SCT-013-000 very confused!

I’m implementing a second CT on the same Arduino device. What I did is just create another circuit, on the same 5V out, It seems my readings on the two CTs are different, is what I’m trying to do valid or should I make adjustments?

Basically, I have two dividers, two capacitors and two burden resistance and I split +5V to go on both circuits, one CT going to A0, the other on A1

What you’ve done sounds correct - have you compared it with the emonTx circuit diagram?

You should expect a small difference between the two. The tolerance on the CT is ±3% over the range 10% - 120% of rated current, to that add the tolerance of the burden resistor, and then it’s possible that the two sets are at opposite ends of the tolerance band. So you could have 8% difference between the two with 1% resistors. If your current is below 10 A, then the accuracy of the CT is not specified, and although my measurements indicate that generally it is well-behaved, there’s no guarantee what it will read.

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So, with a meter I get these values :

C1 : 1.9 x 124 = 235W
C2 : 0.8 x 124 = 99W

The Uno actually gives me :

C1 337.49
C2 181.21

Quite a stretch isn’t it?

My Burden calculation : (5 / 2) / 0.05 = 50 Ω, I used 47Ω

The calibration I used is (100 / 0.05) / 47 = 42.55

On the second topic, here is the resultst I get when swapping the two CTs, does that seem to be in the tolerance range? It would seem so :

CT1 156.36
CT2 338.75

<<swap>>
CT1 347.45
CT2 149.77

<<swap>>
CT1 154.67
CT2 338.59

Are the numbers 1.9 and 0.8 the rms currents that you read with your meter? Why are they different? If you are comparing two inputs, you should put both CTs on the same cable so that you can compare like with like.

What load are you using? You should be using an electric heater that does not have a fan inside, or an electric kettle.

Change those things and try your test again. Until I know exactly what you are doing, and it is the same for both inputs, it is very hard to identify your problem or problems.

Yes, these are the number for each phase, sorry I should have said. This is a US installation with 2x110 phases.

When I swapped the two CT it was the idea actually, instead of moving both on the same cable I’m swapping them to see if they approximately read each other’s value.

On the load that’s a good point, I don’t know actually, It’s a weird electrical installation, I’m actually measuring power for the people living in the basement so I can’t really ask. I’m not aware of anything fancy they are doing but I think they do use space heaters.

What makes me think I’m probably just fine is this :

  • The Orange line is CT1+CT2
  • Tthe Green line is the reading counting the revolutions of the meter (or “truth”) minus (CT1+CT2)

Look at how the orange line jumps up and down (assumed space heater), and how the green line doesn’t seem to be impacted by this. To me it proves that I have the right balance, if it wasn’t the case, I would observe some of the orange line “spilling” on the green and have some kind of impact. Not sure I’m making any sense here…

To give you a little bit of background around that project, it all started with a $5000 coned bill in December, following a reading after more than a year of estimate. There was no way our home would use what was the equivalent of $400 every month for the last 16 month, so I started investigating.

The landlord “shares” the meter in the house for our family and people living downstairs (this is quite common in 3 stories homes here) and we established that I pay coned and he reimburses use 15% of the bill. We were ok with that, but didn’t think they would use space heaters as the heating is gas!! Apparantly not enough…

So I will gather some more info and have all the materials to go to my landlord with substantial information for a reimbursement.

Many thanks again!

I don’t understand “coned” - presumably American and not real English?

The second but major point is, if you are going to argue over payments, you better be certain that what you are saying is totally accurate. Hence, you need to carry out the full calibration as accurately as possible given the test gear that you have available to you - or that you can hire. If you are talking about a substantial sum, then it may be worth your while to do so.

Sounds like he’s referring to ConEd, i.e.Cosolidated Edison, his energy supplier.

Lol, tanks Bill. I live in NYC, I assume everyone knows everything about NYC :slight_smile:

Let’s say the project is 75% fun and 35% arguing with the landlord. The point is not to have a discussion on the penny, but to show that the 85% of the bill I’m asked to pay is actually more like 50%.

I’m scratching my head on the Wemos D1 mini now, trying to find the best arrangement of the components on the board, will update the thread when I’m done with pictures of the mess :slight_smile:

Robert Wall said:
you better be certain that what you are saying is totally accurate.

Not to mention that any system he uses to determine a monetary amount may need to be revenue grade.
Depends on state law, local regs, AHJ rules, etc.
AHJ = Authority Having Jurisdiction, usually the energy supplier.

That amount displayed is the overall consumption, that part I know is very precise as it’s based on the revolutions of the meter, the rest has much more margin indeed!

I wanted to thank everyone helping me in this forum. I have the system running for a while and I’m very happy with the result. Here is an example of the dashboard I was able to setup with the data coming from :

  • Light sensor counting the revolution of the meter disc
  • 2xCT, one on each phase going to the basement appartement that is not mine

These two devices feed Watt values to a Graphite Database, the dashboard are made with Grafana.

I will probably be able to get my money back, and it was a lot of fun to put that together! So thank you especially @Robert.Wall !

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So what is the resolution? Did you get a reimbursement? Enquiring minds want to know!

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For now I have a angry landlord which isn’t going after me for not paying my rent. I have neighbours finally admitting they are using a space heater and they’re cold (just to make it clear : I want them to use it if they’re cold, but the landlord or them should pay then). I had ConEd visiting, the guy was an ass and didn’t look at my numbers, so much for that, and he measured near to zero consumption from the neighbours as they were gone for the day (tipped by the landlord? I guess I’m being paranoid…)

Next step for me is to get the landlord to certify I’m up do date on my payments, so they don’t retain the retainer for no reason, and maybe get the neighbours to take a picture of the heater so I can prove at some point. I also have a lawyer filled out a small court document if I want to sue the landlord. The neighbours apartment is probably illegal it would get messy.

In the end I will use these number and apply a 10% security margin in favor of the landlord and deduct from the rent I guess.

I wanted to give you an update with the good news. Got a $10k check from ConEdison, I will never know if the work I’ve done, with your help, was of any assistance but the outcome is great! So thanks everyone!

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That’s brilliant. :tada: Is it good news, or is it GOOD NEWS!

I guess that’s paid for your investment in the OEM kit. It sounds like it’s :christmas_tree:

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Way to go, Yann!

Getting any utility to cough up 10 grand is no small feat.
But getting it out of a major player like ConEd? Nice, very nice!

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Hi Yann Bizeul!
Can i see your codes?
wemos d1 mini pro with the ads1115 analog expander.
Thanks!

Sorry for the super late answer!