How can I measure AC current?
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Posts: 46,084
To the group,
I just joined and am surprised at the quantity of e-mail. I'm also
surprised at the quality (it seems that people get educated answers very
quickly!).
My application is in home control and monitoring.
I want to monitor power usage in appliances. I would like some kind up
inductive sensing of the current used by an appliance (as apposed to a
direct connection to the 120/220v AC).
Thanks,
Randy
I just joined and am surprised at the quantity of e-mail. I'm also
surprised at the quality (it seems that people get educated answers very
quickly!).
My application is in home control and monitoring.
I want to monitor power usage in appliances. I would like some kind up
inductive sensing of the current used by an appliance (as apposed to a
direct connection to the 120/220v AC).
Thanks,
Randy
Comments
> Message: 22
> Date: Fri, 09 Aug 2002 08:50:39 -0700
> From: Randy Saxton <Randy@i...>
> Subject: How can I measure AC current?
>
> To the group,
>
> I just joined and am surprised at the quantity of e-mail. I'm also
> surprised at the quality (it seems that people get educated answers very
> quickly!).
>
> My application is in home control and monitoring.
>
> I want to monitor power usage in appliances. I would like some kind up
> inductive sensing of the current used by an appliance (as apposed to a
> direct connection to the 120/220v AC).
Depending on how much money you want to spend and how much current you want
to measure, you could always go with a LEM module with all the goodies to
take the AC and make it a proportional DC signal. That signal could then be
piped into a DAC and into the stamp. Digikey carries some of the LEM product
line and I have used these gadgets in industrial designs with a lot of
success. The only provisos I can see are:
a. price
b. some LEM's require a split power supply (e.g. +/-15VDC)
Let me know if you need any further information.
Regards,
Gerry Shand
res@i...
Here is a quick, dirty and cheap method I used on DC loads, don't know how
well it would work with AC. I took a Hall sensor and taped it to the wire in
question, used an op amp to amplify it and read the output voltage. Using a
regular current meter I calibrated it. Works well, but has a couple of
limitations. The current range is limited before the Hall sensor saturates,
so for heavier draws the sensor must be placed further from the current
source. It is susceptible to other EMF, so might be problematic in noisy
environments. It certainly isn't the "big kid" way to do it. On the other
hand it is dirt CHEAP, a big plus for me. Just thought I'd throw it out
there, it does work.
Regards,
Jonathan Peakall
Original Message
From: Gerry Shand/Corrinne Bergen <res@c...>
To: <basicstamps@yahoogroups.com>
Sent: Friday, August 09, 2002 1:17 PM
Subject: [noparse][[/noparse]basicstamps] Re: How can I measure AC current?
> Sez Randy:
>
> > Message: 22
> > Date: Fri, 09 Aug 2002 08:50:39 -0700
> > From: Randy Saxton <Randy@i...>
> > Subject: How can I measure AC current?
> >
> > To the group,
> >
> > I just joined and am surprised at the quantity of e-mail. I'm also
> > surprised at the quality (it seems that people get educated answers very
> > quickly!).
> >
> > My application is in home control and monitoring.
> >
> > I want to monitor power usage in appliances. I would like some kind up
> > inductive sensing of the current used by an appliance (as apposed to a
> > direct connection to the 120/220v AC).
>
> Depending on how much money you want to spend and how much current you
want
> to measure, you could always go with a LEM module with all the goodies to
> take the AC and make it a proportional DC signal. That signal could then
be
> piped into a DAC and into the stamp. Digikey carries some of the LEM
product
> line and I have used these gadgets in industrial designs with a lot of
> success. The only provisos I can see are:
>
> a. price
> b. some LEM's require a split power supply (e.g. +/-15VDC)
>
> Let me know if you need any further information.
>
> Regards,
>
> Gerry Shand
> res@i...
>
>
>
> To UNSUBSCRIBE, just send mail to:
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Body of the message will be ignored.
