I just wanted to run these values and ask what you think of them, as they don't seem correct to me. I just built the arduino energy monitor per this website:
http://openenergymonitor.org/
I have my breadboard wired exactly as in the picture. I am using the SCT-013-000 current transformer recommended by the page, as well as a 120v AC to 9v AC adapter.
My burden resistor is 33 ohms.
I am using the 5v arduino input to power the breadboard (just like the picture on the site shows).
For my test, I wrapped my current transformer around a 40W lamp cord which was plugged into a Kill A Watt which was plugged into a power strip which was plugged into my mains (120V AC).
Here is a list of the results...
(realpower, apparent power, Vrms, Irms, power factor)
42040.32 54513.00 384.44 141.80 0.77
1217.19 6081.69 250.90 24.24 0.20
43.94 1043.18 246.00 4.24 0.04
7.87 185.88 245.74 0.76 0.04
6.65 48.15 245.84 0.20 0.14
6.54 36.26 245.30 0.15 0.18
6.09 34.65 245.46 0.14 0.18
7.07 38.32 246.88 0.16 0.18
5.47 29.84 245.82 0.12 0.18
10.38 37.38 245.84 0.15 0.28
10.14 39.00 245.71 0.16 0.26
12.52 49.75 245.72 0.20 0.25
6.10 31.22 245.66 0.13 0.20
6.79 34.68 245.66 0.14 0.20
8.78 48.19 245.51 0.20 0.18
8.03 41.43 245.82 0.17 0.19
9.26 37.36 245.67 0.15 0.25
9.41 36.77 245.81 0.15 0.26
6.42 35.65 245.65 0.15 0.18
5.11 28.49 246.09 0.12 0.18
The arduino is an UNO... before this I tried the same setup on a Mega and the results were very similar, except that the first column of values was reading around 40 instead of 5-10.
A few things make me think that it is not working correctly. First, my Vrms which the monitor says is 246 seems high (as I have 120V AC), but I know I might be wrong.
Second, the values did NOT change appreciably when I turned off the lamp. The Kill A Watt showed 40.1 watts when the lamp was on, and 0 watts when it was off. These readings didn't change, not on the UNO nor on the Mega.
If anyone has any ideas as to the validity of the readings or potential problems, I'd be very appreciative for your help.
Thank you kindly,
Jeff
Re: Arduino OpenEnergy readings seem wrong...
First, as you are on a 120 V supply but you are using an adapter that delivers the same voltage out as the 240 V version, you need to change your voltage calibration constant. (That's not a fault!). Details are here: CT and AC power adaptor installation and calibration theory. Depending on the actual voltage ratio of your adapter, the voltage calibration constant needs to be changed to about 110 (measure your voltage, tweak the constant until you get the same voltage from the sketch and your meter, and mind your fingers!)
Second, are you putting your c.t. around a two or three-core cable containing wires that carry the current in both directions? If so, you won't read anything! The c.t. operates on the magnetic field surrounding the wire - it is a transformer after all - and if the two fields are equal and opposite, they cancel. The c.t. needs to be around either the line or the neutral, not both.
Your c.t. delivers 50 mA per 100 A of primary current, so measured across your 33 Ω burden resistor you should read 1.65 V per 100 A (i.e. 16.5 mV / A).
Otherwise, those numbers look about what I'd expect for a 240 V setup reading nothing! The initial high powers are false values while the digital filters in the software settle, and are nothing to worry about.
Re: Arduino OpenEnergy readings seem wrong...
I sure appreciate your time and help. I placed the transformer around the lamp cord so it must have included the line and the neutral. I have to work today and tomorrow (15 hour days) but I am excited to put your comments into practice and see what happens. I will post the results here in 3-4 days. Thank you sincerely!
Re: Arduino OpenEnergy readings seem wrong...
Robert, I hope you get this...
I just wanted to take the time to thank you for your generous help and time. I went through your response very carefully and looked at the page you sent as well.
Please check out my updated list of values for a 60 watt bulb:
61.52 62.95 122.78 0.51 0.98
63.22 64.68 122.83 0.53 0.98
62.86 64.21 122.64 0.52 0.98
61.50 62.83 122.65 0.51 0.98
62.16 63.56 122.70 0.52 0.98
62.39 63.79 122.69 0.52 0.98
62.96 64.61 122.65 0.53 0.97
61.50 63.37 122.67 0.52 0.97
61.72 63.14 122.66 0.51 0.98
61.58 63.14 122.59 0.52 0.98
61.62 63.11 122.68 0.51 0.98
62.25 63.66 122.71 0.52 0.98
62.86 64.45 122.78 0.52 0.98
61.58 63.03 122.73 0.51 0.98
62.75 64.21 122.17 0.53 0.98
62.17 63.90 122.76 0.52 0.97
63.05 64.42 122.81 0.52 0.98
64.51 66.10 122.82 0.54 0.98
60.74 62.25 122.70 0.51 0.98
62.58 64.16 122.72 0.52 0.98
My Kill A Watt showed 122.7 volts and 63.6 watts, right on the money with the results of my monitor. This helps me a lot as I am going to use this in my home for some awesome projects... I was so disappointed initially, but with your help, I am so excited now. Thank you again.