OpenEnergyMonitor Current Sensor Calculator

OpenEnergyMonitor current transformer (CT) value calculators

These calculators are designed to help you determine the values of the components you'll need for the current transformer(s) used in the Open Energy Monitor project. Go check it out!

Please note these calculators do not take into account core permeability and core AL value. Use at your own risk.

Update November 2017: Fixed formulas displayed below each calculator to halve the system voltage as was originally intended.

System voltage: Volts
For energy monitors based on 5V arduinos (mostly older ones), enter 5 above

Burden Resistor

Calculates the value of the burden resistor to use across a current transformer
Max RMS current: Amps
Current sensor turn ratio: :1
Calculated Resistor value: Ohms

Formula: burden_resistor = (system_voltage / 2.0) / ((I_RMS * 1.414) / ct_turns)

Max current

Calculates the maximum current you can reasonably expect to measure using a current transformer
Burden resistor value: Ohms
Current sensor turn ratio: :1
Calculated max RMS current: Amps

Formula: I_RMS = (((system_voltage / 2.0) / burden_resistor) * Turns) * 0.707

Current Sensor Turns

Calculates an estimate of the number of turns a current transformer would need
Burden resistor value: Ohms
Max RMS current: Amps
Current sensor turns:

Formula: turns = (I_RMS * 1.414) / ((system_voltage / 2.0) / burden_resistor)