EmonTX EU Power adapter VCal in default scketch

I recently bought an emonTX with an EU AC-AC power adapter from ideal power.
The values metered with emonTX were different from the values metered with a multimeter and i’m trying to find the issue.
In the source code i found that you have
float Vcal= 268.97 for UK AC-AC adapter 77DB-06-09 and
//const float Vcal= 260; // Calibration for EU AC-AC adapter 77DE-06-09
My doubt is about the firmware that came installed in my emonTX, was it compiled with Vcal= 268.97 or was it compiled with Vcal= 260 even buying the 77DE-06-09 power adapter.

Unless you asked with your order for the calibration to be set at 260.0 (the nominal value for the EU adapter), it will be 268.97.

In any case, the initial calibration value in the sketch is only the value we expect if every component has exactly the correct value. For best accuracy, you should calibrate all the inputs to take account of component tolerances arising from the manufacturing process.

Do you have a programmer, or are you using emonHub?
If you have a programmer, you can change the constant and recompile, or if you are using emonHub you can use a web browser to change the number in scales = to make a small correction (but you must do this for the voltage and all the power values, because power is calculated before the numbers reach emonHub).

I don’t have a programmer, i didn’t know that it was necessary to configure the device for a correct operation outside UK. If i knew that it was necessary i had ordered one. Like i bought a EU adapter i thought that emonTX was with VCal configured for this type of power adapter.
I’m using Emonhub but i think that change it in scales it’s not the more accurate/correct thing because the values are not normalized. Why didn’t you send normalize values to EmonHub and in it we can tune it.

Any usb to UART works or i’ve to buy one from you?


The short answer to your question is history. I submitted a proposal to do exactly as you suggest some time ago, but thus far, it has not been taken up. It would also allow remote adjustment of the compensation for the transformers’ phase errors, which would add to the processing needed in emonHub. I called it “unitless” - because the numbers sent are arbitrarily scaled, and not in engineering units.

Indeed, that is correct, and I agree with you; but it is a practical means of getting more accurate results.

Not all work, and I am afraid that I don’t have a list of the ones that do, or the ones that don’t.

I am sorry you have this problem, but I don’t work for Megni, I am just an electrical engineer by profession and moderator here.

1 Like

I’ve had sucess with the CP2102 based USB adapters. Here’s an example:

1 Like

I’ll try with a FTDI232 if it doesn’t work i’ll have to buy another one.