Portable Bench Power Supply (1.25V–10V) in a Backpack

Portable Bench Power Supply (1.25V–10V) — A Full Electronics Lab in Your Backpack

Humanix Tech Lab | DIY Tech & Innovation

A compact, battery-backed, adjustable 1.25V–10V bench power supply with USB output, banana jacks, and 2+ hours of battery backup — small enough to fit in a backpack.

Why I Built This

Bench power supplies are bulky, and a fixed 5V USB charger doesn't cut it for testing components at different voltages. This is a truly portable variable-voltage supply that works through a power cut and travels anywhere.

What You Can Do With It

Test components at variable voltages · power Arduino/ESP32/Raspberry Pi in the field · mobile repair workbench · vary motor/fan speed · charge 18650 cells via the banana terminals

Step 1: Building the Enclosure

Cut a lightweight PVC enclosure — front panel holes for the voltmeter, USB, banana jacks, potentiometer, and switch; back panel for the 12V input, main switch, and ventilation.

Step 2: Battery Pack & Charging Circuit

4 × 18650 cells wired in series (4S) — 14.8V nominal, 16.8V full charge. Step-up module trimmed to 16.2V for charging.

[IMAGE: (battery pack in blue heat-shrink wrap, on cutting mat) — assembled 4S pack]

⚠️ Use a 12V SMPS charger only — standard 12V wall adapters won't charge it correctly.

⚠️ Use a 12V SMPS charger only — standard 12V wall adapters won't charge it correctly.

Step 3: Wiring Everything Together

DC input → fuse → switch → BMS → main rail. Step-up boosts to 16.2V for charging. Step-down feeds the adjustable 1.25V–10V output. USB module taps a fixed 5V.

Step 4: Testing & Results

Battery charging test — voltage set to charge the pack, current tapers correctly near full charge.

COB light test — turns on around 4.5V, stable brightness with no sag.

Speed varies smoothly with voltage — tested with cooling fans and a small DC motor.

Step 5: How It Works

12V SMPS → Fuse → Switch → Step-Up (16.2V) → BMS charge input
Battery Pack ↔ BMS (protection & balancing)
BMS output → Step-Down → Variable output (1.25V–10V) → Banana / DC jack
BMS output → USB module → 5V USB output

The BMS handles overcharge, over-discharge, short-circuit protection, and cell balancing automatically.

Future upgrades: current meter, USB-C PD output, 3D-printed enclosure, CC/CV current limiting.

Safety Notes

Check polarity and input voltage before connecting. Avoid short circuits. Don't touch live wires. Use proper insulation throughout.

Follow the Build

• 📺 YouTube: https://www.youtube.com/@HumanixTechLab/
• 📸 Instagram: https://www.instagram.com/humanixtechlab/
• 💻 GitHub: https://github.com/humanixtechlab

Thanks

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