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AC current sensor research — Parallax Forums

AC current sensor research

Timothy D. SwieterTimothy D. Swieter Posts: 1,613
edited 2009-06-25 00:26 in General Discussion
I am cooking up some "green" ideas that involve monitoring current. Soon I will be moving to a new home and I thought a little home project of monitoring my electricity would be fun. While out and about I saw the Wattson device (www.diykyoto.com) in a store which inspiring me. I am thinking of making a system with a similar architecture and the part I am researching now is the current sensor/amp clamp portion. I could probably just buy an amp clamp from the company that makes the Wattson, but I thought I would ask around and see what other advice other users might have. The Wattson probe is here: shop.diykyoto.com/products/clip-for-2-or-3phase-system

The amp clamp should probably be a clamp so it can easily be added to the house wiring without removing and replacing any conductors. I know there were some other IC for measuring current, but I think those ICs required that the power be passed through the IC which would mean lifting a conductor or doing wiring. Maybe those ICs could be used to read the current probe/amp clamp.

My overall system will probably use a Propeller as the base microcontroller. I will probably have to build some interface circuitry to the amp clamp, which is fine.

So, any thought on sources for amp clamps like the Wattson version? Any other recommendation on best how to measure the AC current into the home? Any ideas on the interface circuitry?

Thank you.

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com

Comments

  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-03-29 15:40
    This overall concept is a great idea. I once got an electric bill that was 4x my normal bill because a repair man hooked up my heat pump so it would run its 10 Kw heater while also running its cooling system at the same time. What would be a great feature is an alert capability that would notify the owner if the current consumption goes above a specified level or exceeds some kind of average (for both short periods of observation and long). Also, I suspect, it's not the really big power guzzlers that will waste as much energy as all those little current leaks that are not immediately obvious. Over time, though, the small leakers can cost a fortune. So if the device can have the ability to measure very small currents so people can shut down their appliances and still get a reading, that might be useful in tracking down leak paths or faulty appliances.

    Good luck!


    smile.gif
  • SteveWSteveW Posts: 246
    edited 2009-03-29 16:05
    Energy meters (in the UK, at least), if they're even remotely modern, have a LED that ticks to indicate a set unit of energy. Mine says "1000 imp/KWh".
    Watching that, if possible, should be cheap, safe, accurate, and all sorts of good things.

    Of course, if that's not an option, the clamp widget, plus a lot of fast sampling and maths are heading your way.
    Bear in mind that, if you care about accuracy, you'll need to measure the voltage as well as the current. You can't simply assume the power is a nice sine wave, it'll undoubtedly be clipped, for a start.
    (measuring the voltage at the output of a step-down isolated transformer should be fine, just be wary of the phase shift across it)

    Steve
  • FranklinFranklin Posts: 4,747
    edited 2009-03-29 20:31
    Found this www.kondra.com/circuit/circuit.html might help.

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  • Brian CarpenterBrian Carpenter Posts: 728
    edited 2009-03-29 23:11
    It is not what you are asking for. (it is not a clamp) but ti works very well and will run at 3.3 volts for the prop. www.AMPLOC.com

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    It's Only A Stupid Question If You Have Not Googled It First!!
  • PhilldapillPhilldapill Posts: 1,283
    edited 2009-03-29 23:28
    My dad recently replaced his pool pump and he said the new one was pulling too much current - not ALOT, but 20% more than it should. It got me thinking about making my own power meter. What I had imagined doing, was this:

    Use a voltage divider to measure the 120V voltage. Use a Hall-effect sensor and measure the current. Write a program that would hunt for the "peaks" of voltage and peaks of current, record the values, and record the times between each. From these, it would be easy to calculate power AND phase angles.
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-03-30 00:01
    Thank you guys for all the feedback and encouragement.

    I like to dream that if my little home experiment goes well that I could build an open source design and kit so that others could use it. My specialty would be more in the overall system concept and the embedded design. My short coming is in the tracking or logging software on the PC or web. This project probably won't be heavily "staffed" for a few weeks, so right now I am researching. I think I will want to get some hardware working by middle of June or so.

    @Franklin - that is a great link. I am reading through that now, thank you.

    @Brian Carpenter - I have seen this device mentioned in other threads. From what I can see I have to run the wire through the device because I am not able to put the device around the wire, true? In other words it isn't a split ring for clamping around the wire? I like that this device looks easy to use and I saw it mentioned in other threads on the forum.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • icepuckicepuck Posts: 466
    edited 2009-03-30 00:34
    Here's something worth reading...
    http://www.google.org/powermeter/smarterpower.html
    -dan
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-03-30 00:52
    I have been subscribed to the Google Power project for some time. I think it looks exciting. There are some very clear trends to making the power grid "smarter" so that is one reason why I am interested in building my own power meter tracking system for my home/apartment.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-03-30 19:57
    Yup, the power companies are looking towards 'smart' networks. It's been a while since Iive seen one, but in the US, mini Watthour meters ( ~ for 100 to 300 amp service ) have a couple of leads that wrap around each leg of the the 220 vac --- I think they looked something like the KYOTO you linked to above. I bet you could feed that coil's output into an op amp set for current sensing, and use a zero crossing detector for timing. Stick a known load on it and then tweek until you get uAmps x (fudge factor) x 120hz x ( how-many 120 cycles are in 1 Hour) = Watt Hour. (Or am I nuts?)

