Methods of charging of batteries
(a) Constant Voltage Method
(b) Constant Current Method
Constant Voltage Method : In this method, the voltage of the source is kept constant
and current passes through the battery is regulated.
•
This
method is preferred owing to the fact that the charging current would
automatically taper off due to the growth of emf of the cell.
•
This
method needs lesser attention compared to Constant current method
In this method, charging current is
maintained constant till the battery is
fully charged.
• Figure shows the method of charging a
battery.
• The battery to be charged is
connected to the DC source.
• The charging current can be
maintained constant by a resistor connected in series with battery as shown in
figure.
• The charging current is measured with
the help of a ammeter connected in series with the battery.
• Care is to be taken, such that the
temperature of the battery should not to exceed 40°C
• If the temperature exceeds 45oC,
the charging process should be stopped for a while.
• This method of charging takes longer
time than that of constant voltage method, but the life of battery is
increased.
• This method is safe and causes less
damage do the plates.
Efficiency of a
battery
The efficiency of a
battery is expressed in two ways
(i) Ampere-hour efficiency or
Quantity efficiency
(ii) Watt-hour efficiency or
Energy efficiency
Ampere-hour efficiency (or) Quantity efficiency
Ø It is the ratio of out put in ampere
hour during discharge to the input in ampere hour during charge
Ø It is denoted by ηAH
Ø %ηAH = [(Ampere hour during discharge) /
(Ampere hour during charge)] X 100
Ø If Id is the average
current in amperes during
discharging,
discharging,
Ø Td is the time of discharge in
hours,
Ø Ic be the average charging
current in ampere
Ø Tc be the time during charge
in hours
Ø Then, %ηAH =[(Id X Td) / (Ic
X Tc)] X 100
Ø The ampere hour efficiency varies
between 90% to 95%.
Ø It means that if lead acid cell
provides 90 AH on complete discharge,
then 100 AH must be put back into the cell to restore it to original condition.
Watt - hour efficiency (or) Energy efficiency
Ø It is the ratio of out put energy in
watt hours during discharge to the input energy in watt hour during charge
Ø It is denoted by ηWH
Ø %ηWH
= [(Output
in watt hours during discharge) / (Input
in watt hour during charge)] X 100
Ø The Energy or Watt hour efficiency
can be determined from the ampere hour or quantity efficiency
Ø If
Vd & Vc is the average terminal voltage
of the battery during discharge time & charging time respectively in volt,
Ø Td
and Tc is the time of
discharge in hours during discharging and charging respectively.
Ø Ic
and Id be the average charging current and
discharging current respectively in
ampere.
Then,
%ηWH
= [(Vd
X Id X Td) / (Vc
X Ic X Tc)] X 100
= {[(Vd ) / (Vc)
] X [ ( Id X Td)
/ ( Ic X Tc)]
} X 100
= [ (Vd
) / (Vc) ] X % ηAH
