I agree, and I am lucky to work in a space where budgets are usually healthy.
On the other hand, oversizing the battery negates one of the best benefits of an LFP upgrade – less capacity needed due to deeper discharge. I would be great if they could find a way to reduce parasitic draw in paralleled inverter units in particular. The numbers add up fast. I think the attitude has become that PV is so cheap and batteries are coming down, so who cares? But the issue is real when you throw into the mix nuisance shutdowns and lack of dark start resilience. Jason Szumlanski Principal Solar Designer | Florida Solar Design Group NABCEP Certified Solar Professional (PVIP) Florida State Certified Solar Contractor CVC56956 Florida Certified Electrical Contractor EC13013208 On Sun, Feb 23, 2025 at 1:44 PM Bill Battagin via RE-wrenches < re-wrenches@lists.re-wrenches.org> wrote: > Of course not all clients are monetarily capable or willing to oversize a > Lithium based battery but many can. In my mind this is a simpler solution. > Its a strategy we're using more to avoid that voltage cliff and reduce the > likelihood of even nearing the BMS shutting down with all of its hassle > factor. This higher battery capacity allows a little higher LBCO voltage > again to keep the system away from the dreaded BMS cutting out. With the > availability of Midnite's PowerFlo batteries at a much more reasonable > price, the added cost for an increase in off-grid reliability may not be > out of budget for many systems. > > Gotta love the conversation about parasitic loads also, I hope > manufacturers are looking at that. > > My $.02 > > Bill > > Feather River Solar Electric > Bill Battagin, owner > 4291 Nelson St. (Shipping) > 5575 Genesee Rd. (USPS, UPS) > Taylorsville, CA 95983 > 530-284-7849, 258-1641(cell) > CA. C10 Lic # 874049 > Solar Powered since 1982 > Home of the Sunny Side Up > > On 2/22/2025 1:06 PM, William Bryce via RE-wrenches wrote: > > Everyone wants to compare the AIO inverters to the older low > frequency inverters when it comes to the idle power draw. But everyone now > wants all the bells and whistles. > > Nothing is free, and if you take an older system then add up the charge > controllers draw, SCP monitoring system, Gateway device, and then add a > battery monitor to the mix you will find the Idle draw is much higher than > what the MFG says for the inverter alone. > > Feel free to check the math with a Schneider XW with 3 VH MPPT > controllers, a gateway, a SCP, and lithium batteries running closed loop. > Oh, the Schinder does not have any smart loads like most AIO do. > > My 2 cents. > > Logan > > > > On Sat, Feb 22, 2025 at 12:03 PM Jason Szumlanski via RE-wrenches < > re-wrenches@lists.re-wrenches.org> wrote: > >> The voltage cliff is a real issue. Even though LFP batteries can be >> pretty deeply discharged without damage, for practical purposes we need to >> set the LBCO on the inverter at a relatively high voltage (or SOC) to avoid >> the steep part of the cliff altogether, rendering a good part of the >> capacity essentially useless. In situations where there is a readily >> available charging source at all times (auto-start generator or grid), >> there really should be a way to overcome this game of chicken between the >> battery protect mode and inverter LBCO. In the off-grid world, I don't >> consider that a bell & whistle, but more of a required feature. >> >> Maybe it's not so much an inverter issue as much as it is a needed >> battery feature. Imagine if there were a dry contact on a battery BMS that >> told it to stay on regardless of how it was feeling that day (subject to >> safety shutdowns, of course). Then you could force the battery to be alive >> with 48V DC connected when there is generator output voltage present, for >> example. Of course, there are risks with this simplistic example, like if >> the inverter/charger is faulted and cannot charge the battery. >> >> I think the right answer is closed-loop communications that can tell a >> BMS in protect mode to wake up because there is a charging source ready to >> go. If Midnite could implement this with AIO/Powerflo, it could be a very >> powerful selling point. On the other hand, maybe it's not that important as >> long as the inverter reliably reaches LBCO well before the battery goes >> into protect mode. That answer could be in closed loop communication logic >> where the BMS sends a warning to the inverter that it is about to shut >> down, so the inverter can stop inverting on the command of the battery, but >> keep the battery connected so a charging source will charge it. >> >> In other words, maybe it would be better for the battery to be in command >> of the inverter's LBCO rather than the inverter's own fuzzy logic. >> >> The parasitic draw issue does need to be addressed. I went through some >> calculations on some typical systems I have in the field. For example, one >> system has a 120kWh battery with four Sol-Ark 15Ks. I think the inverter >> manufacturers prefer "idle consumption" to the derogatory parasite >> comparison, but whatever you call it, let's assume 360W for four inverters. >> If the inverter LBCO is set at 12% and the protect mode is triggered at 2%, >> that gives us 33 hours until the battery reaches protect mode in theory. >> That is a substantial amount of time to get a charging source on the >> battery. But in practice, I have seen many batteries enter protect mode >> before a "properly" programmed inverter LBCO engages itself. >> >> That brings up another feature request. How about dropping the idle >> consumption of paralleled inverters and just keeping the primary inverter >> at full idle? >> >> >> Side note: I inherited a site where a Lithionics battery BMS is in >> control of the 2-wire start for a generator. In theory, this should work, >> but in practice, the owner often finds the BMS in protect mode with the >> generator not started. I haven't dug too deeply into this issue yet, but >> direct BMS control of the generator is another interesting option. But then >> you would want to build in all of the quiet time, charge percentage/voltage >> limits, exercise, and other logic that typically an inverter handles. This >> is an example of how a BMS is in control of the charging source, but it >> would be better if the BMS was telling the inverter what to do in terms of >> AGS and LBCO. >> >> Jason Szumlanski >> Principal Solar Designer | Florida Solar Design Group >> NABCEP Certified Solar Professional (PVIP) >> Florida State Certified Solar Contractor CVC56956 >> Florida Certified Electrical Contractor EC13013208 >> >> >> On Sat, Feb 22, 2025 at 11:17 AM Steve Higgins <st...