EmonTX measuring strange values

averri · 2018-07-06T16:22:43.655Z

I have connected the CT sensor to the live wire and plugged the AC-AC adapter. From the UART interface, I can see the EmonTX logging data, which is the following:

When there is one 40W lamp connected to the live:
ct1:-35,ct2:0,ct3:0,ct4:0,vrms:24514,pulse:0

When there is no load:
ct1:9,ct2:0,ct3:0,ct4:0,vrms:24489,pulse:0

The question is why ct1 is measuring 9 when there is no load, and ct1 is measuring -35 (minus 35) when there is a 60W load?

Bill.Thomson · 2018-07-06T16:45:54.861Z

averri:

why ct1 is measuring 9 when there is no load, and ct1 is measuring -35 (minus 35) when there is a 60W load?

Hi Alexandre,

The FAQ section has answers to both of those questions.

In addition to that, you need to use a load much larger than 40 or 60 Watts to get meaningful output from the EmonTX. That’s covered in the FAQ as well.

averri · 2018-07-06T16:49:40.260Z

Hi Bill, that’s great. Thank you very much for the information. The power measurement is working fine now.

After calibrating with a load of 850W, the power reading when there is no load has been reduced to 3W. I’ll try to calibrate using the recommended load of 2000W.

Robert.Wall · 2018-07-06T18:00:06.851Z

Or you can cheat. If you wind several turns of wire through your c.t., you multiply your load by the number of passes through the core. That’s how I can get 100 A for testing - though actually it is the same 5 A going through the c.t. twenty times, so it looks like and reads 24 kW.

averri · 2018-07-08T14:37:50.734Z

Thanks Robert for reminding about the Faraday’s law of induction.