Energy meter schematic query

Thread Starter

Vindhyachal Takniki

Joined Nov 3, 2014
579
I have made a schematic using ADE7753. Attached is the ckt.
ADE7753 is powered from 5V & micocontroller is 3.3V one.

1. In the ckt I found that neutral of system has to be shorted with microocntoller ground & ADE7753 ground. Is it ok? Is this how it is done?

2. Is there any way I get to know that line & neutral are interchanged in the system. Because I have seen generally in house meters there is led indication showing if line is connected to neutral & neutral is connected to line.

3. I have to connect it to 3.3V micocontroller. In datasheet of ADE7753 VIH is 2.4V or I think all ouput lines on SPI can be connected to MCU directly while for MISO I connected a 1K resistor in between. Is it ok?

4. Max adc inputs for ADE7753 are 0.5V max. So calaculations for voltage are:
R4: 1M (will connect two 500k in series)
R5:1K
At 275Vacrms, 50Hz, Vp= 389Vp
So voltage at input = (R5/(R4+R5) * Vp = 0.39
So I think its ok

5. Max cuurrent to be measured = 50Aacrms
So Ip= 70.71V
With CT of 1800:1; I = Ip/1800 = 0.039V
With burden resistor of 10ohm V = 0.392V

6. Are above calaculations ok?
7. Is ckt ok?
8. Is there any example code. I found some of net: https://searchcode.com/codesearch/view/17414705/
Will took reference from this code & see if it works.
Design4-1.png
 

DickCappels

Joined Aug 21, 2008
7,163
I can only offer opinions on your first two questions, but there are others (who should be along shortly) that understand the rest of them.

I have made a schematic using ADE7753. Attached is the ckt.
ADE7753 is powered from 5V & micocontroller is 3.3V one.

1. In the ckt I found that neutral of system has to be shorted with microocntoller ground & ADE7753 ground. Is it ok? Is this how it is done?

2. Is there any way I get to know that line & neutral are interchanged in the system. Because I have seen generally in house meters there is led indication showing if line is connected to neutral & neutral is connected to line.
<some text removed for clairity>
View attachment 114320
1. No, they are not supposed to be connected together. Neutral is referenced to earth and purpose of the connection to Neutral through R6 is to measure the voltage on Neutral with respect to earth. Shorting them together is not only unsafe, but it would prvent the measurement from being made.

2. In short, You can tell the difference because Neutral had just a few volts AC between it and earth and Line has about the fully mains voltage between it and earth.

Swapped Line and Neutral occurs and that's one reason using Neutral as ground can get you into trouble. In the systems I've measured (United States and Thailand, but I am pretty sure this works for the rest of the world as well) there is very little voltage from Neutral to earth and it is usually there as a IR (current x resistance) drop in the Neutral wife between the load and the point at which it is earthed. Something like 5 VAC or less is common in typical residential systems. The voltage on Line is very close to the full voltage (220 VAC, etc.).

Line usually has the full voltage across it (such as 240VAC) while the Neutral
 

Alec_t

Joined Sep 17, 2013
11,981
In the ckt I found that neutral of system has to be shorted with microcontroller ground & ADE7753 ground. Is it ok?
No. I agree with Dick. I also think it would be safer to measure mains voltage by measuring the voltage at the cathode of D2 or D4 then multiplying by the transformer turns ratio, rather than use the 1megohm to Line connection.
 

RichardO

Joined May 4, 2013
2,271
I also think it would be safer to measure mains voltage by measuring the voltage at the cathode of D2 or D4 then multiplying by the transformer turns ratio, rather than use the 1megohm to Line connection.
I don't think the waveform at the diodes will be very sinusoidal due to non-linearities caused by the diodes. The filter capacitor will also distort the peak of the sinewave as the cap charges.

I will do a LTpice simulation when I get time...
 
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