Solar PV / current sensing

What make of inverter, OOI?

I don't have specific experience here, but I wonder if the CT on the inverter is not accurate enough to measure that kind of load? A lot of the monitoring is interested in kW (make sure you don't overload your 100A supply, etc) and maybe the CTs aren't sized to measure currents down at the <1A level. CTs are fairly sensitive devices (the magnetic field from 0.5A flowing in a mains cable is not that strong, and the clipon ones don't have a lot of turns) and I wouldn't be surprised if accuracy suffers at the bottom end.

I'm a bit puzzled as to why you get periodic measurement drops though, if that's what you mean (ie every couple of hours or whatever the power drops to 30W?). Do you by any chance have anything kicking in on that kind of interval that might interfere with the CT? For example a fridge compressor could spew out some EMI that made a false CT reading.

Are the CTs connected via their own cable (twisted pair, screened?), or have the electricians done their own cable runs for them? I wonder if the wiring isn't properly balanced and is admitting EMI.

Rough translation: "we haven't the foggiest either and CBA to learn".

Theo

It's a Sofar hybrid inverter HYD-6000 generally reckoned to be pretty good kit... And - to be fair - it seems to be working well. Just the engineer in me wants to know where these odd data-points are coming from.

Thing is - the other 'eddi' device uses the same technology (CTs) - but doesn't show these impossibly-low data-points.

Doesn't seem to happen overnight - it's usually at random times between

They used Cat5 cable to connect the CT (located in the fuseboard, by the back door) up to the inverter (two floors up in the attic).

One thing I did wonder about - they've run the Cat5 down from the attic, cable-tied to the 6mm2 cable that carries the output power from the inverter back to the fuseboard. This cable run could be 30 or 40 ft - I was wondering if the unshielded Cat5 could be picking up spikes from the mutual coupling..?

That was my reading of it - strong smell of bullsh*t, mixed with a healthy amount of 'we've got your money - now go away...'

My own background is 55 years in electronics, A-levels in maths & physics, some physics at degree level, and so on....

Have contacted the inverter manufacturer to see what they say...

Thanks! Adrian

Under or over voltage causing the inverter to drop off grid? Do you get voltage graphs as well as current graphs?

Funny you should say that - the grid just dropped for 2 seconds - long enough to reboot the pcs!

As I say - strange thing is that the graph from the eddi does not show any of these dips....

Sounds like a software issue, or in fact it is getting the rest of the current from somewhere else which is not being monitored. Brian

If its during the day only then that seems to be a good clue. The sun does not shine at night, at least not around here. Brian

Heh... I have the Sofar ME3000SP in the post to me. Allegedly 'faulty', so we'll see how it goes. I think that uses the same CTs.

(The HYD series look nice though, especially if you can have everything in one place)

They're doing different slightly jobs so might be optimised in different ways.

That is interesting. Does it happen when you're out? That suggests the cause is something related to human activity.

Cat5 should be OK I think. The manual:

I wonder if they've installed the CT on unbalanced wires - two wires not in the same twisted pair?

The way it's written in the manual (p15):

"Step 2: You can use network cable & terminal caps to extend CT wires if necessary, the maximum CT cable length is 200m. CT wire Extension cable (network cable) HYD‐ES inverter

-------------------------------------------------------------------------------- Red Orange / white orange / brown / white brown CT+ Black Green / white green / blue / white blue CT‐ "

they seem to be putting each wire expressly on different pairs, ie unbalanced. That seems a very surprising thing to do.

(The first time I read that, I was thinking the dozy electrician might have picked any wire from the list, rather than obeying the pairs - eg orange and white+blue, instead of orange and white+orange. But looking more closely at the list it's actually impossible to obey the table and end up on the same pair)

Yep. BTDT.

Perhaps you should be teaching them :-)

Be interested if they have something to say on the pairs issue.

Theo

I've not seen that effect with my PV monitoring using a 'Holmes + Wattson' system, but the current sensor on the output is non-directional so it reads output in daylight and input to the inverter in the dark. It says it consumes 12W at night.

HI Brian (sorry - sent my reply direct to to you rather than via the group)

No - much the same situation over here in Ireland - sunshine during the day only <grin>

I've a theory - well, two of 'em really

No1 - badly-terminated cable to the Current Transformers. The installers have 'previous' for this - at least two of the cat5 cables on the original install had been stripped in such a way that the wire cores had been 'nicked', leaving the connection only intermittent

No2 - The cat5 cable is cable-tied to the 6mm2 cable which carries 'produced' power from the inverter down to the main fuseboard. I think there's a possibility that the small current in the cat5 cable could be affected by the large currents in the 6mm2 cable, inducing these odd reading from time to time..

Probably nothing to worry about, either of them, though if the potential intermittent contact in No1 were to become a full-time open-circuit then that'd be a worry.

