I dissasambled a current transformer for the "incompatible" 3EM non-pro version and compared it to a Pro 3EM version. I did the same with the four transformers (Original A,B,C) and my new N.
This was documented and tested february 2024.
Inside
There is no hall sensor for DC or any other electronics, its just the coil. Predictible for a two wire configuration. Same height and width for the ferrite.
You can't tell which one is pro and which one is non pro.
_ Comparison (Personalizado).jpg
Measurements
The non-pro CT is marked as "N" on its plastic shell, all other A,B,C CTs are the originals from the Pro 3EM package.
Impedance is the same (within an acceptable range) for both. Coil seems to have the same configuration: a single coil (no parallel paths) same number of turns (inductance) same wire (resistance).
Inductance
_ Original L (Personalizado).jpg_ Non Pro L (Personalizado).jpg
Resistance
_ Original R (Personalizado).jpg_ Non Pro R (Personalizado).jpg
The only difference is the connector.
The connector used is MOLEX micro-fit 3 (not specified in the CT documentation). Pro version uses 2pin connector (2 wires used). Non Pro uses 4pin connector, only 2 wires used. Unfortunatelly molex micro-fit is a very bad connector to reassemble, especially the female connector.
It is possible if you have two strong <0.1mm thick and about 2mm wide very-rigid metal sheets to push on both sides (left and right) of the connector from the outside.
Modification
I decided to addapt the 4 pin to a 2 pin version until a new 2 pin connector and pins arrives.
To do it you only need to move the red wire from the side to under the black wire.
Warnings:
- In this case the coil will be "reversed" so you can either: reverse the CT when installed, use the software feature to reverse it.
- You need to carve a little the connector flap for a tight connection.
Because you need to destroy part of the connector to fit it into Pro 3EM you don't need to care about disassembling the female pin from it. Just destroy the plastic carefully until the red pin is released.
_ Modiffied 2 (Personalizado).jpg
Test
Go to the Pro 3EM webserver: first calibrate the probe and check the results.
The calibration menu since 1.2 firmware (or maybe prior to that) is not located where documentation states.
You have to go to HOME --> To see full EM data info click here >
Then on the top mini central menu click on Settings
Screen 2.PNG
There you can, among others:
- Reverse the CT measurement direction (if needed)
- Phase to phase calibration the new N current
Screen 3.PNG
Remember to calibrate any CT: ambient should be free of other current sources, both CT should be connected on the same wire and if possible well aligned.
If you did the connector recycling trick (4pin to 2pin): neutral CT should be connected facing the other power-flow direction (reversed).
Then Select the Source and Destination calibration CTs and calibrate.
Screen 4.PNG
In this case I'm testing all probes wired in a single phase resistive load. 8A.
Screen 5.PNG
Conclusion
Both types of CT seems to be the same except for the molex conector and pinout. They share electrical properties, configuration and size to be interchangleable. Any 4pin-to-2pin molex and and Xpin-to-terminals dongle should do the trick to use the CT on any of the shelly power measurements devices. Connector specifications should be available as well. The pro version should always include this dongles no matter the "eco" argument. The instructions in the official documentation to calibrate CTs on Pro 3EM is outdated and points to the wrong direction.
The Current Transformer situation in the Shelly cosmos is rather dissapointing, especially on the "pro" version of its hardware. Lack of stock, lack of specifications, lack of updated documentation, thats not pro at all.
