There’s something deeply satisfying about building a piece of equipment that can stress-test power—literally. Whether you're experimenting with homemade battery packs, evaluating solar panel performance, or testing power supply units, one tool that quickly becomes essential is a DC load tester.

In this project, we’ll build a high-power DC load tester using the VHF15-16IO5, a robust and efficient IGBT module capable of handling serious current and voltage. It’s a hands-on, hardware-centric project that puts you in full control of how much power you burn—and where. You'll learn how to handle large currents safely, how to control power flow precisely, and how to read what's happening in your circuit in real time.

This is not just a tool—it’s a piece of equipment that you’ll use again and again.

What is the VHF15-16IO5?

At the heart of this build is the VHF15-16IO5, a power IGBT (Insulated Gate Bipolar Transistor) module. It’s designed for switching and controlling high voltages and currents, often in industrial motor drives, UPS systems, or solar inverters.

This particular module combines the efficiency of a MOSFET at the input with the high-power capabilities of a bipolar transistor at the output. That makes it ideal for handling high current loads while still being controllable with relatively low voltages.

The module features two IGBTs in a half-bridge configuration, which makes it versatile for AC or DC load control. In our case, we’ll use it in a linear control mode to simulate a resistive load, one that can be adjusted on the fly with a potentiometer and monitored with voltmeters and ammeters.

Project Overview: A DC Load Tester for Real Work

What Are We Building?

We’re going to build a manual, adjustable DC electronic load, capable of safely dissipating power from a DC source—like a battery, a DC power supply, or a solar panel—by converting electrical energy into heat through high-power resistors and controlling current draw with the IGBT module.

This load tester won’t rely on a microcontroller or display—it will be raw and mechanical. A few knobs to adjust, meters to observe, and power components to handle the heat. This is a tactile, analog experience.

Applications of a DIY Load Tester

● Testing Power Supply Units (PSUs) under load

● Evaluating battery packs under stress

● Checking voltage stability and ripple performance

● Discharging batteries in a controlled manner

● Simulating real-world power consumption

It's a powerful tool, especially if you deal with DIY energy systems or tinker with high-capacity electronics.

What You’ll Need

Major Components:

● VHF15-16IO5 IGBT module

● High-wattage resistors (aluminum-housed or wire-wound, e.g., 100W units)

● Potentiometer (10kΩ linear)

● Gate driver or simple buffer circuit (optional for finer control)

● Heat sink (large, with fan if possible)

● DC ammeter (analog or digital)

● DC voltmeter

● Power connectors (XT60, Anderson, or heavy-duty binding posts)

● Toggle switch (for load activation)

Support Tools:

● Soldering iron and solder

● Drill, files, screwdrivers

● Thermal paste

● Insulation washers or mica sheets

● Wires rated for high current (10AWG or thicker)

● A test power source (12V battery, power supply, etc.)

Step-by-Step Build

Step 1: Understanding the Load Concept

At its core, the DC load tester acts as a variable resistor. But instead of a giant resistor bank (which would be huge and inefficient), we use the IGBT to control the amount of current flowing through a smaller set of power resistors.

By adjusting the gate voltage of the IGBT, we control how much it conducts—thus adjusting how much current flows from the power source, through the IGBT, and into the resistors (which turn it into heat).

This gives us fine-grained manual control over the current we draw from the source.

Step 2: Mounting the VHF15-16IO5

This module isn’t your average transistor. It’s big, industrial, and demands respect. Start by mounting it securely on a large heat sink—the kind you’d find in an old amplifier or industrial equipment. Use thermal paste generously, and insulate the mounting screws if the heat sink is grounded.

Cooling is absolutely critical. Consider mounting a 12V fan on the heat sink to actively pull heat away during extended tests.

Step 3: Wiring the Power Section

● Connect the collector terminal of the IGBT to the positive terminal of the load input.

● The emitter connects to the load resistor.

● The other side of the load resistor goes to ground or the negative terminal of the DC source.

