Open Energy Monitor Port

Yes it would be nice to have a project box that will hold a Particle and with space for a battery, a couple of buttons, LEDs and sockets. I’m afraid my energy monitor is just a bit of strip board sitting on a shelf next to the meter though the display in the hall is quite tidy.
We could do with a project box not just for this project but in general. It seems to be particularly difficult to find a box that will take either an LCD display or a small touch screen.The Raspberry Pi is reasonably well provided for. Any plans wonderful Particle.io people?
Here is what typically needs to fit in the box … this is an acoustic anemometer.

@phec Quick question.

I’m wanting to read the AC output Voltage & Power in watts that is being supplied via a Pure Sinewave DC to AC inverter. I don’t need all the Open Energy Monitor functionality.

Couldn’t I just strip down this library and use the blue current clamp to calculate the AC voltage & current/wattage output only using the Photon?

How accurate would you say the readings are for your AC measurements when it comes to voltage and power?

You can certainly strip down the hardware for what you want. However you would need a low voltage power supply as well as the current clamp if you want to measure the real power rather than the apparent power that you generate. The real power takes into account inductive or capacitive loads that shift the phase of the current relative to the voltage. If the load on your generator is always resistive and so in phase with the voltage you could just measure the current and use the nominal inverter output voltage.

The quick answer is to how accurate it is is “not very”. If you were very careful lining up the current clamp and used a good quality ac power supply to measure the voltage I’m sure you could do better that me.
I have compared the current clamp readings with the electricity company meter flashes averaged over 15 seconds. These are bound to differ sometimes because the current clamp measurement is collected over 20 mains cycles = 0.4 sec shortly after the 15 seconds of flash counting. Also bear in mind that the current clamp and voltage readings need to be calibrated so even if the clamp and power supply are perfect, the results will only be as good as your calibration.
Picking a random day and correlating the flash count value with the current clamp value I get y=0.98x with an R squared value of 0.9667.
In other words my calibration is 2% out and (I think) 96% of the variation in the measured curent is consistent with the expected values.
This is based on 5744 measurements.

I hope that this helps with your project. Good luck.

@phec Thanks for the detailed reply.

I don’t need the readings to be 1% accurate, hell the current readings being supplied by the inverter are probably only 10% accurate or less as it is now. I’m just needing a close to accurate reading for AC volts & Current so I can send it out along with battery status info.

So 90% accurage would be fine for now.

Can you elaborate on “If you were very careful lining up the current clamp” . How touchy is the blue current clamp? Any time saving advice on this would be helpful since I’m going to embark on this journey in the near future.

Also about the AC power supply, do you have any recommendations on what you think would be a step up from yours now?

I suspect that what I’ve got meets your requirements then.

The low voltage ac power supply was the only one I could find. It does not output a nice sine wave. The RMS voltage is 1% different from the RMS of a sine wave so that may account for up to half my error… This is all way out of my comfort zone so do not rely upon what I suggest. I think any cheap plug in adapter will be similar. If you need the gold standard then a mains to low voltage toroidal transformer should follow the mains voltage waveform more accutately.

I find that the current clamp readings change a bit if I move the clamp and other people have reported very inaccurate readings when they have not closed the clamp properly. (A 0.1mm gap between the two halves of the clamp gives a 7% change in measured current.) The OpenEnerguMonitor people checked a clamp from the same manufacturers that made mine and found it was accurate to between 1 and 2%. Ideally the clamp should also be centred on the cable - I guess you could pack it out with a bit of plastic.

I suggest you try the cheap solution first and only start looking for more expensive bits if the first attempt doesn’t meet your needs.

@Phec Thanks agian for the info.

I’ll give this a try and report back on my findings.

Greetings. I was wondering if anyone has any input on how to use one of these hall effect current sensors with a Photon running the open energy monitor port:

http://www.aliexpress.com/item/1-Pcs-New-30A-Range-ACS712-Current-Sensor-Module-Electronic-Parts-Hall-Effect-Detector/32389194543.html

I haven’t read the specs in great detail yet, but I assume that it outputs an analog signal whose amplitude varies with the current draw. If so, I assume I have to read a sample at least as many times per second as the cycles on the AC line and average the measurements or something like that? These devices are dirt cheap and very small, so I prefer using them over a regular CT clamp type sensor. Any ideas are greatly appreciated. Thanks!

Hey everyone.

I know I’m a little late to this party but I saw this post and thought I would chime in that we are developing a Particle based Current Monitoring board. We have a processor on board that Particle communicates with via I2C and can monitor multiple current monitors. We plan to have a 4, 8, 12, and 32 channel input boards. Headphone jacks on board so the sensor just plugs right in. See photo.

Controller in photo is Electron version but works well for prototyping since you can plug a Core, Photon, or Electron in.
Once released it will be sold on www.controleverything.com

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Hello everybody,

We have developed a Particle based energy monitor.

Features:

  • It is DIN rail installable.
  • It measures Voltage RMS, Current RMS, (up to 4 different lines) and Power RMS.
  • It does not need external power supply.
  • To set the Wifi Credentials it could be use our own responsive website.
  • To manage the measurements we have a Web Platform.
  • It is fully isolated.
  • It is protected against shortcircuit and over voltage.

If you are interested in purchasing one, you could contact to

info@smartsens.net

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@IOTrav Sweet! I’m looking for something like this. The 4 channel board would work for me.

