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Beginner's Questions about OEM


(Rowan Sylvester-Bradley) #1

I am looking at the options for installing an energy monitor system for my home. I am trying to understand whether Open Energy Monitor (which I have only just discovered, and therefore know very little about) will do what I want, and have the following questions:

  1. Why do you offer both clamp-on current transformers, and sensing the flashing LED on the meter? At first sight these seem to be doing pretty much the same thing. Is there any benefit to having both of these? If they are alternatives, what are the pros and cons of each?
  2. If I am going to use the LED sensor, then the meter for my Solar PV is quite a long way from my main meter (in my detached garage). What is the best way of integrating these? Can I fit an ESP8266 with an LED sensor, and use WiFi to communicate back to the house? What software would I use for this?
  3. What is the best way of monitoring (oil) boiler run time?
  4. I would like to monitor the level of oil in my oil tank, which is fitted with an Apollo oil level meter. Has anyone integrated this into Open Energy Monitor?
  5. Can I install emoncms on my web server, which is a shared Linux/Apache server to which I do not have command line access (except that I can run CRON jobs)? Or do I need a server that I have full access to?
  6. I have a Power-One (taken over by ABB in 2013) Aurora Solar PV inverter. This seems to have an RS485 port that gives information about the operation of the inverter. Has anyone interfaced this to Open Energy Monitor? This would (I think) be better than just measuring the AC output power, because I could then monitor the outputs of the two individual strings of PV panels.
  7. How many DS18B20 temperature sensors can I monitor? Are they just connected using OneWire (with which I am reasonably familiar)?
  8. Can I use ANY clip-on current transformer, with any current range? E.g. can I use a 60A CT for the mains input to my house, and a 20A CT for the output from my solar PV?

Many thanks - Rowan


(Robert Wall) #2

Welcome, Rowan.

To answer the ones I can, and I’ll leave the rest for experts in those areas:

1 - It’s your choice. When you export energy, many if not most meters do not flash the LED, the LED only flashes when importing. Therefore, you cannot measure exported energy at the grid connection using the optical sensor. That isn’t a problem with the generation meter. But, as I always say, the supplier’s meter is 100% accurate, even when it isn’t. Many users have both, and adjust the calibration of the analogue inputs to get agreement with the supplier’s meter. The second point is, the LED flash is historical - you only know the energy when 1 flash has passed (normally 1 Wh), the c.t’s will give you readings in between flashes.

2 - Bear in mind you cannot have two optical sensors on one sensing node. I don’t know the ESP8266 well enough to answer that, but you could use an emonTH (battery-powered).
This was posted after I’d written the above: ESP8266 post to EmonHub

5 - Some have installed emonCMS on shared servers, but have experienced difficulties. You might be able to search here and find out more. But emonCMS will of course run on an emonPi, and you can add a spinning (or otherwise) HDD if you wish.

7 - Lots - limited principally by the wiring. The default sketch is set up for a maximum of 6, the real limit will be the message length permitted by Jeelib when you’re sending by radio, which from memory is 60 bytes. Excluding temperatures, we use 14, so (60 - 14) ÷ 2 = 23 as it’s sent as integers. If you’re thinking of connecting the sensors to an emonPi, that’s a bit different for several reasons.

8 - Yes, provided it is capable of generating about 1 V and you might need to change the burden resistor, and the calibration of course.