    This is an interesting to me too - I have a bunch of computers networked together, but never really know how much juice they drink. Afterall, a PC's power supply, at 350 Watts say, is it's optimum max rating (I assume), but it probably doesn't pull that much unless the CPU is maxed and all the bays are full of whirring drives. So, if I add say ten PC's to the net, how much will my bill go up? It would be nice to know ahead of time for budgeting.

    Keep in mind too that it would be cool for your device to account for 'reverse metering' for those of us futurists who would eventually like to have solar panels on the roof and generate a bumper crop of electrons!

    cheers
    - Howard in Florida

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  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-03-30 23:18
    Good thoughts Howard, I like the idea that it should work in both directions.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-03-30 23:41
    Was curious to see what's Watt [noparse]:)[/noparse] in the US:

    http://www.weemscreeksolutions.com/energyconservationpowermonitors.htm?gclid=CNrippPqy5kCFRUhnAodEg8PuA

    - H

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    Buzz Whirr Click Repeat
  • parskoparsko Posts: 501
    edited 2009-04-03 17:34
    Tim,

    I just came across these guys (I was looking at PTC's) and immediately thought of this thread. Not sure if any of these current sensors would work, but I think they would. Have a look. I'm in the process of buying a house also, and I will need to upgrade to 200amp service. This would be a good time to implement these!

    www.amecon-magnetics.com/
    www.amecon-magnetics.com/pdf/5300%20series.pdf
    www.amecon-magnetics.com/pdf/5304.pdf
    www.rtie.com/

    I'm curious of the experts would think this would work. Seems like a good fit. No clue on prices though.

    -Parsko
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-04-03 23:30
    Thank you Parsko, those look like another option too. If you buying a new house and need to upgrade the electrical service then for sure over size the breaker box to fit a few more components in it. It would great to get the box ready for a system that you can add in as you want to. In my case I am moving to a condo/apartment in Singapore so I will have to jack into the breaker box and work with the space that is there.

    I have thought a lot about this idea, but haven't gotten into details. I have mostly been thinking about the system level and the larger pieces before getting back into the specific parts. I am looking forward to building this project when the time is right.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-04-05 22:25
    Tim there are numerous CT's(current transducers) available with 0 - 5v output .. just add an ADC and a Prop !

    e.g.

    http://veris.com/file_uploads/h722lc_i0a2.pdf

    Regards,
    John

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    'Necessity is the mother of invention'

    Those who can, do.Those who can’t, teach.
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-04-05 23:46
    Thanks John.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-04-18 02:27
    I think I found a source for a clamp on current clamps like what is used in the Wattson device. The current clamps I found are either red or blue and there are different products for different max current ratings. The products I am considering look to be voltage output although there is one that is a current output. I attached a spec sheet from the Chinese manufacturer. There is a minimum order quantity, the price is reasonable, so I am thinking I can sell them through Brilldea for others that are interested.

    So, the plan would be...
    -use a voltage version of the current transformer
    -use an ADC (any recommendations, I see other threads I should search through)
    -use a Propeller

    I will probably create a simple PCB that has a Propeller, a couple connection points for the current clamps and maybe a socket for a WIZnet Ethernet module. What do you think?

    What current rating clamps should I buy? In the USA I know branch circuits are usually 15amp or 20amp. I am not sure about Singapore (where I am moving to and where my little project would be in installed). I also want to stock clamps that are rated for the incoming power.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
    pdf
    pdf
    SCT-013 reduced.pdf
    2M
  • CapdiamontCapdiamont Posts: 218
    edited 2009-04-19 15:11
    Some power meters have a coil that energizes every kw. You can use a hall effect sensor to sense this.
  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-04-23 21:48
    Tim,
    ···· I threw a quick demo together .. Uses 722LC Hawkeye CT - 0-5v output (self powered). These have range settable 10A, 20A and 40A. I used an LTC1298CN8 ADC .. and a prop..

    see attached images (low res. - sorry - from phone).and a small vid.

    Demo shows a dual heating element - second one switched in and out.
    Doh - spot the typo in the vid 'curremt' as opposed to 'current'

    Rgds,
    ······ John

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    'Necessity is the mother of invention'

    Those who can, do.Those who can’t, teach.

