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Hall sensor question Answered

Hey all.

I want to be able to measure the current draw through an AC wire in a confined space. I'm thinking hall sensors would be ideal for this due to small size and less chance of frying things (as opposed to a split-core transformer).

Unfortunately all of the hall current sensor projects I've found here on instructables are for the pre-made ACS712 board. This is a no-go for me because of size, the need for cutting the wire to make the connection, and also cost is a factor too.

Are there other options? I see a lot of three-wire sensors in through-hole transistor packages out there which would be ideal, but can you get the sensor voltage out of any of these, or is it strictly on/off?

Any hints welcome.

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Jack A Lopez

6 weeks ago

I was going to suggest you try reading the data sheets for these, what you call, "a lot of three-wire sensors in through-hole transistor packages out there..."

But you would probably think that is condescending.

Instead, I am going to ask you to look at some pictures attached to this post.

I stole these pics from Allegro Microsystems, and I will link to the pages I stole them from at the end of this post, but for now I want you to just sort of ponder these images.

The artist who created them is trying to communicate some of the basic physics of Hall Effect sensors, but in a visual form.

The blue arrows represent electric current, and these are double-sided arrows because, the current could flow in either direction, or it could be current whose direction changes periodically; i.e. alternating current.

The red arrows represent magnetic field lines, which came into being due to the presence of electric current nearby.

There is also some mojo happening with those C-shaped pieces of ferrite, for those pictures which include one of those.

I claim, in a hand waving kind of way, what the ferrite is doing is sort of concentrating the influence of magnetic field due to currents, in wires enclosed by the ferrite piece, and also excluding the influence of magnetic fields due to currents in wires outside the ferrite piece. So the HE sensor chip, just feels the influence of currents, in wires, enclosed by the C-shaped ferrite.

In practice, it is usually just one wire enclosed by the ferrite, and that wire carries the current you want to measure.

Alternatively, the same wire could be looped through the ferrite N times, and that would make the flux through the ferrite, and the HE sensor chip, N times larger. You know, this is the usual trick for making a stronger electromagnet: just put more turns on it. But a trick like that would only be needed if the current to be sensed was very small to start with.

https://www.allegromicro.com/en/Products/Current-Sensor-ICs/Zero-To-Fifty-Amp-Integrated-Conductor-Sensor-ICs.aspx

https://www.allegromicro.com/en/Products/Current-Sensor-ICs/Fifty-To-Two-Hundred-Amp-Integrated-Conductor-Sensor-ICs.aspx

https://www.allegromicro.com/en/Products/Current-Sensor-ICs/SIP-Package-Zero-To-Thousand-Amp-Sensor-ICs.aspx

allegromicro-HEcurrentsense-illustration-1--0-to-50-A-Integrated-Current-Sensor-ICs.pngallegromicro-HEcurrentsense-illustration-2--50-to-200-A-Current-Sensor-ICs.pngallegromicro-HEcurrentsense-illustration-3--0-to-1000-A-Sensor-ICs.png
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Downunder35m

6 weeks ago

Depends on what your skills are and how good you are with Arduino or Raspberry PI.
It is quite possible to extend the wires for a sensor so it can be placed into a ube or in very thight spaces.
This however can mean you need to compensate for the extra wire lenght if accuracy is a priority.

You should also keep in mind that a hall sensor reacts to ALL magnetic fields close enough, so interence can be an issue as well as placement.
For example a standard 5 core cable for a 3-phase motor not only has two live wires more but also the back emf from the motor.
In many cases it turns out that providing extra length in the cable or wire to be measured is far easier than anything else.
For example a little loop to the outside with a small boxcontaining the current transformer or sensor.