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SCT-013-050 with NodeMCU


(omer) #1

Hi,
I want to have information about when our coffee machine is ready. This machine is open to common usage for about 20 people. I have a SCT-013-050 sensor and NodeMCU. My plan is simple, measure the current values and do the math. Figured the circuit without a burden like; https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/how-to-build-an-arduino-energy-monitor-measuring-current-only?redirected=true I have two questions.

First question: Do i need a burden? I have information about SCT-013-050 that says it has its own burden. So i figured calibration like below. Is it right?
emon1.current(1, 50);

Second question: I read some noisy values from sensor when it is connected to usb cable to computer and i see (near)zero value when i remove the sensor from the cable. But, when i power nodemcu from the power adapter (apple’s usb charge adapter) the value of sensor data dramatically increases and zero value is never seen. What should i do?

Thanks.


(Robert Wall) #2

Yes, the SCT-013-050 is a voltage output, the burden is internal, so you do not need, and must not have, another burden.
But why have you chosen the 50 A c.t? Surely your coffee machine does not draw 50 A rms, even at 115 V? What is the current rating of the machine - I would have expected not more than about 20 A, and probably not that much. Remember that if you choose a 50 A c.t, you cannot change your mind after. If you choose a lower current rating, you can decrease the sensitivity by adding your own burden later, if that is necessary.

The calibration constant is the current required for 1 V rms output, so 50 is correct.

The first step would be to try a different USB adapter. See http://openenergymonitor.blogspot.co.uk/2011/08/not-all-usb-power-supplies-are-created.html

You might also want to check this archived thread, about noise in Arduino-based builds: https://openenergymonitor.org/forum-archive/node/10111.html

But if you only want an indication that the water is hot, why not simply wire a neon indicator lamp across the contacts of the thermostat that controls the heater? When the water is hot, the thermostat contacts open, the lamp lights. When some water is drawn off, cold water flows in, the thermostat contacts close, the lamp goes out and the water heats up.