High Current Using SCT-019 Sensor

Hi all. I have a project that I need to monitor power from a high current source (about 180A). I found and purchased the SCT-019.

I found this:

My question is what resistors/Cap values need to be used to interface with the particle as in this example.
The sensor has a turns ratio of 6000. Output of .333V.
The sensor states 200A, 33mA on it.

Any help would be greatly appreciated!

OK…so I finally watched the video in the link…DUH! Thanks for looking :slight_smile:

Have you done any calculations yourself yet? The thing I hate about hackster (or any project demo site) is that they don’t always give you a schematic with an explanation of what’s going on. They just give you the fritzing and code. The schematic for that example is this:

Substitute the 5V for the arduino with 3.3V for the particle.

I believe to calculate the Rburden you assume you want to acheive 3.3v max with a known maximum current of 33mA, and that is centered on 1.5V. So Rburden = 1.5V / 0.033A. Rburden = 45ohm. Ra and Rb create a symmetric voltage divider so any 2 equal resistors will do. The 10k specified in the example should do ok.

Edit… I think I originally stated 3.3v when it should have been 1/2 that.

1 Like

The video in link actually ended up being really helpful. He explains what the components are for and what they’re doing in the circuit.
I came out with a 50 ohm burden resistor based on 3.3/2 = 1.65, divided by .033.

Thanks for the detailed post! I have to find my spare particle and do some testing…

So I have everything connected. I purchased the 30A sensor in the tutorial as well. Both sensors seem to be working; reading fairly correctly while a load is being passed through the sensor.
Now, when there is no load…I still read around 7VA with the 30AMP sensor and like 38VA with the 200AMP sensor. Is this just a byproduct of this circuit? Any ideas on how to fix this so that it reads near 0 when the load is off.
I have changed burden resistors and coding accordingly for both sensors. Thanks.

Thinking out loud here:

You might want to check the DC bias. Is it exactly one half of 3.3V? There could be a drift there from temperature change and the resistor performance. Are the DC voltage divider resistors exactly matched? Measure with an ohm meter as exactly as possible.

Also, The V(AnalogIn) is a sine wave. When reading with an ADC, you will get continually fluctuation readings. Have you done anything to rectify the signal to DC, which would me most appropriate for this type of reading?

I’ve been looking to build a relay board with current and voltage sensing so I’m looking into all these same issues as well. I am using this circuit for the AC to DC conversion instead of using a bridge rectifier which will experience voltage drop from the diodes. Precision Full-Wave AC/DC Converter The circuit notes say that it should work with most Op Apms and different supply voltages shouldn’t be an issue. Also, the input will scale to whatever input voltage range you use within the bounds of the Op Amp supply voltages. I am using a 12V supply and I will not be providing the -12 volts to the Op Amp as I will be using the same DC bias method as you to keep the input and output above 0v (GND). I’m not sure if that’s valid yet. I am still putting together a BOM for this prototype.

Edit: This is a better link for that circuit. There are a bunch of Op Amp circuits in that article but the precision rectifier is what I was most interested in.

I just looked at that sample code in the hackster.io link and I just don’t see how that code synchronizes to the sine wave of the input. The number of samples you specify doesn’t correlate to a symmetric sampling of the sine wave and so it could do exactly what you’re seeing… take a skewed/biased measurement. Perhaps I’m off with that understanding… maybe an actual expert could chime in. Perhaps @peekay123?

Although with no load, there should be no current and a reading of 2048 (mid point) on the ADC. And so that’s why I was originally saying to verify the DC bias is where it is supposed to be. It could also be picking up stray EM signals.

Next chance I get I will break out the multimeter and take some readings. There has to be some reason why it’s not reading correctly and I’m getting readings when there’s no power running through it all. I will post as soon as I know more.

So I took some readings.
I am getting exactly 1.65v at my voltage divider.
I am using a kill a watt meter to compare my readings.
I know that I really need to monitor the voltage coming in from the AC as well since it fluctuates to get more precise readings…Not quite sure how to do that yet.

I am using a box fan with a modified extension cord that I am clamping the sensor around.
When the fan is on high the readings are really close.
When the fan is on medium I am reading 14VA higher.
When the fan is on low I am reading 16VA higher.

ninjatill, thanks for this circuit link. Well explained almost everything! I just bought fluke 87v multimeter today https://bestmultimeterreviews.org/fluke-87v-review/ to test this type circuit and electronics devices.