F3600 G3 inverter clipping @3kw!

[thedozzer]

HI
Had my system installed at beginning of Feb
13 x 640Longi panels on two buildings, one with 6 panels on, one with 7.
2 inverters, 1 x 3kw (F3000 G2) for the 6 panel set up 1 x 3.6kw for 7 panel system. (F3600 G3)
these then feed back to house via mains then into inverter and battery.
the system is all set up for G99 as per DNO.
The 3kw system has been working fine and has produced up to 3.2kw
the 3.6kw is not working as it should and have spoken to Fox UK without much luck.
please see a plot from today to give an idea. but basically its clipping at 3kw.
there have been days when it will surge past the 3kw and has even stayed there for 20 - 30 mins, but then will drop well bellow.
All 7 panels are on one string, but both the installer and Fox UK have said this was fine and would help maximise low light power!!
anyone have any idea why this could be behaving like this?
I can add screen shots from the days when it has reached the 3.82kw that the data sheet says but its never for long!

[MaterialBarracuda48]

It does look like the firmware is old, not saying an upgrade will fix the issue, but you never know?
Both inverters would need updating fully, Master/Manager/Slave.
viewtopic.php?p=8069#p8069

What is your export limit and other power limits set in both inverters, maybe they are sharing this between them and it clips because of this?

[thedozzer]

There are 2 DNO's for the system, both are G99 so set to +3.65kw so should be OK up to 40kw i think
The other inverter is running fine. and this one has output 3.92kw but it only seems to last about 10 mins max, and then falls lower. and it seems to need a running start to get there, its almost like a relay or some other component is failing to switch in.
Im beginning to think there is some individual sting limit that's not documented.
and if we split the 7 into 3 and 4 it may work better??
will look at doing an update, but Fox UK say they have already remotely updated!

[MaterialBarracuda48]

I think the spec sheet claims 7.2kW of DC input total.
So you would like to think it can handle the panels you have setup.

Not sure what Fox are saying about the FW, but seems different than what is on Will's spreadsheet to my eyes.
Have to see how this pans out for your.

Have you checked Inverter temps/PV values and other possible logs in the website? Maybe something looks more obvious there.

[thedozzer]

Inverter temps have not been problem, its in a cartlodge, so in the outside but shaded.
PV is showing 332.9v but only 9,1amp
they are rated to 14,4-18.6 amps so not sure if its the inverter holding them down

[MaterialBarracuda48]

If you swapped to PV2 does it still behave the same?
Might be worth a try, and as you said, you could split the strings maybe.

[thedozzer]

Swapped from MPPT 1 to 2, still the same, and then swapped back
Have borrowed an irradiance meter from installer and it was showing 1024W /M2 and temp around 18c.
with the 7 x Longi 640w Calcs show i should have been getting a minimum of 3.9Kw but its still showing 330v 9,1amp. 3.09w
installer is going to fit a meter in-between the panels & the inverter to see where the extra energy is hiding.

[MaterialBarracuda48]

Be interesting to hear an update on this, broken panel or Inverter (maybe neither!)

[thedozzer]

If it was a dead diode or other panel problem, i would expect the bell curve to ramp up slower?
a faulty panel wouldn't just die at a very specific power! the ramp is quite quick as the sun comes over the hill in the morning, and the way its stays in a very specific power range for around 5hrs would suggest the inverter is the restriction.

if all the system was working 100% there is 4.48kw of panels working at around 1020W m2 even if you said 0nly 90% of efficiency because of lower temp 18c not 25c you would still be seeing 4.03kw, and the inverter is Supposed to max out at 3.98kw, so something it definitely not 100%
Im tempted to buy another inverter to test the panels out. would be relatively conclusive then.

[MaterialBarracuda48]

Tempting on the latter

[thedozzer]

Well another day and another 1kw + per hour lost!!
Have emailed Fox UK and spoken to installer, Installer thinks it may well be inverter.
FOX ESS Uk completely disinterested and say there is nothing wrong!! very disappointed in the level of customer service.

the plot shows the inverter/panels can make way more than 3kw, but always default back. its like there is some component that unless it gets a sudden surge is limiting the current.
Have ordered a second hand 5kw inverter from ebay (not fox) and will see what the panels do then.

[MaterialBarracuda48]

I am still paying attention to your thread, wanting to see the outcome of your inverter swap when that occurs.

[thedozzer]

Have now had a Solex inverter fitted to the string that the F3600 G3 was fitted to, and it has been able to maintain up to 3800w with peeks of 4040w

So its quite clear that the Fox F3600 is at fault, but getting Fox UK to accept is going to be the next challenge.
Its quite odd that a second hand Solex that is 6 years old is working better than a bran new Fox unit, under identical conditions.

images from sunny periods at 10am this morning.

[MaterialBarracuda48]

Interesting outcome, and nice to find out what Fox has to say about the Inverter.

[thedozzer]

Another update.
So while the Solex inverter has proved the Cart lodge string can produce in-excess of 4kw.
Have moved the F3600 G3 to the workshop string where the 6 x 640w panels are split into 2 strings 3 in each.
Had read on other forums from Australia that many people have seen the inverters cap/clip @3kw on a single string. even 5.7kw units.
So this is a picture from the Workshop with the F3600, it had no problem with producing 3.2-3.4kw consistently, which would confirm my original thoughts that 3kw is the max per string. sorry second pic is blurry but phone wouldn't focus on bright display.