Garmin GI 275 Installation Manual page 101

EMERGENCY POWER OPERATION CALCULATION EXAMPLE
Date: 08/04/2017
POWER SOURCE QTY. INSTALLED
ALTERNATOR
BATTERY
Assumptions:
1. Most severe operating condition is considered to be night IFR with the pitot heat operating.
2. Load demands are shown for steady state operation and do not include inrush current draw.
3. Load shedding is accomplished manually by the pilot within five minutes of warning
annunciation.
4. Loads measured using a calibrated Extech DC ammeter clamped on the cable between battery
terminal and master relay.
Analysis:
(1) Battery Capacity
0.75×35 Amp hrs = 26.25Ah×60 min = 1575 A-min
(2) Normal Operation Load [t
Current drawn in normal cruise 43.5 A
Load 5 min×43.5 A = 217.5 A-min
(3) Emergency Landing Load [t
Current drawn in emergency landing 48.1 A
Load 10 min×48.1 A = 481 A-min
(4) Emergency Cruise Load.
Current drawn in emergency cruise 34.0 A
(5) Battery capacity for emergency cruise
(1) - (2) - (3)
t =
3
(6) Total duration of flight on emergency (battery) power
t = t + t + t
1 2
t = 5 min + 10 min + 25.8 min = 40.8 min
Results:
The total required flight duration on emergency power is 30 minutes. The existing battery capacity
provides 40.8 minutes for emergency flight duration. The battery is adequate.
190-02246-10
Rev. 11
VOLTAGE
1 13.75 VDC
1 12.00 VDC
= 5 minutes duration]
1
= 10 minutes duration]
2
=
(4)
3
Registration No.: N5272K
MANUFACTURER
PRESTOLITE
GILL
1575 - 217.5 - 481
34
GI 275 Part 23 AML STC Installation Manual
MODEL
AL 12-P70
G-35
= 25.8 minutes
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