Chapter 2: Analyzer Description
ABL77 Service Manual
Module Descriptions,
Continued
Battery Pack
Battery pack
The battery pack contains 12 nickel metal hydride (NiMH) cells (see Figure 2-33).
The pack has a nominal DC voltage of 14.4 and a rated capacity of 3.8 Ah. The
battery pack stores power for use by the analyzer when not connected to an AC
power source. After use, the battery pack should be disposed of in a safe and
proper manner consistent with disposal of any battery.
Figure 2-33
Charge cycle of
the battery pack
The analyzer controls the charge to the battery pack using a counter and charge
controller. The counter value is reflected in the value displayed in the
Bat
field on
the
Hardware
screen.
The input charge increments the charge counter, which reflects the charge capacity
of the pack. The charge rate is a function of the current control circuit. As the
battery charges, the current applied will decrease in proportion to the battery
voltage. As the battery voltage increases, the temperature of the pack increases.
This increased temperature increases the internal pressure of the cells, causing a
higher voltage across the pack. This results in varying charge rates based on the
charge state of the battery pack. To ensure maximum charging of the pack, the
charge controller (on the Battery Control Board) provides a six-hour charge cycle.
For safety purposes, the maximum allowed charge current is 650 mA.
The counter decrements based on the normal operation of the analyzer on battery
power. The counter also decrements based on the self-discharge rate of the battery
with storage and age. The self-discharge rate is accelerated with increased
temperatures.
Battery pack
temperature
The battery pack contains an internal safety switch that is triggered based on the
current output over time and monitored by an internal thermistor. This switch
prevents unsafe levels of operation. During charging, if the temperature of the
battery pack rises above 45
°
C, charging is terminated. In addition, there is an
integral temperature cutoff switch which opens if the pack reaches 70
±
5
°
C. If
this switch is triggered, the battery pack will no longer be operational.
Continued on next page
2-44
Rev.
F