Hall sensors

@krassimir_db_forum There are lots of A/C current sensors. They are used in Home Automation projects, and by hobbyists/companies to display mains usage often for a specific thing like washer, or the entire house. Just google.

Hi @krassimir_db_forum,

   As Ron (@zander) says, there are lots of current sensors in the marketplace, including ones with Hall-Effect sensors and ferrite ring, so if I were in your position, I would consider getting one, to learn how it works.

As I can't see your equipment, I will also briefly discuss two queries that I have. Please forgive me if I am pointing out the obvious:

• I assume you are only passing one 'live' wire through the core, NOT the whole cable, including the current return ('neutral')  as well. If you have both wires, the net magnetic field will be (approximately) zero, as they will cancel each other out.

• I also assume you are only looking to detect when a substantial current is flowing through the load. I am aware of contactless voltage detectors, that can detect when a mains wire is 'live', regardless of whether it is actually passing any current. This requires a different approach.

And of course, be careful. A 'live' wire with only one layer of insulation can become lethal, if the insulation becomes damaged.

Good luck in your research, Dave

@davee Hi and thanks for your attention! As I have tried to explain as clear as possible, which is the focus, in the consumer there is a built-in thermal breaker which breaks the heater from the mains as soon as the (say the water) has reached the temperature set for the device. From the other hand I am controlling the On/Off of the consumer by a solid state controller (MOC & Triac), so, the MCU code "has to know" if the consumer is "available" or not, which means if the control level is '1' and no current goes to the consumer (the thermal breaker is open), the logic will set the control level to '0'.
The consumer is well away from the MCU and any low power cabling is not acceptable and also I want to keep the consumer construction intact as it has been installed as per the maker's instructions (example: domestic boiler). 
At the main switch board there is only an automatic fuse and the solid state control switch (DIY).
Of course, I can use current transformers and I am using such for the main meters on each phase and they are made to measure values, which is not necessary in the case - too expansive to waste their capabilities.
The code logic is to set the control level to HIGH for few seconds, to test if the particular consumer current has changed (thermal breaker contacts are closed) or not (the thermal breaker contacts are opened).
Presently, I am testing the change of total power consumption for change for about 30 seconds, which is too much and vulnerable to false result (if meanwhile the other, say air condition control switches its compressor or etc., or my wife decided to cook something), which would lead to false indication that the boiler was active, which might not be true.

You are correct that I want just to 'see' if there is a current flow or not. Any voltage detectors will always be on, so I decided to use Hall sensor to find out if I would have a current flow or not.... 

Hi @krassimir_db_forum,

 Apologies, you clearly have significant experience, and hence some of my comments would not have been that useful.

I confess I have never tried building a Hall-effect current probe, so I can't provide any practical tips on that. Nor have I bought one, so I can only look at the adverts and other articles on the Web, and leave the reader to judge whether the information and claims are accurate.

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To anyone reading this, please understand that the remainder of the message is only a brief summary of what I found. I have not tested, nor do I endorse or refute anything mentioned. I have merely provided it for you to look at, and make your own decisions, as to whether, it is accurate, helpful, safe, and appropriate. Please remember you are dealing with a potentially lethal power source, and that only you are responsible for any decisions or actions.

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A quick Google suggests they are available for a few US dollars upwards. e.g.

https://www.aliexpress.com/i/4000048977436.html

Note this is a 'sealed' unit, so it will be necessary to feed the AC wire through the hole.

Also note that the claimed output voltage is conveniently high, perhaps 2.5V for the rated current, implying it includes amplification of the signal, etc., hopefully making it easier to interface to a microcontroller.

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There are YouTube videos about making a clamp device that may be helpful. e.g.

www.youtube.com/watch?v=SH0AMdRiYTE

Note that this video demonstrates that the signal from the Hall-effect device is very small, and that it will need to be amplified. It also explains that it is common to use the sensor in a closed-loop configuration, involving a second coil which is driven to counterbalance the magnetic field of the wire being sensed.