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>
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>
>
>
>
>
Original Message
> From: Randy Saxton [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=5HRiliX0IH94BA3I7zPXlgIoxdV6H7hSPqoGGi20mVSTvZKqDsdyXy-Y9vWdPN7_6XTYxcBUKWA]Randy@i...[/url
> Sent: Friday, August 09, 2002 10:51 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] How can I measure AC current?
>
<snip
> My application is in home control and monitoring.
>
> I want to monitor power usage in appliances. I would like
> some kind up
> inductive sensing of the current used by an appliance (as
> apposed to a
> direct connection to the 120/220v AC).
>
Here is an idea, if you just need a rough idea of the current and if you
know the approx. value of the current before you start. Take a ferrite
ring core (Digikey has them), pass one leg of your AC line through the
center, and wind a secondary around the ring, passing the secondary wire
through the center and spiraling it around the ring. Now you have a
current transformer. It will have a small AC signal out the secondary
wires. I have one if these with an LED across the secondary that will
light when my well pump is running (well pump is in an out building).
The number of secondary turns can be varied to change the output. Also,
if the signal is too low, you can wrap the primary wire around one side
of the ring a time or two, to increase the induced field. You can
saturate the ring, if the current is too high, but that had not been a
problem with my experience. I am only a beginner with the Stamp, so I
am not sure how to best interface this with the Stamp. By rectifying it
and putting a load on it, you might be able to make a one or a zero out
of the output. I helped my son with a science fair project where we
wound two transformers with different secondary turn counts. We had a
60 and 100 watt light bulbs connected with separate switches. The
transformers were both on the main AC line. The transformer with the
fewer secondary turns would only light an LED when the 100 watt bulb was
on (meaning we expected the 60 watt load to be there and we did not want
to detect it). The second LED would light when both the 60 and 100 watt
lights were on. In effect we made a window detector (if I can call it
that). Maybe with a zener diode and a transistor you could clean up the
DC to get a clean 1 or 0.
Dan Thames
> Thanks,
> Randy
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in
> the Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
bridge rectifier.
If you put a bridge rectifier in series with the load you can use a DC
ammmeter at the DC connect points in the bridge.
--- In basicstamps@y..., Randy Saxton <Randy@i...> wrote:
> To the group,
>
> I just joined and am surprised at the quantity of e-mail. I'm also
> surprised at the quality (it seems that people get educated answers
very
> quickly!).
>
> My application is in home control and monitoring.
>
> I want to monitor power usage in appliances. I would like some kind
up
> inductive sensing of the current used by an appliance (as apposed to
a
> direct connection to the 120/220v AC).
>
> Thanks,
> Randy
Thank you for the suggestion. However, (here's where I start to feel
really dumb) I tried that and it yielded no voltage!
I took a red (I don't know if they are color coded) .8" (approx.)
ferrite/toroid ring, ran one leg of the AC through it, wrapped 31 wraps
of 24 gauge aluminum wire through it. I even used a scope to check the
output so I didn't load it down with my DVM, but nothing!
This can't be this difficult. Does the type of secondary wire make a
difference?
Any ideas would be greatly appreciated...
Randy
Dan Thames wrote:
>
> Randy,
>
> >
Original Message
> > From: Randy Saxton [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=H6meCJAlgSdYA1RFXDOySxRo7gGk8h1v-TIHwi0d_vWSwr2b6PpcJnQsr650p2b-DdyQ5wX1]Randy@i...[/url
> > Sent: Friday, August 09, 2002 10:51 AM
> > To: basicstamps@yahoogroups.com
> > Subject: [noparse][[/noparse]basicstamps] How can I measure AC current?
> >
> <snip
> > My application is in home control and monitoring.
> >
> > I want to monitor power usage in appliances. I would like
> > some kind up
> > inductive sensing of the current used by an appliance (as
> > apposed to a
> > direct connection to the 120/220v AC).
