Detecting current in a wire

W

Wing Fong Wong

Guest
If you've already read this please ignore, tin just crashed on me again
for the second time. Who said unix was uncrashable anyway...

I need to detect current flowing in a wire going in to an appliance. I
have used google and could only find multimeter type devices(perhaps
my search terms were wrong?). I don't need such a device, I don't need
to know the magnitude of the current, I just need to know that exists.

The story behind it.
Need to detect whether if some appliances(heaters, fans, lights and mixers)
are on or off. Then I need to log the times. So far as logging is concerned
I've got no probs with that and I've done dozens of times. What i need is
some way to sense whether is an applicance is on or off. I had considered
making individual sensors(eg an ldr for the lights) but that would make
the system less portable and more appliance specific. So i'd thought that
it might be easier to see if there is a current flowing into an appliance
and this will be the way it determins whether is the thing is on or off.
Is this do able? Can anyone suggest a way I could implement this? Should
I just make multiple sensors? Is there a God out there? All unanswered
questions so far as I'm concerned.

--
Answers to some FAQs:
No this is not homework, yes I'm an undergraduate, yes I'm looking for
work experience and no I'm not crazy.

Wing Wong.
Webpage: http://wing.ucc.asn.au
 
Wing Fong Wong wrote:

Is this do able? Can anyone suggest a way I could implement this? Should
I just make multiple sensors? Is there a God out there? All unanswered
questions so far as I'm concerned.
Click to expand...
Is this only with mains appliances? If so, current sensing with a toroid is
easy, electrically isolated, has no effect on the equipment it's sensing and
relatively cheap.

Wrap a number of turns of fine wire around a smallish toroid. Pass one of
the mains wires (active or neutral) through the toroid. Don't loop it around,
just straight through (effectively one turn).
I suppose this would be best accomplished with a very short extension lead
with the toroid sensor inbetween. This way, it can be portable too.

Look for the prescence of AC across the fine coil on the toroid. It
basically measures current, the more current, the more voltage across the coil.

Might be a good idea to have a sensitivity adjustment on the trigger too, to
allow for appliances like TVs and VCRs which are always powered on (and thus
draw relatively small currents), but suck more current when they're actually
powered up and running.

Or, for appliances that can vary the amount of power they consume (like
electric heaters) you can have a number of outputs triggered on different
current levels. So you not only know that it was on, but the setting too.

--
Linux Registered User # 302622 <http://counter.li.org>
 
John Tserkezis <jt@techniciansyndrome.org.invalid> wrote:
Wing Fong Wong wrote:

Is this do able? Can anyone suggest a way I could implement this? Should
I just make multiple sensors? Is there a God out there? All unanswered
questions so far as I'm concerned.

Is this only with mains appliances? If so, current sensing with a toroid is
easy, electrically isolated, has no effect on the equipment it's sensing and
relatively cheap.

Wrap a number of turns of fine wire around a smallish toroid. Pass one of
the mains wires (active or neutral) through the toroid. Don't loop it around,
just straight through (effectively one turn).
I suppose this would be best accomplished with a very short extension lead
with the toroid sensor inbetween. This way, it can be portable too.

Look for the prescence of AC across the fine coil on the toroid. It
basically measures current, the more current, the more voltage across the coil.

Might be a good idea to have a sensitivity adjustment on the trigger too, to
allow for appliances like TVs and VCRs which are always powered on (and thus
draw relatively small currents), but suck more current when they're actually
powered up and running.

Or, for appliances that can vary the amount of power they consume (like
electric heaters) you can have a number of outputs triggered on different
current levels. So you not only know that it was on, but the setting too.

*smacks head* that exactly what i'm looking for, I can't belive I forgot that.
Click to expand...
Thats was the kind of stuff I did in first year. Thanks for the suggestion.
--


Wing Wong.
Webpage: http://wing.ucc.asn.au
Email: wing@tartarus.uwa.edu.au
 
On Thu, 20 May 2004 07:30:13 +0000 (UTC), Wing Fong Wong
<wing@tartarus.uwa.edu.au> wrote:

John Tserkezis <jt@techniciansyndrome.org.invalid> wrote:
Wing Fong Wong wrote:

Is this do able? Can anyone suggest a way I could implement this? Should
I just make multiple sensors? Is there a God out there? All unanswered
questions so far as I'm concerned.

