Hardware 1. Acquiring the Components
This documentation is for software version 0.2.0 and earlier. Click here to see this page in the latest docs.
Please see my website for kits that contain everything needed (except for the Raspberry Pi) to get started. The sensors in my shop are manufactured specifically for this project. There is both a self-assembled kit and a factory-assembled kit.
https://power-monitor.dalbrecht.tech/
Your purchase of sensors and hardware from my shop directly supports my development and maintenance efforts for this open source project. Thank you for choosing this option.
In addition to the power monitor, sensors, and Raspberry Pi, you'll also need to have some accessories handy for the installation and calibration:
- [Optional] bulk shielded cat5e cable to extend the CT leads to your Raspberry Pi (also available from my shop)
- AC clamp meter, for validating that the sensor readings are accurate
- A high powered purely-resistive load
- A light duty extension cord (16 AWG or smaller)
If you're looking to source the PCB and electrical components on your own, continue reading see below.
To make things as easy as possible, I've included a bill-of-materials for LCSC.com. Unfortunately, they don't offer the MCP3008, so you'll have to source that separately. Here is the BOM for LCSC, which you can import directly in their website: BOM_Latest.xlsx
Here's the PCB gerber fabrication file, which you can submit alongside an order with your favorite PCB manufacturer.
The remaining components are listed below, which you should be able to source easily online:
- Raspberry Pi 4B (2GB) with power supply and at least a 32GB microSD card.
- Up to 6 current transformers
- Bulk UTP cat5e cable to extend the CT leads to your Raspberry Pi (and one shielded RJ45 connector to terminate the cat5e cable).
- 9V AC Transformer
- Four M2.5 standoffs to support the custom PCB over top of the Raspberry Pi.
- A "light-duty" extension cord (16AWG or smaller)
When self-sourcing current sensors, you'll need to validate their outputs and calculate the optimal burden resistor value to use on the PCB. See here for more info. Note: the reference voltage used in the burden resistor calculation is 3.3V, not 5V. Always round the calculated burden resistance value down to the nearest integer to prevent an overvoltage event on the ADC input. One burden resistor per CT is required.
The leads on the YHDC CTs are only about 3ft in length, but they come pre-terminated with a 3.5mm male plug. The leads on the PZCT CTs are much shorter and will need to be extended. OpenEnergyMonitor has thorough documentation about proper ways to extend the CT cable here, so I won't repeat the information already shared there.
Instead, I will explain what is required to use the custom PCB. The custom PCB has a standard RJ45 ethernet jack to accommodate 4 CTs. The leads of each CT can be wired to a single pair within a cat5e cable. Following a standard TIA-568B ethernet termination, here is how the cat5e colors map out to the analog to digital converter input channels:
| Cat5e Pair Color | Channel # |
|---|---|
| Orange | Ch. 1 |
| Green | Ch. 2 |
| Blue | Ch. 3 |
| Brown | Ch. 4 |
And here is the previously mentioned TIA-568B cable termination standard:
You should document the channel number associated with each CT somewhere to avoid confusing yourself in the next steps. I labeled the actual CT leads. Here is my finished CT / cat5e extension.
You'll need a device that you can use during the calibration process, and the only type of device suitable for the job is one that is purely resistive. These are usually devices that put out heat. Devices with electric fans or digital circuitry should not be used.
I recommend purchasing a simple halogen work light from your nearest hardware/home-improvement store. They're inexpensive, consume several hundred watts, and perfect for our purposes. Plus, you can always keep it around the house when you need some extra light.
Why so specific?
Later on in the process, prior to installing the Pi power monitor in your electrical panel, we'll be fine-tuning and calibrating the Pi to improve the accuracy. The Pi needs to be calibrated because the individual components on the custom PCB and the current transformers all have unique variances.
We need a purely resistive load for one major reason: the current and AC voltage wave forms from such a load are in phase with each other. This means that the power-factor from such a load should be exactly 1. Don't worry if you don't understand what this means yet. There will be more on this subject in the Phase Correction section of the Wiki.