I too disable the FNDC, although I call it something else. You do seem to have a grasp on it, but Ill ask anyway. The batteries were fully charged prior to connecting? Again I have found, that device has allowed me to charge for many miles to disconnect it for excessive inaccurate readings. > On Aug 25, 2026, at 9:50 PM, Jason Szumlanski > <[email protected]> wrote: > > I have hesitantly removed the FNDC from a few systems for the same reason. > The accuracy is poor, especially when batteries don't reach full charge > frequently, which is an epidemic around here with undersized arrays and > oversized lead acid batteries. > > Accurate SOC is the holy grail of off-grid monitoring systems. My > understanding is that EVs do this at least slightly better because they > consider the rate vs capacity curve. My suspicion is the FNDC and other > inverter and BMS systems ignore current rate versus capacity and are just > dumb coulomb counters. But I don't know enough about how they work. > Interested in learning, though! > > > Jason Szumlanski > Florida Solar Design Group > > > On Tue, Aug 25, 2026, 8:55 PM William Miller <[email protected] > <mailto:[email protected]>> wrote: > I’m with Jeremy in that I never use the FNDC. SOC calculation drift is a > problem with any battery chemistry. Clients freak out about an inaccurate SOC > reading and it causes headaches for all. > > William Miller > Miller Solar.com > 805-438-5600 > www.millersolar.com <http://www.millersolar.com/> > > On Tue, Aug 25, 2026 at 5:49 PM All Solar <[email protected] > <mailto:[email protected]>> wrote: > FWIW, I usually unhook the FNDC, as I’ve found that it is more suited for a > lead acid battery bank. > I do have one with a large bank of 16 cell Lithiums and It often does report > critically low SOC , so it’s not very useful in my opinion. > > > Jeremy Rodriguez > All Solar Inc. > Penrose CO > 719-276-4954 > Established 1998 > > On Tue, Aug 25, 2026 at 5:37 PM Jay <[email protected] > <mailto:[email protected]>> wrote: > Hi Zeke > > The lightning is the issue. > > I would replace all the fndc wires, make sure the shunt is clean. And of > course all the cat 5 cables. > > Check every wire connection to every buss. > > Good luck. > > > > > > > >> On Aug 25, 2026, at 5:14 PM, Zeke Yewdall <[email protected] >> <mailto:[email protected]>> wrote: >> >> > >> Trying to troubleshoot an outback FNDC that's giving completely wacky SOC >> readings. Yet the current readings all appear to be reasonable. We just >> replaced the FNDC because of a lightning strike -- came in through the >> ethernet to the mate it seems (took out a router too), and took out the >> mate3s, hub10, and possibly the old FNDC. So all of those are new. Rest of >> the system is maybe 5 to 6 years old -- four radians, four FM100's, 1200AH >> of 16 cell LFP batteries (open loop). Has been operating pretty well for >> the past few years other than some battery BMS failures. About 6 weeks ago, >> it looks like the SOC started being completely wrong on the old FNDC as >> well... which makes me question something about wiring... a wire coming >> loose from the shunt or or ?? >> >> Whenever I do a spot check for amperage from it, it looks right. But then >> it bounces from 100% SOC to 2% SOC in one hour... physically impossible. >> And then, I drain 23kWh out of the batteries, and it stays at 100% SOC for >> the next 6 hours. Recorded voltages also look good during spot checks, and >> for the recorded min-max on the graph (not sure if those are from the FNDC >> or the inverter though). System is operating fine, as long as I do all >> controls based on voltage, not SOC. >> >> Of course the system is 2500 miles from me, so I'm also trying to >> troubleshoot remotely. >> >> I did ask outback tech support, and was surprised to get an answer back... >> which turned out to be completely useless. They said the FNDC only works >> with lead acid batteries, and lithium batteries are used in closed loop. >> Nevermind that I have well over a dozen radian systems with lithium >> batteries and FNDC's working correctly, and this exact system was working >> correctly that way for 5 years. >> >> Zeke >> >> -- >> Zeke Yewdall >> PV Engineer >> NABCEP #031508-89 >> [email protected] <mailto:[email protected]> >> 303-523-3592 >> _______________________________________________ >> List sponsored by Redwood Alliance >> >> Pay optional member dues here: http://re-wrenches.org >> <http://re-wrenches.org/> >> >> List Address: [email protected] >> <mailto:[email protected]> >> >> Change listserver email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> >> >> There are two list archives for searching. When one doesn't work, try the >> other: >> https://www.mail-archive.com/[email protected]/ >> <https://www.mail-archive.com/[email protected]/> >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org> >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> <http://www.re-wrenches.org/etiquette.htm> >> >> Check out or update participant bios: >> http://www.members.re-wrenches.org <http://www.members.re-wrenches.org/> > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > <http://re-wrenches.org/> > > List Address: [email protected] > <mailto:[email protected]> > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > <https://www.mail-archive.com/[email protected]/> > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org> > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > <http://www.re-wrenches.org/etiquette.htm> > > Check out or update participant bios: > http://www.members.re-wrenches.org <http://www.members.re-wrenches.org/> > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > <http://re-wrenches.org/> > > List Address: [email protected] > <mailto:[email protected]> > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > <https://www.mail-archive.com/[email protected]/> > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org> > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > <http://www.re-wrenches.org/etiquette.htm> > > Check out or update participant bios: > http://www.members.re-wrenches.org <http://www.members.re-wrenches.org/> > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > <http://re-wrenches.org/> > > List Address: [email protected] > <mailto:[email protected]> > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > <https://www.mail-archive.com/[email protected]/> > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org> > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > <http://www.re-wrenches.org/etiquette.htm> > > Check out or update participant bios: > http://www.members.re-wrenches.org <http://www.members.re-wrenches.org/> > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. 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Blair “TUMP” May Solarwinds Northernlights east "We must all learn to live together as brothers, or we all will perish as fools." MLK
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