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New Propeller based open source energy meter — Parallax Forums

New Propeller based open source energy meter

Jay KickliterJay Kickliter Posts: 446
edited 2011-03-28 15:34 in Propeller 1
My friend just got back from Memphis showing off our student project at the APPA conference there. Since it's out in the open, I figured I'd officially post it here. In a different thread I asked for name suggestions, and am leaning towards MegaJoule, but Frank and I havent had time to discuss a name, so for now it's nameless.

What is it? An energy meter. Meant as wireless equivalent off the Kill A Watt, or for a house's primary energy meter. Read more about it at my website. As I mention on my site, this project is going to be on hold for about four months. My design partner is getting commissioned as a nuclear officer in the Navy, and I have to go to sea for a few months. If anyone wants to work on it while I'm gone, go ahead. I'll give you contributor acces to our google code page.

The funny things is that this started off as just a senior EE side project for us. We designed and built it in one month and didn't expect as good of results as we're getting. At the conference, Frank said several utilities were actually interested in it. Particularly since it can be built so cheap, and they don't have to pay royalties for the design. That might sound like a bad deal for us, but the original contract we had to sign for scholarship had us signing away intellectual property rights for the project. We figured if we can't make money off it, might as well make it open source, so we modified the contract.

If all you want is details, here they are:
* Propeller based of course
* Mesh networkable
* Uses a current transformer for current measurements
* True RMS, so accurate even with non-pure sine waves
* Accounts for power factor using Heater's FFT (his code should help us calculate THD also)
* In it's current configuration, can accurately read currents to about 12 A, with about 10 mA precision
* Open source, so you can make and sell them if you want

Just be careful, it is beta, and some obvious safety precautions are still missing, like on-board fuses for both neutral and hot mains wires. That one bit me in the rear. I hooked up the leads backwards. You're thinking, it's AC, why does that matter? It matters when you hook the ground clip of an oscilloscope probe to the board's ground, which is connected to AC hot, and you blow an entire PCB trace.

So have at it. Just remember you're working with mains voltage.

Comments

  • pgbpsupgbpsu Posts: 460
    edited 2011-03-25 07:50
    Hi Jay-

    Another very cool project. Thanks for sharing both to the forum, so we can see what you're up to, and for making it open source so that others can use it and learn from it. Best of luck to you and your buddy while deployed. Be safe. And thank you both for your service.

    Regards,
    Peter
  • Jay KickliterJay Kickliter Posts: 446
    edited 2011-03-25 09:08
    Hey Peter. Thanks for the compliment. I'm sorry for the lack of documentation on this project. I wanted to wait to post until we had some more to show, but we just don't have the time. Now that we demonstrated this meter we have a month to build an ROV (I'm using a Prop for the brains, of course). Frank's the one to thank for the service; I got out of the Navy in '03 and am a merchant mariner now. That guy is the smarted dude I've ever met (picked up PASM in about 20 minutes), but chose to enlist and is now being commissioned.

    If I find any time to do a write up for this project, I'll post it here. But otherwise this project is going straight to abandon-ware until next Fall. If anyone does want to build one, I'll be around for another month and will clarify any questions.
  • PyrotomPyrotom Posts: 84
    edited 2011-03-25 11:33
    Jay - very cool. Is there a parts list here somewhere? In particular, what is the part info for the current transformer? I live in upstate New York half the year and in rural Jamaica the other half, and like to be able to do remote monitoring of the house I'm not in. I have the temperature monitoring working nicely (by far the most important part), but some energy monitoring would be a great addition!
  • Jay KickliterJay Kickliter Posts: 446
    edited 2011-03-25 11:58
    Pyrotom, the current transformer I'm using now is a CR8420-1000-G from CR Magnetics. However, that's only good to 20 A, so it might be enough for your purposes. Pretty much any transformer will work, but you'll have to adjust the burden resistance. The board as it is has a 200 ohm trimpot configured as a variable burden resistor, set at around 75 ohms to keep the voltage developed below 1 V rms, since the CR8420 datasheet says that's the max to keep readings linear with a max current of 12 A. Read the datasheets of some current transformers that can handle the max current you are likely to see, and they should have an equation to keep everything linear. Unfortunately, it isn't as simple as dropping in a new CT and powering the unit up. There's no reason you can't use a shunt. We only went with transformers as to avoid shunting or having to disconnect wires.

    As for a parts list, I'm attaching a BOM file from DigiKey. It doesn't have part names, sorry. If I can figure out how to use Eagle's BOM function I'll post a proper parts list with part names.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-03-25 12:31
    Jay posted"...I hooked up the leads backwards. You're thinking, it's AC, why does that matter? It matters when you hook the ground clip of an oscilloscope probe to the board's ground, which is connected to AC hot..."

    So that's what it was! Here I was thinking, of course they're running their 'scope from an isolation transformer (or battery powered ScopeMeter".)

    PE -- I had a supervisor insisting that I run the scope across a live ac circuit much as you describe. I stood my ground (!!), refusing, and it went **kapow** when he landed that probe. Everyone but everyone turned around, but I was in the clear. "I'll go get that unneeded isolation transformer - for the others, [name withheld]." In my tool box I still have the TO-3 FET that he blew a hole in the top of.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-03-25 13:14
    For reasons I've never fully understood, the analog grounds of scope input leads are connected to the power cord's ground lead, even though the scope's own power supply is isolated. The ground and "neutral" of an AC outlet are connected together at the breaker box. Even without a separate isolation transformer, this is the kind of thing which, I believe, a GFI outlet would protect against.

    -Phil
  • Heater.Heater. Posts: 21,230
    edited 2011-03-26 06:32
    Jay,

    Well done, that's a neat project and nicely documented as well. I'm a proud to have been able to donate a little software to the cause. I might try to find time to try and put the THD calculations in there.

    Now you've done it. "Her in doors" has no understanding or appreciation of my electronics and programming tinkering at home. But when I showed her your project she immediately perked up a suggested I build one. She has a thing about "green issues" and is always on about all the energy my computers and gadgets are wasting:)
  • Jay KickliterJay Kickliter Posts: 446
    edited 2011-03-28 14:46
    This project is on Hackaday today. I'm surprised at the negative comments it got; at least it wasn't another clock.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-03-28 15:34
    Man, you're playing to a rough crowd over there! And I bet they didn't even pay a cover charge. :) Congrats, nonetheless for making Hackaday!

    -Phil
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