> >
> Here is an idea, if you just need a rough idea of the current and if you
> know the approx. value of the current before you start. Take a ferrite
> ring core (Digikey has them), pass one leg of your AC line through the
> center, and wind a secondary around the ring, passing the secondary wire
> through the center and spiraling it around the ring. Now you have a
> current transformer. It will have a small AC signal out the secondary
> wires. I have one if these with an LED across the secondary that will
> light when my well pump is running (well pump is in an out building).
> The number of secondary turns can be varied to change the output. Also,
> if the signal is too low, you can wrap the primary wire around one side
> of the ring a time or two, to increase the induced field. You can
> saturate the ring, if the current is too high, but that had not been a
> problem with my experience. I am only a beginner with the Stamp, so I
> am not sure how to best interface this with the Stamp. By rectifying it
> and putting a load on it, you might be able to make a one or a zero out
> of the output. I helped my son with a science fair project where we
> wound two transformers with different secondary turn counts. We had a
> 60 and 100 watt light bulbs connected with separate switches. The
> transformers were both on the main AC line. The transformer with the
> fewer secondary turns would only light an LED when the 100 watt bulb was
> on (meaning we expected the 60 watt load to be there and we did not want
> to detect it). The second LED would light when both the 60 and 100 watt
> lights were on. In effect we made a window detector (if I can call it
> that). Maybe with a zener diode and a transistor you could clean up the
> DC to get a clean 1 or 0.
>
> Dan Thames
>
> > Thanks,
> > Randy
wire shielded with enamel. Available at rat-shack. If you used
unshielded alum wire you esentially shorted all of the turns. Alum
wire sucks as a conductor. Use copper magnet wire 24 to 30 ga. If
your core was red with a white face that is a mu metal core used for
torroidal power inductors. Low loss core. You will need a couple of
hundred turns tightly wound to pick up anything. I have made my own
and it isn't fun.
MagneTek makes current sense transformers. Much easier to open up the
box and solder it in.
Jason
--- In basicstamps@y..., Randy Saxton <Randy@i...> wrote:
> Dan,
>
> Thank you for the suggestion. However, (here's where I start to
feel
> really dumb) I tried that and it yielded no voltage!
>
> I took a red (I don't know if they are color coded) .8" (approx.)
> ferrite/toroid ring, ran one leg of the AC through it, wrapped 31
wraps
> of 24 gauge aluminum wire through it. I even used a scope to check
the
> output so I didn't load it down with my DVM, but nothing!
>
> This can't be this difficult. Does the type of secondary wire make
a
> difference?
>
> Any ideas would be greatly appreciated...
>
> Randy
>
>
> Dan Thames wrote:
> >
> > Randy,
> >
> > >
Original Message
> > > From: Randy Saxton [noparse][[/noparse]mailto:Randy@i...]
> > > Sent: Friday, August 09, 2002 10:51 AM
> > > To: basicstamps@y...
> > > Subject: [noparse][[/noparse]basicstamps] How can I measure AC current?
> > >
> > <snip
> > > My application is in home control and monitoring.
> > >
> > > I want to monitor power usage in appliances. I would like
> > > some kind up
> > > inductive sensing of the current used by an appliance (as
> > > apposed to a
> > > direct connection to the 120/220v AC).
> > >
> > Here is an idea, if you just need a rough idea of the current and
if you
> > know the approx. value of the current before you start. Take a
ferrite
> > ring core (Digikey has them), pass one leg of your AC line
through the
> > center, and wind a secondary around the ring, passing the
secondary wire
> > through the center and spiraling it around the ring. Now you
have a
> > current transformer. It will have a small AC signal out the
secondary
> > wires. I have one if these with an LED across the secondary that
will
> > light when my well pump is running (well pump is in an out
building).
