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7 Lead-acid activator (reviver) function
The ALC 8500-2 Expert features a lead-acid activator function which can be selected when charging
a lead-acid battery at channel 2. This function eliminates the problem of crystalline sulphate deposits
on the plates of lead-acid batteries which have not been used for a long time, or are only ever dischar-
ged at low currents when in use.
Lead-acid batteries are designed to provide a useful life of eight to ten years or more, provided that
they are maintained properly. However, in practice they very rarely last this long, and in fact the average
useful life of a lead-acid battery is generally far below the theoretical maximum. A particular problem
is the lead-acid battery which is only used seasonally; these regularly fail prematurely.
Many owners of motorcycles, boats and ride-on lawnmowers will be all too familiar with this problem:
in the Spring the expensive battery fails the first time it is called upon, and has to be replaced. The
formation of sulphate deposits is fundamental to lead-acid batteries, but the problem is particularly
severe when they are slowly discharged, e.g. when they self-discharge under storage conditions; the
result is a covering of crystalline sulphates all over the lead plates. The thicker the deposits become,
the less energy the battery can store, and - of course - the less it can deliver. At higher ambient tem-
peratures the rate of sulphate build-up rises considerably. Sulphate deposits are the primary reason
for the premature failure of lead-acid batteries.
The Activator function can be set to switch in automatically if desired, as soon as the ALC 8500-2
Expert switches to trickle charge mode when charging a lead-acid battery
Periodic pulses of peak current prevent the build-up of sulphate deposits on the lead plates. The
process also dissolves existing sulphate deposits, and the material is re-absorbed into the battery
fluid in the form of active sulphur molecules.
Although the pulses of current are high, relatively little energy is removed from the battery, as the
duration of the discharge current pulses, which occur every 30 seconds, is only 100 micro-seconds.
The trickle charge process soon compensates for the energy discharge.
The BA function works at battery voltages of up to 15 V.
The discharge pulse is indicated by an LED on the front panel (next to the channel 2 LED); this enab-
les you to check that the process is in action. The LED indicates the actual current flow, allowing you
to monitor the operation of the circuit.
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