VRLA Battery Charging|Charging Of VRLA Batteries

Charging of VRLA Batteries: As you alreday read what is VRLA battery, VRLA Battery storage, Installation of VRLA batteries you can learn how to do VRLA battery charging.

Contents

VRLA Battery charging

General Instruction for charging of VRLA

For a good performance, it is better to follow the procedure defined by the manufacturer for charging. The procedure is as under.

Ensure that the entire cell in the battery set is of the same type and capacity. Charging individual cell separately is not advisable.
Correctly connect the battery charger output terminals to the battery set i.e. positive to positive and negative to negative.
Ensure that all electrical connections between the battery charger and the battery are tight and offer good conductivity.

Voltage settings of power plant with VRLA Batteries

In the float mode, the float Voltage is 2.25 V per cell. In normal cases, the float voltages work out to be as under.

(i) 56 Cells battery bank – 126.0 +1.0 /–0.5 Volts
(ii) 54 Cells battery bank – 121.5 +1.0/–0.5 Volts.

Freshening Charge VRLA Battery

In case the batteries are to be stored for longer duration, the battery must be charged for the freshening charge.

♦ Charging must be carried out at constant potential with the current limited to the maximum 0.2 C10 Amperes (where C10 refers to the numerical value of the nominal capacity of the battery).
♦ In charge mode, at a charge voltage of 2.3 Volt per cell for a period of 16 hours.
♦ In the float mode, at a float voltage of 2.25 Volts per cell for a period of 72 hours. Say, for 48 Volts, 400 AH battery consisting of 24 cells, charging must be carried out in the charge mode at a charge voltage of 55.2 Volts ± 0.1 Volts for a period of 16 hours. Or charge in the float mode at a float voltage of 54 Volts ± 0.1 Volts for a period of 72 hours. The current
should be limited to maximum of 80 Amps. (400X0.2 = 80).
♦ The above charging procedure is to be used for giving a freshening charge to the battery for extending the storage period.
♦ This charging procedure is also valid for charging the battery to determine the rated capacity of the battery after installation.
♦ Battery located in areas having very low average ambient temperatures (below 15° C) will require the charging time recommended above to be doubled in order to fully charge the battery.

Float charging method

Under normal condition the batteries are charged with float charge method.

This type of charging sustains the battery in a fully charged condition and also makes it available to resume the emergency power requirements in the event of an AC power interruption or charger failure.

♦ Float charging of battery is carried out as under.
♦ 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 normal connected load.
♦ After the batteries has been given its freshening charge the charger should be adjusted to provide the recommended float voltage at the battery terminals.

♦ Adjust the charger voltage to 2.25V per cell. (i.e. in a 24V system, 12 Cells are floated 27 Volts).
♦ During charging as the cells approach full charge, the battery voltage rises to approach the charger out put voltage. (i.e. 27 Volts in the above case). The charging current decrease to the float current value of around 50 mA per 100 AH.
♦ When the charging current has stabilised at the float current for three consecutive hours or the voltage across the battery bank terminals is constant for six consecutive hours, the battery bank can be considered as having reached the fully state of charge.
♦ Recommended float charge voltage for state of charge is given the table below.

sl no	Item	Nominal required value
1	Float Voltage setting at battery terminals	2.25 X No. of cells
	(i) 24 V system	27 Volts
	(ii) 110 V system	123.75 Volts
2	Normal battery charging current when battery put into charge after discharge.	10% of AH capacity i.e. for 100 AH battery to be charged at 10 A current.
3	Maximum battery charging current when battery put in to charge after discharge.	20% of AH capacity.
4	Ripple content in DC voltage.	Should be less than 2% rms
	(i) 24 V system	0.48 V rms (Max.)
	(ii) 110 V system	2.20 V rms (Max.)
5	Battery charging voltage (High protection).	Charger should trip at 2.37 Volts per cell
	(i) For 24 Volts system	Charger should trip at 28.44 Volts
	(ii) For 110 V system	Charger should trip at 130.35 Volts.
6	Battery under voltage (Trip on discharge)	Charger should trip 1.75 Volts per cell
	(i) For 24 Volt system	Disconnect the load at 21 Volt
	(ii) For 110 Volt system	Disconnect the load at 96.25 Volt

Equalize charging of VRLA Batteries

Under normal operating conditions an equalizing charge is not required.

