November 20, 2017

Why sulphation remains an operator’s headache

Lead-acid batteries have been around a long time – 160-odd years since Gaston Planté invented the basic cell in 1859.

In this time, manufacturing techniques and additives such as antimony, calcium and silver have steadily improved the performance and storage capacity resulting in the high power, compact modern battery design.

Despite these improvements, the lead-acid chemistry has remained essentially the same, and so has the battery’s Achilles heel: sulphation.

How does this occur? As a battery discharges, the lead and lead oxide plates change to lead sulphate. When the battery is recharged, the lead sulphate changes back to lead/lead oxide.

To be more accurate, most of the lead sulphate reverts to lead and lead oxide. Due to a change in the crystal structure, some does not, and this permanent lead sulphate is known as sulphation.

Batteries that are kept fully charged will suffer less deterioration than those left in a state of partial discharge over longer periods of time. Batteries operating in high temperatures sulphate quicker than at low temperatures.

Sulphation gradually builds up as a battery ages, causing the battery performance to decrease as a result of the following factors:

  • Lower capacity (runs flat quicker)
  • Lower peak current (lack of power)

The domino effect of sulphation can cause premature failure in the following ways:

  • Overheating (sulphation greatly increases internal resistance)
  • Sludge (made worse by the crystal structure of sulphation)
  • Warped plates (caused by overheating)
  • Cell short-circuit (caused by warped plates and sludge)

Sulphation starts the day that battery acid is added to the dry plates, usually the last stage of the manufacturing process. Initially, the decrease in performance goes unnoticed until it reaches the point where the effects become severe. The typical service life may be anything from a few months to a couple of years, far short of the true life of a battery if sulphation did not exist.

Can the process of sulphation be slowed, halted or even reversed? And if so, can the price of a longer battery life be financially justified, compared with the cost of morefrequent battery replacement? In short, yes, particularly when the knock-on effects of battery failure are taken into account: downtime costs, vehicle starter motor replacement, etc.

So what can be done about it? Normal charging has no effect on sulphation, nor does replacing the old acid with new, nor discharging the battery right down to zero.

Pulsing

Various pulsing products have been found to work with various degrees of success. In most cases, simple pulsing has been incorporated into the battery charger. This is effective up to a point, but only if the batteries are regularly put on charge – typically this is not the case with automotive batteries which are charged by the alternator in the vehicle.

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