Motorola Astro Dimetra MTP, Instruction Manual, Page: 29 / 76

19
The battery voltage and temperature are monitored, and when the
proper condition exists, a rapid-rate charge, 0.35C rate (approximately
one-third the current rating of the battery), proceeds. The rapid rate
continues until one (or more) of the following occurs:
a. the rate of temperature rise and the rate of voltage decrease
are exceeded
b. the voltage limit (10.3V) is reached
c. the temperature limit (45°C) is reached
d. rapid charging times out (2.4 hours)
These conditions indicate charge complete, and the charger switches
to a trickle rate of 0.05C.
The charger consists of the following circuits:
• a 5-volt regulator (U7),
• a microprocessor (U5),
• a digital-to-analog converter (DAC) (U3, R74-81),
• a current regulator (Q1, Q2, Q3, Q13, and U3), and
• a self-test, switchable load (Q17, R68-71).
The vehicle A+ battery voltage (13.8 Vdc) is applied, via the dc switch,
to the 5V regulator (U7), which provides supply voltage to the
microprocessor (U5). When the radio/battery is inserted into the
XTVA, sensing of battery connected is processed by the dc switch (Q6,
Q19 and Q4), which connects the charger to A+, and charging begins.
The microprocessor interrogates the radio battery for type and
temperature by measuring the voltage at the R
C
(code) and R
T
(temperature) battery contacts. The valid R
C
values identifying the
designated battery type are as follows:
The voltage at the R
T
contact is pertinent because the processor is
programmed to apply the rapid charge current rate only if the battery
temperature is between 10°C and 40°C. Once the rate resistor (R
C
) is
determined, and the battery temperature is within the prescribed
limits, the charger will begin supplying rapid-rate charging current.
The processor illuminates the XTVA’s red LED, indicating a rapid-
charge condition. If the battery temperature is colder than 10°C or
hotter than 40°C (outside the prescribed limits), the charger will apply
the trickle current rate, and the processor will illuminate the XTVA
LED to an orange color. When the battery temperature changes to
within the limits, the charger will begin its rapid-charge rate and the
LED will turn red.
R
C
Resistance Battery Type
5.1 k
W
Ultra-High Capacity, NiMH
10 k
W
Ultra-High Capacity, NiCd