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10.2 Absorption Charge (2
10.3 Equalizing Charge (3
10.4 Float Charge (4
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Voltage remains constant and current gradually tapers off as internal
resistance increases during charging.
It is during this stage that the charger puts out maximum voltage.
Voltages at this stage are typically around 14.2 to 15.5 volts.
This optional equalizing phase is a controlled 5% overcharge, which
equalizes and balances the voltage and specific gravity in each cell, the
effect of increasing the charge voltage.
Equalizing reverses the build-up of chemical effects like stratification,
where acid concentration is greater at the bottom of the battery. It also
helps to remove sulfate crystals that might have built up on the plates.
The frequency recommendation varies by manufacturer from once a
month to once a year, from 10 to 100 deep cycles, or when a specific
gravity difference between cells reaches .03 (or 30 points).
To equalize a battery, fully recharge it; next, increase the charging
voltage to the manufacturer's recommendations (if you cannot find one,
add 5%). Heavy gassing should start occurring at this stage (be very
careful about safety precautions).
Take specific gravity readings in each cell once every hour. Equalization
has occurred once the specific gravity values no longer rise during the
gassing stage.
th
After batteries reach full charge, charging voltage is reduced to a lower
level (typically 12.8 to 13.2) to reduce gassing and prolong battery life.
This is often referred to as a maintenance or trickle charge, since its
main purpose is to keep an already charged battery from discharging.
Charger with PWM, or "pulse width modulation" accomplishes the same
thing. In PWM, the controller or charger senses tiny voltage drops in the
battery and sends very short charging cycles (pulses) to the battery.
This may occur several hundred times per minute. It is called "pulse
width" because the width of the pulses may vary from a few
microseconds to several seconds.
NOTE: For long term float charging, such as backup power systems
that are seldom discharged, the float voltage should be set around
13.02 to 13.20 volts.
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Battery Analyzer Series
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