June 16, 20242 yr I just got a new Sumry 6.2Kw inverter as my previous one popped a capacitor. Installed it without issue same as the old one. Power's up & works fine/charging on Utility power however when I connect the PV, it's reading 210v & 0.9kw PV input AT NIGHT, followed by the inverter shutting down with an error code "output power derating". I have 2 x 100ah, 48v lithium batteries that were around 50v when the inverter shut down so I'm 100% sure it's not a low battery condition. It only happens when I turn on the DC breaker for the PVs. I confirmed the voltage on the PV input side with a multimeter & it's around 210vac. However, I did a search & this Voltage seems to be typical of this type of inverter. What's not typical is that for whatever reason, the inverter is detecting 0.9kw of solar input when there should be almost zero at night. I'm pretty sure the alarm is somehow related to this but can't figure it out. Any help would be greatly appreciated! Thanks, Kris
June 17, 20242 yr 13 hours ago, Klinky said: PV input side with a multimeter & it's around 210vac If you're getting AC voltage out or in on the DC input side, you have some serious problems, some cross connected wiring? the inverter faulty?...
June 17, 20242 yr 19 hours ago, Klinky said: I confirmed the voltage on the PV input side with a multimeter & it's around 210vac. If that's from one or other PV input to earth, that is probably normal for a high PV voltage model. If that's from PV+ to PV-, then as Kalahari Meerkat says, you have some serious problems. Unless perhaps your meter is reading true RMS, then 210VDC might read as 210 VAC on the AC scale, depending on how it works.
June 17, 20242 yr Author These are the stats. It's a brand new inverter, yes PV to earth. I'm thinking I have a panel shorted to earth so I'll be disconnecting them one by one to test.
June 17, 20242 yr 25 minutes ago, Klinky said: These are the stats. It's a brand new inverter, yes PV to earth. I'm thinking I have a panel shorted to earth so I'll be disconnecting them one by one to test. I believe it's normal for there to be voltage potential diffrence between the DC conductors and earth ground specifically at high voltage because most PV systems are isolated but not AC measured voltage between + - of the mppt, what instrument are you using to measure this? Edited June 17, 20242 yr by TaliaB
June 17, 20242 yr With everything shut down and PV wires unplugged, check resistance from pos and neg PV panel lines to frame of panel. Infinity resistance would be nice but should be at least greater than 1M ohms. Edited June 17, 20242 yr by TaliaB
June 18, 20242 yr Author Thanks, I've measured resistance & I'm getting a couple of Kohms resistance between PV inputs & earth. I will have to climb into/onto the roof & investigate further. This solar system came with the house when I bought it so don't know the history or indeed how the panels are arranged etc.
June 18, 20242 yr Author I'm using a Fluke multimeter, not sure of model off the top of my head. Can I use a meggermeter to check the insulation on the panels/panel wiring or is this not a good idea?
June 18, 20242 yr 2 hours ago, Klinky said: Can I use a meggermeter to check the insulation on the panels/panel wiring or is this not a good idea? Yes you can, neg lead to array earth pos lead to neg(array) then pos lead to pos(array). Start with 250v then 500v and lastly 1000v should be above 30Mohms @250v could be lower @1000v but not below 10Mohms. REMEMBER TO DISCONNECT POS AND NEG FROM MPPT. Edited June 18, 20242 yr by TaliaB
June 18, 20242 yr Author Thanks so much, I'll give it a go when I get some time & let you know the outcome! It won't pinpoint where the issue is, just confirm that there is actually an issue. I'm still going to have to disconnect each string & test individually which will be fun. Edited June 18, 20242 yr by Klinky
June 22, 20242 yr Author Hi guys, Just an update - I finally got some time to use the megger to insulation test my PV array. It failed instantly on 250v so there was an obvious problem. I climbed up on the roof & after unbolting one side of each panel I could lift up the side of the panel containing the connectors. What I found wasn't a pretty sight. 2 strings of 6 x 420w 36VOC panels, wired in series. The MC4 connectors between each panel were fine but the extension cables coming into the house were just wrapped wire with insulation tape & both the positive & negative connections were completely burnt up on one of the strings & obviously making contact with the chromadeck tin roofing! I'm going to get some MC4 connectors & join them correctly but in the meantime I soldered the connections (with solder & a lighter) & covered with heat shrink tubing. Everything is working perfectly now & no more faults on the inverter! Thanks for your input, I probably would have broken down & called out a solar guy if it wasn't for your suggestions! If you ever find yourselves in sunny Mutorashanga, Zimbabwe, right next to the middle of nowhere, I owe you a beer!
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.