Non-contact AC current sense

HAVE you thought of a reed relay attached to the one of the wires., . . I DO NOT FOLLOW MANY OF THESE NEWS GROUPS To answere me address mail to snipped-for-privacy@aol.com

go to your local appliance parts store and ask for a live wire detector, about the size of a pen, runs about $10.

see what they have.

I got mine a few years back for $15 - but mine does a lot more than just check for a field - also checks fuses, hi voltage, and a couple other tricks.

or wait for christmas and get a few of those bulb checkers for $5 a piece

Sounds interesting, but I dont see how this would be non-contact. The reed relays I have seen require around 10mA coil current (or a magnetic field) to activate. A CT can produce maybe 1mA AC on the secondary.

I like the reverse engineering idea, but I need to sense current. These cheap pens are probably not doing this but I'll check it out. My wires are live all the time. I am trying to detect when a load is present. I did see that Extech has a new non-contact current probe for around $40. I am wondering how this works, since it does not use a clamp-on transducer. My application is in an electrical cabinet chock full of

60hz EMI. Any method that cannot isolate the magnetic field around the wire I want is going to fail.

sorry - I thought you were wanting to sense "live wire"

so you have voltage at all times, and you wish to sense current? i.e., you wish to sense magnetic field but not electric field?

IMHO an easier way is to sense heat from the additional current (I had a similar problem of sensing load light-weight and cheap years ago, and finding nothing I took another tack)

- try a low resistance power resisitor in series with the load and bond any one of a number of fairly cheap heat-sensitive solid state devices to the insulation on the resistor - using a heat conducting glue or motor tape.

the heat sensitive ssd can be integrated into lights or switching controls (or whatever) fairly easily.

although there may be other values now. A 550 mu would do you just fine.

two parts of the torroid you cut in half.

directory and ask them to send you a Moly Perm core catalog. Just get the two halves of the core back together tight. If you wrap the hot wire through the center 4 or 5 times it will be more sensitive.

core in half and can use any nickel core and it will be more sensitive but nickel and most metal cores do not lend them selves to be cut in half.

very simple, wrap a few turns of the power conductor size wire around the core and then put the two ends to the the cut ends and splice them in.

Thanks, I will look into these cores. A U shaped core with a strap-on flat could work for me. If it already had a sense coil on it that would be better. It would have to be lower priced than the CR Magnetics split core transducer (~$12) I have used. I don't mind doing things the hard way for a proto, but the economics have to make sense in the end.

The wires cannot be disconnected, and at .5" dia, I think I'll opt for more turns on the secondary :).

I did pick up one of these pens for $7 . What is interesting is that when I use it on some 110 zip cord, it lights up only for the hot wire regardless of whether there is a load present or not. If I add a triac style dimmer, then it lights up for both hot and neutral wires. I'd like to see an explanation for how these work.