Power System

Complete guide to the H7-Digital power architecture, voltage regulators, battery monitoring, and power management features.

Table of Contents

  1. Power Architecture Overview
    1. Power Flow Diagram
  2. Input Power
    1. Voltage Specifications
    2. Power Input Connection
    3. Reverse Polarity Protection
  3. Voltage Regulators
    1. 5V BEC - Current Budget Planning
    2. 10V BEC - VTX Power Management
    3. 3.3V LDO Regulators (Onboard)
      1. 3.3V MCU Power Rail
      2. 3.3V IMU Isolated Power Rail
  4. VTX Power Control (Software-Controlled 10V)
    1. Control GPIO
    2. ArduPilot Configuration
    3. Betaflight Configuration
    4. Protection Features
  5. Battery Monitoring
    1. Voltage & Current Sensing
    2. ArduPilot Configuration
    3. Betaflight Configuration
    4. Low Battery Warnings
  6. Power Distribution to Components
    1. Component Power Map
  7. Power Wiring Best Practices
    1. Wire Gauge Recommendations
    2. Connector Types & Wiring
  8. Troubleshooting Power Issues
    1. No Power to flight controller
    2. Brownouts During Flight
    3. VTX Not Powering On
    4. Insufficient Current for Peripherals
  9. Power Consumption Estimates
    1. Typical Build Power Budget
  10. Related Documentation
  11. External Resources
  12. Support

Power Architecture Overview

The H7-Digital features a sophisticated power management system with multiple voltage regulators (3.3V, 5V and 10V), battery monitoring, and software-controlled VTX power.

Power Flow Diagram

H7-Digital Flight Controller Power Diagram Power Flow on USB or Battery

Input Power

Voltage Specifications

Parameter Specification Notes
Input Voltage Range 9.9V - 25.2V 3S–6S LiPo (usable pack range)
Recommended 14.8V - 25.2V 4S–6S LiPo (most common use)
Absolute Maximum 28V Do not exceed; risk of regulator damage
Absolute Minimum 8V Below this, flight controller power is not guaranteed; VTX voltage will track battery voltage

Voltage Limits: Do not exceed 28 V input. Operation above this may permanently damage the regulators and destroy the board.
On the low side, the regulators remain enabled down to ~8 V. This is below the absolute 3.0V/cell minimum on 3S packs—while the system may still power in an emergency, operation in this region places severe stress on the battery and can cause permanent damage.

Power Input Connection

Primary Power Input: ESC Connector (8-pin JST-SH) - See ESC Connector Pinout for complete pin assignments

  • Pin 1: VBAT (Battery positive, 9.9V - 25.2V)
  • Pin 2: GND (Battery negative, common ground)

Connection Methods:

  1. Via 4-in-1 ESC (Recommended)
    • Use included JST-SH ESC cable
    • ESC provides battery power to FC
    • ESC current sensor provides telemetry data to Pin 4 (optional)
  2. Direct Battery Connection (Alternative)
    • Solder battery leads directly to ESC connector pads
    • Use for standalone FC testing or non-ESC applications
    • Requires external current sensor for telemetry

Reverse Polarity Protection

Limited Reverse Polarity Protection: The H7-Digital has NO reverse polarity protection on the main power input. Connecting battery backwards will cause immediate and permanent damage. Always double-check polarity before connecting power.

Protection Best Practices:

  • Use pre-wired ESC cables (JST connectors prevent reverse connection)
  • Mark polarity clearly on custom cables
  • Use a multimeter to verify polarity before first connection
  • Consider adding external diode or dedicated reverse-polarity module for critical applications

Voltage Regulators

For complete BEC electrical specifications, see Specifications - Power System.

This section covers practical power planning, current budgeting, and wiring guidance.

5V BEC - Current Budget Planning

5V BEC Rating: 2.0A continuous, 2.5A peak (< 10 seconds)

5V Powers:

  • Flight controller MCU and logic (via onboard 3.3V LDO)
  • GPS module (via GPS connector)
  • RC receiver (via RC INPUT connector)
  • Servos (via SERVOS connector)
  • External I2C compass (via GPS connector)
  • Onboard sensors (IMU, barometer)
Device Typical Current Peak Current Connector
H7-Digital Logic 150mA 200mA Internal
GPS Module 50-80mA 100mA GPS connector
RC Receiver 30-50mA 80mA RC INPUT
Servos (2x) 200-500mA 1000mA+ SERVOS
Compass 10mA 15mA GPS connector (I2C)
Reserve - 200mA Safety margin
TOTAL ~600mA typical ~2A peak -

Servo Current Draw: High-torque servos under load can draw 500mA+ each. Two servos at full load can approach or exceed the 2.5A peak limit. For demanding servo applications, consider:

  • Using low-current digital servos
  • Adding external BEC for servo power
  • Limiting servo speed/torque in firmware

Reducing Servo Noise: For applications with high servo current draw, add a 470–1000 µF low-ESR capacitor (≥10V rated) across the servo power pins (5V and GND) as close as possible to the SERVOS connector. This capacitor acts as a local energy reservoir to absorb millisecond-scale current spikes during servo motion, preventing voltage sag and reducing electrical noise coupling into the flight controller. Use a polymer or low-ESR electrolytic capacitor for best performance, and add a 0.1 µF ceramic capacitor in parallel for high-frequency filtering.

