PwrTool 500 is an open-source battery and power monitor designed for off-grid energy systems. It integrates seamlessly with Home Assistant and supports direct customization via ESPHome or your own firmware. Designed for most 12-48 VDC systems, PwrTool 500 is built to handle up to 500 A peak current across 6–60 VDC, and provides detailed insight into your energy flow, generation, storage, and usage so you can monitor and automate data-informed actions.

Whether you’re automating energy systems, visualizing battery status, or controlling power routing hardware, PwrTool 500 gives you full visibility and control, all from within your existing Home Assistant dashboard.

Open Source Smart Shunt

Conventional "smart shunts" lock your data into proprietary apps and ecosystems. Even when modified, they typically require decoding undocumented protocols. PwrTool 500 is different thanks to its fully open hardware and software. With direct access to the sensors, firmware, and GPIO, you can configure PwrTool 500 to meet your system’s exact requirements with no vendor lock-in.

Versatile Off-Grid Applications

PwrTool 500 is suitable for monitoring at various points in a DC power system. For example:

• Battery Monitoring: Track your battery's condition and state of charge using accurate coulomb counting.
• Load Segregation: Use multiple shunts to differentiate between loads and generation sources.
• Extend an existing system: Many newer hybrid MPPT inverters and large charge controllers (50 A+) lack DC load output monitoring, which can leave out key metrics for maintaining a healthy system. Add a PwrTool 500 to any part of your system that lacks monitoring.

Monitor & Automate

Once connected to Wi-Fi, PwrTool 500 quickly appears in Home Assistant, providing a deluge of data to be used in your own dashboards. You can then zero the current offset and know you have an eye on the most crucial part of your system, with the ability to trigger automations based on voltage, current, power, and environmental data.

PwrTool 500 entities in a dashboard representing available data as of firmware 25.04

Need automated protection? Use the onboard MOSFET to control a high-current relay and shut off loads during faults, or activate resistive loads (such as a water heater) to soak excess solar after batteries are full.

Fully Extendable Hardware

PwrTool 500 without cover showing FLIP_C3 and mainboard.

The heart of PwrTool 500 is our FLIP_C3 microcontroller, which comes packed with features for futher customizing and controlling your environment. Expand your system using the various I/O, such as:

• A robust 5 V / 2 A buck converter tolerant to 60 VDC
• GPIO expandability from ESP32-C3
• WS2812 addressable LED & expandability
• USB Type-C for easy firmware recovery or replacement
• Solderless expansion via Stemma QT/Quiic compatible connectors

with the PwrTool 500 mainboard bringing 2x more Stemma QT/Quiic compatible connectors for I2C devices

ESPHome: Accessible Smart Device Development

ESPHome base YAML highlighting the reference to our in-house configurations on Github

Each PwrTool 500 ships with custom ESPHome firmware installed. When adopted into ESPHome Builder, you inherit our maintained configuration base designed for easy extendability and customization.

ESPHome provides a user-friendly, YAML-based approach to microcontroller programming, and represents a paradigm shift in accessibility to writing code for microcontrollers destined to be smart devices. With the vast array of supported sensors, motors, lights, etc., you can quickly get your devices up and running with a simple YAML configuration file.

Add any modules you’d like with many copy/paste examples across the web including our own repository full of modular YAML configurations to help you get started. You can even grab data from the rest of your power system over UART and other protocols.

ESPHome is well supported and updated monthly, so you get bug fixes and new features managed by the Home Assistant team and a massive pool of open source contributors.

We’d also love to hear about what you’d want to see in our default configuration. There is so much more we can do with the base dataset from our sensors and we’d love to get your feedback to constantly improve the PwrTool 500 over time for everyone!

Features & Specifications

An image showing a common wiring example with callouts for certain features

Power Monitoring

• System Voltage: 6–60 VDC (compatible with all lithium, LiFePO₄, and lead-acid batteries)
• Current: 500 A peak / 300 A continuous current shunt
• Accurate Monitoring: INA238 16-bit pre-amp & ADC with on-die temperature sensor facing shunt
• Polarity: Jumper-selectable hot- or cold-side monitoring (comes set to cold)
• 45 W N-channel MOSFET for PWM LED lighting control or high-power load control via relay or contactor

FLIP_C3 Controller Board

• ESP32-C3 with Wi-Fi and BLE
• 5 V / 2 A (10 W) buck converter
• GPIO-expandable with support for UART, I²C, SPI, PWM, etc.
• USB Type-C for firmware flashing and recovery
• Level-shifted WS2812 output, capable of powering 100+ LEDs
• User-configurable BOOT button
• Onboard status LED and Reset button

Additional Hardware

• 2x Stemma QT/Qwiic ports for I²C expansion
• Integrated SHTC3 sensor for monitoring ambient temperature and humidity

Flexible Polarity

Close up of the back and front of the polarity jumper showing orientation notes on the PCB.

Most shunt-based monitors only work on the cold (negative) side of the battery. This can be a limitation when physical layout makes ground-side monitoring impractical.

PwrTool 500 includes a jumper-selectable hot-side mode, offering flexibility for advanced or unusual setups.

Comparisons

¹: Polarity refers to whether the shunt body is placed on the high (hot/positive) side of the battery or the low (cold/negative/ground) side. Industry standard is cold-side (so your shunt will be in line with ground), but this may cause issues in some systems.
²: Comes default in cold mode, and can be set to hot mode with a jumper.

Compared to other 500 A shunt-based monitors, such as the Victron SmartShunt, Thornwave PowerMon, and REDARC offerings, PwrTool 500 is:

• The only fully open hardware solution
• The only one with native Wi-Fi + Home Assistant integration
• Built for expansion, not ecosystem lock-in
• Priced competitively at $149 USD

Documentation & Support

All hardware files — including schematics, board layouts, and BOM — are open source and available on our wiki. Our ESPHome YAML configurations are available and maintained on GitHub.

ESPHome is maintained by the Home Assistant team and supported by one of the largest open-source communities. You’ll always have access to the latest updates and improvements.

PwrTool 500 in hand for scale

Manufacturing Plan

We have completed and tested designs ready for production. Once our circuit boards are manufactured and assembled, we will be performing final assembly and packaging in Joshua Tree, California.
Alternatively, we are in talks with Elecrow as a contract manufacturer if we end up surpassing our goal. Elecrow has been crucial to several Crowd Supply campaigns including our favorite: Jumperless.

Fulfillment & Logistics

After assembly and testing in Joshua Tree, we will box up each PwrTool 500 and send them to Crowd Supply’s fulfillment partner, Mouser Electronics, who will handle distribution to all backers. You can learn more about Crowd Supply’s fulfillment service under Ordering, Paying, and Shipping in their guide.

Risks & Challenges

• Tariffs: Ongoing fluctuations in U.S.-China import tariffs may impact our margins. We’ve accounted for this and believe the project remains viable even under current rates.
• Certifications: We are preparing CE and UKCA certifications to ensure we can sell in Europe and the UK, broadening our market beyond the U.S.
• Supply Chain: Component availability and global logistics remain a risk, but we are working with known partners and will maintain clear communication about our shipping timelines.