Additional current tranformer for Neutral measurements

Hi,

I have one of the Pro 3EM and I bought an additional 120A current clamp for the neutral.

Problem is, it comes with 4 pin connector instead of the two pin connector.

Searching in the documention:

https://kb.shelly.cloud/knowledge-base/shelly-pro-3em

States that the correct part number is:

https://kb.shelly.cloud/knowledge-base/ct-120a

Now I'm trying to buy the correct part but I don't seem able to find a shop where the specific clamp for the pro 3EM is available.

Either:

don't show the connector

there is no connector (bare wire)

its the four pin connector

In the official site there is no variant for the "pro 3EM":

https://www.shelly.com/en-es/products…dise#unfiltered

Can you help me find the proprer part for this device at any shop in Europe?

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.

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

Resistance

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.

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

There you can, among others:

- Reverse the CT measurement direction (if needed)

- Phase to phase calibration the new N current

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.

In this case I'm testing all probes wired in a single phase resistive load. 8A.

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.

Zitat von thgoebel

Thema

Einsatz von Fremdwandlern an Shellies der "EM"-Familie

Der erhebliche Preisunterschied zwischen den Original-Stromwandlern für die "Energy Meter"-Shellies und online angebotenen Stromwandlern haben mich dazu bewogen, ein paar Muster vom Laden des wackeren China-Manns zu bestellen:

Der Inhalt kann nicht angezeigt werden, da Sie keine Berechtigung haben, diesen Inhalt zu sehen.

Hier ein Größenvergleich aller Wandler mit den Originaltypen:

Von links nach rechts:

(a) in blau ein Durchsteckwandler, Typ DL--CT08CL5, Nennstrom 80A, 2000/1

(b) in…

thgoebel

24. März 2023 um 13:43

Unfortunately I don't understand German so my searches are limited to English/Spanish/Catalan in most of the cases. I translated your topic and Its quite informative.

I didn't find any trace of diodes in the CT from Alterco, coil is direclty soldered to the harness's cables. Maybe I'm missing something in the translation.

black

red

For me further tests are absurd because right now I don't have the proper AC source/load.

I like the idea to swap all CTs to the 50A version, I'ts more within my working range (2-25A). 120A is too much for most SOHO European appliances.

I assume calibration is a simple linear function (slope) or does it use a LUT for lower currents as well?