CT Inaccuracies?

[radiomean]

SEG with Octopus on their Octopus Go for my EV, but well worth the wait now...
considering what has happened. Really glad I made the choice, decision then in late April 2022.

Hello again... Just popped in to say I have today changed over to Octopus, (currently away for a few days) but when I get back I am ready to do the setup to go onto Intelligent Octopus tariff. Suggest you investigate it as it's 6 hours at 10p overnight (up from 4 hours on the Go tariff). I think I said I also have an EV...

Will have a look at your answers shortly. Still have to get my Eastron SDM230 wired in fully, and am investigating a 'Chinese' sourced battery as my 6.5 kW does not quite last overnight. Considering a 3 kW rack mounted unit, which at around £850 is dirt cheap and the supplier claims it works with Growatt... Battery is - https://www.aliexpress.com/item/1005004004392051.html

 

[FVScimitar]

Update on last month the setting for the Solax CT clamp have not changed, Grid Off Peak usage 350 kWh and 14.5 kWh for Peak usage so well pleased.

Electric Bill of £46.48 with Standing daily charge of £14.66 included
So we’ll pleased

 

[MACNETWORK]

I think one of the problems with Growatt and the CT is that Growatt supply a plastic coupler to extend the cable - this leaves the shield on the CT end un-earthed - it needs a shielded coupler. And of course the installer coiled the excess cable up in the meter cabinet next to the power cables. Notice how the cable supplied with the CT clamp is very neatly looped and not coiled - it's important.
Also, I see someone used Wago connectors - these are specifically not recommended in the CT datasheet.

 

[FVScimitar]

After reviewing the amount of batter kWh per day to prevent Grid Import; my Live Data from Octopus Home Mini was reporting fluctuating negative -80 to -150 hour per day to prevent Grid Import from my battery storage of SolX 11.6kW minus 10% so 10.2 kW of usable energy, so my daily export for battery was about 2.4kW considering a lack of sun for this March,

I looked at the how the the CT cable was arranged from inverter to Main Meter Box located on outside wall, RJ 45 was unshielded cable and ran along the new Tails to the Mini CU that the installer put in for solar and battery systems.

Purchased a 5m Shielded cable STP, drilled a new hole in brickwork away from the Tails from Henley Block, connected up to the CT using inline wago connectors and guess what the negative - 100 to - -150 W Battery consumption to prevent Grid import reduce the number to under -50w which is probably less than 0.8 kWh so less than 1kW export daily compared to the usual 2.4kW daily as Octopus app now reads so know doubt save battery export plus less Off-Peak battery charging from now on.

 

[nathanharryuk]

Hi all, with regards to the meter and pigtails needing to be done by an electrician because of the main fuse, is it possible to flick the main breaker in the CU and add it to that breaker itself? Meaning when flicking the breaker back on the meter should come on and should give the same reading as if it was connected to the pigtails? Hope that made sense!

 

[radiomean]

Hi all, with regards to the meter and pigtails needing to be done by an electrician because of the main fuse, is it possible to flick the main breaker in the CU and add it to that breaker itself? Meaning when flicking the breaker back on the meter should come on and should give the same reading as if it was connected to the pigtails? Hope that made sense

I suppose it's possible but I can't say I like the idea. Many (most?) consumer units will have bus bars on the output of the main switch, to connect to the MCBs, so I can't see how easy it will be to connect (eg) an Eastron. Also, I would prefer such a meter on its own in the external meter cabinet (to avoid any possible noise from inside the consumer unit).

With Octopus, they put an isolator at the output side (my side - the customer's side) of the meter so I could connect my Eastron after the isolator myself. Octopus did the installation for free... Everything after the isolator is the customer's property/responsibility. HTH...