    Post Edited (QuattroRS4) : 4/24/2009 12:04:31 AM GMT
    avi
    avi
    Quick_Vid.avi
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    722LC Hawkeye.jpg
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    easyprop_to_ADC.jpg
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  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-04-30 10:10
    John - Thank you!! Very nice to have an example here to be able to work from and duplicate. What development board are you using in that second picture? Is that board one of your creations?

    I will be getting some current transformers from my Chinese source. I probably won't make much progress on this project until the June time frame though. So much going on until then and it is still April! Once I get the current transformers I will offer them through Brilldea so that we can collaborate together on a current measuring project or two.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-04-30 10:22
    Timothy,
    Sounds good ! The Dev board I am using there is an EasyProp .. made by a friend Franz Achatz .. It is pretty damn cool. Can be powered via USB directly (great when travelling ... just connect usb programming connection to laptop !) or via separate power supply ... Has onboard enc28j60 ethernet,SDcard slot,Keyboard,Mouse,Composite,Vga,Audio, Xbee Header .. can be programmed via usb (has onboard FTDI) or prop plug.Has a nice SIL i/o header .. and is a very compact size ..100mmx80mm.

    See it here ..

    www.igniteautomation.com/easyprop.html


    Regards,
    John Twomey

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    'Necessity is the mother of invention'

    Those who can, do.Those who can’t, teach.
  • PhilldapillPhilldapill Posts: 1,283
    edited 2009-04-30 16:14
    Timothy, put me down for a couple of those CT's when you get them! My Hall-Effect sensors work GREAT, but I can see having to disconnect, then re-connect a load in series(to get a measurement), is going to be a big hassle. Having a unit that I can just clamp around the existing wire, will be super nice.
  • Zap-oZap-o Posts: 452
    edited 2009-04-30 16:31
    Timothy D. Swieter

    Not sure it its been mentioned above my reply, but:

    I ran the propeller(via USB) into my home computer (it ran 24 hours a day) that ran a program (made it in Visual basic). That program sent text files up to my website (via FTP) where I can view from the web.

    What your asking is not difficult by any means. Video, text, sound all can be done.
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-06-20 02:22
    A quick update on this thread. I have purchased a handful of the clamp on current transformers that I posted the data sheet for. I have 20 amp version, a 60-amp version and then all the 100 amp version. Note that the 100 amp version varies from the 60 and 20 amp version.

    I haven't had a chance to try this current devices out just yet. But, I thought maybe a little encouragement and peer pressure from the forum would get me going again.

    I am looking at the AMPLOC again (because I think the CTs I bought are too big for my breaker box), has anyone used them in detail? With some current transformer you have to loop the wire around the CT. With the AMPLOC you just pass the wire through, correct? I wish they offered a split core type of style to make it easier to install in exist location where you wouldn't want to disconnect the AC.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-06-20 02:41
    Tim,
    The loop you speak of is usually only employed when measuring low currents < 1 Amp .. A lot of the CT manufacturers specify a loop in these scenarios.

    Regards,
    John

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    'Necessity is the mother of invention'

    Those who can, do.Those who can’t, teach.
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-06-23 17:16
    @Tim: where did you post the clamp-on data sheet ? I couldn't find it on your sites.

    @John: thanks for posting the link back in April to the easyprop --- odd that I missed seeing that great looking board before.

    thanks,
    - Howard

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  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-06-24 08:39
    Howard - the data sheet was attached to a post I made on April 18. Very easy to miss those attachments (I just tried reattaching the file here but I keep getting an error). I haven't had a chance to update Brilldea's site with a product page yet, but that will happen in a week or so (or maybe this weekend). You can PM if you are interested in purchasing any products. I have the 100A, 60A, and 20A versions but haven't employed them yet.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-06-25 00:05
    Timothy D. Swieter said...
    Howard - the data sheet was attached to a post I made on April 18. Very easy to miss those attachments
    DOH !· think I need to put a damper on my scroll wheel ;-)· OK cool, I'll study the specs and get back to you in c.a. a week. - thanks - Howard

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  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-06-25 00:12
    Howard,
    No Problem - Yip the EasyProp is pretty cool .. Can be USB Powered, SD Card, Enc28j60, KB, Mouse, TV,VGA, Xbee slot nice SIL access to I/O's

    Rgds,
    John

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    'Necessity is the mother of invention'

    'Those who can, do.Those who can’t, teach.'
    'Convince a man against his will, he's of the same opinion still.'

    ·
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-06-25 00:26
    John, yeah, that things pretty impressive --- seems like its only missing the washer/dryer combo and coffee maker [noparse]:)[/noparse])

    I've just started looking at Xbee recently ... is using it and the ether/Enc28j60 on there draw too much for using USB power only?

    thanks
    - Howard

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