10V BEC - VTX Power Management

10V BEC Rating: 2.0A continuous, 2.5A peak (< 10 seconds)

Software Control: GPIO PE2 (RELAY2 GPIO 80 / PINIO1 10V BEC)

Powers:

  • Digital HD VTX ONLY (via VTX connector)

10V is VTX ONLY: The 10V output is designed exclusively for digital HD video transmitters (OpenIPC, DJI, Walksnail, HDZero). DO NOT connect 5V peripherals to the 10V rail. Damage will occur immediately.

The 10V rail requires VIN ≥ ~10.5 V to regulate; below this it tracks VIN (pass-through).

Compatible Digital VTX Systems:

  • ✓ OpenIPC (most require 9-22V)
  • ✓ DJI Air Unit / Vista (7-26.4V range)
  • ✓ Walksnail Avatar / VRX (9-25V range)
  • ✓ HDZero VTX (typically 7-25V range)

Typical VTX Current Draw:

  • Idle: 200-400mA
  • Transmitting: 600-1400mA (depends on system and TX power)
  • All common digital VTX systems compatible within 2.0A continuous rating

Check your specific model’s datasheet; input ranges and typical/peak current draw vary.

3.3V LDO Regulators (Onboard)

The H7-Digital features two independent 3.3V LDO regulators for clean, isolated power:

3.3V MCU Power Rail

Specifications:

Parameter Value
Output Voltage 3.3V
Continuous Current 1.0A
Input Source 5V BEC or USB (auto-select)

Powers:

  • STM32H743 microcontroller
  • Onboard status LEDs
  • SD card interface
  • DPS368 barometer

3.3V IMU Isolated Power Rail

Specifications:

Parameter Value
Output Voltage 3.3V
Continuous Current 250mA
Input Source 5V BEC or USB (auto-select)
Noise Performance Ultra-low noise, high PSRR

Powers:

  • ICM-42688-P IMU only (isolated for noise immunity)

Why Isolated IMU Power? The ICM-42688-P gyroscope is extremely sensitive to power supply noise. Digital switching noise from the STM32H743 MCU can couple into the IMU power rail and appear as false vibrations in sensor readings. A separate, ultra-low-noise LDO with high PSRR ensures the cleanest possible power delivery to the IMU, improving flight performance and reducing “noise floors” in Blackbox logs.

VTX Power Control (Software-Controlled 10V)

Control GPIO

Pin: PE2 (GPIO 80 in ArduPilot, PINIO1 in Betaflight)

Default State: ON (HIGH) - 10V enabled at power-up

ArduPilot Configuration

RELAY2 is pre-configured in the H7-Digital firmware:

// Pre-configured in hwdef.dat:
RELAY2_PIN_DEFAULT = 80    (GPIO PE2)
RELAY2_DEFAULT = 1         (ON at startup)

To Control via RC Switch:

Assign the Relay2 On/Off function to any RC channel (e.g., channel 7):

RC7_OPTION = 34  (Relay2 On/Off)

Save parameters and flip the channel 7 switch to control VTX power.

Mission Command Control (Advanced):

  • Use DO_SET_RELAY command in autonomous missions
  • Relay Number: 2
  • Setting: 0=OFF, 1=ON

Pre-configured: RELAY2 is already mapped to GPIO 80 in firmware (see Specifications - VTX Power Control). No manual RELAY2_PIN configuration needed - just assign an RC channel switch.

Use Cases:

  • Power off VTX during ground operations (save battery)
  • Disable VTX for regulatory compliance (RF off zones)
  • Power cycle VTX without full reboot (troubleshooting)
  • Automated VTX control in missions

Betaflight Configuration

PINIO1 is pre-configured in the H7-Digital firmware target with the following settings:

// Pre-configured in firmware:
PINIO1_BOX = 40        (User 1 box mode)
PINIO1_CONFIG = 129    (Output mode, default HIGH)
BOX_USER1_NAME = "10V BEC"
resource PINIO 1 E02

To Control via Switch:

  1. Go to Modes Tab in Betaflight Configurator
  2. Add “10V BEC” mode (appears as “User 1” or “10V BEC”)
  3. Assign to auxiliary channel switch (e.g., AUX1-4)
  4. Save and reboot

Pre-configured: Unlike most boards, the H7-Digital firmware has PINIO1 already mapped to GPIO PE2 with “10V BEC” naming. No CLI commands needed - just assign a switch in the Modes tab.

