If you're looking to fully understand a truly open smart shunt, Voidbox's PwrTool 500 is a strong entry into the world of self-consumption and off-grid installations. It natively integrates Home Assistant and allows direct customization with ESPHome or proprietary firmware, something unusual for this type of hardware. In figures, it works with 6–60 V DC systems and supports peaks of up to 500 A with a 300 A continuous shunt, offering detailed telemetry to visualize and even automate energy flow, generation, storage and consumption.
This device is positioned as a bridge between battery monitoring and load orchestration, with a clear focus on open data and the absence of ties to a closed ecosystem. accessible sensors, available GPIOs and transparent firmware, is aimed at both those who want a dashboard ready in Home Assistant, and those who need to squeeze the most out of it with advanced integrations, high-current relays, and resistive load control to manage solar surpluses.
What is PwrTool 500 and who is it for?
At its core, PwrTool 500 is an open-source, intelligent shunt that monitors critical variables such as voltage, current, and power in systems from 12 to 48 V nominal, while maintaining true compatibility with a wide range of lithium, LiFePO4, and lead-acid batteries. Its strength lies in offering Visibility and control from Home Assistant without external gateways, reducing friction in adoption and leaving the door open to expansions through ESPHome.
The device is designed for owners of off-grid solar installations, caravans, boats, makers, and professionals who demand more than an isolated state-of-charge figure. By offering a comprehensive approach to telemetry and control, it enables Automations based on voltage, current, power, and environmental data that go from measuring to acting, for example to protect batteries or to use surpluses intelligently.
Smart shunt truly open
Many shunts on the market encapsulate data in opaque apps and protocols, making them difficult to integrate. PwrTool 500 breaks that dynamic: both the hardware and software are open, with direct access to sensors, firmware, and expansion pins. This means you can adapt the equipment to very specific requirements without supplier lock-in, and without having to decipher undocumented protocols.
This philosophy makes life easier for those who want to audit, extend, or maintain their energy systems over the long term. Furthermore, Documentation, schematics, PCB and BOM are available publicly, which reinforces transparency and speeds up the resolution of doubts in the community.
Applications in isolated and DC systems
The shunt is versatile enough to be placed at various points in the DC system, covering applications ranging from battery health monitoring to load segmentation. With its open architecture, it is easy to combine with other modules to separate consumption and generation, or add monitoring where it is missing in recent hybrid controllers and inverters.
- Battery monitoring: State-of-charge tracking with high-precision coulomb counting, useful for realistic range estimates.
- Load segregation: use of multiple shunts to differentiate between consumption and generation sources, providing diagnostic clarity.
- Expand existing systemsMany MPPT hybrids and large controllers lack monitored DC output; here the PwrTool 500 fill that void telemetry.
Monitor and automate with Home Assistant
Once connected to your Wi-Fi network, the device quickly appears in Home Assistant and pulls up a comprehensive set of metrics ready for your custom dashboards. From there, you can calibrate the current offset, monitor the most critical point of the system and, most interestingly, trigger automations by voltage, current, power or even temperature and humidity thresholds.
For automatic protection, the equipment includes a 45 W N-channel MOSFET that can control a high current relay and disconnect loads during faultsThis same control is useful for activating resistive loads, such as an electric water heater, to absorb excess solar energy when the batteries are already full, maximizing the system's energy utilization.
Scalable hardware based on FLIP_C3
The heart of the PwrTool 500 is the FLIP_C3 board, a proprietary ESP32-C3 microcontroller that provides Wi-Fi and BLE, as well as pin expansion for UART, I2C, SPI, PWM, and more. Designed for integration into 12 to 48 V DC ecosystems, this board features a 5V, 2A buck converter tolerant to 60VDC that simplifies feeding in demanding environments.
- ESP32‑C3 with Wi‑Fi and BLE, ideal for telemetry and wireless control in home and professional environments.
- 5 V / 2 A buck converter (10 W) with 60 V DC tolerance, robust to bus variations.
- Expandable GPIOs with support for UART, I2C, SPI, PWM, among other common protocols.
- USB Type-C for direct and convenient firmware flashing and recovery.
- WS2812 output leveled, capable of powering and controlling strips of more than 100 addressable LEDs.
- Configurable BOOT button, integrated status LED and Reset button for maintenance.
Additionally, the design exposes Stemma QT and Qwiic connectors for I2C expansion, duplicated on the main board to facilitate the solderless connection of multiple peripherals. All of this allows scale the system with sensors, relays and displays in a modular and orderly manner.
ESPHome: Accessible development step by step
Each PwrTool 500 unit ships with custom ESPHome firmware. By adopting it in ESPHome Builder, you inherit a maintained configuration base, designed to be easily extended. With ESPHome's YAML approach, The entry curve is gentle and well documented, which democratizes the development of smart devices.
The ESPHome community offers an array of copy-and-paste examples for sensors, motors, lights, and more, including its own repository of modular configurations to help you get started quickly. You can also Bring data from your power system via UART and other protocols, integrating controllers and inverters that you already have installed.
ESPHome is updated monthly according to the Home Assistant roadmap and a massive base of open source contributions. This cycle ensures bug fixes and new features consistently, reducing the risk of being locked into old or abandoned versions.
The team behind the project invites suggestions for improvements to the default configuration. With the data set provided by the shunt, there is room for creation. more advanced templates and logic, benefiting the entire community with continuous iterations.
Key specifications and capabilities
Power monitoring
- System voltage: 6–60V DC, compatible with lithium, LiFePO4 and lead acid batteries.
