Power negative values

Submitted by carticy on Mon, 30/12/2013 - 23:12

Hi Guys,

I'm using the emonTx V3 with the AC/AC and 3 phases.

all is working good, except sometimes the negatives values (one exemple below).

I use the latest emonTxV3_RFM12B_DiscreteSampling.ino.

any idea why negative values ?

Re: Power negative values

Submitted by Robert Wall on Mon, 30/12/2013 - 23:35.

1. You are returning energy into the supply, in which case negative values are correct (assuming you are measuring real power).
2. Your data has been corrupted somewhere.

Re: Power negative values

Submitted by carticy on Thu, 02/01/2014 - 20:35.

Hi Robert,

It is really possible to return energy in an house where no device made for this ? i.e below, around 5 minutes at -150W !

In the mean time, I see that regulary there are power dropping on some secondes (red arrows)

Is it the same for you ? any ideas about this ?

Concerning the code, I use the stock squetch "emonTxV3_RFM12B_DiscreteSampling.ino"

Re: Power negative values

Submitted by wbortz on Sun, 09/02/2014 - 07:06.

Can you look at the individual phase data? Maybe one phase is reversed? I'm not familiar with a 3 phase setup, but I have 2 phase power to the house, and a third CT setup on the water heater. After rewiring the water heater, the heater power came out negative because the CT had been reinstalled the other way around on the same wire. I just added a *-1, but you could also flip the CT.

Wade

Re: Power negative values

Submitted by Robert Wall on Sun, 09/02/2014 - 12:55.

If you have three phases and you are using the single phase sketch, then you will see negative powers on phases two and three. The answer, assuming that you want to measure real power, is to use the three-phase sketch, which provides a delayed voltage wave to the other two phases. I didn't notice that you had a 3-phase supply the first time round.

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