H1-3.7-E inverter second string: zero current issue

[rob19473]

I have a H1-3.7-E inverter. I have one string of 8 panels in series and a seperate string of 3 panels in series.

The 8 panel string works fine. The 3 panel string does not appear to work.

I have tested the panels, they are 34-35V each and individually show an expected short circuit current for sun (3-11A).
The cable between the panels and the inverter has been tested and has an expected resistance (0.4 Ohms).
Both pv1 and pv2 inputs on the inverter appear to work - as if I swap the strings around, the 8 panels continue to work as expected on pv2 - just as they do on pv1.
The PV Config setting (Setting -> Feature -> PV Config) is 'Independent'.
The inverter reports the 3 panel string as 104V (when not particularly sunny) but current is always 0.0A. (8 panel string is 250+V as more panels and current ~10A as reported by the H1 unit).
If only the 3 panel string is connected to the inverter without the 8 panel string, the inverter reports 'waiting' and does nothing (still reporting 104V, 0.0A).

The datasheet suggests the MPPT voltage range is 80-550V so I believe at 104V there should be current/generation.

Any ideas why there is no current on the 3 panel string?
Does the inverter have a 'PV start voltage setting' or equivalant? (which maybe set higher than 104V but lower than 250V?)

Thanks,
Rob

[Dave Foster]

From the tests you've done it sounds like the 3 panels are wired correctly, but even though you've got enough voltage to get over the PV startup voltage, irrespective of what the datasheets say for startup voltage (75V) and MPPT range (min 80V) I wouldn't expect 3 panels to work particularly if they are larger panels (~400w), normally I would recommend a minimum of 5 panels, I have seen some smaller 4 panel strings work ok - but 3 panels just doesn't work.

Are you in a position to add another panel(s), even if just to test ?

[rob19473]

Hi Dave, thank you for your reply,

I've no practical way to add another panel (without buying one), no.

Is three panels not working a Foxess specific issue? It is of course a shame that the data-sheet is misleading.

Is there anything written down where I can give myself confidence even 4 panels will work (the actual voltage level - or what parameters influence this)?

Thanks,
Rob

[Dave Foster]

Sadly nothing in writing, the specs suggest it should work but i’ve spoken to a few people that have been unable to get 3 panels working even with their installer and Foxess scratching their heads on it, they had the same as you 105V on the string and it wouldn’t start up.

I can guarantee that 5 panels work perfectly in all conditions (I have that on my second string), and i’ve just done a quick check on what others have and there are a few with 4 panel arrays using JA 365w, and Jinko 415W panels.

If panel space is the problem you could get a small solar inverter and use that for the 3 panels, if you connect a CT clamp around it’s live tail and feed it to CT2 on the Foxess inverter it would report and work with all your generation correctly.