I am using a 2000:1 coil around one leg of an AC main to simply detect the presence of current or not.
The coil leads are across a simple half wave rectifier (1n4148) with a 100 ohm resistor. I have a ESP32 as the test controller with code that reads A0 and prints the value every second. My scope reads 4.2v across A0 and ground.
The readings stay above 0 and will count up to 4095 and stay there for 20 or more ticks and then start slowly dropping to 0. It will stay at 0 for several counts then start counting up to 4095. The scope wave and voltage does not waver. What is going on that I'm not getting?
All I want to do is detect a value greater than 0 to determine current is on the main with a non-intrusive coil.
Please read the post at the start of any forum , entitled "How to use this Forum".
OR http://forum.arduino.cc/index.php/topic,148850.0.html.
Then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
So just a diode and resistor? So you are presenting 50 or 60 Hz half wave rectified to the pin? I don't believe you are getting a steady 4V2 at A0 based on your circuit description, doesn't make sense. Show us the trace and a schematic.
Anyway, assuming you do have what I think you have then you are measuring the voltage at different points in each half cycle so getting different outputs.
Hi,
What is the value of the current you are measuring?
What do you calculate your transformer output should be with the 100R burden resistor?
With the single diode, your output to the controller input will not start till you have 0.6 or 0.7V being developed and you will have that as an offset for the rest of your readings.
You should always have the 100ohm burden resistor directly across the CT output .
If you put a single diode in series with its output before the resistor then , when the diode doesn’t conduct the CT will generate a very high voltage as it’s effectively open circuit . ( google “ open circuit CT”) .
After the 100ohm you need a full wave rectifier in parallel and capacitor to produce a steady DC voltage. ( assuming the voltage generated is sufficient)
As such, you are catching the signal at different points, sometimes creating a much lower sub frequency, sometimes stalling out, but otherwise highly distorted.
Since you're only detecting "presence" of ½ wave AC and not "measuring" ½ wave AC, then just take say 8 readings spaced about 3 ms apart ... if any readings are over a certain noise level (you decide) then AC is present.
EDIT: Before further testing, see reply#2 ... looks like some serious circuit corrections need to be made first.
Simple circuit to detect the presence of current using a current transformer. Connection "current" is supposed to go to an Arduino input pin (5V logic level).
Mine are 1:1000, principle remains the same. R12 may not be necessary (zener current limiting). C9 can be electrolytic instead of ceramic. R10 is there because I'm using the MISO pin that I also need for programming, this way its safe to program, otherwise C9 will cause problems. If you don't need this, R10 may be omitted.
You should not ever never put a diode in the output of current transformer . When not conducting the transformer will generate a high voltage - enough to be hazardous or damage the windings .
The burden resistor should be upstream of any plug abs socket
Voltage transformers and current transformers are different.
“CT burden resistor is the resistor which will be connected across the current transformer terminal S1 and S2. The main purpose of the burden resistor is to protect the current transformer under open conditions. As we have seen earlier current transformer’ secondary should be always in a closed circuit to avoid extreme voltage built up in the second terminal.”