Think of this like a valve: the more the IGBT conducts, the more current flows through the resistors and is "burned off" as heat.

Use heavy gauge wires for this part. Current may exceed 10A during testing, and wire resistance matters.

Step 4: Building the Control Section

Controlling an IGBT requires only a small voltage at the gate, but it should be clean and stable. You can:

● Use a simple potentiometer voltage divider to feed the gate directly (for low current testing).

● Add a gate driver circuit or buffer amplifier if you're working with higher gate currents or need better responsiveness.

Wire the potentiometer so that turning the knob increases the voltage to the gate. This will increase conduction, causing the IGBT to pull more current from the source.

This is where the fun begins: as you turn the knob, you’re adjusting the load. It’s like a throttle for power dissipation.

Step 5: Mounting Resistors

The load resistors are where the energy goes. Use multiple high-power resistors (50W, 100W) in parallel to distribute heat. Mount them to a metal base or heat sink, and make sure there’s airflow.

Consider using a modular resistor bank: a grid of resistors with spade terminals or bolts, so you can easily swap them out or change configurations depending on the test scenario.

Step 6: Monitoring with Meters

Install a voltmeter and an ammeter to monitor the source voltage and the current being drawn. This is essential not only for safety, but also for getting usable test data.

Analog meters give a classic look and tactile feedback, but digital meters are more precise. Mount these on a panel or small enclosure if you want a more finished appearance.

Step 7: Finishing Touches

● Add a power switch to enable or disable the load.

● Consider a fuse or circuit breaker for protection.

● Use banana jacks or heavy-duty terminals for the input and output connections.

● Label everything. High power electronics are not forgiving if misconnected.

The First Test

Choose a known power source, like a 12V battery. Connect it to the load tester. Make sure the potentiometer is turned all the way down (minimum gate voltage).

Flip the switch.

Turn the potentiometer slowly and watch as the current increases on your ammeter. The resistors will get hot. The fan will spin. You’ll feel the heat rise—and realize that you’re in full control of where every amp goes.

There’s something immensely satisfying about this. You’re not just measuring power—you’re shaping it.

Use Cases in Real Life

This load tester becomes a versatile part of your bench. Use it to:

● Check how a PSU performs under load before deploying it

● See how long a battery lasts under real-world conditions

● Test current limiting behavior on lab bench supplies

● Discharge lithium battery packs before recycling

● Stress-test charging circuits or solar converters

You’ll use it more than you think. And you’ll appreciate the insight it gives you into the nature of electricity under stress.

Lessons Learned

Working with high-power components like the VHF15-16IO5 teaches you a different kind of respect for electricity. It’s no longer abstract—it’s heat, light, and movement.

You’ll learn:

● How to dissipate power safely and efficiently

● Why thermal design matters

● How gate control influences transistor behavior

● How to build test tools that rival commercial gear in function

You also realize that simplicity can be elegant. There's no screen, no firmware, no protocol—just you, a knob, and a glowing ammeter needle.

Expanding the Build

If you fall in love with this device (and you might), you can enhance it further:

● Add a digital display for voltage/current

● Include a fan controller that adjusts based on temperature

● Use a microcontroller for programmable loads (later down the line)

● Add a USB or SD logger for performance data

● Build an enclosure with a carrying handle for mobile testing

But even as-is, the basic version is a powerful, practical, and hands-on tool that gets the job done.

Final Thoughts

Building a high-power DC load tester with the VHF15-16IO5 isn’t just a fun electronics project—it’s an invitation to play with power. It connects you to the raw physicality of electricity, where you can feel the heat of every amp drawn, watch the swing of the needle, and fine-tune current flow with your fingertips.

In a world of virtual gadgets and invisible code, this project reminds you that electronics is, at its core, a physical art. This isn’t simulation—it’s real. And once you build your own load tester, you’ll never look at your workbench the same way again.

So fire up your soldering iron, find that heat sink, and take control of the current. The VHF15-16IO5 is waiting.