse you can force the reaction to a higher level that you can't do using DC without causing problems such as boiling the electrolyte. For more info see Burp Charging: http://www.prc68.com/I/BatChg.shtml#Burp Have Fun, Brooke Clarke
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