- Current: 500 A peak and 300 A continuous through the shunt, sized for demanding installations.
- precise measurement: INA238 with preamplifier and 16-bit ADC, plus on-chip thermal sensor oriented to the shunt.
- Polarity: Jumper selection for hot or cold side, delivered as standard in cold side mode.
- 45W N-channel MOSFET for PWM control of LED lighting or control of powerful loads using a relay or contactor.
FLIP_C3 controller board
- ESP32‑C3 with Wi‑Fi and Bluetooth Low Energy connectivity.
- Buck 5 V / 2 A with a total power of 10 W.
- Expandable GPIOs with UART, I2C, SPI, PWM and other standard interfaces.
- USB Type-C for flashing and recovery.
- WS2812 output leveled, suitable for more than 100 addressable LEDs.
- Configurable BOOT button, plus status LEDs and Reset button on board.
Additional hardware
- Two Stemma QT/Qwiic ports for solderless I2C expansion.
- Integrated SHTC3 sensor for ambient temperature and humidity.
Flexible polarity and mounting
Most shunt-based monitors operate only on the cold side, i.e., the return or negative side of the battery bank. In designs with physical restrictions or safety features, this can complicate wiring. PwrTool 500 incorporates a jumper-selectable hot side mode, adding freedom for advanced or unusual configurations. It comes standard in cold-side mode, but switching modes is quick and documented.
This flexibility allows it to adapt to electrical panels where the ground bar is not ideal for the shunt, or when it is required to measure on the positive rail for reasons of diagnosis or protection of loadsRegardless of the orientation chosen, the INA238's precision and offset compensation help ensure consistent readings over time.
Comparison against popular alternatives
In the 500 A range, there are established options such as Victron SmartShunt, Thornwave PowerMon, or REDARC. Compared to these, PwrTool 500 stands out for its the only fully open solution in hardware and software, with native Wi-Fi integration in Home Assistant, and a design that favors expansion over a closed ecosystem. It also comes at a competitive price of 149 USD.
Note on polarity: It is called the hot side when the shunt is located on the positive side of the bank, and the cold side when it is installed on the return or ground. The industry standard is usually the cold side, but the possibility of using the hot side avoids conflicts in certain installations. As standard, the equipment is delivered on the cold side and can switch to hot side using jumper.
Documentation and community support
The hardware files, including schematics, board layout, and bill of materials, are available as open source on the project wiki. YAML configurations for ESPHome are also offered and maintained on GitHub, with a focus on reusable modules and clear templates to accelerate deployment.
Since ESPHome is maintained by the Home Assistant team and a large community, updates and fixes arrive regularly. This provides a solid foundation for secure updates and continuous improvements without relying on closed vendors or discontinued software.
Manufacturing, logistics and risk plan
The PwrTool 500 design is complete and tested, ready for production. The final assembly and packaging stages will take place in Joshua Tree, California, with the option to collaborate with Elecrow as a contract manufacturer if demand exceeds projected targets. Elecrow has previously been instrumental in Crowd Supply campaigns, which provides confidence in processes and quality.
After validation and testing, each unit will be sent to Crowd Supply's logistics partner, Mouser Electronics, who will handle distribution to backers. You can check out the Crowd Supply guide for details. order, payment and shipping, something that provides logistical transparency from day one.
Among the risks considered, the team points to variations in import tariffs between the United States and China, which could impact margins, and the preparation of CE and UKCA certifications to expand the market to Europe and the United Kingdom. The availability of components and global logistics remain factors to monitor, although the project is working with known suppliers and clear communication about deadlines.
Events and ecosystem: FLIP_C3 and PwrTop 18
Voidbox Industries has been showcasing PwrTool 500 at events such as Teardown, alongside prototypes based on the FLIP_C3 development board, a base designed to integrate hardware into 12–48 V DC systems. Also at the showcase were PwrTop 18, a simplified USB-C power bank circuit using a single 18650 cell, developed in collaboration with Alpenglow Industries. Initiatives like this demonstrate the bets on practical and open solutions in the DC power ecosystem.
Beyond the core product, the team promotes community feedback with demos, giveaways, and prototypes, with the goal of gathering real-world feedback from users and professionals. This cycle of listening and continuous improvement reinforces the team's approach. open hardware and long-term support.
Price, stores and usual policies
The manufacturer positions the PwrTool 500 at a competitive price of $149. In the retail channel, it's common to find forms to report lower prices at other stores, which helps maintain competitiveness. These practices, along with clear shipping and return policies, they usually improve the shopping experience and the confidence of the end user.
Likewise, e-commerce sites display cookie notices with mandatory functional options and statistical or personalized preferences. Although unrelated to the device's technical performance, understanding these policies facilitates navigation and the purchasing process, and it is common to see categories such as strictly necessary and analytical cookies controlled by the user.
In terms of availability, the manufacturing strategy and logistics alliance with Mouser facilitate orderly fulfillment, while open documentation and the ESPHome community provide a stable base for support and updates in the medium and long term.
With an approach that combines complete openness, direct integration with Home Assistant, solid specifications and an expandable ecosystem based on ESP32-C3, PwrTool 500 presents itself as an attractive option for DC monitoring and automation. Its ability to work in 6–60 V, measure up to 500 A peak, select polarity, control high-current relays and expand via I2C and GPIO, combined with the transparency of the project and the planned logistics, form a well-rounded package for those who want to go beyond the simple state of charge number and seek Fine control, useful data and freedom to evolve your installation.