I am using an YHDO-SCT013 100A/50mA CT with a 33Ω burden resistor connected to my Arduino at 5v. I have connected an extension cored with the wires separated and clamped the CT onto the load wire. I used a Kill-A-Watt measurement device to check the current draw of an appliance to adjust the curren…

Welcome, Jake, to the OEM forum. What you might be seeing is the inherent inaccuracy of a current transformer at low currents. What you have there is a 100 A device that’s specified to have a 3% linearity between 10% and 120% of the rated current. In other words, the manufacturer won’t even give a …

[image] Jake: the current draw of an appliance Is that “appliance” by any chance a hair dryer?

Thank you for your reply, Robert. After calibrating for a 9A current then increasing the power draw of the appliance to 13A the reading I get from the Arduino is in the 20A-21A range. I will increase the number of times the load wire passes through the CT as you have mentioned.

Yes, I am using a hair dryer for testing. Any similar experiences with this?

Yes! Typically the low setting on a hair dryer uses a diode in series with the heating element for the “low” setting. Have you got something like a toaster or space heater that you can use as a test load?

Here’s an explanation of what’s happening: [image] Trouble calibrating SCT-013-000 Hardware Hey all, I’m having a little trouble calibrating the SCT-013-000 current transformer with the emon library. I understand that the calibration value is supposed to be however many a…

The calibration constant - I think you must be using emonLib - is the current that gives 1 V rms at your Arduino input. That’s easily calculated, it is 60.6 (or 20.2 if you have 3 turns for the primary winding). If you set that, does it read the correct current at full power (with due allowance for…

[image] Jake: After calibrating for a 9A current then increasing the power draw of the appliance to 13A the reading I get from the Arduino is in the 20A-21A range. What results do you get if you calibrate using only the full power setting on the hair dryer?

I adjusted the calibration constant to 61 to match the 13.16A reading on the Kill-A-Watt meter with the hair dryer on hot high setting. Then when I switched the hair dryer to the hot low setting the meter read 9.26A while the Arduino read 5.95A.

This is because the hair dryer is effectively working on direct current (the heating element is, the motor of course will not be, but that represent a tiny fraction of the overall current), but no transformer will pass direct current, therefore the half wave that passes through the rectifier diode g…

SCT013 reading inconsistencies

Hardware

Bill.Thomson (Bill Thomson) 17 September 2021 20:31 7

Here’s an explanation of what’s happening: