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Avionics Load Analysis

Power Requirements on the Ground

Section titled “Power Requirements on the Ground”

Estimated Avionics Current Draw (14 V System)

Section titled “Estimated Avionics Current Draw (14 V System)”

Bottom Line: Provide a power source that can supply the 5 A continuous load comfortably and also withstand short surges of several amps above that. A 10 A supply gives a healthy cushion. Monitor the voltage when first turning everything on; a slight dip is normal, but a well-sized supply will hold ~12–14 V steady throughout the startup. By accounting for inrush and using a supply with headroom, you’ll avoid inadvertent undervoltage resets or overload of the supply during your RV-14A’s software updates.

Below is an approximate current draw for each avionics component when the aircraft is on the ground with all avionics ON, under the given conditions (no transmissions, no servo motion, moderate display brightness, etc.). These values assume a 14 V electrical system (nominal ~12 V battery, ~14 V alternator output):

  • Primary Flight Displays (Garmin G3X Touch): Each 10.6-inch G3X Touch display (GDU 460) draws about 1.0 A typically at 14 V (with 100% backlight). A 7-inch G3X display (GDU 470) draws ~0.6 A. In a dual-screen setup, expect roughly 1.6–2.0 A total for the G3X displays in normal operation. (Typical draw is measured at full brightness, so actual draw may be slightly lower if screen backlighting is dimmed on the ground.)

  • Backup EFIS (Garmin G5): The G5 electronic flight instrument draws approximately 0.2 A on average (max about 0.25 A) at 14 V. This includes its internal sensors and display (it also has its own backup battery, which may draw some charging current if low).

  • GPS/NAV/COM #1 (Garmin GTN 650Xi): In receive-only mode (no radio transmit), the GTN 650Xi navigator draws about 0.6 A at 14 V under typical operating conditions. (This is the nominal draw with its touchscreen, GPS/Nav receivers, and COM radio receiver active but not transmitting.)

  • COM #2 (Garmin GTR 200/205): The second COM radio (e.g. GTR 20/200/205) draws roughly 0.6 A when receiving only (no transmit) at 14 V. This covers the radio’s receiver and audio circuitry. Transmitting would draw much more (up to ~3 A typical, 7.5 A peak), but we assume no COM transmissions during the update.

  • Audio Panel (Garmin GMA 245): The audio panel consumes about 0.3 A under normal conditions at 14 V (with audio amplifiers on but no audio output at high volume). Peak draw can rise toward 1 A if driving many audio outputs at high volume, but that’s unlikely during software updates.

  • ADS-B Transponder (Garmin GTX 45R): The transponder’s average draw is on the order of 0.5 A (estimated). It’s a solid-state Mode S/ADS-B unit and max power consumption is around 15–18 W (≈1.3 A at 14 V) in full transmit. However, during ground ops with no ATC interrogations, it will only transmit occasional ADS-B bursts, so the average current is much lower (a few hundred mA). Note: The transponder will still produce short peak pulses up to ~1–1.3 A when it broadcasts, even though the duty cycle is low.

  • Autopilot Control Panel (Garmin GMC 507): The mode controller draws very little, roughly 0.1–0.2 A (estimated) for its lights and electronics. With the autopilot servos unengaged and not moving, their motors draw negligible current.

  • Air Data/AHRS (Garmin GSU 25 + GMU 11 + OAT): The ADAHRS module and its associated magnetometer and temperature sensor draw about 0.25 A in total at 14 V.

  • Engine Monitoring Module (Garmin GEA 24): The engine interface module draws roughly 0.2 A at 14 V during operation.

  • Interface Modules (Garmin GAD 27, GAD 29, etc.): Each of these small interface units (discrete I/O module GAD 27, ARINC429 adapter GAD 29, etc.) draws on the order of 0.1 A or less. They have minimal current requirements since they are essentially signal converters.

  • Radar Altimeter Module (Garmin GHA 15 “Height Advisor”): The GHA 15 uses very little power (it transmits only milliwatts of radar energy). Its current draw is extremely low – on the order of a few hundred milliamps or less (likely ~0.1 A range). It’s designed to run on thin 22 AWG wiring, indicating minimal current demand.