I just want to measure AC voltage and current for a portable solar generator system that has AC input and 2 AC output ports.

What data will your breakout offer exactly?

Hi @RWB

The device is still in development. The only one we have right at the moment is a 12 channel for those plug in AC current Transducers.

We have found however that those current transducers can only be so accurate. The PCB mount current Transducers we are testing with are much more accurate but the downfall with those is they can be more difficult to install. So there is a dilemma there. See photo here:

We will also have some controllers with AC voltage input so you can monitor current and voltage. What would be the maximum current and voltage you would need to monitor?

A Library will be provided for interfacing to our IC from the Particle module. It looks like this:

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What exactly do you mean by so accurate with the blue current clamps? Like 1% 5% 10% accurate?

I’m probably going to be working with 16 amps max AC current in most situations.

They are spec’d to be accurate to within 5% or so but I only have the 100 amp rated version so that is a variance of around 5 amps which is way outside my liking for accuracy.
Now that is not to say that this sensor is not available in other ranges because it is.
Honestly I just have not been astounded by this current transducer yet. That said it is super convenient for installation because it is a split core and has a nice cable for connecting back to the board.
The PCB mount current transducers are more accurate +/- 1% and I have those on hand rated for different amperage ranges. I have gotten extremely accurate results with them, better even than my fluke clamp meter. I can tell if my 30" LCD display TV has a solid White or Blue screen!

I have enjoyed both versions very much but if you have the capability in your installation to use the PCB mount current transducers I would probably nudge you in that direction.

That’s good to know.

When do you think you would have a 4 port version of this board available using the more accurate sensors?

We are still working on the board mount CTs but the plug in version is complete and has been sent out for PCB manufacturing:


The engineer working on this project is out today but I will check with him to see when the PCB mount CT version will be ready. It could already be done for all I know.

Sounds good.

I have the 30A version of the blue current clamp so I’m wondering how much more accurate that one is compared to the 100A version your testing with a 5A / 5% accuracy gap. Even if the 30A version is in the 2% range I think that might work. I could probably just use a 15/20A clamp if they have them.

Can you guys pick up a 15,20, or 30A clamp to see how it compares to the 100A clamp your testing now?

@IOTrav - neat looking project - congratulations. As smart meters are rolled out across Europe I can see a growing market for a simple consumer product to check that the smart meter is behaving itself.
If your wire is long enough and you have enough slack in it you can always run it 2 or three times through the current clamp to get more effective current and so reduce the error.

Someone has checked the accuracy of the split transformer “current clamp” type current sensors for the Open Energy Monitor project.
Testing a YHDC SCT-013 current transformer
Apart from a few percent error in the current there is a variation in phase errorof up to 6 degrees or so over the current range. You will see that I have calibrated my phase correction to be most accurate at higher powers where price matters.
You are quite right that the non-split current sensors are always likely to be more consistent than a split clamp because of the great sensitivity to leaks in the magnetic circuit but of course not a lot of use when you can’t break into the circuit. I guess you have to identify your market.

The spreadsheet I have linked to shows a typical day’s data from my system. It covers 24 hrs measurements at 15 second intervals. Early on you can see a spell where I have a 3kW immersion switched on. In the middle of the day you can see me exporting about 3.8kW between clouds.
Excel spreadsheet 1 day’s data.

You will see that a few times during the day the readings aren’t at 15sec intervals. This is when the Particle Core was renegotiating either WiFi or Cloud communication.
Apart from the errors in a current clamp and ac transformer, another source of discrepancy is that the current clamp reading is averaged over something under 1/2s at 15s intervals while the meter flashes are accumulated continuously.

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p.s. there is a non current specific version of the current clamp where you add your own ballast resistor to suit your measured current and ADC input voltage. I don’t use these because you have to be a little careful with back emf when disconnecting them.
se for example:

The 100A in this case refers to the current that will saturate the core. Below this current you can get pretty much as high a voltage as you like for a particular current by choosing the appropriate balast resistor.

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All these sensors have a 5% +/- error. On a 100 amp sensor 5% = 5 amps. On a 30 amp sensor the margin of error would only be 1.5amps(30*0.05). So it is more accurate per say.

We will be getting more of these sensors in soon with different amperage ratings. We need them in order to test because resistors on the board need to change to accommodate the different amperage ranges. We will also need to modify our code to convert the readings into amperage depending on the sensor range. Hopefully we will have some different versions in a few days.

In order to reduce stocking overhead we have toyed with the idea of only carrying the 100 amp version of the split core CT and just having people wind the wire through the clamp 5 times if it is only a 20 amp circuit. We can then have them enter this information in software and accommodate for the winds in firmware/software. This drastically increases accuracy of the sensor and allows you to use the same sensor for almost anything.

That said you just cant beat a solid core CT.

Thank you very much for sharing your testing data. I plan to setup a test at my house and monitor all 30 circuits in my breaker panel, take readings as often as possible and publish kWH variables to the Particle cloud. I have a pretty good idea of how to structure it but I was going to use Google Sheets. I would have a google app script get the variables from Particle once per day and publish the readings per circuit to the sheet so I can see how many kWH were used that day by each circuit and even estimate my bill based on kWH pricing from the electric company.

I think this is something people will be getting into more and more as Electricity prices continue to rise.