Load readings from Inverter don't match Smart Meter

[StealthChesnut]

I have had this issue from install, but haven't been able to figure it out. Here's some background info, followed by some questions.

I have three sources to tell me the Load my house is pulling - the Fox inverter (via home assistant, modbus), my smart meter display and a shelly EM. The Shelly and the smart meter generally agree, but the inverter reading is usually more - and the higher the number the more "out" it is. as an example:
Smart meter: 2.72kw export
Shelly - 2.74kw export
Fox: 3.28 kw export (grid feedin) ~20% higher

Being clear about what/how each source is measuring.
Smart meter: the power passing through.
Shelly EM: CT Clamp on the live feed cable, on the house side of the meter
Fox: CT Clamp on the live feed cable, on the grid side of the meter, for separation from the shelly clamp

I have tried my installer, but they are unhelpful and have argued that a CT clamp can't be wrong.

The CT clamp is connected to the inverter via a longish run of cat5 cable (using 2 TP strands for each leg of the CT clamp wire, so 4 strands in total). The CT clamp wires are connected to the cat5 via a wago connector. It's a mienergy ct clamp.

Questions:
Do different CT Clamps have different signal output curves? Is there a good way to measure this?
Should my fox inverter be able to use a mienergi clamp? Is it plug and play or are there settings that should've been set up?

I also have an odd issue where the Load reading goes to zero, or even negative. This may or may not be related.
E.g. right now my Load is reading at 0.07kw in home assistant, where it's likely to be 300W minimum, and more likely 400-500W. Interestingly, this also fits with the difference between Grid Feedin (2.96kW) and the shelly/smart meter readings (2.47kW).

[canton7]

Your ct clamp needs to match the spec of the foxess one, which iirc is 100A/33.33mA. The datasheet for the clamp should give its spec, or it might even be written on the clamp. (The output from a ct clamp should be linear, but the gradient can differ between models).

Load is calculated from inverter output/input and ct clamp (the inverter doesn't measure how much your house draws - it just knows that if it's sending out X, and you've also got Y coming in from the grid, the house must be consuming X + Y). So if the ct clamp is wrong, load will also be wrong.

[StealthChesnut]

Thanks @canton7 - I know the Load is not a direct reading, and it's important to understand what exactly is being read, and where, to generate the data points!

I see in the datasheet for the mienergy clamp (part number CT100-16-05) on their website that the current ratio is 100A/40mA. I haven't been able to find a similar "official" source for the Fox clamp - do you know anywhere where it's listed please? It sounds like my installer has fitted the wrong part, but I want to have solid information so there's no runaround or excuses to not come out and rectify it.

[canton7]

It's written on the back of the foxess clamp. Mine's inside the fuse box so I can't photo it, but there are pics and similar discussion on the Facebook group.

Code: Select all

https://m.facebook.com/groups/foxessownersgroup/permalink/1723788324670009/

https://m.facebook.com/groups/foxessownersgroup/permalink/1660348067680702/

https://m.facebook.com/groups/foxessownersgroup/permalink/1812452332470274/

[StealthChesnut]

Thanks for the links - I'm giving the installer a try one more time.

[StealthChesnut]

The CT clamp has been replaced from a mienergi one to a proper fox clamp and now all the readings match up.