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Battery Sulphation

If lead acid batteries are left uncharged for lenghty periods, they deteriorate. This is because the sulphuric acid electrolyte attacks the electrode plates and forms the compound lead sulphate as the battery self-discharges. This is unfortunate for two reasons: firstly lead sulphate is an insulator and thus prevents current flowing between the plates, and second, the acid becomes weaker and is thus prone to freezing in cold conditions. This frequently splits the hard rubber casing of the battery rendering it useless.
In a 'young' battery, the (soft) lead sulphate is forced back into lead and sulphuric acid by the charging process. If the lead sulphate is allowed to harden over a long period of time (typical neglect) it will not dissolve easily and normally, such a battery is considered suitable for scrap only. BUT, there is a way to save sulphated (but not mechanically damaged) batteries! By hooking on a clever little piece of electronics, the lead sulphate can be persuaded to soften and dissolve in many cases. Contact Don for more details (see Homepage for email address).

Case history

A set of 12 cells from long abandoned coach was set up on a 24v charger. None of the cells was split (luckily) and terminal corrosion was not too bad. These cells were thought to have lain for up to 5 years since their last charge. The cells were of the 4-post type.

Batteries were charged to maximum capacity, then discharged while being monitored.  Cycle 1 yielded a capacity of just 8Ah.  The s.g. of the acid in all the cells was measured and it was between 1.00 and 1.05 (at full charge).  This showed that much of the Suphate in the acid had been deposited on the plates.

The cycle was repeated with the de-sulphator attached.  This time 62Ah was recorded.

The cycle was repeated with the de-sulphator attached.  This time 160Ah was recorded.  At this stage, the discharge monitoring showed one cell suddenly going into reverse voltage, so the discharge was stopped.  It transpired that one terminal of one cell had gone almost open circuit.   Fortunately, the other terminal on the same plate was OK, so it was connected instead for the next cycle. Before discharge, the acid s.g. was measured and was seen to be in the 1.15 to 1.2 range.   Desulphation was obviously working.

The charging was repeated with the de-sulphator attached.  The initial charge rate was 8A for about 10 hours, then the rate was reduced to about 1A while "the boss" went offshore for 2 weeks to do the "day" job. On return, the batteries were checked and were giving a capacity of up to 300Ah, i.e. almost 'as new' capacity.
The batteries in this experiment were of 'middle' age. Some much older cells of type BRA1 have also been brought back to life. These cells have date stamps from 1974 to 1981, and it has been possible to raise the sg of the electrolyte from 1.0 (at the start) to 1.25 (after several weeks and cycles).