To clarify a conversation I had with a reliable source. Does the FNDC take charge of the parameters for charging when used with all OB gear and a Hub? Of course we should have no BTS plugged in with Lithiums. I was told yesterday that a battery bank had failed due to overcharging by the FNDC and was not going to be covered under warranty. Not my system. Cold temps sent the absorb voltage 2 Volts higher.
Thanks ! Jeremy Rodriguez All Solar Inc. Penrose CO 719-276-4954 Established 1998 On Wed, Aug 26, 2026 at 2:09 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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