> > The number of secondary turns can be varied to change the
output. Also,
> > if the signal is too low, you can wrap the primary wire around
one side
> > of the ring a time or two, to increase the induced field. You can
> > saturate the ring, if the current is too high, but that had not
been a
> > problem with my experience. I am only a beginner with the Stamp,
so I
> > am not sure how to best interface this with the Stamp. By
rectifying it
> > and putting a load on it, you might be able to make a one or a
zero out
> > of the output. I helped my son with a science fair project where
we
> > wound two transformers with different secondary turn counts. We
had a
> > 60 and 100 watt light bulbs connected with separate switches. The
> > transformers were both on the main AC line. The transformer with
the
> > fewer secondary turns would only light an LED when the 100 watt
bulb was
> > on (meaning we expected the 60 watt load to be there and we did
not want
> > to detect it). The second LED would light when both the 60 and
100 watt
> > lights were on. In effect we made a window detector (if I can
call it
> > that). Maybe with a zener diode and a transistor you could clean
up the
> > DC to get a clean 1 or 0.
> >
> > Dan Thames
> >
> > > Thanks,
> > > Randy
Original Message
> From: Randy Saxton [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=o9rFoIkfcQ2yoJdeJNKkXc4oL1giYjOOXp-ul-yE-X9VTnHBmlXgjqM_MrUnzMEE7U6PJAEu2Q]Randy@i...[/url
> Sent: Tuesday, August 13, 2002 12:21 AM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] How can I measure AC current?
>
> Dan,
>
> Thank you for the suggestion. However, (here's where I
> start to feel
> really dumb) I tried that and it yielded no voltage!
>
> I took a red (I don't know if they are color coded) .8"
> (approx.)
> ferrite/toroid ring, ran one leg of the AC through it,
> wrapped 31 wraps
> of 24 gauge aluminum wire through it. I even used a scope
> to check the
> output so I didn't load it down with my DVM, but nothing!
>
> This can't be this difficult. Does the type of secondary
> wire make a
> difference?
It must be insulated. Fine magnet wire is best. Magnet wire is coated
with a thin varnish and it the type used in electric motors. You can
get a small spool at Radio Shack, I think. You may need something like
100 turns, not 30. It all depends on the current in the primary. You
might loop the primary around a time or two. Also, make sure you are
testing with something that uses some real power. Something like a
clock would not pull many amps but a hair dryer would.
Dan Thames
>
> Any ideas would be greatly appreciated...
>
> Randy
>
>
> Dan Thames wrote:
> >
> > Randy,
> >
> > >
Original Message
> > > From: Randy Saxton [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=o9rFoIkfcQ2yoJdeJNKkXc4oL1giYjOOXp-ul-yE-X9VTnHBmlXgjqM_MrUnzMEE7U6PJAEu2Q]Randy@i...[/url
> > > Sent: Friday, August 09, 2002 10:51 AM
> > > To: basicstamps@yahoogroups.com
> > > Subject: [noparse][[/noparse]basicstamps] How can I measure AC current?
> > >
> > <snip
> > > My application is in home control and monitoring.
> > >
> > > I want to monitor power usage in appliances. I would
> like
> > > some kind up
> > > inductive sensing of the current used by an appliance
> (as
> > > apposed to a
> > > direct connection to the 120/220v AC).
> > >
> > Here is an idea, if you just need a rough idea of the
> current and if you
> > know the approx. value of the current before you start.
> Take a ferrite
> > ring core (Digikey has them), pass one leg of your AC
> line through the
> > center, and wind a secondary around the ring, passing
> the secondary wire
> > through the center and spiraling it around the ring.
> Now you have a
> > current transformer. It will have a small AC signal out
> the secondary
> > wires. I have one if these with an LED across the
> secondary that will
> > light when my well pump is running (well pump is in an
> out building).
> > The number of secondary turns can be varied to change
> the output. Also,
> > if the signal is too low, you can wrap the primary wire
> around one side
> > of the ring a time or two, to increase the induced
> field. You can
> > saturate the ring, if the current is too high, but that
> had not been a
> > problem with my experience. I am only a beginner with
> the Stamp, so I
> > am not sure how to best interface this with the Stamp.
