AC Current Sensor

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I know I have asked similar questions before, but I have switched sensors and encountered interesting results that I do not understand.

Purpose: I intend to use an AC current sensor to measure electrical current flow running through a simple table lamp, and record these results on my raspberry Pi. I want to record the results in Amperes.

Setup: I am using an SCT013 (rated max current 100A and output is 50mA, 100A:50mA), clamping it around the hot wire running into the lamp. Then after I plug the ‘audio cable’ output from the SCT013 into an SKU_SEN0211 AC current sensor. I then plug the out put of this current sensor into an MCP3008 ADC on my breadboard, with a 5V reference voltage. From there I measure the result on the Raspberry pi.


SCT013 (100A:50mA) > SKU_SEN0211 > MCP3008 (5V ref) > Raspberry Pi

Results The results read from the Pi seem intuitive at first. They hover at around 10 when the light is off. Shoot up to ~200 when one of the lightbulbs in the lamp is on, and then up to ~400 when the second lightbulb is on. HOWEVER, when I plug in a different SCT sensor that is rated (30A:1V), the results hover at 10 when the light is off, but only go up to ~20 when both lights are turned on.

My Thought Process Since the MCP3008 is a 10-bit converter, in order to convert the result read to voltage I have to do (10/1023) * 5V or, (Vout/1023)*Vref? Which comes out to around 0.09 V or 0.09A?

Question: I don’t know how to interpret the read result properly depending on the current sensor I use, and I don’t know how to convert that result to Amps. I also have no idea how the signal is transformed as it passes from the AC current sensor to the ADC?

Useful data sheets

SCT013 and AC current sensor https://wiki.dfrobot.com/Gravity_Analog_AC_Current_Sensor__SKU_SEN0211_

Guide I was following but don’t fully understand https://www.poweruc.pl/blogs/news/non-invasive-sensor-yhdc-sct013-000-ct-used-with-arduino-sct-013

  • how are you connecting the second sensor? … you said that the output of the first sensor is current and the output of the second sensor is voltage – jsotola 5 hours ago
  • @jsotola sorrry I forgot to mention, the lights are two 120V 40W bulbs – Tuomas Talvitie 2 hours ago
  • The second sensor has a signal output: (0.2-2.8VDC). But I don’t really understand what that means? What is VDC? – Tuomas Talvitie 2 hours ago
  • Vdc means Volts dc – jsotola 2 hours ago
  • How should I ‘backwards convert’ the readings from the ADC to determine what the actual measured current is? – Tuomas Talvitie 1 hour ago
  • @Tuomas Talvitie, Ah, let me see. Your project is in two parts (1) SCT013 AC current sensor, with analog DC voltage output, (2) MCP3008 to convert analog to digital for Rpi. I have played with AC and DC current sensing, with and without ADC built. You might like to let me know which part of the two references you find confused, and I will try to clarify. I have searched a couple of my old current sensing answers to refresh my memory. I have played thing similar to yours. These are about half of my posts. Might find more later. – tlfong01 24 mins ago   
  • I skimmed your reference and I think I understand 95% of the practical and theoretical side of the things mentioned. The thing is that you need the prerequisite of middel school physics in electricity and magneticism to understand terms such as AC (current) transformer, the meaning of RMS etc. poweruc.pl/blogs/news/…. Perhaps I can show you a tutorial for newbies later. – tlfong01 15 mins ago   
  • This is what I suggest newbies to read: (1) AC Waveform and AC Circuit Theory – Electronics Tutorials: electronics-tutorials.ws/accircuits/ac-waveform.html. Take your time. Last year I actually spent over 10 hours to try to understand everything, including RMS, the meaning of the weird qualifier “j”, and AC phasers. – tlfong01 11 mins ago   
  • I started with ACS712, and later more other AC/DC current sensing devices. You may like to read the following two answers:(1) raspberrypi.stackexchange.com/questions/94403/… (2) raspberrypi.org/forums/…. To measure AC current without physical touch dangerous current, you need to use something called CURRENT TRANSFORMER which convert AC current of DC current (sort of), then you now measure DC current, / to continue, … – tlfong01 5 mins ago    
  • As I said, some products are fully integrated, (1) current transformer and rectifying circuit, (2) DC current sensor, (3) ADC (4) LCD/OLED disaply, all above for less than 10 US dollars (see my second answer mentioned above. – tlfong01 just now   Edit   

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