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Equalizing / Refreshing / Boost Charge
At times a ni-cd battery system may benefit from a high rate charge. By increasing the chargers voltage output the charger will deliver
more current to the batteries. This in beneficial:
After a deep discharge, or after an inadequate recharging, an equalizing charge can help reduce the charging time.
Every 3-6 months – this will help keep cell voltages in line and will assure 100% capacity.
When individual cells fall below 1.36 Vpc.
Equalize charge the system for 72 hours at a voltage of:
Flooded Pocket Plate Ni-Cd batteries: 1.54-1.69 Vpc
Valve Regulated Pocket Plate Ni-Cd batteries: 1.45 Vpc
Flooded Fibre Plate Ni-Cd batteries: 1.52-1.57 Vpc
Recharging times vary depending on the charging procedure and on the charging current available. Higher voltages will typically
recharge a system faster however many systems have a high voltage limit so suitable measures should be taken to protect the load
circuits (e.g. charging off-line or limiting the equalize voltage).
Recharge 1.2 times the discharged capacity.
Upon completion of the equalize charge place the batteries back on float charge.
Warning! Leaving batteries on an equalization charge for long periods of time may result in: voided warranty, seriously overcharging
the battery causing loss of electrolyte (dry out) and shortened system life.
Voltage Spread Correction
Voltage spread is when the voltages of individual cells in a system vary significantly (typically by 0.08 Volts or more). Voltage spread
occurs due to a short or long term undercharge and it also can occur over time naturally if a system is not periodically equalize charged.
An equalize charge applied to the system every 3-6 months will typically prevent voltage spread from occurring.
Make the following corrective actions if any individual cell drops below 1.36 Volts:
First, make sure that the chargers float and equalize voltage settings are at the correct levels (as measured at the battery terminals).
A. Minor Voltage Spread.
If individual cell voltages are above 1.32 Volts a 72 hour equalize charge to the system will typically remedy the situation.
When equalize charging a full system to correct voltage spread the charger should be set to the highest possible voltage
(without exceeding the voltage sensitivity of your connected load). Disconnecting the load and using the highest equalize
voltage setting possible will produce the best results. When a charger is in equalize mode, the cells that are accepting a
charge readily will consume the majority of the extra voltage, leaving very little increase in voltage on the low voltage cells. So
the higher the equalize voltage setting the less time it will take to raise the voltage of the lowest cells.
Equalize charge the system for 72 hours and monitor the low voltage cells periodically to see when their voltage stops rising.
Continue equalizing these low voltage cells to until no further increase in voltage over a two hour period.
B. Major Voltage Spread
If minor voltage spread is not corrected in a timely manner individual cell voltages can fall as low as 0.00 Volts. If any cells
drop below 1.31 Volts the procedures to fix ‘major voltage spread’ are as follows:
1. Discharge entire system at 0.2C5 (20 Amp per 100 Ah of rated capacity) to 1.0 Vpc
2. Recharge system with a constant-current charge at 0.2C5 for 8 hours. If a constant current charge is not available
equalize the system at as high of a voltage and with as much current as possible for 72 hours.
3. Discharge entire system again at 0.2C5 (20 Amp per 100 Ah of rated capacity) to 1.0 Vpc
4. Recharge the system for 72 hours per equalize charging instructions and monitor the cells periodically to see when
their voltage stops rising. Adjust the equalize time until there is no further increase in voltage over a two hour period.
5. Put system back on float charge
C. Use of a Single Cell Charger
If only a few cells have a low voltage applying a high-rate charge to an individual cell via a single cell charger is ideal.
Applying a high rate charge to an individual cell is generally more effective than equalize charging the entire system. While the
main charger remains in float mode and the system is still online, a single cell charger can be connected to the cell with a low
voltage. Once the voltage of that cell stops increasing for a period of 2 hours the charger can be moved to the next cell with a
low voltage. To order a single cell charger, contact SBS.
If there are still voltage discrepancies contact SBS.
