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Topic starter
2024-10-24 4:00 pm
I am trying to detect when a machine starts in my workshop so that I can start the extraction system.
I have bought the following current sensor and have been playing around with it.
HALJIA SCT-013-000 Non-Invasive AC Current Sensor Split Core Transformer 10A 1V for Arduino Project, SCT013-000 Non-invasive Split Core Current Transformer Sensor (10A 1V)
I wrongly thought the 0/1V output was going to be DC, which was a bit daft considering… So my problem is now how to get the ESP32 to read the voltage so I can trigger the extraction.
The sensor is commonly used in house automation to read the current to display on a house screen. In these cases I have seen people add a DC bias voltage so the sinewave doesn't go below 0V. I've tried this and then realised that when the machine is off, the DC bias voltage remains so the MCU will measure the DC volts.
In this case an option might be to just measure the DC volts and then remove that offset in software.
Another option I considered was to just measure the raw AC signal from the sensor. I assume this would just measure the positive going signal. It will only be half the signal of course, but if I amped it first I could make it measurable.
Would this approach damage the MCU?
Another slight worry I have is the startup spike. As you can see from the table above, it can be nearly 43A.
If I use a 50A sensor, the running signal is minute, hence the 10A sensor to give a better signal at the running amperage.
So, will the spike damage the sensor (It hasn't so far, but…)?
Can I/should I limit the voltage into the MCU/op-amp? Zener diode?
Am I on the right track with any of the above, or is there a different approach I should take?
Well, that could’ve gone better 😬
2024-10-24 4:53 pm
@andydowns I think those startup Amps are for the machine. This is a very standard device designed to do exactly what you want. Maybe wander over to a home automation site and check there.
First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, 360, fairly knowledge in PC plus numerous MPU's & MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.
Topic starter
2024-10-24 6:43 pm
Yes, the machines have quite large motors and some turn fairly heavy shafts, hence the large current draw when starting up. Once the machines are turning they need less current to run.
This is not some thing that the home automation guys typically do and their sites and youtube videos don't really cover it. Hence the questions on here. I have visited many other sites looking for answers to my questions, but haven't been able to find any. If you know of relevant sites to try, please add the links.
Well, that could’ve gone better 😬
2024-10-24 8:17 pm
@andydowns I had them, my neighbour had them, and I know companies that sell them to homeowners by the tens of thousands. So not sure why you think that.
First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, 360, fairly knowledge in PC plus numerous MPU's & MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.
2024-10-24 9:04 pm
Maybe this comment is not too much use for your case as I spout from memory of using a similar looking current sensor that I had linked to a raspberry pi some years ago to experiment with monitoring the house power usage. This was soon discarded when I had one of those smart meter displays installed. The smart meter was utterly useless, but the automatic transmitting of the meter readings to the energy company meant that I could download hourly power usage direct from the energy company and play with it in a spreadsheet.
Anyway I remember hooking the current sensor to an Analogue to Digital converter that had either an i2c or an SPI (cant remember) to link it to the rpi. I was logging power usage whereas I see you are only needing to know the current is flowing so I would guess that a simple check that the output of the sensor is not zero volts would suffice for you. Without looking it up I'm not sure what the AtoD capabilities of your ESP32's are, so I guess you may also need an AD converter.
AndyD reacted