Design of Arduino 3-phase Energy meter - Suggestions / Reccomendations /Errors?

Hi all,

Attached is my design for an arduino 3 phase Energy Meter based on Analog Device’s ADE7758 marked as U2.

The attached schematic sheet only shows the power meter part. The Arduino based on an ATMEGA32U4 part is on separate sheet and not shown, however its a standard arduino Micro setup with an LCD display and RS485 interface.

I am looking to any recommendations or error spotting to improve the design before I move on to the PCB.

There are two separate 5v supplies for the circuit : Vdd and Vcc. Vdd supplies the ADE7758 both the analog and digital part while Vcc supplies the rest of the circuitry including the Arduino. The two supplies as well all signals from and to the ADE7758 (connected to mains voltage 230V AC) are kept isolated for safety reasons. The ADUM1402s are used to provide galvanic isolation between the two parts of the circuitry.

I had to somehow provide for the two 5V DC supplies and the only way I could think of was a transformer with two secondary windings fed from phase A of the mains, as shown in the diagram.

Pin jumpers on power supplies (JP6,7) and grounds (JP5) are used to temporarily power the unit from the USB supply for easy testing purposes. ( in this case other USB isolation is needed)

Please note that power requirements are small and not more than 100mA.
However the transformer is bulky and … I dont like it sitting on the PCB!
If anyone can think of another easy way around , I would be more than happy to listen. (I wonder how commercial utility power meters solve this issue…)

Any other recommendations also welcome.

PowerMeter.pdf (88.7 KB)

Be careful with your transformer selection. I would not expect the limited secondary to secondary isolation of a dual output winding general purpose transformer to be sufficient for the needs of that project.

Option 1: A four winding transformer - four different coils on a closed U core. Signal Transformers "Flathead" series as an example. Others make similar stuff. Standard product with high isolation.

Option 2: DC feed the box and use two commercial high isolation voltage dc-dc convertors.

Thanks AVR-fred!

I was also worry of the isolation between the two secondary coils since they are usually wound on top of each other.

Do you know of any specific transformers for option 1, PCB mounted?

I also thought of option 2 as well. 24V DC is locally available but I couldn't find any small sized PCB mounted DC-DC converters with enough isolation that would do. And since there have to be two of them, size is an issue. The PCB measures only about 80x100mm

You realize both the AP1117 regulators and bridge rectifiers are backwards?

Dear Mark, you are a real life saver. - I could never thank you enough!!! :slight_smile:

I might have checked the design something like 20 times and I completely missed that.

I wanna buy you a beer but... for now Karma points will have to do! :slight_smile:

Thanks again!

Do you know of any specific transformers for option 1, PCB mounted?

Yes, the brand and model I mentioned. These are wound with four separate coils on dual plastic bobbins, they are not overwound with just paper layers for isolation.

Signal Flathead low profile PC mount transfomers

If you're within the USA, both DigiKey and Mouser stock this product. Several other transformer manufacturers make similar products but I'm most familiar with Signal.