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Goodwe 5048EM and VMIII and Pylon Tech problems


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Hi all. I apologise in advance for what may seem a number convoluted questions! Please note, we are totally off grid.

We have been on our land for 3 years, built a hangar and installed a Goodwe 5048EM inverter, 12 x 275w panels and 4 x PylonTech US2000 Plus batteries (4 x 2.4kW - 50ah in parallel). This was on a temporary frame, all worked well but the inverter was insufficient for our eventual needs, or rather, I made the blunder being a newbie, that it was a 5kW system, it does take up to 6kW+ of panels via 2 MPPTs but only outputs a maximum of 2.7kW, would't even start our vacuum cleaner!. 6 months or so ago I bought and installed a 5kW VMIII inverter and another single battery, this time a PylonTech US2000. There is a further model, a US2000b available, as far as I am aware they are all compatible, the two models we have do although I kept the single new battery on the Goodwe as a backup system. More on that later.

I have a problem with the new battery and also with the new VMIII Inverter.

Battery. We recently came back after a weekend away to find the battery displaying a red light.  On restart the battery flashes all green lights then the red light by itself accompanied with a thud sound from the rear part of the battery. Anyone got an idea what this signifies and whether it may be repairable in some way. Being the most recent purchase it is well within warranty but I would rather sort the problem if it means less fuss, I fully realise the potential dangers of opening these batteries up, I have thus far managed to curtail the temptation. I also realise this might invalidate my warranty with PylonTech. Reinvention of the wheel hasn't refined it much. I'm happy to share anything I know and feel sure I'm not unique. I'd be grateful if anyone could share a similar experience and whether/how it was remedied.

VMIII Inverter: The fan runs constantly, there seems no information in the manual to rectify this. So, one day I decided to press the off switch, the inverter went into solar only mode, ie. it was charging the batteries only. Pressed it again and it all came back as normal, so supplying AC as well as charging. Fan continued for around 10 seconds and then went off completely. Inverter behaved as normal otherwise. When the sun hits the panels in the morning or someone draws 1kW or above, eg fridge freezer and freezer come on together, the inverter will immediately power up the fans and stay like that until I go through the whole rigmarole of switching it manually. At a later date we will be using higher loads more often, boiling a 2kW electric kettle. I'd really like to try and sort the fan issue or rather the associated noise. Also no matter how minute the power these fans use is, half the year at 8 hours a day unnecessary running must surely add up?  Highest charge rate I've seen so far was 57a, System works great, always have power, slight shading from a forrest of sweet chestnuts and a couple of big oaks (a lot of trees coming down soon!). I had obviously done some basic research and read reviews before purchasing, there were a few mentions of noisy fans, so I had been warned, being 7m/20' away from a house with 2' thick straw walls, it's not audible in the house

I totally get that these inverters are cheap, I truly believe their quality has vastly improved, the output and general practicality, if you're on site, is second to none. The Goodwe is a lump that is well engineered on the outside, have no idea what's actually on the inside. The build quality and I suppose much higher price should be an indicator of the quality of components, major assumption maybe! It has a huge, nicely machined aluminium heat-sink on the rear, no fans, no noise, no issues. Software works fine on WiFi, tells me everything I need to know, ie. it tells me the things I understand! The VMIII is lighter, noisy fans and to this day I cannot get the serial connection to work on my MacBook, serial to USB converter works fine on a borrowed Windows 7 machine! Same with my phone on Bluetooth, tried until I'm blue in the face. Again, any ideas truly welcome.

Finally, hope this doesn't make me sound a total plonker? My original idea was to use the Goodwe as a second system to service a small, equally off grid guesthouse at the opposite end of our hangar from the house, the system would live in this end of the hangar, feed would be 20m or 60'. This is about the same distance as the house system(the VMIII) at the other end.  We would then have the option to run both systems independently or connect them via changeover switches. This would, in theory, give us full coverage from either inverter, albeit reduced power to the house if that system failed in some way. A second, probably slightly more contentious idea would be to feed AC power from the Goodwe to the VMIII, the latter having both AC mains input and AC from a generator as options. 

Many thanks in advance for any input you're able to offer.

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