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Thread: multiple current sensors advice needed

  1. #1
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    multiple current sensors advice needed

    Hi all,
    Need some advice from people much smarter than me in the ways of the electricity.
    Quick overview: a Teensy 4.1 is at the center of a new prototype I'm working on, essentially a networked lighting fixture. The fixture has 8 outputs powered by an external 48V power source. I wanted to be able to detect when a functional device was connected into one of these outputs (not just plugged in, but plugged in and drawing power/doing its thing). Since I have a few extra analog inputs on the t4.1 thought I'd use them in conjunction with a current sensor (specifically the INA169, but probably not important for this question) and sense the current output on *each* of the outputs independently. The assumption: if current on an output >= threshold, something is attached and drawing power. However as I was building the circuit I had a a big duh moment: all the outputs share the same 48V power supply so when I plug in one device, in theory all the current sensors will register a change in the current. At least I think that is what will happen!

    So question: Even though all the outputs are supplied by a singular 48V power supply, is there a way to "isolate" the 48V for each of the 8 outputs? A combination of schottky diodes or similar? I figure once I can get each output isolated I can get back to figuring out how best to sense the current draw on that output.

    Here's a quick screen grab showing what I have so far pertaining this question (half the current sensing circuits, at least). Note that the outputs all share the same "48V" and "GND_IN", which I believe is what is where my issue will be.

    I'm sure more info is needed...please let me know. Thanks in advance for any pointers.

    David

    Click image for larger version. 

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  2. #2
    Are your lights connected in parallel? If so I'm not sure I see the issue. Can you put a current sensor to the supply for each light? I'm not familiar with that current sensor, I use ACS758's but as you say, that should not matter.

  3. #3
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    Your shunts are all wired in parallel to 48V and GND. Shunts go in series with the load. I'm not familiar with the chips, but your schematic shows 4 shunt resistors shorting out 48V to GND.

  4. #4
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    @KrisKasprzak: yes, parallel.
    @boxxofrobots: well yes, that it is a problem, isn't it! That's a bit embarrassing.

    Let me fix my mistakes and come back. I'll also look into the ACS758.

    Thanks for the input!
    David

  5. #5
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    OK. Now that I know how to wire the current sensor, the question above is easily answered. I saw VIN+ and VIN- in the docs and immediately associated VIN- with ground. Nope! Also switched to the ACS70331 sensor.
    Thanks for the help and apologies for the noise.

    Cheers,
    David

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