Finally rebuilt my emonTX on a fresh PCB, and it works fine, with no clue as to why the original build didn't.
Still got there in the end!

Just run Robin's tools on the inputs, and got the following;

The load is about 7.5kW, and I presume that the reference voltage input is excessive as it flattens at the peak's, so presumably I need to lower the value of R14 to keep within scale. 
The current waveform is also flattened at the peak's, is this normal?


Robert Wall's picture

Re: Success!

I need to lower the value of R14 to keep within scale

Indeed. The mains voltage wave is flattened anyway by rectifed d.c. loads (not just yours) that pull a spike of current at the peak of the wave (see the pretty pictures). But your transformer is saturating a bit!

You should be getting about 11 V rms out of your 9 V adapter unloaded at 240 V, any more than 12 V at max mains (253 V) and you'll need to reduce R14 or increase R13 (whichever suits the values you have to hand) so that you have about 1 V rms or a little more across R14. Here are the gory details about how to get the value right.

[I edited your post to get the picture inside the column]

Paul Reed's picture

Re: Success!

Following your calculations, if I replace R14 (10K) with 8.1K, that should (and does) give me 1.02V  rms across R14, and the resulting waveform now sits nicely within the limits (@ 243VAC).

Just got to calibrate the current now!

Thanks again Robert.


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