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When battery voltage drops below the FLOAT setting for a cumulative period of one hour, a
new BULK cycle will be triggered. This typically occurs each night. If the battery is full at
the start of the day, it will receive an ABSORPTION charge for one hour and then be held at
the FLOAT setting for the remaining period of the day. Should the battery voltage drop
below the FLOAT setting for a cumulative period of one hour, another BULK and
ABSORPTION cycle will be initiated.
This three stage charging process results in faster charging compared to on-off relay type
or constant voltage solid state regulators. Faster recharging increases the performance of
the system by storing more of the PV array’s limited output. The final FLOAT voltage
setting reduces battery gassing, minimizes watering requirements and ensures complete
battery recharging.
Approximately every month, some batteries may need to be "equalized" (a fancy term for
overcharged). Since the individual cells of the battery are not identical, some cells may not
be fully charged when the charging process is completed. If the batteries have been left in
a discharged condition for long periods of time, the plates will have sulfates on them from
the electrolyte. If the sulfate remains on the plates for an extended period of time, it will
harden and seal off a percentage of the plate area, reducing the capacity of the battery. By
equalizing the batteries before the sulfate hardens, the sulfate is removed from the plates.
Batteries with liquid electrolyte may become stratified. Stratification concentrates the
sulfuric acid into the bottom of the cell while the top becomes diluted. This corrodes the
lower portion of the plates, reducing battery life. Mixing of the electrolyte by the formation
of gas bubbles during the equalization process reduces stratification.
Two methods can be used to determine if a battery needs to be equalized. If possible,
measure the voltage of each individual cell while the battery is at rest (not being charged or
discharged), a variation of 0.05 volts between cells indicates an imbalance exists. If the
battery construction prevents measurement of the individual cell voltages, use a
hydrometer. A variation of 0.020 in the specific gravity between cells is considered
significant. Both conditions can be corrected by an equalization charge.
A proper equalization charge will not damage a vented, liquid electrolyte type battery. It
may, however, cause significant electrolyte usage and require that the battery be refilled
with distilled water to the correct level. This may be a problem with unattended systems in
remote areas which do not receive regular maintenance. Consult the battery manufacturer
for their recommendations.
DC loads may need to be disconnected by turning off circuit breakers or removing fuses
before equalization to prevent damage by the required higher voltages.
Equalization (Non-Sealed Batteries Only)
CAUTION: Equalization should be done only on vented (not sealed or maintenance
free) lead-acid, liquid-electrolyte batteries. The battery manufacturer should be
consulted before attempting to equalize any other battery type. Add clean, distilled
water to the battery following the equalization process.
Copyright Trace Engineering Co. Inc. Tel (360) 435-8826 Part Number 2680 Rev. C
5916 195 Street, NE Fax (360) 435-2229 November 4, 1998
Arlington, WA 98223 USA www.traceengineering.com Page
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