Emon tx v3 input seems limited to 4kW-ish

charlesty · 2024-08-03T20:03:27.843Z

I have been using an emonPi (v1) and emonTX (v3) for some time. I had an issue with two input clamps on the TX3 not quite matching and discovered that there was a foreign object in one of the clamps (thanks Robert).
I have now discovered a different issue. I was suspicious of the reading from one of the (4) input clamps on the TX, so I swapped them around so the that dodgy one was spare. I then moved that spare clamp onto the same cable as one of the emonPi inputs, and can now see that the TX input seems to be limiting at around 4kW-ish, when compared to the readings from the emonPi clamp.

image1124×614 99 KB

Hopefully the attached image shows the difference between the orange (correct) and blue (limited) clamps.
This feed is the grid on a sunny day.
Any thoughts?
Thanks in advance.

Robert.Wall · 2024-08-03T21:51:23.100Z

charlesty:

I then moved that spare clamp onto the same cable as one of the emonPi inputs,

So the yellow line is your emonPi1, and the blue line is which input of which emonTx - V3.2 or V3.4?
What are the type numbers and ratings of your current transformers?

If you’re looking at the “flat” line between about 11:30 and 14:30, I agree it looks weird but with the limited information so far, it doesn’t make sense. I’d need to see the voltage for the same period as well, because those lines are power, and if it’s a problem with the current transformer or the emonTx input, I need current. If the current transformer is limiting, why are the negative peaks each side at about 10:30 and 15:30 present? It’s those which are raising doubts and need to be explained.

I’d also be quite interested in seeing how the power factors compare for the same inputs for the same times.

Finally, are the values you graphed ‘log to feed’ direct from the emonCMS inputs before any further processing has taken place?

For what it’s worth, I can see 24 kW on inputs 1-3 on an emonTx V3 (either version) using my test rig, and the standard SCT-013-000 and UK a.c. adapter. The CT4 input is of course limited to about 19 A (approx 4.6 kW depending on the voltage) unless you’ve uprated it by changing the burden resistor.

charlesty · 2024-08-04T17:20:01.356Z

Oh, I never realised that CT4 was a more sensitive input on the emonTX v3.1.4, (bought Oct 2021) although I can see it stated in the documentation - doh. That would explain the ‘limiting’ I’ve noticed. I’ve since found information in this forum about it, and how to de-sensitise it. All my clamps are the blue 100A SCT013 type and I’m using the supplied AC mains adaptors for both the TX and Pi.
Thanks for replying so promptly with the solution!
In answer to your other questions, these two lines are ‘log to feed’ with no extra processing.