I know Midnite has the whizbang JR for accurate SOC counting, however you’d need to us a Classic CC with it. Good topic !
Jeremy Rodriguez All Solar Inc. Penrose CO 719-276-4954 Established 1998 On Wed, Aug 26, 2026 at 2:24 PM Jason Szumlanski < [email protected]> wrote: > Zeke's last paragraph says it all. The AIOs from Sol-Max and EG4 are > pretty good at reporting an accurate SOC, regardless of charge and > discharge rate, as long as the manufacturer-matched batteries reach 100% > reasonably often. Even when the batteries sit in the mid-range for > several days, the SOC seems to remain pretty accurate. When they hover near > the low end for extended periods is where they will drop to zero without > warning. > > I find it hard to trust external shunts for Lead Acid over time for the > reasons Zeke mentioned, and for the reasons I mentioned previously > regarding aH capacity depending on rate of charge/discharge. And for LFP, > it generally makes more sense to rely on the battery BMS stated SOC, even > though that can't be completely accurate, either. It's pretty wild to watch > the discrepancy between a large EG4 rack-mounted bank versus what a Sol-Ark > 15K reports in open loop. I have watched this pretty closely at a few > sites, and the Sol-Ark seems to be all over the map. > > I have pretty limited experience with the Victron shunts, so I can't speak > to those. I am getting ready to do a small Multiplus installation where SOC > is going to be important due to tight margins between solar production and > load, so I will be interested to see how well it does. > > Jason > > > > On Wed, Aug 26, 2026 at 4:09 PM Zeke Yewdall <[email protected]> > wrote: > >> I did not expect this to be such a controversial topic... but since it >> is... here goes :P >> >> I consider having an AH counting SOC meter absolutely vital on most LFP >> projects -- at least on any older equipment. Voltage is just way too flat >> on LFP to make any reasonable decisions based on it, except below 25% SOC >> maybe, and above 90% SOC. But that entire range in between there is very >> difficult to tell where you are based on voltage. And most of the older >> LFP had no display for SOC (or at best a couple segment bar graph), and no >> way to do comms to them for many of them either. So to allow the customer >> to actually know what their batteries are doing, and make decisions on >> operation, they need to know SOC -- especially at middle levels where >> decisions can still be made (other than it's full, or it's empty, start the >> generator asap). >> >> Even on lead acid batteries, I would almost always do an AH counting SOC >> meter rather than relying on voltage, as it was just too complicated for >> about 75% of customers to grasp voltage -- that's it's non-linear, 0 volts >> is no 0% charged, and that it changes at the same SOC depending on whether >> you are charging or discharging. >> >> I've used the FNDC, Victron Smartshunts, and Trimetrics on LFP >> batteries. And even a Schneider conext battery monitor thing once or >> twice. For the most part, I've been quite happy with how they've >> functioned. >> >> Thats not to say that there aren't a number of issues with AH counting >> SOC meters, whether on lead acid or lithium batteries, and there are some >> cases where they just don't work. >> >> With lead acid, the biggest issue was usually declining battery capacity >> over time lead to the SOC being unreasonably high compared to reality. So >> it worked great to begin with, but 4 or 5 years later, it would start >> kicking the generator on (or shutting down) at much higher indicated SOC >> than it used to. >> >> For lithium, SOC drift can definitely be a problem. I do tell people >> they need to get the SOC to 100% once every two weeks minimum, in the >> winter, to prevent this -- 1% accuracy error per day doesn't sound bad... >> till you go a full month without recalibrating.... >> >> Many BMS's built into the batteries experience the same issues with SOC >> drift too. Most internal BMS's are blind to currents less than 1 amp or so, >> so people who are very good at conserving electricity, reducing their loads >> to less than an amp per battery for large portions of the day or at night, >> seem to have bigger issues with SOC drift than heavy users. >> >> The new heated batteries are a big problem with AH counting, and can >> cause the SOC meter to be completely wrong and useless at times. I have >> not figured out a way around that yet (other than not using heated >> batteries in cold climates... they have many other drawbacks IMO, compared >> to a separate heating system that's not internal). >> >> SOC meters that reset to 100% if they lose power, rather than retaining >> SOC, can also be a problem if you ever trigger the emergency protection on >> the lithium battery. Battery shuts off from low state of charge then SOC >> meter resets to 100%, then customer is super confused. The Victron shunts >> are the only ones I've found that can be programmed to keep the same SOC >> over a power outage. Batteries that disconnect just the charging FET due >> to cold temperatures, can also cause a unintended reset, by making it >> appear the battery rises to absorb voltage with very low amperage while >> charging, when really it's just the charge FET is off. >> >> For any new systems, I am coming around to using closed loop batteries of >> the same manufacturer as the AIO inverter, and everything is just built >> in... the BMS reports to the inverter, everything is based on the BMS >> control, and the same monitor shows SOC along with everything else. My >> first attemps at closed loop control were disasters, and I stayed away from >> that for several years, but recently I've been much happier with it and the >> level of control it gives you. So that's a different case, and eventually >> that'll be all the systems out there. But for now... there's a lot of >> legacy systems still out there, and first gen lithium batteries on legacy >> equipment -- no SOC display on batteries and no comms. So, that's where I >> still believe that AH counting SOC meters are critical for system >> operation, as long as the customers know the potential trip-ups and don't >> view the SOC meter as gospel. >> >> Zeke >> >> _______________________________________________ > 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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