Measuring negative active power values (but not always...)

[malonip]

Hello,
I am a bit perplex and look for help in understanding what could be wrong.

I am trying to measure power (and energy) values of my heatpump (PAC pompe à chaleur, in French) - triphased - with a Shelly Pro 3EM-120. I wired it upstream of the 3-phase input to the heat pump (electric current up > down, there is another (main) electrical cabinet above it). Like this :

When the heatpump is in a "standby" mode or just make run a circulating pump, the power values from the Shelly seem to be completely fine (around 10W, up to 30W when the solar circulation pump is running - see screenshot) :

But as soon as the heatpump starts "big activity", such producing hot water, which usually consumes around 2500 W, I am getting negative and mad values from the Shelly Pro :

On my Home Assistant dashboard, the problem is clear :

Globally the house consumes 3.3 kW. 500-600W is standard stuff, so the heatpump should show something around 2500W usage, and not this -223W negative values.

As soon as the heatpump stops to need high power, normal power values get back, as explained above.

As shown in the Home Assistant screenshot above, my global electric installation use solar panels (Enphase). Could the negative values be linked to this and how can I correct the Shelly power values ? Or should I connect the Shelly Pro to other phase locations ? (or is it an hardware issue, very unlikely because hardware is new ?).

Thanks for your ideas...

PS : curiously, the clamps are supposed to be in the correct direction (K->L, up->down), but I had to invert the values in the Shelly interface for displaying the "correct" low W values, when the heatpump is in standby mode. This explains perhaps partially negative values when the heatpump is at max power.

 

Pierre

 

[thgoebel]

Please double check if the wire at terminal A of the Shelly is connected with the wire at which is current clamp A is installed! The same please for B and C. You may test this with a two-wire voltage checker:

[malonip]

Hi @thgoebel,

This is clearly not the case : the Shelly Pro is connected "further down", after a circuit breaker.

Is it necessary that it must be connected to the same wire the clamp is connected to ? I thought it didn't matter (because we are just measuring a magnetic current passing through the clamp). If yes, so I need to connect it in another location.

Thanks a lot for your help !

 

[thgoebel]

1 hour ago, malonip said:

? I thought it didn't matter (because we are just measuring a magnetic current passing through the clamp).

It does matter, indeed! This is because power measurement in AC systems needs the knowledge of the phase shift between voltage and current. Formula is P = U * I * cos φ, where P is power, I is current and φ the phase shift between current and voltage. If you interchange two phases, the phase shift is misaligned, thus showing erroneous power values.

Edited September 10 by thgoebel

[malonip]

Thanks a lot, @thgoebel !
The phases were fine, but I've connected the Shelly PRO to other wires (under the circuit breaker 2), with the clamps measuring the same wires where the Shelly PRO is connected to, and now I am getting correct values !

Again, thanks a lot !