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Subject: Re: Sensing mains current
X-Newsreader: Forte Agent 1.92/32.572
Date: Sat, 30 Nov 2002 21:08:30 -0500
NNTP-Posting-Date: Sat, 30 Nov 2002 21:08:31 EST
Organization: Bell Sympatico
I have built a clamp current meter, using a small ac transformer and
cutting the I part of the W .
Do you get it ?
Inserted a coil with thousands of turns but left room to pass the
mains wire between the UU and the ___ .
Connected that to a meter like the one you have and That's it.
For your application you need an amplifier, a full wave detector
and a comparator with some positive feedback.
You can do the amplification, the full wave detector and the
comparator with a quad op amp like the 4136 (less than one dollar )
plus a small capacitor a few resistors and a power supply common to
the complete system.
On your old design you have two problems
a) the signal is to low. Increase the number of turns.
b) you have multiple output instances because the signal is not clean
and you don't have positive feedback, required to over ride the noise
if the signal is used to trigger another device.
On 30 Nov 2002 07:20:56 -0800, email@example.com (ted) wrote:
>Any ideas for sensing the current taken by a mains appliance (mainly
>ligthing equipment 50-300W each) in the cheapest possible way?
>There may be 50-60 of these connected at the same time, so a very-very
>cheap solution is paramount.
>It must be non intrusive (no connections with the mains circuit, i.e.
>It should not add any resistance or components in series with the
>Some form of magnetic coupling is obviously the way to do it, but I
>can't figure out how to do it in practice, or what cheap components to
>Trying to make an "air" transformer, by winding the mains line cable
>with a bit of extra secondary couple of turns connected to a
>voltmmeter only produces a few microvolts of 50Hz signal (and quite a
>lot of HF noise as well). Not very practical.
>Also tried wrapping around a ferrite with similar results, obviously I
>am not using the rignt kind of magnetic material. but I wouldn't know
>how to choose one anyway. or where to find cheap ones..
>The system does not need to be accurate, more like an on/off detector,
>say detect from 1/5Amp in 1/10 Amp steps (or even less accurate).
>Any ideas anybody?
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