📋 Overview
The 2-in-1 DC Voltmeter & 5V USB Charger Buck Converter Module (model HW-318) is a compact DC-DC step-down power converter that combines two useful functions into a single board: a real-time LED voltmeter that monitors your input voltage, and a regulated 5V USB output capable of delivering up to 2A for charging phones, tablets, and other USB devices.
The module accepts a wide input voltage range of DC 4.5V to 40V and displays the input voltage on a 3-digit red LED display. When the input voltage is between 6.5V and 40V, the module generates a stable regulated 5V output through a standard USB-A port. Built-in protections for reverse polarity, overcurrent, and over-temperature make it a safe and practical choice for automotive, solar, battery, and bench 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.
⭐ 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 input — 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 — suitable 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
- Compact and Lightweight: Just 58 × 21 × 10 mm and 13g — fits easily into enclosures, dashboards, and portable projects
📐 Specifications
| Parameter | Value |
|---|---|
| Model | HW-318 |
| Module Type | DC-DC Buck (Step-Down) Converter with Voltmeter |
| Input Voltage (Voltmeter Range) | DC 4.5V – 40V |
| Input Voltage (for 5V USB Output) | DC 6.5V – 40V |
| Output Voltage | 5V DC (regulated) |
| Output Current (Max) | 2A |
| Output Connector | USB-A female port |
| Voltmeter Display | 3-digit red LED |
| Voltmeter Accuracy | ±0.1V (after calibration) |
| Protections | Reverse polarity, overcurrent, over-temperature |
| Input Connection | Screw terminals (+ and −) |
| Control Buttons | Enable Output, Low Power (standby) |
| LED Indicators | USB power status, terminal wiring status |
| Dimensions | Approx. 58 × 21 × 10 mm (2.28 x 0.83 x 0.39 inches) L × W × H |
| Weight | Approx. 13g |
📌 Pinout / Connection Diagram
The module has a simple two-wire input connection via screw terminals and a USB-A output port. There are no signal pins — this is a standalone power module.
Input Connections (Screw Terminals)
| Terminal | Label | Description |
|---|---|---|
| Positive (+) | IN+ | Connect to the positive terminal of your DC power source (4.5V–40V) |
| Negative (−) | IN− | Connect to the negative / ground terminal of your DC power source |
Output Connection
| Connector | Description |
|---|---|
| USB-A Port | Regulated 5V output at up to 2A — plug in any standard USB cable to charge your device |
On-Board Controls
| Button / Indicator | Function |
|---|---|
| Enable Output Button | Turns the USB 5V output on or off. Press once to enable, press again to disable. |
| Low Power Button | Puts the module into standby mode to reduce power consumption when the USB output is not needed. |
| USB Power LED | Indicates whether the USB output is active (on) or disabled (off). |
| Terminal Status LED | Indicates correct input wiring polarity. |
🔧 Setup / Getting Started
Setting up this module is straightforward — just connect your DC power source to the screw terminals and plug in a USB device.
Step 1: Connect the Input Power
- Identify the positive (+) and negative (−) wires from your DC power source (battery, power supply, solar panel, etc.).
- Loosen the screw terminals on the module using a small flathead screwdriver.
- Insert the positive wire into the IN+ terminal and tighten the screw.
- Insert the negative wire into the IN− terminal and tighten the screw.
- The LED voltmeter should light up and display the input voltage.
⚠️ Warning: Double-check your polarity before connecting power. While the module has reverse polarity protection, it is always best practice to verify positive and negative connections before applying power. Do not exceed 40V input.
Step 2: Enable the USB Output
- Press the Enable Output button on the module. The USB power LED should illuminate.
- Plug a standard USB cable into the USB-A port.
- Connect the other end of the USB cable to your device (phone, tablet, GPS, etc.).
- Your device should begin charging.
💡 Tip: The USB output requires a minimum input voltage of 6.5V to produce a stable 5V output. If your input voltage is between 4.5V and 6.5V, the voltmeter will still display the voltage, but the USB output may not function correctly or deliver full current.
Step 3: Calibrate the Voltmeter (Optional)
If the voltmeter reading does not match your known input voltage (verified with a multimeter), you can calibrate it:
- Connect a known, stable DC voltage source to the input terminals.
- Measure the actual input voltage with a trusted multimeter.
- Use the on-board buttons to adjust the displayed voltage up or down until it matches the multimeter reading. Press and hold the buttons to increment or decrement the displayed value.
- Once calibrated, the module will retain the calibration setting.
💡 Tip: Calibration is optional but recommended if you need precise voltage readings. The module ships with a factory calibration that is typically accurate to ±0.1V.
🎯 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 absolute minimum input for the voltmeter function is 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. Drawing more than 2A may trigger the overcurrent protection or damage the module. Do not use this module to charge devices that require more than 2A (such as some tablets with fast-charge requirements).
- Heat dissipation: At high input voltages (e.g., 24V–40V) and high output currents (close to 2A), the module will generate heat. Ensure adequate ventilation and do not enclose the module in a sealed space without airflow. Consider reducing the load or 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 intended for monitoring purposes and is accurate to approximately ±0.1V after calibration. For precision measurements, always 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 or higher currents, use thicker wire to minimize voltage drop.
- Polarity protection: While the module includes reverse polarity protection, do not rely on this as a primary safety measure. Always verify correct polarity before connecting power.
- Not for AC power: This module is designed for DC input only. Do not connect to AC mains power.
📦 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.
🏪 Where to Buy the 2-in-1 DC Voltmeter & 5V USB Charger Buck Converter Module
Buy the 2-in-1 DC Voltmeter & 5V USB Charger Buck Converter Module →
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This guide is provided by Envistia Mall for educational and technical reference purposes. 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.