SPD 150V

Building a 150V DC Surge Protection Device for a Solar Inverter

When working with solar inverters, especially those with unusual voltage ranges, finding the right protective components can be a challenge. My inverter has a maximum input of 145V DC—an oddball spec that made sourcing a suitable Surge Protection Device (SPD) nearly impossible. So, I decided to build one myself.

⚡ Why Surge Protection Matters
Lightning strikes—even those that occur miles away—can induce powerful electromagnetic surges in solar wiring. The longer the wire, the greater the risk of voltage induction. These surges can reach millions of volts, posing a serious threat to your equipment. While no SPD can protect against a direct lightning hit, having one in place offers a critical layer of defense against indirect surges.

🔍 The Challenge
Most commercially available DC SPDs are rated for 600V or higher, which is far too much for my low-voltage setup. I needed something tailored to my system’s 145V max input. With no off-the-shelf solution in sight, I rolled up my sleeves and got to work.

🛠️ First Prototype
My initial build was a rough-and-ready assembly of Metal Oxide Varistors (MOVs) and Transient Voltage Suppression (TVS) diodes. It wasn’t pretty, but it did the job. This prototype helped me validate the concept before moving on to a more refined version.

💻 Designing the PCB
Using EasyEDA, I designed a proper schematic incorporating MOVs and TVS diodes. I paid extra attention to the layout, especially the terminal placements—yes, I got a bit obsessive there! The result was a clean, functional PCB design ready for fabrication.

🍪 Manufacturing the PCB
I exported the Gerber files and sent them off to JLCPCB. A week later, the boards arrived, and they looked fantastic—like freshly baked cookies straight from the oven.

🔧 Final Assembly
I salvaged components from my prototype and carefully populated the new PCB. I also added a Gas Discharge Tube (GDT), which can handle surge currents of 10,000 to 20,000 amps. That’s serious protection.

🛡️ Triple-Layer Defense
The final SPD features three layers of protection:
•     MOVs for clamping high-energy transients
•     TVS diodes for fast response to voltage spikes
•     GDTs for handling massive surge currents
With this setup in place, I can rest easier knowing my solar inverter is shielded from unexpected surges.