> By rectifying it
> > and putting a load on it, you might be able to make a
> one or a zero out
> > of the output. I helped my son with a science fair
> project where we
> > wound two transformers with different secondary turn
> counts. We had a
> > 60 and 100 watt light bulbs connected with separate
> switches. The
> > transformers were both on the main AC line. The
> transformer with the
> > fewer secondary turns would only light an LED when the
> 100 watt bulb was
> > on (meaning we expected the 60 watt load to be there and
> we did not want
> > to detect it). The second LED would light when both the
> 60 and 100 watt
> > lights were on. In effect we made a window detector (if
> I can call it
> > that). Maybe with a zener diode and a transistor you
> could clean up the
> > DC to get a clean 1 or 0.
> >
> > Dan Thames
> >
> > > Thanks,
> > > Randy
>
> To UNSUBSCRIBE, just send mail to:
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> the Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
Leroy
Randy Saxton wrote:
>
> Dan,
>
> Thank you for the suggestion. However, (here's where I start to feel
> really dumb) I tried that and it yielded no voltage!
>
> I took a red (I don't know if they are color coded) .8" (approx.)
> ferrite/toroid ring, ran one leg of the AC through it, wrapped 31 wraps
> of 24 gauge aluminum wire through it. I even used a scope to check the
> output so I didn't load it down with my DVM, but nothing!
>
> This can't be this difficult. Does the type of secondary wire make a
> difference?
>
> Any ideas would be greatly appreciated...
>
> Randy
>
> Dan Thames wrote:
> >
> > Randy,
> >
> > >
Original Message
> > > From: Randy Saxton [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=inh5AEMcSxl4JUr3v4ufX0JuTFiyQ3VjKzEqdz9xWbsorr3Xok8fKCawyPSue7InNTIDaGc]Randy@i...[/url
> > > Sent: Friday, August 09, 2002 10:51 AM
> > > To: basicstamps@yahoogroups.com
> > > Subject: [noparse][[/noparse]basicstamps] How can I measure AC current?
> > >
> > <snip
> > > My application is in home control and monitoring.
> > >
> > > I want to monitor power usage in appliances. I would like
> > > some kind up
> > > inductive sensing of the current used by an appliance (as
> > > apposed to a
> > > direct connection to the 120/220v AC).
> > >
> > Here is an idea, if you just need a rough idea of the current and if you
> > know the approx. value of the current before you start. Take a ferrite
> > ring core (Digikey has them), pass one leg of your AC line through the
> > center, and wind a secondary around the ring, passing the secondary wire
> > through the center and spiraling it around the ring. Now you have a
> > current transformer. It will have a small AC signal out the secondary
> > wires. I have one if these with an LED across the secondary that will
> > light when my well pump is running (well pump is in an out building).
> > The number of secondary turns can be varied to change the output. Also,
> > if the signal is too low, you can wrap the primary wire around one side
> > of the ring a time or two, to increase the induced field. You can
> > saturate the ring, if the current is too high, but that had not been a
> > problem with my experience. I am only a beginner with the Stamp, so I
> > am not sure how to best interface this with the Stamp. By rectifying it
> > and putting a load on it, you might be able to make a one or a zero out
> > of the output. I helped my son with a science fair project where we
> > wound two transformers with different secondary turn counts. We had a
> > 60 and 100 watt light bulbs connected with separate switches. The
> > transformers were both on the main AC line. The transformer with the
> > fewer secondary turns would only light an LED when the 100 watt bulb was
> > on (meaning we expected the 60 watt load to be there and we did not want
> > to detect it). The second LED would light when both the 60 and 100 watt
> > lights were on. In effect we made a window detector (if I can call it
> > that). Maybe with a zener diode and a transistor you could clean up the
> > DC to get a clean 1 or 0.
> >
> > Dan Thames
> >
> > > Thanks,
> > > Randy
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/