Q:   There's a lot of info here. It's overwhelming! Where do I start?

A:

  • See Getting Started for an overview of the OEM system.
  • See the articles in Resources for detailed info on hardware,
    schematic diagrams, sketches, and theory of operation.

 

Q:   I'm having trouble with... Can you help me?

A:

  • Search the forums first. Someone else may have had the same issue you're having,
    and the solution might be documented there.
  • Search the web. stackoverflow.com and linuxquestions.org are two examples of sites
    with large collections of answers to many computer related issues.
  • DO NOT write "I'm using the latest... or I followed the guide..." and expect us to know what you are referring to. There are many guides and everything was the latest once upon a time. You must tell us exactly which guide and which download you used.
  • Tell us as much as you can about the problem you're having and the results you are
    expecting. For example: A full list of your hardware, including the version(s),
    and any changes or substitutions you've made.
  • Be as specific as you can. For example: Are you trying to send data to emoncms.org, to
    emoncms on your Raspberry Pi, or to emoncms running on a shared Linux host?
  • The version of the software/sketch you're running.
  • The OS are you running it on. Linux? Unix? Windows? What version of Windows?
  • If possible, attach the relevant log file to your post.
  • If applicable, attach a screenshot to your post. 
  • If you bought items from the OEM Shop, include your order number and purchase date.
    This will help us identify exactly what hardware you are using. 

 

 

Q:   Do I need any special skills, knowledge, tools, etc. to use OEM?

A:

  • While not absolutely necessary, experience with, and/or knowledge of, the following
    subject matter/tools will help a great deal, especially with configuring your system,
    troubleshooting and calibration.
  • Read through the Getting Started Guide to see what's required
  • Linux - modifying scripts, installing software, updating your OS etc.
  • Raspberry Pi hardware and software environment.
  • Arduino hardware and the Arduino programming environment - modifying/uploading sketches.
  • The Python programming language - configuring/troubleshooting emonHub issues.
  • Applicable terminology. e.g. script, sketch, CT, kWh, VA, etc.
  • Electronics in general, soldering, using a multimeter.
  • Basic Radio Frequency theory - calculate antenna length, maximum range, RF obstacles, etc.
  • Serial communication.
  • Networking and/or WiFi.
  • An accurate multimeter.

 

Q:   I want to ask a question about my electricity supply. What information do you need to know?

A:

  • As much as possible! Knowing which country you are in is helpful. Is your supply single phase or three-phase? If it's three-phase, is it 3-wire or 4-wire? What voltage and frequency? What current do you want to measure? e.g. PV production?, house consumption?
  • If you can't find the answers by looking at your electricity meter or your distribution board, posting a good picture of both, and telling us what country you live in, might give us enough information.

 

Q:   Why doesn't my CT work?

  • Why do I read only a few watts when I should read a lot more?
  • Why can't I get a power reading?
  • Why doesn't the reading change when I switch the load on and off?

A:

  • The CT must be clipped around a single current-carrying wire (either Line or Neutral).
  • Ensure the CT is fully closed, i.e. no air gap exists where the core faces meet.
  • Ensure the plug is pushed into its socket completely.
  • See the CT installation guide.

 

Q:   Why are my readings negative when they should be positive? (or vice-versa)

A:

  • Detach the CT from the wire, flip it over and re-attach it to the wire,
  • OR
  • If access to the CT isn't possible, the value can be multiplied by -1, in emoncms.
  • Do one or the other, but not both

 

Q:   Why do I see power readings when the CT is not clipped around a wire?

A:

  • What you're seeing is noise generated by the Arduino electronics, or possibly your USB power supply.
    Unless the value you're seeing is more than a few Watts, it can be ignored.
  • If you search the forums for "noise", you'll find many references to this problem.
  • See Measurement implications of ADC resolution at low current values.

 

Q:   The YHDC CT sold in the shop won't fit my wires. Are CTs with larger openings available?

A:

  • Yes. Magnelab, Wattcore and CCS make CTs that fit AWG 4/0 wire. (~0.63 inches OD)
  • North American users can find additional info here.

 

Q:   I'm trying to calibrate my system with a 60 Watt lamp. Why are my readings wrong?

A:

  • You need to use a resistive load much larger than 60 Watts, e.g. a 2000 Watt heater.
  • Attempting calibration with a motorized load, especially one that draws a substantial amount of current, such as a vacuum cleaner or air conditioner, will not yield correct results.

 

Q:   I calibrated my system with a 2000 Watt heater, but my low power readings are still wrong!

A:

  • All CTs are inherently inaccurate at low currents. Most are accurate down to about 5% of their max current rating. To improve on that, you'd need a "revenue" grade one, which will be costly.
  • When the current is very low, below about 2% of the CT's max current rating, errors in the analog to digital converter start to become significant too.

 

Q:  I can't buy an AC - AC adapter with the correct plug. Will an ordinary transformer work?

A:

  • Yes. You need a low power mains isolation transformer with a 9 V secondary. Don't worry if the output voltage is higher than 9 V, it's normal for this type of transformer to give about 11 V with no load. You'll need to put it in a proper enclosure, and add a fuse (~500 mA) to the primary side circuit. You will also need to calibrate the output. The adapters sold via the Online Store are pre-calibrated for use with emonTx / emonPi. 

 

Q:   Can I use a voltage divider and connect straight to the mains instead of using an A.C. - A.C. adapter? Surely it would be more accurate and cheaper.

A:

  • NO! For safety, you MUST isolate your low voltage circuit from the mains supply. If you don't, it is possible with certain fault conditions, to have lethal voltage where you normally expect a safe 3.3 V or 5 V.

 

Q:   I want to monitor multiple circuits, but the emonTx has only four inputs.

A:

  • Although OEM was designed for whole-house monitoring, multi-circuit monitoring is possible
  • You can use more than one emonTx
  • You can build a custom front-end for an Arduino with multiple analog inputs.
  • More info here and here.

 

Q:   I deleted the mysql database and the emoncms folder, then reinstalled emoncms. I still have the inputs from the previous installation. How do I delete them?

A:

  • Execute the command: sudo redis-cli FLUSHALL

 

Q:   Where can I find the emonCMS installation instructions?

A:

  • The emoncms installation guides are here

 

Q:   Ubuntu Linux gives me this error: The requested URL /emoncms was not found on this server.

 A:   See this forum thread.