Battery Operation, Recommended Float Range @77F

STEP 3

1. The initial charge is complete. Charger voltage can now be reduced to float voltage setting per Section 13.2. For a target float charge of 2.25 VPC on a 24-cell system, you would set the charger voltage to 54 volts.

SECTION 13: BATTERY OPERATION

13.0 Cycle Method of Operation

In cycle operation, the degree of discharge will vary for dif- ferent applications. Therefore, the frequency of recharg- ing and the amount of charge necessary will vary. Generally, Absolyte GX cells require approximately 105- 110% of the ampere-hours removed to be returned to a full state of charge.

The upper voltage settings recommended, given that the maxium charge current is 5% of the nominal C100 Amp-hour rating and the ambient temperature is 25°C (77°F), are as follows:

2.28 ± 0.02 VPC @ 0-2% DOD

2.33 ± 0.02 VPC @ 3-5% DOD

2.38 ± 0.02 VPC @ >5% DOD

Due to the variety of applications and charging equipment (particularly in photovoltaic systems) it is recommended that you contact a GNB representative when determining proper recharge profiles.

13.1 Floating Charge Method

In this type of operation, the battery is connected in parallel with a constant voltage charger and the critical load circuits. The charger should be capable of maintaining the required constant voltage at battery terminals and also supply a normal connected load where applicable. This sustains the battery in a fully charged condition and also makes it available to assume the emer- gency power requirements in the event of an AC power interruption or charger failure.

13.2 Float Charge - Float Voltages

Following are the float voltage ranges recommended for the Absolyte Battery System. Select any “volts per cell” (VPC) value within the range listed that will result in the series string having an average volts per cell equal to that value.

RECOMMENDED FLOAT RANGE (@77°F)

2.23 to 2.25 VPC

NOTE: Recommended float voltages are for 77°F. For other temperatures a compensation factor of .003 V/°F (.0055 V/°C) per cell is recommended. The minimum volt- age is 2.20 VPC, temperature correction does not apply below this voltage. The maximum voltage is 2.35 VPC, temperature correction does not apply above this voltage.

TEMPERATURE CORRECTION

V corrected = V25°C - (( T actual-25°C) x ( .0055V/°C)) or

V corrected = V77°F - ((T actual-77°F) x (.003V/°F)) See Appendix A for standard values.

Modern constant voltage output charging equipment is recommended for the floating charger method of opera- tion of GNB Absolyte batteries. This type of charger, prop- erly adjusted to the recommended float voltages and fol- lowing recommended surveillance procedures, will assist in obtaining consistent serviceability and optimum life.

After the battery has been given its initial charge (refer to Section 12), the charger should be adjusted to provide the recommended float voltages at the battery terminals.

Do not use float voltages higher or lower than those rec- ommended. Reduced capacity or battery life will result. Check and record battery terminal voltage on a regular basis. Monthly checks are recommended. See Section 15.0, Records. If battery float voltage is above or below the correct value, adjust charger to provide proper voltage as measured at the battery terminals.

13.3 Recharge

All batteries should be recharged as soon as possible fol- lowing a discharge with constant voltage chargers. To recharge in the shortest period of time, raise the charger output voltage to the highest value which the connected system will permit. Do not exceed the voltages and times listed in Table E in Section 14.2.

13.4 Determining State-of-Charge

If the normal connected load is constant (no emergency load connected), the following method can be used to determine the approximate state-of-charge of the battery. The state-of-charge can be identified to some degree by the amount of charging current going to the battery. When initially placed on charge or recharge following a dis- charge, the charging current, read at the charger amme- ter, will be a combination of the load current plus the cur- rent necessary to charge the battery. The current to the battery will start to decrease and will finally stabilize when the battery becomes fully charged. If the current level remains constant for three consecutive hours, then this reflects a state-of-charge of approximately 95 to 98%. For most requirements, the battery is ready for use.

If the normal connected load is variable (i.e. telecommuni- cations), the following method may be used to check the state-of-charge of the battery. Measure the voltage across a pilot cell (See Section 15 for definition of pilot cell). If the voltage is stable for 24 consecutive hours, the battery reflects a state of charge of approximately 95%.