Use Cases:

  • Power off VTX in pit area
  • VTX power cycle via OSD menu
  • Switch-controlled VTX enable/disable

Protection Features

Current Ratings:

  • Continuous: 2.0A
  • Peak: 2.5A (< 10 seconds)

Best Practices:

  • Keep continuous current draw ≤ 2.0A for optimal reliability
  • Brief peaks to 2.5A are acceptable (VTX boot, mode changes)
  • Ensure adequate airflow around flight controller for thermal management

VTX Selection: Most digital VTX systems draw 0.8-1.4A during transmission, well within the 2.0A continuous rating. Choose VTX with ≤ 2A peak current for best compatibility. Allow 5-10 seconds for VTX boot before arming.

Battery Monitoring

Voltage & Current Sensing

Voltage Input: PA0 (ADC1 Channel 16)

  • Voltage divider ratio: 11:1
  • Measurement range: 0-26V (covers 6S LiPo)

Current Input: PA1 (ADC1 Channel 17)

  • Scaling: 18 mV/A (from ESC current sensor)
  • Typical range: 0-180A (depends on ESC sensor)

ArduPilot Configuration 

BATT_MONITOR = 4           (Analog Voltage and Current)
BATT_VOLT_PIN = 16         (PA0 = ADC channel 16)
BATT_CURR_PIN = 17         (PA1 = ADC channel 17)
BATT_VOLT_MULT = 11.0      (Voltage divider ratio)
BATT_AMP_PERVLT = 18.0     (Current sensor scaling)

Calibration Procedure:

  1. Voltage Calibration:
    • Measure actual battery voltage with multimeter
    • Compare to GCS reported voltage
    • Adjust BATT_VOLT_MULT if needed: 
      New_VOLT_MULT = Old_VOLT_MULT × (Multimeter_Voltage / GCS_Voltage)
  2. Current Calibration:
    • Use known current draw (e.g., bench power supply)
    • Compare to GCS reported current
    • Adjust BATT_AMP_PERVLT if needed: 
      New_AMP_PERVLT = Old_AMP_PERVLT × (Actual_Current / GCS_Current)

Betaflight Configuration

Power Tab:

  • Voltage Meter Source: Onboard ADC
  • Battery Cells: Auto-detect or manual (3S/4S/5S/6S)
  • Voltage Scale: 110 (default for 11:1 divider)
  • Current Meter Source: Onboard ADC
  • Current Scale: 180 (default for 18mV/A sensor)

Calibration:

  1. Connect battery and power on
  2. Measure battery voltage with multimeter
  3. Adjust “Voltage Scale” until Configurator matches multimeter
  4. Use known current source or ESC calibration for current scale

Current Sensor Source: The current sensor input (Pin 4 on ESC connector) receives data from the ESC onboard current sensor. If your ESC does not have a current sensor, current monitoring will not function. Voltage monitoring works independently.

Low Battery Warnings

ArduPilot:

BATT_LOW_VOLT = 14.0    (4S: 3.5V/cell)
BATT_CRT_VOLT = 13.2    (4S: 3.3V/cell)
BATT_LOW_MAH = 3000     (mAh consumed before warning)
BATT_CRT_MAH = 3500     (mAh consumed before critical)

Betaflight:

  • Warning Cell Voltage: 3.5V/cell
  • Critical Cell Voltage: 3.3V/cell
  • Capacity Warning: mAh threshold

Power Distribution to Components

Component Power Map

Component Voltage Current Source Connector
STM32H743 MCU 3.3V 150mA 5V BEC → 3.3V LDO Internal
ICM-42688-P IMU 3.3V 5mA 5V BEC → Isolated 3.3V LDO Internal
DPS368 Barometer 3.3V 1mA 5V BEC → 3.3V LDO Internal
GPS Module 5V (4.5V via USB) 80mA 5V BEC or USB GPS connector Pin 1
External Compass 5V (4.5V via USB) 10mA 5V BEC or USB GPS connector I2C
RC Receiver 5V (4.5V via USB) 50mA 5V BEC or USB RC INPUT Pin 1
Servos (S1/S2) 5V 500mA+ 5V BEC (battery only) SERVOS Pin 1
Digital VTX 10V 1000mA+ 10V BEC (battery only) VTX Pin 1
SD Card 3.3V 50mA 5V BEC → 3.3V LDO Internal

USB vs Battery Power: Through diode protection, 5V peripherals typically see no less than ~4.5V (within 5V tolerance) whether powered from USB or battery.
The 5V servo connector and 10V VTX connector bypass this diode and are battery-only (not powered from USB). See Power - Power Flow Diagram.

