Low Volts Warning Light - Cirrus DESIGN SR20 Information Manual

Cirrus Design
SR20

Low Volts Warning Light

The airplane is equipped with a red LOW VOLTS warning light in the
annunciator panel located on the left side of the instrument panel. The
alternator control unit (ACU) located within the master control unit
(MCU), which is mounted on the engine side of the firewall, operates
the warning light.
In the event an over voltage condition occurs, the alternator control
unit (ACU) automatically removes alternator field current to shut down
the alternator. With the alternator off line, the battery supplies system
current and a discharge rate is indicated on the ammeter. Under these
conditions, depending on electrical system load, the LOW VOLTS
warning light will illuminate when system voltage drops below 25.5 ±
0.35 volts. Turning the ALT MASTER switch off and back on again may
reset the alternator control unit. If the warning light does not illuminate,
normal alternator charging has resumed. If the light illuminates again,
a malfunction has occurred.
Illumination of the LOW VOLTS warning light and ammeter
discharge indications may occur during low RPM conditions
with an electrical load on the system, such as during a low
RPM taxi. Under these conditions, the light will go out at
higher RPM. The master switch need not be recycled since an
over voltage condition has not occurred to de activate the
alternator system.
Warning light operation can be tested by turning the landing light on
and momentarily turning off the master switch ALT portion while
leaving the BAT portion ON.
P/N 13999-002 Info Manual
September 2011
• Note •
Section 7
Airplane Description
7-53