Why is it impossible to find a non-invasive DC current transformer in the milliamp range that is split core (can open and close around wire)?

I would like to sense when a wire is carrying current or not. This wire when active will have 300 mA DC.

Using this meter: https://www.digikey.ca/en/products/detail/b-k-precision/316/1682098 I am able to easily sense this current non invasively. Has anyone ever seen something exactly like this meter, but instead is powered by 5V dc and outputs an analog voltage proportional to the current being sensed? I have searched digikey and some other electronics sites only to find a few solutions that either only sense current from 1A and higher, or need a 24V input.


I think I found one. Has to be ordered from China, and my source needs to be boosted from 5v to 12v, but I think it will work. Seems like the only supplier on earth who sells something like this! https://www.chenyang-gmbh.com/en/split-core-dc-current-sensor-cyct04-xnsl.html

  • \$\begingroup\$ Use a hall-effect sensor. \$\endgroup\$
    – Andy aka
    Jul 27, 2020 at 17:30
  • \$\begingroup\$ That's what I have tried, but it is not sensitive enough to pick up 300mA... I even tried to amplify using an instrumentation amplifier. I just find it strange that you can buy an amp meter like this and it works so great, but I can't find a permanent sensor that is always measuring. Part of me wants to dismantle this meter and see if I can disable the auto-off feature but I know that's a bad idea! \$\endgroup\$
    – MattG
    Jul 27, 2020 at 17:44
  • \$\begingroup\$ The BK meter couples lots more magnetism to it's hall sensor by using ferrite in the clamps to act as a low-loss magnetic conduit. \$\endgroup\$
    – rdtsc
    Jul 27, 2020 at 18:06
  • \$\begingroup\$ Yes I have also sandwiched the hall effect sensor between 2 ferrite cores. I still get a messy unrepeatable signal. I'm sure someone with more skill could get this working but I am at the point where I wish I could just purchase something commercial \$\endgroup\$
    – MattG
    Jul 27, 2020 at 18:17
  • \$\begingroup\$ Why do you need split core? \$\endgroup\$ Jul 27, 2020 at 19:15

1 Answer 1


Have you tried a reed switch? They generally switch with 20 amp-turns, so you would have to wind the wire you are trying to sense current in 20÷0.3 = 67 times around the reed switch. Is your circuit OK with the added inductance?

Alternately, add "process loop" to your search term. Process loops run at 4-20mA, and there are current clamps to measure that non-invasively. Often, they go higher to 100mA. In your case, the 300mA won't be accurately measured, but you only want to detect the current, not measure. I imagine there must be always-on clamp sensors for current loops.

  • 1
    \$\begingroup\$ Thanks for the answer unfortunately I don't have enough slack to wrap the cable 20 times \$\endgroup\$
    – MattG
    Jul 28, 2020 at 9:12

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