Battery - Mallinckrodt NELLCOR NPB-195 Service Manual

Section 11: Technical Supplement
11.6.1 Fan Control
11.6.2 Battery Circuits
11.6.2.1 Charging Circuit
11.6.2.2 Battery Protection

11.7 BATTERY

11-4
Two outputs from the bridge rectifier are used in the NPB-195. The fan control
circuit uses the negative output. The positive output is the Main DC ranging
from 7 to 18 VDC. This positive voltage is used for the battery circuit and to
power the UIF PCB.
A fan control circuit on the Power Supply PCB is used to control the temperature
inside the case of the NPB-195. The temperature sensor used in this circuit is
U3. U3 turns on the cooling fan if the temperature inside the case gets above
approximately 31° C. The cooling fan runs on approximately 15 VDC.
Note: The fan is disabled if the unit is running on battery power.
Two circuits are included in this section of the Power Supply PCB. One circuit
is used to charge the battery and the other circuit provides battery protection.
The power supply will charge the battery any time the NPB-195 is connected to
AC power even if the monitor is not turned on. The voltage applied to the
battery is 6.8 ± 0.15 VDC and is current limited to 400 ± 80 mA.
Battery voltage is checked periodically by the processor. A signal from the
processor turns the charging circuit off to allow this measurement to be taken. If
the processor determines the battery voltage is below 5.85 ± 0.1 VDC, a low
battery alarm is declared.
Two types of battery protection are provided by the power supply: protection for
the battery and protection from the battery.
SW2 is a resettable component that protects the battery. SW2 opens and turns
the charging circuit off if the temperature of the battery rises above 50° C. If the
output of the battery exceeds 2.0 amps, F3 opens. F3 protects the battery from a
short to ground of the battery output.
Protection from the battery is provided in the event of the battery being
connected backwards. Components on the UIF PCB and the Power Supply block
and limit the voltage, to provide protection to circuits in the instrument.
A lead-acid battery is used in the NPB-195. It is rated at 6 VDC 4 amp-hours.
When new and fully charged, the battery will operate the monitor for 6 hours
with no backlight or alarms. The battery can withstand 400 charge/discharge
cycles. Recharging the battery to full capacity will take 14 hours in standby or
18 hours if the instrument is being used.
Changeover from AC to battery power will not interrupt the normal monitoring
operation of the NPB-195. However, when the unit is running on battery power,
the cooling fan, serial port, nurse call, and LCD backlight will be turned off.