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Topic: Energy monitor values (Read 19693 times) previous topic - next topic


With the AX-1500 CT I'm using I have put a 50 Ohm burden resistor so it behaves like the YHDC-013-030 from the Emon guide. As you will see, this CT can output as much as 2 volts with a 200 Ohm burden. In my case I have put 2x 100 Ohm in parallel.

The yhdc 013 030 current sensor has 500mV output at 15A (datasheet).

That's exactly 100 digital steps per 15A. =150mA/step. = 34.5watt/step (on 230v mains).
That is the threshold. Below that, nothing  is detected.

You can lower that with an opamp to 10watt/step. Opamp gain = 3.5x
If the CT can give what an op-amp outputs, why would I use one? Is the waveform kept between specific values or it won't be susceptible to noise?


Apr 27, 2015, 06:37 pm Last Edit: Apr 27, 2015, 06:45 pm by sonnyyu

Since you are Arduino Yun based why to use Smart Meter IC/Energy Processor.


Ton of IC manufactures produce Smart Meter IC include Atmel



The method of sensor AC:

Voltage Sensing Unit:

  • Resistor divider
  • AC Voltage stepdown transformer

Current Sensing Unit:

  • Current transformer
  • Hall effect-based current sensor
  • Rogowski coil sensor
  • Shunt resistor

Rogowski coil sensor is my favor.



This would've been perfect but deadline has passed and I'm in a tight spot. What we've accomplished so far should do, with some available and fast adjustments.


I did'nt read correctly the AX-1500 datasheet. It is an external burden. I thought it was internal...

Why do you use a 50 ohm burden ??? (100//100)

you need a 200 ohm burden, not 50 ohm, in order to get 4Vpkpk with 15 amps pkpk at input (roughly 10 amps RMS).

The difference is 2 bit for the ADC.


So this means I won't be needing an op-amp? Won't the higher voltage require some updates to the schematic? The output is maintained at 2.5V.


Apr 27, 2015, 07:43 pm Last Edit: Apr 27, 2015, 07:45 pm by AppCrash
You don't need anything else than a correctly sized burden. The datasheet allows you to use a 200 ohm burden. (some manufacturers indicate min/max values, but here, you're fine with 200 given the curves). Doing this you will get 4x the resolution.

Someone else already told you this !

Before you connect to the arduino, test with your friend's DMM. It has probably peak to peak and RMS functions. Don't let voltage go over 4 V peak to peak. Or protect analog inputs.

If you are perfectionist, you could calibrate : have a look at the curves, you don't get exactly 2 volts. There's a tiny difference. Is it worth it ? Certainly not !

But one more time, you won't get anything interesting except with resistive loads if you don't replace the voltage sensor ! For example you *can not* correctly measure power drawn by a transformer + diode bridge + capacitor because of the crappy sine. You could get 20% error or so. Any wall transformer found in a dump will be better.

You're very near to a perfect result !


I have a 9V transformer, like the ones you'll find in a power adapter. Problem is, I think, that's a major source of el.-mg. waves and it might affect the circuitry. This PCB type looks like it won't be a major problem.


Apr 28, 2015, 12:08 am Last Edit: Apr 28, 2015, 12:19 am by AppCrash
It *IS* an issue, in terms of phase and linearity ! It is easy to see and to measure.

If it was'nt, manufacturers would'nt design and sell specific voltage transformers.

Just for you, I made a a comparison between a miniature transformer like yours (9V 55mA), and a measurement voltage transformer. See attachement.

yellow trace : measurement transformer
blue trace : 9V 55mA

(yes, mains are slightly clipped, it is normal)
(probes are set to 1:10, but not the scope : just x10)

Do you think you can calculate a representative RMS voltage from the blue trace ?
Do you think you can calculate a representative RMS power from the blue trace ?
Do you think Openenergymonitor software will get a correct zero crossing phase reference  from the blue trace
Do you think the phase correction factor you used is normal ? (-1 insteed of +1.7 and you can see why on the scope !)

If you can answer "yes" to these questions, then you're fine (or you don't understand how power is calculated and coded) ! On my side, I stopped thinking, I measured and immediatly seen why it did'nt work as expected.

Otherwise, replace this transformer, and you'll turn your circuit into a reliable instrument. Why the hell do you use a measurement current transformer for current, and not a measurement voltage transformer for voltage (or at least a more suitable one, like one of those tested, measured, approved and shown on Openenergymonitor website) ???

The measurement transformer I use is smaller, lighter, and not more expensive than the 9V crap. And it is toroidal.


Apr 28, 2015, 12:39 am Last Edit: Apr 28, 2015, 12:45 am by cipri92
This is the transformer I'm looking to buy. No waveforms present in the datasheet. This is a different manufacturer and, as suggested, higher power.


Or this one, which has 2x9V output, 600mA:



Before ordering, condider this :

Search on eBay for "TV19 current transformer" or "TV19E current transformer".