Power Wiring Best Practices

Wire Gauge Recommendations

Connection Current Recommended Gauge Notes
Battery to ESC >60A 12-14 AWG As short as possible
ESC to FC (VBAT) <5A 22-24 AWG Standard JST-SH pre-wired cables (< 30mm)
5V Peripherals <2A total 24-28 AWG ≤30cm
10V VTX <2A 22-26 AWG ≤20cm
Signal Wires <100mA 26-30 AWG ≤30cm

Short Wire Ampacity: Standard ESC-to-FC connector cables use 22-24 AWG wire at < 30mm length. At this short distance, 22-24 AWG easily handles 5A+ due to excellent heat dissipation and negligible voltage drop. Pre-wired JST-SH cables are appropriately sized.

Connector Types & Wiring

ESC to FC Connection:

  • Use JST-SH 8-pin (included)
  • Pre-wired ESC cables prevent polarity mistakes
  • If soldering directly, use heat-shrink and label polarity

Troubleshooting Power Issues

No Power to flight controller

Symptoms: No LED lights, no USB connection, completely dead

Check:

  1. ✓ Battery voltage (use multimeter on battery directly)
  2. ✓ VBAT and GND on ESC connector (check continuity to battery)
  3. ✓ Polarity (VBAT on Pin 1, GND on Pin 2)
  4. ✓ Fuse or inline switch (if used)
  5. ✓ Battery connector/XT60 integrity (solder joints, crimps)

Possible Causes:

  • Dead/discharged battery
  • Reversed polarity (if previously connected backwards → board likely damaged)
  • Broken solder joint on power connector
  • Damaged voltage regulator (if previously overvolted)

Brownouts During Flight

Symptoms: FC reboots mid-flight, sudden loss of control, log shows voltage sag

Check:

  1. ✓ Battery capacity (undersized battery for application)
  2. ✓ Battery C-rating (insufficient discharge rate)
  3. ✓ Wire gauge (voltage drop on thin wires)
  4. ✓ Connector resistance (XT60/ESC connectors damaged or loose)
  5. ✓ Battery age/health (internal resistance increased)

Solutions:

  • Upgrade to higher capacity or higher C-rating battery
  • Use thicker battery-to-ESC wires (reduce voltage drop)
  • Replace worn XT60 connectors (high resistance)
  • Set BATT_LOW_VOLT higher to prevent deep discharge

VTX Not Powering On

Symptoms: No video feed, VTX LEDs off, cold to touch

Check:

  1. ✓ 10V output enabled (check GPIO PE2 state in GCS or OSD)
  2. ✓ VTX connector wiring (Pin 1 = 10V, Pin 2/5 = GND)
  3. ✓ VTX voltage rating (confirm VTX accepts 10V input)
  4. ✓ 10V BEC overcurrent shutdown (thermal protection)

Solutions:

  • Enable 10V output via RELAY2 (ArduPilot) or PINIO1 (Betaflight)
  • Verify VTX voltage range (some VTX require 7-12V, others 5V only)
  • Check VTX current draw (if >2.5A, may trigger overcurrent protection)
  • Allow airflow over FC for BEC cooling (thermal shutdown recovery)

Insufficient Current for Peripherals

Symptoms: Peripherals resetting, servos jittering, GPS losing lock

Check:

  1. ✓ Total 5V current draw (see current budget table)
  2. ✓ Servo peak current (measure with current clamp if possible)
  3. ✓ Multiple high-current devices on one connector

Solutions:

  • Add external 5V BEC for servos (offload from FC BEC)
  • Use lower-current servos or limit servo speed/torque in firmware
  • Remove non-essential peripherals

Power Consumption Estimates

Typical Build Power Budget

Example 5” Freestyle Quad (4S Battery):

Component Voltage Current Power
H7-Digital FC 5V 150mA 0.75W
RC Receiver (ELRS) 5V 40mA 0.2W
GPS + Compass 5V 80mA 0.4W
DJI Air Unit 10V 1200mA 12W
4x Motors (hover) 16.8V 8A total 134W
TOTAL (hover) - - ~147W

Flight Time Estimate (1300mAh 4S battery):

  • Battery capacity: 1300mAh × 14.8V = 19.24Wh
  • Average consumption: 147W (hover) to 400W+ (aggressive flight)
  • Flight time: 3-6 minutes depending on flight style

External Resources

Support

For power system questions:

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