Desulfation is the process of reversing the process of sulfation that occurs to a lead-acid battery over time. Desulfation restores, at least partially, the ability of the battery to hold a charge over the life of the battery originally caused by sulfation). Sulfation is the formation of large non-conductive crystals of lead(II) sulfate (PbSO4) on the battery plates. Eventually so much of the battery plate area is unable to supply current that the battery capacity is greatly reduced.
Most DIY desulfator circuits in use today can trace their roots back to an article in issue # 77 of Home Power magazine written by Alistair Couper in June/July of 2000. Many versions were spawned by his design but they all accomplish the same thing, that is, they use various pulsing circuits to force the lead sulphate crystals back into the electrolyte thus rejuvenating the battery and restoring its lost capacity.
The desulfator shown schematically above is being simulated. So far it shows promise. It combines features from multiple sources and sequences through them using a simple arrangement of 555 timers. Microprocessors are great for things like this, but for many people the programming tools are not available.
The planned cycle has four steps. The first step is to pulse the battery for 15 seconds using a Charged-Induced-Pulse described by desufonator2. The second cycle is a settling period of 1 second. Third is a 100 microsecond pulse that shorts the battery (180 amps?) to remove dendrites. And finally, a 5 second period to measure the battery voltage.