Battery Capacity Analysis - Garmin GI 275 Installation Manual

3.5.2

Battery Capacity Analysis

NOTE
A Battery Capacity Analysis is not required if only installing the GI 275 as an MFD.
The capacity of the aircraft battery must be verified if the GI 275 installation increases the electrical load
on the system. The capacity of the existing battery is adequate if it supports loads essential to the continued
safe flight and landing for a minimum of 30 minutes. For aircraft with a maximum service ceiling greater
than 25,000 feet and certified with FAR 23.1353(h) at amendment 23.62, the battery must support
60 minutes of continued safe flight. Otherwise, the battery must be replaced with a battery that has
sufficient capacity.
Refer to ASTM F 2490-05 Standard Guide for Aircraft Electrical Load and Power Source Capacity
Analysis for more information.
Verification of the battery capacity can be accomplished following these steps:
1. Battery Capacity (de-rated) – 75% of the battery capacity (as indicated on battery nameplate) is
assumed available (this value has units of Amp Hrs). Ensure the value is converted to Amp Mins.
2. Normal Operation Load – Worst-case cruise condition (cruise at night) during normal operation
is assumed with 5 minutes given to the pilot to shed non-essential loads. Any automatic load
shedding can be considered immediate and does not need to be considered in the calculations.
Multiply the normal operation load (Amps) by t
3. Emergency Landing Load – Electric load during the approach and landing with failed generator/
alternator. This load is assumed to drain the battery for 10 minutes and needs to be determined.
Multiply the emergency landing operation load (Amps) by t
4. Emergency Cruise Load – Minimum load necessary to maintain flight in cruise after the
generator/alternator has failed needs to be determined.
The following equation determines the battery capacity for emergency cruise expressed as time (
Battery Capacity - Normal Operation - Emergency Landing
t =
3
The duration of the entire emergency flight on battery power is:
t =
t + t + t
1 2 3
t = 5 min + 10 min + t
t = 15 min + t
3
190-02246-10
Rev. 11
Emergency Cruise Load
3
(mins) [t = 5 min].
1 1
(mins) [t
2 2
=
GI 275 Part 23 AML STC Installation Manual
= 10 min].
):
t
3
(1) - (2) - (3)
(4)
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