Datasheet : http://www.yhdc.com/en/product/521/

$7.50 from eBay. That's what I'm using. Slighly more expensive than the transformers you linked (and that are certainly far better than the tiny one you actually use)

These devices are amazingly small. And most of all, they are *measurement* transformers. AFAIR, I received it within two weeks from HK. I did'nt find any source in Europe, but it was worth waiting !

Yes !!! Current transformer for voltage !!!

They are current transformers with primary and secondary, 1000:1000 ratio or so.

They have to be used with a resistor in series with the primary ; for testing : 3x 270k 0.25W // = 90k 0.75W (max dissipated power = 0.7 W). For the final version, it will be 39k 1W + 39k 1W in series (=78k, 2 watts).

Burden at secondary : recommanded value, 500 ohm.

The output level is adjusted by varying the primary series resistor. With the given values, it can be connected directly to a 5V Arduino (the same way, with 2.5V middle point). Just now : 3.32V peak to peak for 230V input (0.84V to 4.14V, so there is room for mains peaks)

The yellow trace on the image I posted is taken from a TV19. Tested it against the signal comming from an isolation transformer (for safety !) : phase, visual aspect of the trace and FFT for distorsion. The result was excellent.

Yes it need some power (less than 1 watt), but it is linear, accurate, with very little phase shift and distorsion, and large bandwidth. It is toroidal : no EM disturbance for and from the current sensor. You also can use the TV16 (less primary current needed), or reduce primary current (larger resistor) with the TV19, but you will need an amplifier on the secondary. Not that good an idea...


If I'd knew this from the beginning...
Thanks for the effort.

The reason I chose the 2 mentioned above is because they are delivered fast and the deadline is a few days away.

With the 9V I'm using now I am getting a steady read, for now. I don't think will be this accurate again with the use of a different consumer. You suggested higher VA. What would you choose between the 2 given the El. mg waves?


I'd probably chose any of them !

I'm currently testing different transformers. This is something I was waiting being on vacancy to do, but you stimulated me... (different transformers and solutions against a measurement transformer)

I just tested a 5VA Myrra branded (Germany), and that gives excellent results. I took some pics.

Don't bother with "If I'd knew this from the beginning". Reading Openenergymonitor is a pain in the ass. It makes think it is rocket science. Simple have to be simple to find and to read ! Sorry for the authors, but that's what I think...

I also forgot to say that the crappy signal I shown came from a 0.55VA. (yours is 0.35VA, imagine the disaster !).

Some pics later in the night. Like you I burn the midnight oil, but I have to watch "The return of the king" with my teen aged daughter... It will take some time...

Attachment : a Myrra 5VA 9V PCB transformer : very nice trace. Yellow = source (230V), Blue = output (9V). Fine. I also took FFT pics for distorsion. For transformers, larger is better, and there is probably a soft point. Don't have enough of them to find this point : somewhere between 1VA and 5VA.


Enjoy the movie!

Do you think PCB transformers are a smaller source of el.mg. waves than mounted transformers or the other way around?

The transformer shown here http://bit.ly/1POi4WW has a 2x9V, 600mA output. Does this mean it gives max. 600mA per 9V winding meaning with 18V I'll get 1.2A? I don't have much experience with this type.


Apr 29, 2015, 01:07 am Last Edit: Apr 29, 2015, 01:27 am by AppCrash
PCB transformers are mounted on PCB, so they are nearer...

Current does not change. You will get 18V 600 mA. Otherwise you'd get double the power ! (but free energy fools could explain something different).

But if windings are connected in parallel (and in phase !) you will get 9V 1200mA.

I tested all the small transformers I have on the shelf. The results are as expected. The winner is the measurement transformer, and the 2nd is the 5VA transformer. By far !

First, the transformers, from left to right ; they are all brand new, never used :

- chinese YHDC TV19 1000:1000 5mA current transformer
- chinese YHDC 0.5VA 9V
- german Hahn 0.75VA 2x9V
- german Hahn 2.6VA 12V
- french Myrra 5VA 9V

(but all are most likely made in China)

Then, the tests. Primary is always connected to an isolation transformer. I dont want to kill myself, or worse, my oscope.

yellow : the 230V source
blue : the secondary signal

As a starting point, the measurement transformer :  3x270k// = 90k inseries with the primary, and 470 ohm for the burden. The result is perfect : phase and linearity (it has to be !)

primary FFT : as a reference for distorsion

TV19 output : one can see there is no or nearly no distorsion :

Now, the transformers, bigger to smaller :

Myrra 5VA 9V : good !

Hahn 2.6VA 12V : not too bad

Hahn 0.75VA 2x9V : bad

YHDC 0.5VA 9V : crappy !

smaller transformer = less iron + smaller wire + more turns (more primary resistance) = distorsion

The 5VA transformer is nearly as good as the tiny measurement transformer, but it is larger and heavier (by far), and costs more. The sweet point is probably around 3VA.

For accurate energy monitor values, the voltage sensor has to be a resistor divider (the best but tricky if the power meter has to be isolated !) or a large transformer... or something like the tiny blue thingy. 

Conclusion : using a power supply transformer is nonsense (larger, heavier, more expensive, and most of all less accurate) !

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