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 On Tue, Aug 25, 2026 at 5:49 PM All Solar <[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]> 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]> >> 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] >> 303-523-3592 >> _______________________________________________ >> 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. When one doesn't work, try the >> other: >> https://www.mail-archive.com/[email protected]/ >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> >> Check out or update participant bios: >> 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. When one doesn't work, try the >> other: >> https://www.mail-archive.com/[email protected]/ >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> >> Check out or update participant bios: >> 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. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org >
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