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Lead-Acid Battery Zapper & Desulphator Mk.3

Here is a revised version of the popular Lead-Acid Battery Zapper featured in the May 2006 issue of SILICON CHIP. It is now separate from the Battery Condition Checker and much easier to build. At the same time it has been revamped for more reliable long-period operation with 6V, 12V & 24V batteries.

By Jim Rowe


Not all batteries can be rejuvenated by zapping. They may be too heavily sulphated or may have an open-circuit cell connection. Nor can the zapper restore a battery which is worn out; ie, one in which the active material on the plates has been severely degraded.

Depending on the battery, it is also possible that any rejuvenation effect may only be temporary.

The Lead-Acid Battery Zapper & Condition Checker published in the May 2006 issue has been a very popular project but since it was published a few shortcomings have become apparent. The metering circuit on the Battery Condition Checker sometimes had a tendency to “lock up” on the 6V range and the current pulse loading circuit was sometimes un­stable with 24V batteries, if the power switching MOSFETs were at the high end of their transconductance range.

In addition, the test current pulse amplitude was fixed at about 30A; OK for car batteries but too high for batteries used in motorbikes and for sealed lead acid (SLA) batteries.

Many readers also found the combination of the Battery Zapper & Condition Checker fairly tricky to assemble and disassemble because it was a bit of a shoe-horn job into the plastic case. In view of this, we recently decided to develop improved versions of both the Checker and the Zapper but to feature them as separate projects, to make them easier to build and use. The revised Battery Condition Checker is planned for publication next month.

What the Zapper does

First of all, let’s have a quick recap about zapping and what it’s all about. Lead-acid batteries have been used to store electrical energy for over 170 years – ever since Gaston Plante built the first one back in 1834. But lead-acid batteries are not without their faults. Probably their main drawback is that they tend to have a relatively short working life, typically no more than about three years although with care, they can last much longer than that.

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