An equalizing charge is a special charge given to battery when non- uniformity in voltage has developed between cell. An equalizing charge should be given when the following conditions exist.

♦ The float voltage of the pilot cell is at lest 0.05 V below the average floats voltage per cell in the bank.

♦ A recharge of battery is required in a minimum time amount of following an emergency discharge.
♦ Accurate periodic records of individual cell voltage show a sudden variation from the previous readings.

Equalizing charging method

♦ Equalizing charging is made using constant voltage method.
♦ Determine the maximum voltage that may be applied to the system (i.e. 2.30 X No. of Cell)
♦ Establish the maximum Voltage apply to the system for equalizing charge in shortest time duration as per the table below.

Sl no	Temperature	Volts/Cell Time
1	Below 15°C	2.30 V 30 Hours
2	15-32° C	2.30 V 20 Hours
3	Above 32°C	2.30 V 12 Hours

Discharging VRLA battery

♦ The discharge duration for the determined rated capacity of the battery is 10 hours. Discharged the battery for 10 hours so as to get an end voltage of 1.75 Volts per cell at an average ambient temperature of 27° C.
♦ It is important to immediately charge the battery in the charge mode after every discharge and maintain the battery in the charged condition by keeping it connected to the battery charger in the float mode.
♦ Ensure that the battery is charged optimally and no over charging, over gassing or heating takes place.

VRLA Battery charger Voltage / Current setting

Float mode

♦ Check the setting of battery charger. The battery voltage is 2.25± 0.05 volts per cell in float mode.
♦ Special care must be taken to ensure that the voltage of the power plant has been set exactly to a value within the specified range is given below.
♦ Voltage setting
a) 2V, 56 Cells – 126 V
b) 2V, 54 Cells – 122 V

♦ Charging voltage 2.25 V per cell
♦ Voltage ripple 5% rpm
♦ Ripple current 10% rpm
♦ Charging current Max 20% of AH rated current
♦ Voltage regulation Set voltage + 3%
♦ Ensure that the battery charger is so adjusted that charger trip at 2.35 V per cell to avoid over voltage of the battery.

Boost mode

♦ Check for cell voltage, if it is falling below 2.0 Volts, boost charge should be given with the following settings.
(i) Set the power plant voltage to 2.3 Volts per cell.
(ii) Set the maximum charging current limit to 20% of AH rating and charge the battery for 12 hours.
(iii) Recommended voltage setting during boost charging is as under.

♦ Voltage setting
a) 2V, 56 Cells – 128.8 V
b) 2V, 54 Cells – 124.2 V

♦ Charging voltage 2.3 V per cell
♦ Voltage ripple Less than 5% rpm
♦ Ripple current Less than 10% rpm
♦ Charging current Max 20% of AH rating, current limit to be set between 10 to 20% based on the time for recharge.

Safety Precautions on VRLA Battery

Before proceeding with the unpacking, handling, installation and operation of the valve regulated lead acid storage battery, the following information and the recommended safety precautions are to be followed.

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♦ Wear a rubber apron, rubber gloves and safety goggles or other eye protection to
prevent injury if contact is made with the acid.
♦ Under abnormal usage batteries can generate explosive gases. Under such conditions, the safety vent opens while the gases are being generated so keep sparks, flame and smoking materials away from the battery area.

♦ Ensure that tools are adequately covered with insulation tape or suitable non- conducting material to minimise possibility of shorting across connections.

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VRLA Battery Price

VRLA Battery price ranges from 500 Rs to 5600 Rs depending on the brand, features and quality. Some Examples are given below.

VRLA Battery charging|Charging of VRLA Batteries