@surrette.com> >> wrote: >> >>> Hello all... >>> >>> The first issue is that inverter/charger parasitic loads have increased >>> exponentially in the past 20+ years. When the LBCO cuts out, the inverter >>> may shut off, but it does not remove itself or any other DC-connected >>> device from the battery. These devices still draw a parasitic load. In >>> the 1990s, the Trace SW would pull about .3 to .4 amps of current from the >>> battery when connected to it. Today, many manufacturers use cheaper >>> transformers, and the high-frequency inverters draw a much higher current. >>> Some of these all-in-one inverters draw 1-2 amps of current from battery >>> banks, just connected and not even turned on. >>> >>> What's important here is that the battery voltage is already very low >>> when you trigger an LBCO shutdown (it's not a disconnect). For a 48-volt >>> system, this is 44 to 47 volts, depending on where you set the LBCO. When a >>> Lithium battery is this low, the voltage dropoff is much higher. With a >>> lead battery, the voltage dropoff is much more linear, but with Lithium >>> chemistry, this voltage dropoff is more like a cliff. This is why it's >>> important for many of these Lithium systems to set the Battery cutouts a >>> bit higher so people have more time to fix the situation before the BMS >>> shuts down. Ideally, the customer should be educated not to >>> over-discharge the bank, which would help. Many of these customers want >>> turnkey systems that they don't want to think about but don't want to pay >>> for it or do the work that is required to maintain it. >>> >>> Now, if the battery had gone into "Protect" mode and the BMS had shut >>> down, the battery is outputting very little votlage... the inverter/charger >>> needs voltage to run. There used to be a line of inverters in the marine >>> and RV market that would do what we called "Dead Battery Restart". This >>> meant there was a parallel circuit in the power supply so that when you >>> supplied AC to the input, a secondary power supply bypassed the regular >>> battery power supply and would power up the inverter and allow the charger >>> to run. Most of the inverter manufacturers got rid of this circuitry >>> because it was not cheap, took up space on the boards, and was just another >>> circuit that could get damaged with generator/shore power surges. I don't >>> know of an inverter today with this dead battery restarting circuit. >>> >>> With this, you need to be very careful. If the customer has cratered the >>> battery voltage and drawn down the voltage so low that they have damaged >>> the cells, jumpstarting the battery can create a charging hazard, and that >>> could cause the cells to swell internally. If that happens, the battery >>> will get warmer and warmer under charge, and eventually, you could have a >>> cell rupture. This can happen quickly with Li-ion, but with LFP, it's much >>> harder to create this problem. Usually, in LFP, cells will swell a bit, and >>> the current interrupter on the individual cell will open up and drop that >>> string, and you will lose capacity. >>> >>> Like everything else, it's a race to the bottom on cost; this affects >>> quality and features... Everyone wants the "Bells & Whistles," but they >>> don't want to pay for it. >>> >>> Steve Higgins >>> >>> >>> On Sat, Feb 22, 2025 at 5:08 AM Jason Szumlanski via RE-wrenches < >>> re-wrenches@lists.re-wrenches.org> wrote: >>> >>>> I have been thinking a lot recently about the reasons off-grid systems >>>> can shut down, and working on strategies to prevent these nuisances that >>>> require manual intervention. >>>> >>>> Ideally, a BMS should never shut down due to low voltage/SOC because a >>>> properly programmed inverter should reach it's cut off well before the BMS >>>> decides it needs to protect the battery, especially where there is closed >>>> loop communication. But let's say that happens, where the BMS does make the >>>> DC battery output go to zero. >>>> >>>> It seems to me like the inverter should be able to start a generator, >>>> and then signal to the BMS that a charging source is available. But I'm not >>>> aware of any system that actually does this. The inverter should be able to >>>> wake up the battery. I can see this being particularly possible where one >>>> manufacturer is writing the code (I'm thinking Midnite AIO/Powerflo). >>>> >>>> Of course, the inverter would have to have power in order to do that, >>>> so if it's nighttime and there is no PV, the inverter power would need to >>>> come from somewhere. I have two thoughts. First, someone could manually >>>> start the generator, waking up the inverter, but they would not have to >>>> reset the BMS if the inverter told it to wake up. The second way would be >>>> for the inverter to somehow close the 2-wire start circuit upon inverter >>>> shutdown, restoring power to the inverter automatically. >>>> >>>> If those are not options, an external NO relay powered by the inverter >>>> output could be added to the 2-wire start circuit, perhaps with a time >>>> delay to return to the NO position to allow the generator to remain powered >>>> until the inverter does it's thing and starts charging the batteries. >>>> >>>> Anyway, my question is whether any inverter/battery combination out >>>> there works in a way that the inverter tells the battery there is a >>>> charging source available to wake up the BMS and reconnect DC power. And if >>>> not, why? >>>> >>>> Jason Szumlanski >>>> Florida Solar Design Group >>>> >>>> >>>> _______________________________________________ >> List sponsored by Redwood Alliance >> >> Pay optional member dues here: http://re-wrenches.org >> >> List Address: RE-wrenches@lists.re-wrenches.org >> >> 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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