Hey everyone, I’ve been experimenting with DC power measurement using the Shelly UNI Plus, and I thought I’d share my journey and findings with you! 
For those who aren’t familiar, DC power measurement involves capturing both voltage and current to calculate power (P = V × I). While the Shelly UNI Plus doesn’t natively support this out of the box, its customizable inputs for voltage and pulses make it a great candidate for some DIY magic. 
Here’s what I did:
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Hardware Setup: I used a HA4009 Hall-effect current sensor, which can handle DC currents up to 50A. This sensor converts current into a voltage signal, which I then scaled to fit the Shelly’s ADC range using a simple resistor network. The sensor requires a symmetric power supply, which I provided using a 3W DC/DC converter.
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Voltage Measurement: To measure voltage, I connected a voltage divider directly to one of the Shelly’s ADC inputs. This allowed me to monitor the voltage across a load in real time.
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Current Measurement: For current, I used a U/f converter module based on the LM331 chip. This converts the current sensor’s output voltage into a frequency signal, which the Shelly can then measure using its pulse input. While this setup works well for varying currents, it does have a minor limitation: it can’t measure zero volts accurately due to the nature of frequency-based measurements. However, this trade-off is acceptable for my use case.
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Software Integration: The final piece of the puzzle is a custom script that multiplies the measured voltage and current values to calculate power. I plan to publish this script soon, so stay tuned!
Challenges and Learnings:
- The biggest hurdle was ensuring accurate scaling of the sensor outputs to fit within the Shelly’s measurement range. Too high or too low, and the readings become unreliable.
- I also noticed that the Shelly’s web interface doesn’t update in real time, which means I have to manually refresh the page after making changes. Hopefully, this can be improved in future firmware updates.
Why This Matters:
Accurate DC power measurement is crucial for optimizing energy usage, especially in solar setups or high-current applications. By leveraging the Shelly UNI Plus, I’ve been able to create a cost-effective solution that integrates seamlessly with my smart home ecosystem. 
If anyone has questions or suggestions, or if you’ve tried something similar, I’d love to hear from you! Let’s continue to push the boundaries of what these devices can do. 
Cheers,
[Your Name]