Repurposing server power supplies as adjustable bench units is a classic hardware hacking challenge. The HPServerPSUHack repository tackles this for HP’s popular 1200W server PSUs, providing two distinct modification paths: hardware-level circuit tweaks and a firmware-only patch for the onboard microcontroller. Both approaches unlock higher, adjustable output voltages useful for vehicle programming, RC charging, and amateur radio applications.
What the HPServerPSUHack project offers
This project focuses on HP’s HSTNS-PL11, PL30, PD44, and PD52 1200W server power supplies—robust units originally designed for server racks. These PSUs are attractive for bench use due to their high current capacity and low cost on the secondary market. However, their original hardware and firmware limit output voltage to levels insufficient for many bench applications.
The repository documents two main modification strategies. The first involves hardware changes to the PSU’s analog control circuits—specifically, the Type III analog compensator and the Over Voltage Protection (OVP) divider network. By carefully soldering parallel resistors, the modder can adjust the feedback loop and trick the PSU into allowing a higher output voltage without triggering safety shutdowns.
The second approach is firmware-centric. It targets the dsPIC33FJ64GS606 microcontroller embedded in the PSU, used for voltage and current regulation. Through reverse engineering, the project identifies how the firmware implements voltage scaling using fixed-point Q15 math and patches it to accept higher voltage setpoints without tripping the OVP. This method is elegantly clean since it requires no hardware soldering—only reflashing the firmware, but it is currently specific to the PL30 Rev10 variant.
Beyond these core mods, the repo includes detailed reverse-engineered pinouts for both LiteOn and Delta PSU variants, ICSP headers for in-circuit programming, and I2C monitoring setups using a Raspberry Pi Pico. It also dives deep into the Average Current Mode Control (ACMC) feedback loop, illustrating how the PSU maintains stable output under varying load conditions.
The documentation is rich with PCB photographs, circuit schematics, and oscilloscope captures showing performance during load testing—valuable for anyone looking to understand or replicate the modifications.
The dual-mod approach: hardware tweaks vs firmware patching
What sets this repo apart is the dual pathway it offers. The hardware mod approach is a traditional analog hack, manipulating the physical circuitry. This involves soldering parallel resistors onto the OVP voltage divider and tweaking the Type III compensator circuit to shift the feedback thresholds. The tradeoff is clear: it requires a steady hand and a good understanding of analog electronics, and any mistake could damage the PSU or void warranties.
Nevertheless, this approach works across multiple PSU variants and is more universally applicable. It also leaves the firmware intact, preserving the MCU’s original safety checks except the voltage thresholds.
On the other hand, the firmware patch method is more elegant and less invasive but also more specialized. It hinges on deep reverse engineering of the dsPIC33FJ64GS606 MCU firmware, which controls the PSU’s voltage scaling and protection logic. The project authors dissect the assembly code to locate the Q15 fixed-point multiply operation that scales the voltage setpoint and patch this to accept an increased maximum output voltage (up to about 14.4V).
This firmware-only mod avoids soldering and hardware risks, making it attractive for those comfortable with embedded MCU programming and flashing. However, its applicability currently appears limited to the PL30 Rev10 PSU variant due to firmware differences in other models.
Under the hood, the repo’s analysis of the Average Current Mode Control (ACMC) loop is particularly insightful. ACMC is a feedback control strategy that regulates current and voltage by averaging the inductor current over switching cycles. Understanding this loop is key to grasping why these modifications work without causing instability or oscillations.
The repo also provides detailed pinouts and wiring diagrams for the LiteOn and Delta versions of these PSUs, which helps in identifying test points, ICSP headers, and I2C monitoring lines. This level of reverse engineering is invaluable for anyone looking to extend or customize these mods.
Explore the project
Since the analysis doesn’t provide explicit quickstart commands, the best way to approach this project is to start with the detailed README and accompanying documentation inside the repository. Key resources to explore include:
- The Hardware Modifications folder/documentation: photos and schematics showing resistor placements and circuit changes.
- The Firmware Patching section: assembly code snippets, patch instructions, and flashing procedures for the dsPIC33FJ64GS606 MCU.
- The Pinouts and Wiring Diagrams: reverse-engineered mappings for LiteOn and Delta PSU variants.
- I2C Monitoring setup details using a Raspberry Pi Pico for real-time PSU telemetry.
Each section is richly illustrated with PCB images and oscilloscope captures, which help demystify the process and provide practical verification of the modifications’ effects.
If you plan to try the firmware patch, having a PIC programmer and familiarity with dsPIC MCU tools is essential. For hardware mods, a fine-tip soldering iron and a multimeter are necessary.
Verdict
HPServerPSUHack is a solid resource for hardware hackers and embedded firmware enthusiasts looking to repurpose high-wattage HP server PSUs into adjustable bench power supplies. The dual-mod approach is the standout feature: hardware mods offer broader applicability at the cost of complexity and risk, while the firmware patch provides a neat, low-risk alternative for specific PSU revisions.
The documentation is impressively thorough, supported by reverse engineering at both the hardware and firmware levels. This makes the repo worth understanding even if you don’t plan to adopt the mods directly—there’s a lot to learn under the hood about power supply control loops and MCU firmware hacking.
The main limitation is the firmware patch’s narrow hardware compatibility and the mod’s complexity, which may put off beginners or those without embedded programming experience. Still, for the right audience—those comfortable with soldering or MCU flashing—this repo provides a rare, detailed guide to unlocking a commonly available PSU’s bench power potential.
If you’re looking to build an adjustable, high-current bench power supply for automotive or radio projects and don’t mind digging into analog circuits or MCU firmware, this repo is worth your time.
→ GitHub Repo: darwinbeing/HPServerPSUHack ⭐ 130 · HTML