Hardware support > General topics
AC current detection (not measurement)
lukash:
Hey everyone!
I'm trying to make a sensor that would detect if an appliance is running by detecting current in the wire to the appliance. I don't need to measure how much current the appliance is drawing, I just want to detect if it's ON or OFF.
I want this to be contact-less .. I want to monitor basic home-like 120V single-phase things up to stuff in our wood shop (2 or even 3-phase devices (table saw, planer, jointer)). So I don't want to mess with high voltage.
Solutions I came up with and their drawbacks:
Current transformer
PROs: very reliable, precise, can even measure, contactless
CONs: can't just attach it to the cable itself, has to sit on hot (or neutral but not both) wire (as there is neutral and hot running in same cable and they cancel each other out, so CT shows nothing)
EMF reading
PROs: no wire stripping, contactless
CONs: unreliable? I haven't found a good-enough EMF reading sensor (or a technique I wouldn't have to spend weeks on tweaking) to be sure this won't be triggered by random interference.
I want to keep this as simple as possible and I'd like to just stick something to the 3-wire cable (hot, neutral, ground) and detect electromagnetic field in it to know the appliance is on.
IMHO EMF reading is best for this - anybody seen something better than a 2Mohm resistor and a wire to analog input of arduino and yet not a 2-month project thing? ::)
I think this might be a nice addition to the home-automation in general and will be more than happy to try to make this a moteino-shield design.
Thanks!
Lukas
ssmall:
You can take a look at what TomWS did: https://lowpowerlab.com/forum/index.php/topic,1036.msg6649.html#msg6649
Watch John’s Gateway Deep Dive #2: Utility room node: http://lowpowerlab.com/blog/2016/02/01/johns-gateway-deep-dive-2-utility-room-node/
lukash:
Both of these solutions use Current Transformers which require measuring current on a hot OR neutral but won't work on a cable with all 3 wires in one cable scenario :-\
Thanks for the pointers though, I appreciate it. If we won't come up with anything better I guess I'll go with that, but it makes the whole solution not so user-friendly :(
I'd love to have tom EMF probe that just sits on a 3-wire cable without any stripping or otherwise altering the wiring of the appliance itself.
emjay:
@lukash,
A C.T. is useless if you can't easily break out a single conductor to monitor and connecting up to sense the V will pose a safety hazard. You can try the this technique https://moderndevice.com/product/current-sensor/ - it uses the fact that very close to the conductors, the flux doesn't sum to zero.
john4444:
Hi Lukash,
Modern Device makes a "non-contact" but tie-wrap-on current sensing device.
see: https://moderndevice.com/product/current-sensor/
It would not be very precise for current measurement but looks as if it would work for detection.
WhiteHare,
The Home Depot type voltage sensors are very unreliable and prone to lots of false signals.
I don't trust them for verifying that the household power is off.
I've been lied to a couple of times by those devices.
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