    Perhaps the reason you didn't see a voltage on your test, is that it was just too small to be noticed?

I have included this video, as I thought it was informative. I am not suggesting it is a practical solution to your project. In particular, it is a low voltage project, not involving mains voltage.

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In addition, there are many Hall-effect sensors which are designed to be used like a 'virtually zero-resistance' shunt. That is, they include a conductor, which must be spliced into the live wire, similarly to a shunt, but because they sense the magnetic field, instead of measuring a voltage drop, the conductor maybe be very close to zero resistance.

The video at www.instructables.com/Simplified-Arduino-AC-Current-Measurement-Using-AC/

discusses a DIY project, using one such sensor.

Of course, a project like this, will need great care to ensure the insulation is adequate, which may require more insulation, etc. than shown in the video.

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In summary, I hope these references provide some useful ideas and explanations, but please ensure the safety of yourself and others, if you decide to implement a system.

Good luck and best wishes, Dave

@davee There are also units like you show that open up so the cable can be inside, these are what the after market Home Automation guys use.

Hi Ron @zander,

    Thanks for the extra info. I expect there are many variants. I was just showing a few I found with a couple of minutes Googling, intended as an encouragement to look further.

Best wishes, Dave

@davee Hi.

Many thanks for your reply. As I told you, the use of current transformer is not very practical, as it's use just wastes the full scale of capabilities they are designed for - to measure values. I am using such for my meters and they work just fine. Split core construction that is non-invasive to the existing AC wiring. Locally such costs about 10 usd. 

So, I intended to explore the possibility to use hall sensors (few cents each) type 3144 or similar. Despite that the data sheets were so "promising", the tests have failed (eg declared sensitivity of -10 to +10 mT should mean that one should detect values even close to 0 mT. 
Further more, I have consulted ChatGPT and it has provided very detailed "project" even with a lot of calculations etc, eg the use of ferro ring with gap cut to house the hall sensor... but unfortunately those calculations did not work as expected. 

I began thinking that I am doing something wrong, so I decided to post for help here in DB in case if some one has faced the similar problems.

So, I will have to get rid this idea and to make another approach: to use small ferro ring and to wind some 100 turns (or more), to pass the power wire thru the ring hole and then to see on the oscilloscope what is going on, then try to amplify the voltage with an opamp (I have plenty in my basket), say 741 double or other single voltage powered and then to pass the output to Arduino pins for handling by the code...

Thanks again for advises....

Hi @krassimir_db_forum,

   According to the advert, the device(s) I pointed to are Hall-Effect, not current transformers. However, because the Hall-effect signal from just a wire passing through the toroid core just once is very small, temperature dependent, and typically non-linear when the whole system is considered, it is 'usual' to employ it in a closed loop configuration, which means the complete device is rather more complex than just a small, thin 3-legged device inserted into the toroid, as explained in one of the videos I referenced.

A simple current transformer may indeed be simpler. Remember to ensure the 'burden' resistor connected to the output of the transformer is securely connected at all times, to avoid a current transient producing a high voltage spike.

Good luck with your project. Best wishes, Dave

Hi, @davee

You are absolutely right about the hall sensor, without digging more in details.

It came out that a simple DIY current transformer, as I said above, is quite promising! Even with some 50-60 turns on a small (abt 15 mm) ferro ring provide 20-30 mV on test power wire of 50 Wats (incandescent bulb). I did not forget about the 'burden' resistor 😀 !
So, for sure it will provide more when power wire to consumer is say 2000 W.

One classic amplifier (even not Opamp) did the job and I got AC signal of 3-5 v. After rectification I got about 1.5-2 v logic level HIGH and 0 v for LOW. It is nothing left but to make it 5 v for HIGH etc.... I will continue that tomorrow...

Thanks again and I have a half a step away from the Arduino pin.....