 

[Lazy_pete]

Hi - just been reading all this and very interesting. I currently have an Eastron meter reading grid current from a CT clamp on the live main feed before the meter (grid side). Feeds data via radio Modbus to another meter in Garage and hence to Inverter. For some reason however the Eastron under reports by a factor of 3x compared to the Live app for the Smart meter. This is resulting in the daily Octopus usage values being almost exactly 3x higher than the SolisCloud import values. The fact it’s so far off makes me think there is a config issue somewhere from installation, but I can’t think what it is. The only oddity I’ve found is that the CT clamp itself is labelled as having a 120A rating while the Eastron meter is configured for a 100A rated CT clamp.

I presume the inaccuracy in the read from the grid will be resulting in inefficiency in the PV / Battery system along the lines of what you describe above - always drawing a little from the grid.

Any suggest as to what may be wrong ? As far as I can tell the only thing you sorted (after wiring / clamp position) was to reverse a single setting in the inverter ?

Cheers,

Pete

 

[SeaGal]

...Feeds data via radio Modbus to another meter in Garage and hence to Inverter.

What exactly do you mean by feeding modbus data from one meter to another meter?

Either way, I'd first check the reading on the LCD screen of the Eastron and see if that matches the reading the Solis shows on its front screen. That will determine whether the issue is with the meter itself or the meter->solis interface or just an issue with the Solis cloud.

I don't expect any 'inaccuracy' to be of the order of 300%.

 

[Lazy_pete]

Thanks - my Garage is about 25m from the house and main consumer unit, so the installer has attached an Eastron meter in the consumer unit by the main fuse / meter. Rather than run a cable to the inverter in the garage the Eastron is connected to an OBM-Lora-223 long range wireless trasmitter / receiver pair, which transmits the Modbus standard RS485 signal to the garage. This is received and fed to another meter in the garage which is then connected to the inverter to provide the grid feed.

It’s hard to check both the lcd at the consumer unit in the house and the inverter screen simultaneously as they are so far apart, however the data sent to the garage from the Eastron seems to be low by 300%, reading from the Eastron LCD vs the smart meter dongles live display. 300% low matches my daily grid consumption data from Solis compared to Octopus. I’m presuming the smart meter and therefore octopus are correct, but either way they should be the same I think.

I home I’ve explained it correctly.

 

[SeaGal]

This is received and fed to another meter in the garage which is then connected to the inverter to provide the grid feed.

I still don't understand what you mean by feeding the output of the Eastron meter to another meter. I would expect that the receiving end of your Lora/RS485 output would connect directly to the Solis inverter, rather than "another meter".

Anyway, as the Eastron's display is not showing the same as your smart meter display for a steady house load, then, as you worked out, it looks like the Eastron itself not working or not installed correctly. I'm not familiar with the Eastron (my Solis has an Acrel meter), but quick look at Easton's web page shows there are many different clamps with different current outputs. If your's is not the correct one for the meter, or the meter not configured to use the 120A clamp, that would be the most likely cause of the problem. Can you reconfigure the Eastron meter to use the 120A/40mA clamp?

Hmmm, just thinking as I typed that... an image I saw of the SDM-120CT meter shows...



Which refers to 100mA CT. So if the meter is expecting 100A grid draw to generate 100mA of CT current, then a meter that only delivers 40mA @ 120A is exactly 1/3 of the current - so that's where the 300% inaccuracy is coming from IMHO.

Looks like your installer has given you the wrong CT clamp - I suspect the Eastron is not configurable if it specifically says 100mA on the side of the meter.



As you worked out,

 

[Lazy_pete]

That’s what I suspected, though I had not managed to work the maths out as eloquently as you have ! I shall send this to the installer and see if he can come up with a 100A rated CT clamp for me / re flash the Eastron firmware to allow setting up for the 120A rated clamp. Thanks so much for this !

 

[Lazy_pete]

The Modbus radio thing in the garages consumer unit, feeding to another ‘meter’ in the wall between it and the inverter.

 

[SeaGal]

Great, good luck - keep us updated

 

[Lazy_pete]

Hi - just reporting back. The installer came and changed the CT clamp and all the readings seem to match up normally now. Thanks so much for your help @seagal

 

[SeaGal]

Result! Thanks for the update