Open Energy Monitor-Something's not right

I just built the Open Energy Monitor(, and something seems off about the numbers. There are two things I feel could be contributing factors that I should mention first. First off, the CT sensor I have is the SCT-013-000, the one recommended by the guide I linked, which I assume to be the "official" project page for this. By all indications it would seem that this particular CT sensor needs a burden resistor in order to function properly. The only reason I even question this is when I unscrew the cover from the 1/8" jack and test the connections with my meter I get a 200 ohm reading between the lead that I'll call common(the one that is attached to the largest part of the jack, usually ground on a headphone or audio jack) and the other lead, the one that goes to the tip. I know it has a diode installed, maybe that's why I'm getting that, or I thought it could possibly be a pre-installed burden resistor, but the value is too big. in other words, both leads are already tied together somehow with 200 ohms, is this the way it should be?

Secondly I have been unable to find a schematic. All I have to go by is the picture on the page I linked. I know there is a schematic somewhere, but I haven't been able to find it. Would anyone happen to know where one is? I'd feel a whole lot better about the wiring if I could just look at a schematic.

Btw, I do have the right power adapter, 120VAC to 9VAC, if anyone should be wondering. Below are a handful of the values from my serial monitor. The values, from left to right are; real power, apparent power, power factor, rms voltage and rms current. The extreme range of the real power value is mostly what looks wrong, but the others are fluctuating pretty widely as well, but nothing like real power. I should probably mention as well, that this was the maiden voyage with the Open Energy Monitor and just to see it work I put the CT sensor on my laptop's power cable. Not sure if that would cause this ridiculously wide variation in values, but it is worth mentioning.

6.98 33.78 233.25 0.14 0.21 

4.06 30.44 233.13 0.13 0.13 

7.57 36.91 232.99 0.16 0.21 

0.42 29.95 231.97 0.13 0.01 

0.68 34.87 233.18 0.15 0.02 

1.95 26.99 232.97 0.12 0.07 

5.15 32.39 233.07 0.14 0.16 

4.17 30.94 233.17 0.13 0.13 

4.34 31.37 233.01 0.13 0.14 

0.50 29.88 233.24 0.13 0.02 

3.35 30.19 232.07 0.13 0.11 

2.51 21.46 233.03 0.09 0.12 

4.26 27.67 233.24 0.12 0.15 

4.30 28.34 233.20 0.12 0.15 

1.65 28.18 233.05 0.12 0.06 

2.02 25.13 233.06 0.11 0.08 

5.69 33.19 231.96 0.14 0.17 

1.63 29.89 233.07 0.13 0.05 

6.24 29.78 232.89 0.13 0.21 

2.06 27.65 233.05 0.12 0.07 

4.20 28.76 232.96 0.12 0.15 

0.32 25.79 233.21 0.11 0.01 

4.84 31.68 232.03 0.14 0.15 

4.61 32.97 232.99 0.14 0.14 

7.24 32.40 232.99 0.14 0.22 

1.30 26.35 232.81 0.11 0.05 

4.29 29.58 231.89 0.13 0.14 

4.26 41.10 232.83 0.18 0.10 

3.20 30.32 233.10 0.13 0.11

Any advice, clues, rtfm with a link, anything would help. I'm mostly worried about the 200 ohm resistance where I expected no circuit at all.

Thanks guys.

I would appreciate if anyone could make sure my 3 grader level schematics are accurate. I’m just going to start over before I try troubleshooting this thing.

Here’s the pic I am going by

And here are my schematics.

Edit The pin number is wrong in the power supply schematic, it goes to 2, not 1(doesn’t matter but I figured I’d say I did see that). Also I deleted the entire post and changed it to this. If I could verify the schematics I think I could trust it enough to figure it out.

Edit Edit I somehow renamed one of my drawings the wrong thing and they are both the same drawing, just different names. I’m sorry for being such a spaz tonight. Been up for way too long and getting tired. Don’t see a way to delete the attachment. I’m sure I’m just missing it.

Edit Edit Edit Here is the right one for the powersupply, I THINK. I’m going to bed now lol.

The voltage readings, probably wrong. With arduino the max. peak-to-peak voltage can't be more than 5V, or Vrms = 2.5/ sqrt(2) = 1.767766953 V. Using 9V AC power adapter, you should set resistor divider to 9/ 1.767766953 = 5.091168825 , better 6 /10 to give some headroom . 100 k : 10 k

Yes it needs burden resistor. Do you know the exact part number or specs or can you post a photo of the markings on the device?

Luckily that device comes with protection zener diodes to stop it generating dangerously high voltages when open circuit (a current transformer must never be operated with the secondary open-circuit).

To choose a burden resistor you need to know the turns-ratio of the transformer, the maximum (peak) current you want to measure and the maximum voltage you can measure on the output. Lets say you want to measure upto 50A rms, using an Arduino ADC (5V range) and the turns ratio is 1:1000. 50A rms sine wave has a peak value of about 71A. thus the secondary peak current will be 71mA (divide by the turns ratio).

Assuming we bias the output to +2.5V so it can swing from 0V to 5V to represent -2.5V to +2.5V, that means we want 71mA to give 2.5V. 2.5/0.071 = 35 ohms approx.

Actual values depend on your device and requirements of course.

Thanks for the replies, guys. I could not keep my eyes from crossing last night lol. None of this project has been engineered or calculated by me. I’m, following the instructions found at the link I posted as closely as I can. I ordered the parts they said to order, down to doing copy pasta on the item numbers. I can’t imagine why my hardware would be any different at all, or why anything would be different. For the CT power supply I am getting that from the arduino, 5V, unless there is something I am not understanding about the way this is all wired together, which it’s safe to say that I do not. I am afraid now that I’m going to do something to smoke my arduino. Not having a schematic that I trust is about to make me just buy an energy monitor since I can’t stand the thought of seeing the blue smoke.

The burden resistor I am using is 33 ohms. It is what the project page recommended if using 5V. I have to finish this or buy one since I need to begin auditing my energy use in preparation to install solar. I would much rather finish it. I have attached a pic of the front and the back of my CT. I hope that helps. Thanks for the help guys!

I’m, following the instructions found at the link I posted as closely as I can. I ordered the parts they said to order, down to doing copy pasta on the item numbers.

Apparently, you are not. I check on a link you posted, and they recommend:

Voltage sensing electronics:

1x 9V AC-AC Power Adapter

1x 100kOhm resistor for step down voltage divider.

1x 10kOhm resistor for step down voltage divider.

2x 10kOhm resistors for biasing voltage divider (or any equall valued resistor pair upto 470kOhm)

1x 10uF capacitor

As you can see, there are 100 k and 10 k in voltage divider for Voltage sensing.

Yes sir, I'm using both. Would you like a pic of my breadboard? I thought I addressed all the mistakes in my schematics, ie things that aren't like I have them on my breadboard, but I guess not. I really need someone to look at the project page, then my schematic and tell me what's wrong, and then I'll build it like the schematic, rather trying to match a picture, which is what I've done. But the mistakes you point out are not mistakes, I have exactly like you say. Like I said, I'm trying to follow the instructions as closely as possible.

Blue smoke is bad... Black smoke is Really bad...


I've seen the blue smoke before. However, at this time I do not have extra microprocessors, so I have to be really careful. I have a lot going on today, but if I get the chance I will take a pic of my breadboard. Maybe somebody will see something wrong. Worth a shot.