Q: How can one determine of the direction of the current for AC current using a Hall Effect Transducer?

A: There are a few methods to determine the direction of AC current flow

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(1) Acquire the waveform of the AC Voltage and AC current to see if the current is leading or lagging the Voltage.  This is also called “determining the phase angle” between the two waveforms.  One simple device that can acquire this data is LabJACK  U12 USB data acquisition box.    It can measure 4 channels in differential mode (Differential means that two channels are used to get one high quality measurement).   This LabJACK  device comes with free data logging software  and O-scope software with a sampling rate of over 6,000 samples per second.  Plenty of speed when looking at  60 Hz  AC.   The LabJACK  also comes with free LabVIEW drivers so you can customize the software to your liking using LabVIEW.


Measuring the current is easy with this method using one of the Hall Effect  current sensors sold on this website.  They have a -8V  to + 8V output range that  the LabJACK  U12 can easily  monitor.    The challenge is condition the AC Voltage signal so that it is scaled down to within a -10V to + 10V Range for the LabJACK  .   One most also have a way to provide electrical isolation between the AC voltage source and the LabJACK  / Computer you are using.    To do this one can use a simple AC to AC doorbell transformer thac converts 120VAC down to 16V AC.   Like this one:  [amazon text=Transofmer&template=my favourites&asin=B001G0MB46] Then use a simple voltage divider  to divide the Voltage down in half so that it can be monitored by the LabJACK  USB data acquisition box.

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(2) Another method is to use a cheap arduino microprocessor  that monitors the zero cross over points for Voltage and Current,   subtract the time between the two events which will allow you to determine if the current is leading or lagging the Voltage.  For this you will also need to provide AC voltage isolation through a transformer and divide it down to a 5V level so the Arduino can monitor the signal without being damaged.  You will also need to use an AC Current sensor to input into the Arduino.   You will have to divide the voltage down from the current sensor so it falls within a 0 to 5 Volts range.   The current sensors on this website such as the H2A-ACDC-72-MK  can do this.  (See owners manual here)

DATA SHEET / OWNERS MANUAL Current sensor data sheet owner's manual

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(3) One can use a specialized chip and circuit board that is designed to analyze AC power like  the Maxim  78M6613  Single Phase AC Power Measurement IC.    This chip is mounted to an evaluation board  here:  This board can measure up to 20 Amps  and provides some electrical isolation from your computer so it does not damage your computer when you hook AC power to it.   To use this board you will need to use a simple terminal emulator  like hyper terminal.

AC Power Current analyzer board for data logging phase angle of AC current
AC Power Current analyzer board for data logging phase angle of AC current





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