How to ask for help
- Search the forums, 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.
- Tell us as much as you can about the problem you're having and the results you are expecting.
e.g. A full list of your hardware, including the version(s), and any changes or substitutions you've made.
- Be as specific as you can. e.g. 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 OpenEnergyMonitor 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 OpenEnergyMonitor?
- No specific skills are required to set up a basic system, we recommend you read the User Guide before ordering.
Q: I want to ask a question about my electricity supply. What information do you need to know?_
- 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 can't I get a power reading?
- Why is my reading only a few watts when it should read much more?
- Why doesn't the reading change when I switch the load on and off?
- 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.
Q: Why are my readings negative when they should be positive? (or vice-versa)
- Detach the CT from the wire, flip it over and re-attach it to the wire
- If access to the CT isn't possible, the value can be multiplied by -1, in emoncms input processing.
Q: Why do I see power readings when the CT is not clipped around a wire?
- 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. Click here for more info.
Q: The YHDC CT sold in the shop won't fit my wires. Are CTs with larger openings available?
- Yes. Magnelab, Wattcore and CCS make CTs that fit AWG 4/0 wire. (~0.63 inches OD)
- The main concern here is to be sure the CT you choose is either:
Unburdened OR has an output of 1 Volt. i.e. don't select a CT with a 0.333 Volt output.
Q: I'm trying to calibrate my system with a 60 Watt lamp. Why are my readings wrong?
- 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.
- See relevant Learn section
Q: I calibrated my system with a 2000 Watt heater, but my low power readings are still wrong!
- 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.
- See relevant Learn section
Q: I can't buy an AC - AC adapter with the correct plug. Will an ordinary transformer work?
- Yes. You'll need a low power mains isolation transformer with a 9 V secondary. Don't worry if the output voltage is higher than 9 Volts. It's normal for this type of transformer to give about 11 Volts 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'll 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 AC-AC adapter?
NO. For safety, it's important to 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 or 5 Volts.
Q: I want to monitor multiple circuits, but the emonTx has only four inputs.
- Although OpenEnergyMonitor was designed for whole-house monitoring, multi-circuit monitoring is possible.
- You can use more than one emonTx, see emonTx V3 setup
- You can build a custom front-end for an Arduino with multiple analog inputs.
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?
- Execute the command: sudo redis-cli FLUSHALL
Q: Entries under the size heading on my feeds page read n/a
- Try refreshing the feed size. Click the button at the bottom left of your feeds page.
Q: Where is my data stored? I cannot see the mySQL tables
- The default data engines for emoncms are phpfina and phptimeseries, these feed types can be found in their respective data directories, at the location defined in your
- The default location is
Q: My emonPi data partition is full. There is some free space on my disk drive / SD card. How do I expand the data partition?
- Before you proceed, a data backup is highly recommended
- See this post. If you're using a hard disk drive, i.e. not flash media, substitute your drive's device name e.g.
/dev/sda in place of