Summary: Adding up the above nominal draws:

  • G3X displays: ~1.6–2.0 A
  • G5 backup: ~0.2 A
  • GTN 650Xi: ~0.6 A
  • GTR 205 COM: ~0.6 A
  • Audio panel: ~0.3 A
  • Transponder: ~0.5 A (avg)
  • GMC 507: ~0.1 A
  • GSU 25 + GEA 24: ~0.45 A combined
  • GAD 27 + GAD 29: ~0.2 A combined
  • GHA 15: ~0.1 A

This yields a total on the order of ~5 A at 14 V for all listed avionics running under the stated conditions. (If only a single G3X display is installed, the total would be closer to ~4 A; with two large G3X screens it will be nearer ~5 A.)

Section titled “Nominal Total and Recommended Power Supply Rating”

  • Nominal Total Draw: Approximately 5 A at 14 V for the entire avionics suite, given the assumptions (all avionics on, screens at moderate brightness, radios receiving only, no peripheral loads). This ~5 A figure is a steady-state average draw.

  • Recommended Power Supply: A bench power supply or ground power unit capable of delivering at least 8 A to 10 A continuously at ~14 V is recommended for safe margin. This ensures the supply isn’t running at 100% capacity and can handle any momentary surges. In practice, a 10 A rated supply is a common choice to provide comfortable headroom above the ~5 A nominal requirement. Having ~50–100% headroom (i.e. supply rated for roughly double the expected draw) is prudent. This headroom accounts for things like: turning up display brightness, a radio transmission if accidentally keyed, or any additional equipment that might be powered during the update. It also prevents the supply voltage from sagging if the current spikes briefly.

Minimum Safe Current Rating: At an absolute minimum, a ~7–8 A supply could carry a 5 A load with slight margin, but ~10 A gives more buffer. It’s better that the power source (whether an AC-to-DC avionics power supply or an external battery+charger) be generously rated so it runs cooler and more stably during the update process.

Inrush and Peak Current Considerations at Power-On

Section titled “Inrush and Peak Current Considerations at Power-On”

Even though the steady-state draw is about 5 A, be aware of short-duration inrush currents when the system is first powered on, and other transient peaks:

  • Power-On Inrush: Many avionics have internal capacitors and power supplies that draw a brief surge when first energized. For example, the G3X Touch displays can momentarily draw closer to their “maximum” current (up to ~2 A each) at startup, especially if their screens initialize at full brightness or if internal processors are booting at high load. This inrush typically lasts only fractions of a second, but the power supply should tolerate it. Similarly, the audio panel and other LRUs may have a short spike as they power up their electronics.

  • Backup Battery Charging: The G5 backup EFIS contains an internal battery. If that battery isn’t fully charged, upon power-up the G5 will draw extra current to charge it. This could add a few hundred milliamps above the normal 0.2 A for a short period. It’s not a huge surge, but it contributes to initial load.

  • Transponder and ADS-B Pulses: The GTX 45R transponder will periodically emit ADS-B Out and can reply to any ground interrogations. Each reply or broadcast is a very short high-power pulse (200 W RF) which draws a brief peak current (up to ~1–1.3 A). The average current remains low (~0.5 A), but the power supply and wiring should handle these sub-second pulses. Typically, quality bench supplies have no issue with such momentary peaks, especially if rated ~2× the average load.

  • Autopilot Servos (if powered): In this scenario we assume the servos are not active. If they were powered on, an autopilot servo might draw a short surge during its self-test or if it momentarily engages. Since we’re only powering the control head (GMC 507) and leaving servos idle, this is not a factor here.

Sources: Manufacturer specifications and installation manuals were used for these current draw figures. For example, Garmin’s data shows typical current draws of ~1.0 A for a GDU 460 display and ~0.2–0.25 A for a G5 EFIS on a 14 V system. The GTN 650Xi navigator is about 0.6 A in normal operation (no transmit). A GTR-series COM radio draws ~0.6 A receiving only, but up to 7.5 A when transmitting at full power. The GMA 245 audio panel, transponder, and various Garmin LRUs each draw on the order of a few tenths of an amp. The GHA 15 radar altimeter is a very low-power device (milliwatt-level radar) requiring only minimal current. These figures support the estimated ~5 A total and the recommendation for a supply capable of handling both this continuous load and transient surges.