User manual

6.9 Taper Current Charging
Although taper current chargers are among the least
expensive types of chargers, their lack of voltage regulation
can be detrimental to the life of any cell or battery. While
CYCLON
®
batteries have a superior ability to withstand
charge voltage variations, some caution in using taper
chargers is recommended.
A taper charger contains a transformer for voltage reduction
and a half-wave or full-wave rectifier for converting the AC
input into a DC output. The output characteristics are such
that as the voltage of the battery rises during charge, the
charging current decreases. This effect is achieved by using
proper wire size and turns ratio.
Basically, the turns ratio from primary to secondary
determines the output voltage at no load, and the wire size in
the secondary determines the current at a given voltage. The
transformer is essentially a constant voltage transformer that
depends entirely on the AC (input) line voltage regulation for
its output voltage regulation.
Because of the crude method of regulation, any changes
in input line voltage directly affect the charger output.
Depending on the charger design, the output-to-input voltage
change can be more than a direct ratio. For example, a 10%
line voltage change can produce a 13% change in the output
voltage.
There are several charging parameters that must be met. The
parameter of main concern is the recharge time to 100%
nominal capacity for cyclic application. This parameter can
primarily be defined as the charge rate available to the cell
when the cell is at 2.20 volts (representing the charge voltage
at which approximately 50% of the charge has been returned
at normal charge rates between C
10/10 and C10/20) and 2.50
volts (representing the voltage point at which the cell is in
overcharge).
Given the charge rate at 2.20 volts, the recharge time for
a taper current charger can be defined by the following
equation:
In the equation above for the recharge time using a taper
charger, C
D represents the discharged capacity in ampere-
hours while C
2.2V is the charge current delivered at 2.20 VPC.
The 1.10 multiplier represents the 5% to 10% overcharge that
is recommended for a complete recharge.
It is recommended that the charge current rate at 2.50 volts
be between C
10/50 maximum and C10/100 minimum to insure
that the battery will be recharged at normal rates and that the
battery will not be severely overcharged if the charger is left
connected for extended time periods.
7.1 Introduction
All batteries have extremely variable service life, depending upon
the type of cycle, environment, and charge to which the cell or
battery is subjected during its life. CYCLON batteries are no
exception to this rule. There are two basic types of service life:
cycle life and float life.
7.2 Cycle Life
A cyclic application is basically an application where the
discharge and charge times are of about the same order. The
cycle life of a battery is defined as the number of cycles
4
a
battery delivers before its capacity falls below the acceptable
level, usually defined as 80% of rated capacity.
Several factors influence the cycle life available from a battery.
The depth of discharge (DOD) is an important variable affecting
the cycle life. For the CYCLON battery series, the cycle life
expectancy is about 300 full DOD cycles. One can obtain more
cycles with lower depths of discharge as Figure 7-1 shows.
Figure 7-1: Cycle Life and DOD for CYCLON
®
Battery Cells
The quality of recharge is a critical determinant of the life
of a battery in a given cyclic application. In contrast to float
applications where more than adequate time is allowed for a full
recharge, in cyclic applications a major concern is whether the
batteries are being fully recharged in the time available between
discharges. If the recharge time is insufficient, the battery will
"cycle down" or lose capacity prematurely.
In our experience, undercharging is a leading cause of premature
capacity loss in cyclic applications. Although undercharge and
overcharge are both detrimental to the life of a battery, the time
frame over which the effects of either undercharge or overcharge
are felt is very different.
1.10 x C
D
Recharge time =
C
2.2V
Chapter 7:
CYCLON
®
Battery Service Life
1,000,000
100,000
10,000
1,000
100
0 10 20 30 40 50 60 70 80 90 100
Depth of discharge (DOD), %
Number of cycles
Charge profile :
CV @ 2.45 VPC for 16 hours
Current limit at C/10
4
A battery is said to have completed a cycle if it starts out from a fully charged condition, completes a discharge and is then fully recharged, regardless
of the depth of discharge.
15
Publication No: EN-CYC-AM-007 - December 2008
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