Is this only with mains appliances? If so, current sensing with a toroid is
easy, electrically isolated, has no effect on the equipment it's sensing and
relatively cheap.

Wrap a number of turns of fine wire around a smallish toroid. Pass one of
the mains wires (active or neutral) through the toroid. Don't loop it around,
just straight through (effectively one turn).
I suppose this would be best accomplished with a very short extension lead
with the toroid sensor inbetween. This way, it can be portable too.

Look for the prescence of AC across the fine coil on the toroid. It
basically measures current, the more current, the more voltage across the coil.

Might be a good idea to have a sensitivity adjustment on the trigger too, to
allow for appliances like TVs and VCRs which are always powered on (and thus
draw relatively small currents), but suck more current when they're actually
powered up and running.

Or, for appliances that can vary the amount of power they consume (like
electric heaters) you can have a number of outputs triggered on different
current levels. So you not only know that it was on, but the setting too.

*smacks head* that exactly what i'm looking for, I can't belive I forgot that.
Thats was the kind of stuff I did in first year. Thanks for the suggestion.
Click to expand...
Be aware that the secondary winding (the turns you wind on the toroid) needs to
be terminated in a suitably low value resistor. You have created a current
transformer, and an OC secondary -> an OC primary. This also places a
substantial part of the primary circuit voltage across the primary (1 turn).
Guess what sort of voltage that gives you on the secondary. (Hint: you would
have done this in first year or earlier).

Rather than use an arbitrary value, think about your new current transformer.

Or google CT and burden.
 
"budgie" wrote

Be aware that the secondary winding (the turns you wind on the toroid)
needs to
be terminated in a suitably low value resistor. You have created a
current
transformer, and an OC secondary -> an OC primary. This also places a
substantial part of the primary circuit voltage across the primary (1
turn).
Guess what sort of voltage that gives you on the secondary. (Hint: you
would
have done this in first year or earlier).

Rather than use an arbitrary value, think about your new current
transformer.

Or google CT and burden.

**** Budgie,you're talking Latin to an Eskimo,save your breath!

Brian Goldsmith.
 
Brian Goldsmith <brian.goldsmith@nospamecho1.com.au> wrote:
Rather than use an arbitrary value, think about your new current
transformer.

Or google CT and burden.

**** Budgie,you're talking Latin to an Eskimo,save your breath!

Brian Goldsmith.

True, it does sound a lot like latin to me(or greek, I can't really tell).
Click to expand...
All this does sound vaguely familiar. Haven't done any power units since 2nd
year(I'm mainly comms and microelectronics now). I think it probably best for
me to reread stuff on transformer theory from 2nd year and basically do more
reading. Or else I can just go back to plan A. All this stuff is in my brain
somewhere, I just need to reaquaint myself with them.
--
Wing Wong.
Webpage: http://wing.ucc.asn.au
 
On Thu, 20 May 2004 13:34:00 +0000 (UTC), Wing Fong Wong
<wing@tarDONTtarus.uSPAMwa.eMEdu.au> wrote:

Brian Goldsmith <brian.goldsmith@nospamecho1.com.au> wrote:

Rather than use an arbitrary value, think about your new current
transformer.

Or google CT and burden.

**** Budgie,you're talking Latin to an Eskimo,save your breath!

Brian Goldsmith.

True, it does sound a lot like latin to me(or greek, I can't really tell).
All this does sound vaguely familiar. Haven't done any power units since 2nd
year(I'm mainly comms and microelectronics now). I think it probably best for
me to reread stuff on transformer theory from 2nd year and basically do more
reading. Or else I can just go back to plan A. All this stuff is in my brain
somewhere, I just need to reaquaint myself with them.
Click to expand...
Just go read up on current transformers. That should be eskimo/latin/greek
enough to get you out of jail.
 
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