Tracking Welder & Compressor Power Usage with CT Clamps and ESPHome

Introduction: The High-Power Workshop

A workshop isn't like a living room. While a TV or a laptop pulls a few dozen watts, a MIG welder, a 60-gallon air compressor, or a heavy-duty wood lathe can pull thousands of watts in an instant. This high power consumption presents three challenges:

1. Cost: Running a 5HP compressor all day isn't cheap.
2. Safety: Overloading a circuit can lead to tripped breakers or, worse, electrical fires.
3. Logistics: If you know exactly when your compressor is cycling too frequently, you might catch a major air leak before it burns out the motor.

Standard "smart plugs" are rated for 15A at 120V—totally useless for a 240V welder. To monitor these beasts, we need Current Transformer (CT) Clamps. They are non-invasive, safe, and can measure hundreds of amps without you ever touching a bare wire.

In this guide, we’ll build a multi-channel energy monitor using an ESP32 and ESPHome to track your shop's heaviest hitters.

1. Electrical Safety: Read This First!

Working around electrical panels and 240V lines is dangerous. While CT clamps are "non-invasive" (they clip around the wire, not into it), you still need to open your electrical panel or a junction box to install them.

CRITICAL WARNING:

• Never open your electrical panel if you are not comfortable and knowledgeable about high-voltage safety.
• Always turn off the main breaker before removing the panel cover.
• Even with the main breaker off, the lugs coming into the top of the panel are still live.
• If you have any doubt, hire a licensed electrician to clip the clamps on for you. It’s a 5-minute job for them.

2. Hardware Selection: The Tools for the Job

We need CT clamps that match the current rating of our tools and an ESP32 to process the analog signals.

Bill of Materials

Choosing the Right CT Clamp

3. How CT Clamps Work (The 30-Second Theory)

A CT clamp is basically a transformer. When AC current flows through a wire, it creates a magnetic field. The clamp "catches" this field and induces a much smaller current in its own coil.

Important: A CT clamp must only go around one of the wires (the hot wire). if you clip it around a whole power cord (hot + neutral), the fields cancel each other out, and you get a reading of zero.

4. Hardware Wiring: The Bias Circuit

The ESP32’s analog pins can only read voltages between 0V and 3.3V. However, the output of a CT clamp is an AC wave that goes positive and negative. We need a "DC Bias" circuit to shift that wave so it sits right in the middle (at 1.65V).

The Circuit Diagram (Conceptual)

1. Two 100k resistors create a voltage divider between 3.3V and GND.
2. A 10uF capacitor stabilizes this 1.65V midpoint.
3. One leg of the CT clamp connects to this 1.65V midpoint.
4. The other leg goes to the ESP32 (or ADS1115) analog input.

Pro Tip: Use the ADS1115 ADC module instead of the ESP32’s built-in analog pins. The ESP32's ADC is notoriously "noisy" and non-linear, which makes energy monitoring much less accurate.

5. ESPHome Configuration: Calibration and Logic

We’ll use the ct_clamp component in ESPHome. This component samples the AC wave at high speed and calculates the Root Mean Square (RMS) current.

The YAML Configuration

sensor:
  - platform: ads1115
    multiplexer: 'A0_GND'
    gain: 4.096
    name: "ADS1115 Channel 0"
    update_interval: 10s
    id: ads_ch0

  - platform: ct_clamp
    sensor: ads_ch0
    name: "Welder Current"
    update_interval: 10s
    unit_of_measurement: "A"
    # Calibration: clip it on a known 100W lightbulb (0.83A) 
    # and adjust the 'to' value until it matches.
    filters:
      - calibrate_linear:
          - 0 -> 0
          - 0.05 -> 0.83 
      - multiply: 240 # Convert Amps to Watts for 240V
    id: welder_power

  - platform: template
    name: "Welder Power (Watts)"
    unit_of_measurement: "W"
    lambda: return id(welder_power).state;

6. Home Assistant Dashboard and Analysis

Once your data is flowing into Home Assistant, you can create some truly useful insights.

Identifying "The Leaks"

If your air compressor power graph shows a 3000W spike every 2 hours while you aren't in the shop, you have an air leak. Over time, those 2-minute cycles add up to significant electricity costs and wear and tear on the pump.

Automations for Safety

alias: "Warning: Welder Left On"
trigger:
  - platform: numeric_state
    entity_id: sensor.welder_power
    above: 10
    for: "01:00:00" # If welder is drawing power for > 1 hour
action:
  - service: notify.mobile_app_phone
    data:
      title: "Workshop Alert"
      message: "The welder has been active for over an hour. Did you forget to turn it off?"

7. Conclusion: Data-Driven Craftsmanship

By monitoring your high-power tools, you've added a layer of intelligence to your shop that most professional garages don't even have. You can now track the true cost of a project, identify failing machinery before it dies, and ensure your electrical system isn't being pushed to its limits.

Next Steps

• Voltage Monitoring: Add a small transformer to monitor the actual AC voltage. This allows for "True Power" (Watts) calculations instead of "Apparent Power" (VA).
• Run-Time Tracking: Use Home Assistant's history_stats to track exactly how many hours of "arc time" you have on your welder to stay ahead of consumable changes.

Stay safe, watch your loads, and happy building!

This is the sixth article in our "Smart Workshop" series. Check back next week as we automate workshop dust collection!