2-in-1 DC Voltmeter & 5V USB Charger Buck Converter Module (4.5V-40V Input)

📋 Overview

The 2-in-1 DC Voltmeter & 5V USB Charger Buck Converter Module (HW-318) is a compact DC-DC step-down power converter that combines two useful functions into a single board: a real-time 3-digit red LED voltmeter that monitors your input voltage, and a regulated 5V USB-A output capable of delivering up to 2A for charging phones, tablets, GPS units, and other USB devices.

The module accepts a wide input voltage range of DC 4.5V to 40V, making it compatible with 12V and 24V automotive systems, solar panels, battery packs, and bench power supplies. Built-in protections for reverse polarity, overcurrent, and over-temperature make it a safe and practical choice for a wide range of power applications.

Two on-board buttons — "Enable Output" and "Low Power" — give you control over the USB output and standby mode, while a simple calibration procedure lets you fine-tune the voltmeter accuracy to ±0.1V.

🔧 How It Works

1. Connect your DC power source (4.5V–40V) to the screw terminals on the module — positive to IN+, negative to IN−.
2. The LED voltmeter lights up immediately and displays the input voltage.
3. Press the "Enable Output" button to activate the 5V USB port.
4. Plug a standard USB cable into the USB-A port and connect it to your device — charging begins automatically.

💡 Tip: The USB output requires a minimum input voltage of 6.5V to produce a stable 5V output. Below 6.5V, the voltmeter will still display the input voltage, but the USB output may not function correctly.

⭐ Key Features

• 2-in-1 Design: Combines a DC voltmeter and a 5V USB charger in a single compact module
• Wide Input Range: Accepts DC 4.5V to 40V — compatible with 12V and 24V automotive systems, solar panels, and battery packs
• Regulated 5V USB Output: Delivers up to 2A through a standard USB-A port for charging smartphones, tablets, GPS units, and other USB devices
• 3-Digit LED Voltmeter: Red LED display continuously monitors the input voltage with ±0.1V accuracy (after calibration)
• Built-In Protections: Reverse polarity protection, overcurrent protection, and over-temperature protection
• On-Board Control Buttons: "Enable Output" button to turn the USB port on/off, and "Low Power" button for standby mode
• LED Status Indicators: Separate LEDs indicate USB power status and input terminal wiring status
• User-Adjustable Calibration: Voltmeter display can be calibrated using the on-board buttons for improved accuracy
• Screw Terminal Input: Secure, solderless connection for your DC power source
• Compact and Lightweight: Just 58 × 21 × 10 mm and 13g — fits easily into enclosures, dashboards, and portable projects

📐 Specifications

📌 Connections

Input (Screw Terminals)

Output

On-Board Controls

📦 What's in the Box

• 1× 2-in-1 DC Voltmeter & 5V USB Charger Buck Converter Module (HW-318)

USB cable, power source, and mounting hardware are not included.

🛒 What You'll Need

• DC Power Source (4.5V–40V) — Battery, power supply, solar panel, or vehicle electrical system
• Wire — Appropriately rated wire for your input voltage and current (22 AWG minimum for 2A loads)
• Small Flathead Screwdriver — For tightening the screw terminals
• USB Cable — Standard USB-A cable to connect to your device for charging

🎯 Typical Applications

• Automotive USB charger: Connect to a 12V or 24V vehicle battery to charge phones and tablets
• Solar panel projects: Step down solar panel voltage to 5V for charging USB devices off-grid
• Battery monitoring: Monitor battery voltage while simultaneously providing USB charging
• Bench power supply add-on: Add a USB charging port and voltmeter to your workbench power supply
• Portable power packs: Build a custom portable charger with voltage monitoring
• RC and drone projects: Monitor LiPo battery voltage while powering USB accessories
• Marine and RV installations: Charge devices from 12V/24V DC systems with voltage monitoring
• Educational projects: Learn about DC-DC buck conversion, voltage regulation, and power electronics

⚠️ Important Notes

• Input voltage limits: Do not exceed 40V DC input. The voltmeter functions from 4.5V, but the USB output requires at least 6.5V input to produce a stable 5V output.
• Maximum output current: The USB port is rated for 2A maximum. Do not use this module to charge devices that draw more than 2A.
• Heat dissipation: At high input voltages (24V–40V) and high output currents (close to 2A), the module will generate heat. Ensure adequate ventilation and consider adding a small heatsink if the module becomes excessively hot.
• Not a fast charger: This module provides standard 5V USB power at up to 2A. It does not support Qualcomm Quick Charge, USB Power Delivery (PD), or other fast-charging protocols.
• Voltmeter accuracy: The LED voltmeter is accurate to approximately ±0.1V after calibration. For precision measurements, use a calibrated multimeter.
• Wire gauge: Use appropriately rated wire for your input voltage and current. For 2A loads, use at least 22 AWG wire. For longer runs, use thicker wire to minimize voltage drop.
• DC input only: This module is designed for DC input only. Do not connect to AC mains power.

📄 Documentation & Resources

Documentation

Full wiring instructions, calibration procedure, and technical details are available at the Envistia Mall product support website.

• User Guide
• All Buck Step-Down Converter User Guides

Sold and supported by Envistia Mall. Ships from the USA. For wiring diagrams, calibration instructions, and troubleshooting, see the User Guide linked above. The manufacturer and Envistia LLC (dba Envistia Mall) are not responsible for any damages or losses resulting from the use of this product. Always follow proper electrical safety practices when working with electronic components. Specifications are based on manufacturer data and are subject to change without notice.