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I am trying to sense if DC current increases in a wire when the load changes. I do not care about the value of the current, I only want to know if it increases (motor at idle vs motor running). I cannot modify the wiring of this motor, so I need to do it noninvasively. I purchased a few analog hall-effect chips, hoping that if the chip was against the wire it would detect the change in magnetic field, but perhaps I need to brush up on my physics! I am seeing no change whatsoever when measuring the output when the chip is taped to the wire. I tried multiple orientations of the chip, as I know they are sensitive to poles, still nothing. As a sanity check, I used an actual magnet, and the chip responds as I would expect. I am using these (from digikey): part number: Texas Instruments DRV5053VAQLPG TI Chip Can someone tell me if I am close here, or lead me in the right direction? Thanks in advance!

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  • \$\begingroup\$ When finding the correct orientation, remember that the field lines are going in a circle around the axis of the conductor. If you're touching the center of the device to the conductor, no orientation will work. Also, you might want to do some math...it's possible that the field you're generating with the motor current is too small for it to detect. \$\endgroup\$ Nov 13 '19 at 20:47
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    \$\begingroup\$ Matt, what you have is supposed to measure magnetic field intensity. That's what it does. Putting it next to a long wire carrying DC current isn't going to be observable. Even if you get the alignment right (and that's important, too) I suspect it won't give much signal on a straight wire. Can you consider the idea of wrapping the DC-carrying wire into some loops (a coil?) If so, you can create a cross-section that produces enough Gauss so that you may be able to get enough to measure. \$\endgroup\$
    – jonk
    Nov 13 '19 at 20:47
  • \$\begingroup\$ Thanks for the comments and suggestions. @jonk, if I put a coil of wires around the current carrying wire, it will cause the coil to become a very weak electromagnet? \$\endgroup\$
    – MattG
    Nov 13 '19 at 20:55
  • \$\begingroup\$ @MattG I don't think you gathered me. I'm asking if you can coil up the actual DC current-carrying wire itself. Not wrap it with a coil. I think you could also use a separate coil, aligned properly, to notice changes, too. But I'm asking if you can make a coil out of a short length of what's carrying the DC current in question. \$\endgroup\$
    – jonk
    Nov 13 '19 at 20:58
  • \$\begingroup\$ You may be better off using a Current Transformer (CT) if possible. \$\endgroup\$ Nov 13 '19 at 21:04
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The cylindrical field around a wire is fairly weak, so Hall effect current sensors use a C-shaped core to reduce the reluctance and direct the flux so that you get a decent signal from a Hall sensor placed in the gap.

enter image description here

picture from here

It is possible to buy these sensors as ready made, with a 2-part core, that then snap over the wire. enter image description here

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