Electrical Power

ATA Chapter 24 — N720AK Systems Reference

Overview

N720AK’s electrical system uses a dual-bus architecture managed by the flyEFII System32 Bus Manager. Power distribution and electronic circuit breaker protection are provided by the Vertical Power VPX Sport. Two EarthX ETX900 lithium batteries provide redundant power with fully isolated charging systems: a 60-amp primary alternator charges Battery 1, and a Monkworkz MZ-30 generator charges Battery 2.

Components

How It Works

Bus Architecture

• Essential Bus: Powers critical engine systems — ignition, fuel injection, fuel pumps. Managed by System32 Bus Manager.
• Main Bus: Powers avionics and other aircraft systems via VPX Sport electronic breakers.

Emergency Endurance Bus

If a battery fails or bus voltage drops critically, the System32 Bus Manager automatically:

1. Disconnects non-essential loads from the main bus
2. Preserves all available power for the essential bus
3. Maintains engine ignition and fuel injection

The EMERGENCY POWER switch on the panel manually activates this mode.

Endurance bus radio behavior: The GTN 650 is COM1. If power goes out on the GMA 245, it hard-connects COM1 from the GTN 650 directly to the headphones. This ensures radio communication is maintained even if the audio panel loses power on the endurance bus.

VPX Sport

The VPX Sport provides:

• Electronic circuit breaker protection (no physical breakers to reset)
• Load monitoring and display on EFIS
• Automatic load shedding if needed
• Programmable power channels

Fuses (Non-VPX)

Discrete fuses outside the VPX electronic breaker system, located above the essential bus bar behind the pilot PFD:

Monkworkz MZ-30 Generator

Installed 2026-03-09. The MZ-30 is a permanent-magnet generator driven off the engine’s vacuum pump pad, providing independent charging for Battery 2. Manual version 4, dated 2024-10-22.

Specifications

Voltage selection: Ships configured for 14.6 VDC. For lithium batteries (EarthX), the lower 14.2 VDC setting is recommended per Monkworkz Feb 2026 guidance. To select 14.2V, disconnect pin 1 (VSEL) on the input side Pico-Lock connector. Voltage is set at startup and cannot be changed while running.

Architecture

The two battery charging systems are fully isolated:

The bus manager’s internal screw that previously allowed the primary alternator to cross-charge Battery 2 has been removed. Each battery has a dedicated charging source.

Generator → Battery 2 Wiring

The generator output connects to the Battery 2 stud inside the bus manager (Drawing 5A, bus manager installation guide page 13). A BOSCH 0332019155 normally-open relay (30A, 12V, internal diode) sits between the generator output and Battery 2 to prevent parasitic draw when the engine is off.

Relay coil power: Essential bus + generator enable switch. This design means:

• Turning off the ignition key de-energizes the essential bus, opening the relay and disconnecting the generator from Battery 2 — regardless of enable switch position
• The enable switch provides pilot control to disable the generator in flight
• The generator cannot turn itself on (unlike the Monkworkz reference diagram which powers the relay from the generator output)

Note: The manual recommends connecting to the switched side of the master contactor to avoid parasitic draw from the regulator’s ~30mA diagnostic blink code circuit. The BOSCH relay achieves the same purpose.

MZ Regulator Connections

The MZ regulator is mounted on the engine mount with the following connections:

Generator side (3-phase, #6 screw terminals, 12 AWG):

• Terminal 7 (~1), Terminal 8 (~2), Terminal 9 (~3) → MZ Generator (phases can be connected in any order)

Input Molex Pico-Lock (pre-wired, 22-24 AWG):

• Pin 1: Voltage_Select (connected = 14.6V, disconnected = 14.2V)
• Pin 5: GEN_Thermistor → Generator thermistor (required — system will not produce output without it)
• Pin 6: GND

Output Molex Pico-Lock (22-24 AWG):

• Pin 1: Enable → Pilot enable switch (pin 1 to switch center, pin 6 to switch N.O.)
• Pin 2: Output_Active — pulls to ground when regulator is active and maintaining ≥14V (works with Dynon/Garmin EFIS contact inputs). Orange/brown wire, currently coiled up and unused near the Monkworkz enable switch.
• Pin 3: +i_Shunt (internal fuse used as shunt, 1.1 mΩ nominal)
• Pin 4: −i_Shunt
• Pin 5: Proportional_Current → Dynon EMS pin 31 (0–~2.7V = 0–30A, brown/blue wire)
• Pin 6: GND

Power output (#6 screw terminals, 10 AWG Tefzel):

• Terminal 17: Output_Power_Positive → BOSCH relay → Battery 2 stud (bus manager)
• Terminal 18: Output_Power_Ground (to clean metal airframe ground, no paint/corrosion)

Caution: The Pico-Lock connectors are delicate — add ~0.5“ maintenance loops in the connector wires, secured to nearby 12/10 AWG wires with a small pre-load toward the connector to prevent unseating.

