I can't measure power, is it broken??

[Gianluca]

Hi, I have for the first time a Shelly em. I installed it with no problem, but I can't measure power.

I have voltage measure, so Shelly seems to work fine. The clamp is on 1 phase cable, and I tried also to clamp to the Shelly phase cable, so I'm sure to have a little load, but I have only 0 measure, in ch1 and in ch2. 

Mistakes? or fault clamp/shelly for you??

[thgoebel]

Shelly EM (the type at which the cables of the current clamps are fixed with terminal screws) are very sensitive for excess torque. The circuit paths are very thin and tend to rupture with too much torque. If you possess a multimeter you may check the resistance between terminal P1+ and P1- (P2+ and P2-, respectively). You should measure approximately 10Ω. Of course you should take the measurements without powering the Shelly and without clamps attached.

[Gianluca]

thgoebel, thanks.

I made measure and between P1+ and P1- I have OL, while between P2+ and P2- I have 10 ohms. Power check however is not working in P1 and P2. The fact that I have OL in P1  means that something is wrong... what do you think?

[thgoebel]

Obviously, the circuit path at terminal(s) P1 is broken. Please double check input P2 if really no current and power is indicated!

[Gianluca]

if you set the clamp around tha phase of power of the shelly, brown cable, i think I have a measurement, right? but I have zero

[thgoebel]

The current and the power consumption of the Shelly itself may be too low for a display. There is some provision taken to eliminate „meter creep“, which suppresses very low current and power values. Best practice would be to measure a table lamp  or a water boiler. But you have to arrange a plug/jack combination with single wires between to mount the current clamp.

Edited July 31 by thgoebel

[Gianluca]

ok thank you, I'll try to check it with a different power, greater than shelly's one

[thgoebel]

Found a picture of the weak point of Shelly EM:

In the blue and red circle are blow-ups of the circuit paths. It’s easily to understand that this fine paths are very sensitive to excess torque…

 

 

Edited July 31 by thgoebel

[Gianluca]

uau thank you, i'll try to open it and check the soldering

[Gianluca]

waiting for to open it and check the soldering, I made a ohm measurement on the clamp disconnected and i have about 500 ohm. Is it right?

[thgoebel]

Yes, indeed. Current clamps have an internal resistance of approximately 500Ω.

By the way: You’re waiting for an autonomous opening by the device itself? 😎

Edited August 2 by thgoebel

[Gianluca]

he he, no... I have to open it.....

So 500Ω is correct and the clamp is right I think.

[Gianluca]

[Gianluca]

well, p2 is ok and I can measure power!

p1 is broken

thank you for your help