The Big Picture
There’s a quiet revolution happening in the DIY electronics world, and it’s not about the latest microcontroller or flashy display. It’s about power—specifically, the ability to take your workbench wherever you go. Most hobbyists are stuck with bulky benchtop supplies that chain them to a wall outlet. But what if you could build a variable power supply that fits in a small case, runs on lithium-ion cells, and charges via USB-C? That’s exactly what this project delivers, and it’s a game-changer for anyone who’s ever wanted to test circuits in the field, at a meetup, or just away from the garage.
This isn’t just another power supply build. It’s a thoughtful integration of components that solves real-world problems: portability without sacrificing power, dual charging methods for convenience, and thermal management in a tight space. The creator’s approach—using battery holders instead of spot welding, adding a dummy load to fix voltage delay, and securing a heatsink with standoffs—shows a level of practical wisdom that separates a good build from a great one. If you’re tired of being tethered to an outlet, this project will change how you think about your workbench.
Key Insights
The first thing that stands out is the enclosure strategy. Most builders grab a box and start drilling, but this project takes a measured approach. Removing plastic spacers with a rotary tool isn’t just about making room—it’s about maximizing internal volume while maintaining structural integrity. The creator notes that the case will be “a little crowded,” but that’s an understatement. The real insight is how they prioritize component placement: the battery on the bottom for stability, the buck-boost converter on the top panel for easy access, and the fan in the center of the back for optimal airflow. This isn’t random; it’s thermal and mechanical engineering on a hobbyist scale.
Another critical insight is the decision to use 18650 battery holders instead of spot welding. Many DIYers go straight for nickel strip welding because it looks clean, but the creator argues for flexibility. “I may change the lithium ion cells in the future,” they say, and that’s a smart long-term view. Battery holders allow for easy replacement and testing, and they’re rated for high current. The 2mm gap between holders accommodates flex when cells are inserted—a detail most people would overlook. This kind of foresight separates a one-off project from a reusable tool.
The voltage delay fix is pure gold. The buck-boost converter has a capacitor that holds charge, causing a lag when you decrease voltage under no load. The creator solves this by soldering a 3W, 3kΩ resistor across the output as a dummy load. It’s a simple hack, but it’s the kind of troubleshooting that saves hours of frustration. Most tutorials skip this because they assume you’ll always have a load, but in practice, you often adjust voltage before connecting your circuit. This fix makes the power supply responsive and professional.
Practical Application
Building this power supply isn’t a weekend project—it’s a deliberate, step-by-step process that rewards patience. Start by choosing your enclosure. The creator uses a 170x130x55mm plastic box, but you can adapt any similar size. The key is to plan your cutouts before you start cutting. Mark everything: the voltmeter display, potentiometers, binding posts, fan, USB port, and switch. Use a rotary tool for rough cuts and a file or sandpaper for finishing. The creator emphasizes smoothing edges to avoid sharp metal burrs, which is essential for safety and aesthetics.
For the battery pack, go with 18650 cells and a 6S BMS. The creator uses a 6S BMS board, soldering wires directly instead of using the spot-weld pads. This is a personal preference, but it works well if you’re careful. Secure the BMS with sticky foam tape and two screws—this prevents it from vibrating loose. Use short M3 screws for the battery holders, and insulate any exposed nuts with electrical tape. The creator adds a 5A fuse on the positive wire, which is a non-negotiable safety feature. For high-current connections, use 1.5mm² solid copper wire; for balance leads, 0.8mm² is sufficient.
When wiring the buck-boost converter, replace the onboard potentiometers with panel-mounted multi-turn ones. This gives you precise control and a cleaner front panel. Solder flexible wires and secure them with hot glue at the base to prevent breakage. Test the converter before mounting—check for the voltage delay issue and add the dummy load resistor if needed. The creator also adds a diode on the charging converter’s output to prevent backflow from the battery pack. This is a small but critical detail that protects your charging circuit.
What to Watch Out For
Crowded enclosures are a double-edged sword. The creator’s case is packed, and while they measure carefully, there’s always a risk of components touching. Use heat shrink tubing on all solder joints, and double-check clearances before closing the case. The fan converter is mounted on the side panel—only because there’s no other space. That’s a red flag. If you can find a larger enclosure, do it. A cramped build is harder to troubleshoot and repair.
Thermal management is another concern. The fan is small and runs at 9V, but the creator doesn’t specify airflow direction. They mention air entering from the front and exiting via the fan in the back, which is good, but make sure your ventilation holes are aligned. The bottom panel has holes for intake, but if they’re blocked by the battery, you’ll get poor cooling. Test the temperature under load—if the buck-boost converter or charging converter gets hot, consider adding a thermal pad or increasing fan speed.
Battery safety can’t be overstated. The creator uses a 6S pack with a BMS, but they also add a fuse and insulate nuts. That’s good, but they don’t mention cell balancing or over-discharge protection beyond the BMS. If you leave the power supply unused for weeks, the BMS might drain the cells. Add a low-voltage cutoff or a physical switch that disconnects the battery entirely. Also, note that the charging converter draws 1.8A from USB to deliver 340mA to the pack—that’s a slow charge. Don’t rely on this for rapid charging; it’s designed for overnight or slow top-ups.
Expert Perspective
From a professional standpoint, this project is a masterclass in practical compromises. The creator acknowledges that the enclosure is “a little crowded,” but they make it work by prioritizing components. The decision to use battery holders over spot welding is controversial—some engineers argue that holders add resistance and potential failure points. But for a hobbyist build, the flexibility outweighs the downsides. The 91% efficiency on the charging converter is impressive, but it’s achieved at a low current. Real-world efficiency will drop as you push the converter harder.
One area where I’d push back is the fan placement. Mounting the fan converter on the side panel is a kludge. A better approach would be to use a smaller fan or a different converter module that fits elsewhere. The creator’s solution works, but it’s not elegant. Also, the dummy load resistor is a band-aid for a design flaw in the converter. A more robust solution would be to add a bleeder circuit that activates when the output is disconnected, but for most users, the resistor is fine.
What I truly appreciate is the creator’s attention to detail with the BMS mounting and the diode on the charging converter. These are the kinds of things that prevent fires and prolong battery life. The full diagram provided in the description is a goldmine for anyone attempting this build. It’s clear, labeled, and includes wire colors. That’s the mark of a builder who respects their audience’s time.
Actionable Takeaways
1. **Plan your enclosure before cutting.** Measure twice, cut once. Use a rotary tool for rough cuts and sandpaper for finishing. Leave room for airflow and component clearance.
2. **Use battery holders for flexibility.** Spot welding is permanent; holders let you swap cells easily. Insulate all exposed metal to prevent shorts.
3. **Add a dummy load to fix voltage delay.** A 3W, 3kΩ resistor across the output of your buck-boost converter will eliminate lag when adjusting voltage without a load.
4. **Secure all components against vibration.** Use screws, foam tape, and hot glue to prevent loose connections. A crowded case amplifies movement.
5. **Test charging efficiency and safety.** Verify your charging converter’s output with a multimeter. Add a diode to prevent backflow, and use a fuse rated for your expected current.
6. **Document your wiring.** The creator’s full diagram is a lifesaver. Create your own schematic and label wires to simplify troubleshooting.
This portable variable power supply isn’t just a project—it’s a tool that will serve you for years. Build it right, and you’ll never be stuck without a bench again.