Just the engineering in me - asking 'why?' - and being fed a diet of bull from the installer!

Adrian

Yes - generally reckoned to be an OK piece of kit

- though it is, of course, only as good as the inputs it gets!

Possibly. The eddi gets its 'production' figure from a CT located in the fusebox (same as the inverter CT) - but the actual readings are transmitted wirelessly (rather that via a cable) from the harvi by the fuseboard to the eddi in the airing cupboard upstairs - so no opportunity for any odd effects...

Haven't really checked that - I've a feeling that it's related to times when there's a decent amount of power generated, but I've not correlated that...

Now that's interesting - so the wires, being not part of a twisted pair, could be susceptible to inductive coupling effects. It'd be a fairly easy thing to test - simply by chosing two wires that _were_ part of a twisted pair - or, practically, just changing one of the wires at both ends...

Ah - not just me then... Annoys me - that sort of thing....

Believe me - I'm doing my best..

There were a number of snags on the initial install - probably the biggest one being that the comms/logging dongle on the inverter was having difficulty connecting to the range extender on the house wifi.

I told them for 3 weeks that the dongle was faulty - and that, if they'd care to post me a replacement then I'd happily plug it in and see. They said that 'It would take too long to explain to you how to set the dongle up'.....!

As a test, I moved the wifi range extender so it was 2ft away from the inverter / dongle - at which point it all burst into life. They blamed the range extender!

Eventually a man with half a clue came down, with a good dongle, plugged it in, and everything worked - even with the extender moved back to its original location...

They haven't responded at all, so far.... but I'll remember to mention it when they do..

Good thinking.

I might just swap the cores over at both ends of the cable and see if the fault goes away. Can't believe I'm the only person on the planet to have this issue..?

Thanks Adrian

As a hardware engineer, I'm always happy to blame the software! <grin>

When I'm wearing my software engineer's hat then I'm equally happy to blame the hardware!

First things first though - if the software's being fed duff signal-levels then it can't be expected to do very well - and Theo's idea about the twisted pairs in the cat5 might be worth exploring....

What fun - I do like paying people to install stuff so I can waste my time debugging it for them.

Thanks Adrian

Hi John. Thanks for the reply - yes - I'm pretty sure that this CT is bi-directional - although I don't think the inverter cares at all about power that's being imported _from_ the grid ("Not my department" it says).

The eddi (which handles where the generated power goes - to dhw or back to the grid) does know about grid power in/out - and does clever things and displays info on the basis of it...

Thanks Adrian

...

That's what I was wondering, whether the cable runs are different - also the eddi only really cares about 3kW for your immersion so it's fine for the CTs to top out there, whereas the CTs for the inverter might be measuring a lot more than that.

Yes. Basically it's down to the size of the inductive loop formed by the wires (if you think of them being connected together at one end). Magnetic flux lines passing through the loop induce a voltage across the loop, and the number of flux lines cut is proportional to the loop area (assuming uniformity of field). In twisted pair the twists make the area between the two wires very small, while in regular multicore there's a nontrivial area between the two wires running separately, especially at bends.

Given they've clipped it to the current carrying conductor, that conductor will be emitting a strong magnetic field when the system is generating (or charging from the grid). They've located the CT cable perfectly for inductive coupling between the sense wires and the current carrying conductor.

Twisted pair is designed to cope with that, but not if you don't use the twisted pairs!

Worth a try I think. I can't see any harm will come, assuming the wires aren't connected to anything else.

My heat pump installers were similar. Yes it works, but some of the decisions they took were not the best (not helped by dumbness at the UK importer), and so I've had to clear up after them and do it properly. And I started off knowing nothing whatsoever about plumbing (but something about control systems).

TBH I'm not expecting great things out of Shenzhen, but happy to be pleasantly surprised.

I'm quite surprised too - I was wondering whether it got badly translated from Chinese or something, but hard to read that table in a different way. It might be worth asking around

Theo

On 21/08/2022 12:48, Theo wrote: <snip>

Ah well - there's a disappointment - took a quick look at the Consumer Unit end of things, and they've used a twisted pair at this end of the Cat5 cable (so ignored the instructions in the Manual)

Haven't checked what happened at the far end of the cable yet

- but, I guess, even with a twisted pair there might be a chance of some sort of coupling

- though it'd be greatly reduced...

Back to the drawing-board! <grin>

Thanks Adrian

Doncaster cables EV-ultra cable (or whatever it's called) has twisted pairs for CTs or ethernet within the same cable as the main conductors, I think it is STP rather than UTP.

Hi Andy. Ah, that's interesting.... On closer examination today it seems that the installers did actually use a twisted pair on the cat5 for the CT - so that's one elegant theory shot down in flames!

Thanks Adrian