Cooling

Both generator and regulator require cooling via 3/4“ holes in the engine baffling with corrugated nylon tubing routed from the baffling. The duct material is a force fit into the generator, regulator, and baffling holes. RTV can improve the seal.

Generator Enable Switch

Panel-mounted next to the primary alternator field switch. Controls the relay coil circuit (essential bus → enable switch → relay coil → ground).

The enable switch wiring connects pin 1 (Enable) to the switch center post and pin 6 (GND) to the switch’s normally-open terminal, grounded at the regulator end (not at the panel — grounding at the panel can cause ground loops and erratic behavior per manual section 2.1).

Startup Behavior

After engine start, when RPM exceeds ~1200, the MZ-30 performs an internal self-test (2–4 seconds). If all checks pass, it begins providing output voltage. The enable switch can be set ON as part of the pre-start checklist or activated at idle.

Protection Features

• Overvoltage Protection (OVP): Shuts down output in <1 second if overvoltage detected. If OVP triggers 3 times in one flight, system shuts down for the remainder of that flight. If this occurs across 3 separate flights (9 total OVP events), the regulator requires service/replacement from Monkworkz.
• Thermal protection: Two-stage — first reduces to half current limit, then full shutdown if temperature continues rising. Recovers automatically when temperature drops below recovery threshold.
• Current limiting: Electronic current limiting at 30A. Output fuse is internally replaceable by a repair shop only.
• Shear coupling: Located between input spline and motor shaft. Breaks if vacuum drive torque is exceeded — contact Monkworkz for replacement if generator rotates freely.

Regulator Blink Codes

The regulator has a diagnostic LED on the output side:

The Output Active pin (pin 2) also provides status: it “flashes” on an 8-second cycle (4s ground, 4s open) if the generator is overheating, providing an in-cockpit indication.

Dynon EMS Monitoring

The MZ-30’s proportional current output (pin 5, 0–~2.7V = 0–30A) is wired to Dynon EMS pin 31 (previously CO Guardian). This replaces the CO detector wiring.

References

• Monkworkz MZ-30 product page
• MZ-30 Installation and Operation Manual V4 (2024-10-22)
• VAF: Monkworkz Wiring for Amps Readout
• Bus Manager Installation Guide, Drawing 5A (page 13)

Wiring

KiCad migration: All connector pinouts and wiring data below should eventually be ported to proper KiCad schematics. The text tables here are transcribed from build notes and serve as the interim reference.

Wiring Stations (Station-by-Station Topology)

Complete wiring map of the aircraft, from tail to firewall.

Rear Tailcone

• ELT
• SunTail (rear position/strobe)
• Elevator trim servo

Tailcone / Baggage Area Junction (RIGHT)

• Elevator autopilot servo
• ADSB
• Net hub
• Battery 1 positive (large gauge)
• Battery 2 positive (large gauge)
• Main battery negative (large gauge)

Tailcone / Baggage Area Junction (LEFT)

• Alt static line from panel
• EFIS hub connection
• Starter solenoid 1 drive
• Starter solenoid 2 drive
• Starter annunciator wire
• Emergency air override (yellow and red lines)
• O₂ supply and pressure lines (blue and red)
• Oxygen wiring harness
• Pitot air hose (blue)
• AoA hose (green)

Passenger Area (LEFT)

• O₂ lines (blue and red)
• Left passenger O₂ harness
• Left door ajar sensor
• Power wire for left door ajar servos

Passenger Area (RIGHT)

• O₂ lines (blue and red)
• Right passenger O₂ harness
• Right door ajar sensor
• Power wire for right door ajar servos

Left → Center Tunnel

• Flap position sensor harness
• Flap motor wires

Wing Connection Area (LEFT)

• Pitot heat power and ground (14 AWG)
• Heated pitot status wire
• Fuel level sensor left
• AoA air hose (green)
• Pitot air hose (blue)
• 2× shielded 3-wire bundles for left lights
• Green sync wire for left lights
• 5-wire trim bundle for left roll trim

