First monitoring attempt: Running current_only.ino - are my assumptions correct?

Thank you for the excellent resources/people on this site. My immediate goal is to make sure I understand enough of what I am doing to record accurate results given my scenario. My questions are if I have the right settings.

  1. I am using a YHDC-SCT-013-060. In the info on Calibration Theory, it says: “For example, the YHDC SCT-013-030 gives 1 V at a rated current of 30 A”.
    —> For this reason I set emon1.current(1,60); (i.e.: second parameter to 60). Correct to do so?

  2. The Calibration Theory info also notes: “If you use a current transformer with a built-in burden (voltage output type)”
    → For this reason, I did not use an 18Ω Burden resistor since the YHDC-SCT-013 returns 0 - 1 V (i.e.: built in burned resistor). Is this a correct understanding of the YHDC-SCT-013 → i.e.: these type of CTs include a burden resistor?

  3. I got what looked like reasonable results…but not monitoring voltage means I am looking at apparent power for many of the energy sinks (such as microwave, coffee machine…).
    —> would you recommend I get a hand held meter to calibrate with? If so - I live in the US (Seattle area). Is there a CT meter you recommend?

Thank you.

  1. Yes.
  2. Yes - if it gives a voltage, it must have a burden resistor inside the case.
  3. You are measuring apparent power. For things like the microwave, that could be a little way off real power. For the coffee machine, it’s probably closer.
    A hand-held meter?
    There’s a couple of pages in ‘Learn’ that might help you. One lists the sources of errors in your setup. As it looks as if you’re using an Arduino, the numbers won’t necessarily apply to you, but with careful scrutiny of the various data sheets, you should get some idea of the worst-case error in your readings. The other page lists a range of multimeters generally available in the UK (though all should be available to buy on-line, some will be available locally to you). If you’re thinking of buying, it’s your decision about how much to spend, and you must weigh up what you need in terms of accuracy against your budget. The prices are now a little out of date, but that’s easily checked when you have a short list.

You might find that the best way to calibrate is to accumulate kWh in emonCMS, and compare that against your supplier’s meter readings over time, tweaking the constant as necessary until you get good agreement.

Thank you very much for the reply Robert. It helps me better understand. I appreciate it!

Hi everyone and Thank you for your incredible work!
This is my first contact/post and I’ve to tell you first, I’ve some language difficulty and I’n not expert on technology.
I’ve a question about the SCT Sensor:
SCT013-000 is 100A and return range 0/1V.
Due to my domestic provider is 6Kw max, would it be more accurate to use SCT 013-030?

Hope to been clear enough,
Thank you.

No, the output from that c.t. (and any true c.t.) is a current. There is a burden resistor connected across the output that turns the current into a voltage. You can choose any value of burden resistor you like (within certain limits) to change the voltage.

That is what is done with the SCT-013-030. YHDC have put the burden resistor inside the casing and chosen the value so that you get 1 V out for 30 A primary current.

If you use your SCT-013-000 with a 68 Ω / 100 Ω burden resistor instead of the 22 Ω or 33 Ω that we recommend for the full 100 A measuring range (emonTx / 5 V Arduino), then your maximum current will be a little more than 30 A.

“6 kW” means nothing, because you have not told us the system voltage. You must work in amps when using c.t’s. If you are on a 230 V supply, then your continuous maximum current is 26 A, but you should be allowed to take more for short periods.