Hill-Rom CareAssist P1170, Service Manual

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Electrical System
Chapter 3: Theory of Operation
Page 3 - 6 CareAssist™ Bed Service Manual (man330)
Function Control
The motors are controlled by relays. In order to protect these relays from
electrical sparks during switching, the second FET transistor checks the delay
power when a function is activated, thus allowing the switches to close with no
voltage. In the same way, when a function control is released, the FET
transistor cuts the power before the contact opens.
Overload limiting is provided by permanently controlling the current at the
output of each motor. In the event of overload or mechanical blockage, the
supply of the relevant motor is cut off by a control transistor without affecting
the operation of the other motors, except for specific situations. In this case, the
overload is indicated by an audible alarm. This overload indication also
enables failure of a motor end of travel to be detected, except for the hilow
columns, which have a backup end of travel.
Battery Circuit
The bed is equipped with battery backup. This battery backup is internal to the
power supply unit. The charging circuit, situated in the power supply unit, has
current limiting according to the level of the battery charge. Charging begins as
soon as the unit is switched on. At the end of charging, the load current is very
low.
When the power supply is disconnected from the AC power, the battery
backup is activated by pressing the Battery control on the caregiver controls.
The battery charge level is controlled. In this way, a flashing indicator and an
audible low battery alarm by buzzer are activated during movement if the
battery voltage drops (this is a continuous beep of several seconds that is heard
each time a control is pressed).
After connecting to the power outlet, the indicator continues to flash until the
battery has charged.
Battery operation is automatically stopped 30 seconds after the end of the last
movement.