Wing Connection Area (RIGHT)

• AP splice for red, black, yellow — 3-way (rear, connector, front)
• AP bundle extension from connector
• 2× shielded 3-wire bundles for right lights
• Green sync wire for right lights
• Right wing COM antenna coax from panel (inline connector)
• Right wing NAV antenna coax from panel (inline connector)

Gear Support Mount (LEFT) — Under-Seat Terminal Blocks

• EMS ground for trim servo sensors
• Pitch trim motor power and ground
• Roll trim motor power and ground
• Roll trim position sensor
• Pitch trim position sensor
• Trim bundle from left wing
• 5V (red/white) EMS power for trim servo sensors

Gear Support Mount (RIGHT) — Under-Seat Terminal Blocks

• Green sync wire for lights
• Wig-wag power
• Nav power
• Strobe power
• Taxi power
• Landing power
• Tail light bundle from rear
• 16 AWG ground wire for lights
• AP servo black, red, yellow spliced together
• 2× 3-wire light bundles + green sync crossing to left wing root
• 2× 3-wire light bundles + green sync from right wing root

Forward Center Tunnel

• 2× red power wires for fuel pumps
• Ground wire for fuel pumps (1 wire spliced to 2)

Control Sticks (LEFT and RIGHT)

• Main bundle from SteinAir panel harness
• COM flip sensor wire

Pilot Knee Side (LEFT)

• O₂ pilot wiring harness
• O₂ lines (blue and red)

Copilot Knee Side (RIGHT)

• O₂ copilot wiring harness
• O₂ lines (blue and red)

Left Firewall Penetration — Engine Sensors

• CHT wires × 6
• EGT wires × 6
• Fuel pressure ground and data
• Oil pressure ground and data
• Oil temp ground and data
• Spliced 5V wire (red/white) for fuel pressure, oil pressure, oil temp sensors

Right Firewall Penetration — EFII / Power

• 60A fuse → bus manager
• Ammeter shunt wires
• Spark plug wires for EFII
• Ignition coil wires (71 and 88)
• Pressure sensor wires
• All remaining EFII outputs

Terminal Blocks Under Seats

Two terminal blocks located under the front seats distribute wiring between the wing roots, center tunnel, and panel.

Left Terminal Block

Right Terminal Block

Wing Root Connectors (CPC)

CPC barrel connectors (series 1, 17–18 pin) at each wing root carry all wing wiring.

Right Wing Root Exit

Left Wing Root Exit

Autopilot Servo Wiring (Wing)

Wire color mapping between the wing harness and the Dynon roll/pitch servo connector.

Dynon EMS-220 Connector (37-Pin)

Complete pinout for the SV-EMS-220 engine monitoring module. Updated 2026-03-04.

Through Firewall

Across Panel

Down Left (Under Panel)

Shared Power

Unused Pins

Panel Mounting Fasteners

Screw/bolt specs for every panel-mounted component. Useful reference for panel removal and reinstallation.

Connector Inventory

Summary of all connector types used in N720AK wiring (all installed).

Inspection & Maintenance

EarthX Battery & Chargers

Chargers

Charger Behavior Notes

The OptiMate chargers enter sleep/maintenance mode once the battery is fully charged, checking voltage roughly once per hour. Important: If a continuous parasitic load is present (e.g. panel powered on for configuration), the charger may not detect the drain during its sleep intervals and the battery can discharge. This caused a drain-to-zero event during initial setup. The TM-275’s TUNE mode (continuous 13.6V power supply) avoids this problem. (Per EarthX Engineering, Dillon Hinners, 2026-01-13.)

Hartzell Alternator Maintenance

Per the AL 12-E160/V installation manual: battery terminal torque 50 in-lb, safety wire .032. Annual: check bearings. 5yr/1000hr: inspect brushes (replace if <0.250“ from holder case edge). 5A enable CB, 60A main breaker.

References

• VPX Sport Installation & Operating Manual (Rev G4)
• VPX Sport Installation & Operating Manual (Rev G3) — previous revision
• VPX Getting Started Guide (Rev A)
• EFII Bus Manager Installation Instructions
• EarthX ETX900 Installation & Maintenance Manual
• Hartzell AL 12-E160/V Alternator Installation Manual (P/N 99-9900)
• Power & Lighting Schematic
• VPX Pro/Sport Load Planning Worksheet