Bean Posted May 1, 2022 Posted May 1, 2022 Anyone who can shed some light on this problem I’m having now - your input would be greatly appreciated! As stated before, I’m generally quite clueless when it comes to this so any help is hugely appreciated!! My system is set up purely as a backup/oversized UPS system - no solar. - 2 x Axpert 5kVa 4kw in parallel - 8 x 12v 200ah solar gel batteries (series/parallel connection to get 48V 400ah total - 2 series strings of 4 batteries connected in parallel) We had a massive power failure last week which lasted 2 days. This was the first time we had lost power since I put the system in, so I was interested to see how it would fare. Lasted all of 2 minutes before Error 04 started flashing on the screen and the alarm kept beeping! My settings on each inverter are as follows: 01 - Uti (Discharge Priority) 02 - 30A (Total Charge Current) 05 - USE (Battery Type) 12 - 49.0V (Back to Utility) 13 - 54V (Back to Battery) 16 - CUt 26 - 57.4V (Charge Voltage) 27 - 54.4V (Floating Voltage) 29 - 48V (Battery Cut-off) I was so disappointed. I chose to ignore it and went to the forums to see if there was a similar story that I could perhaps pick up some pointers from. I use the system purely as a backup/oversized UPS - no solar. The whole lot is not even 2 months old so I cannot understand how it can last 2 mins before it starts to send an Error 04…… From what I have read in the forums, maybe my batteries aren’t fully charging? Or they aren’t in sync (or whatever the term is)? Or they are damaged? I decided to test the system again today to see what it was doing. When I threw the mains off, it switched over normally and continued as it should. The voltage dropped from 54.4V to 52.2 in the first 2 seconds (the battery display dropped to 2 bars out of 4). Then it slowly and steadily dropped 0.1V every few seconds. At just over 2 mins Error 04 came up and the alarm sounded. The voltage was 49.8V (and battery display was on 1 bar out of 4 and flashing). All these readings taken off the inverter display. Switched mains back on and it switched over without any fuss, alarm stopped, Error 04 stopped displaying and batteries started charging back to 54.4V. Stopped charging within 5 mins of change over. I really have no idea. Any help would be appreciated….. Quote
Arandoza Posted May 2, 2022 Posted May 2, 2022 The quick voltage drop suggests the battery pack is tired or you have heavy load on the batterys? What make model of battery? The bad bit is that Lead acid/sealed lead acid / gel / AGM are not made to take the punch from what I have seen. Only lead acid with very large ah ratings seem to fair a bit better and then also suffer with balancing issues, with a light load. Ideally with LA/AGM/GEL you really only want a low DOD, maybe max 25% to ensure you get the lifespan. Otherwise at 50% DOD or greater you dramatically shorten the lifespan of the above, and for sealed lead acid, GEL and AGM one has to be carefull not to overcharge and dry them out. Also what load were you running when you switched to battery mode? I had been running Lead acid 6V TE35 Trojans x 8 (48v) and they would hold for almost 2 hours after 6 years at Around 1200 watts load, and we always tried to switch off what was not needed when load shedding hit at night. and No microwave for 30 seconds otherwise the inverter would drop the load. Have recently moved to 9 x Pylontech 4.8kw units and have been very impressed, we keep the load light but have no issues, and can run microwave if needed, and still have capacity to run longer, if needed, cable theft for example, which is becoming quite prominent. Quote
Coulomb Posted May 2, 2022 Posted May 2, 2022 3 hours ago, Arandoza said: The quick voltage drop suggests the battery pack is tired No, actually this is to be expected. He has no solar, so disconnecting the AC-in means that there is no charging, so the battery will drop from float voltage (around 13.6 V per nominally 12 V module) to about 13 V (fully charged). 13 x 4 = 52 V; it dropped to 52.2 V. 16 hours ago, Bean said: Then it slowly and steadily dropped 0.1V every few seconds. This is partly to be expected. 13 V on a nominally 12 V isn't sustainable with a load; it's a sort of "surface" charge. So that will blow away fairly quickly (a few seconds, as noted). Depending on the load, it should stop at about 12.6 V in a healthy battery module, so about 12.6 x 4 = 50.4 V. It should hold there for hours, depending on the load and battery capacity. What I think happened is that your load was a bit high for the battery. You have 400 Ah there; some people confuse that with being able to deliver 400 A. But lead acid solar batteries should only be discharged at about 0.15C, so that's 0.15 x 400 = 60 A, which is some 3000 W. You have 8000 W of inverter capacity there, plus losses, which could add up to 8600 W or so. In a household that's not disciplined, it's easy to exceed 3000 W. That's why lithium batteries are popular these days, they allow 0.5C discharges, with up to 1.0C in surges. That's 3.3-6.6 times the load capability for the same installed capacity (same Ah or kWh). Your maximum charge current is 30 A (per inverter), so that's 60 A total, which agrees with the 0.15C calculation above. (Lead acid should also not be charged harder than 0.15C). You didn't say what setting 11 is; it should be 30 A per inverter as well. An undocumented "feature" of these inverters is that they turn on the low battery warning (and beeper) at 2.0 V over the low DC cutoff voltage setting. So that's 50.0 V for your situation; you reported 49.8 V soon after the warning. (Many users confuse warnings and errors/fault codes). Presumably, the inverters were still delivering power to the loads, despite the noise from the beepers? Once the low voltage warning (with the ⚠ symbol rather than the ERROR symbol) comes on, it doesn't go back off until the battery voltage exceeds the low DC cutoff setting by 4.0 V! That's 52.0 V with your present settings. Without utility present, that's not going to happen. I recommend 48 V for the low DC cutoff voltage so that the batteries don't discharge more than about 50%; needed for longevity. It might be better to set it a little lower, unless you can cut your loads a bit or add another string of battery modules. The other thing is that the battery might not have been properly charged. There is the dreaded premature float charge problem, but usually with sensible settings, this doesn't happen when utility charging. As long as setting 11 (maximum utility charging current) is at least 10 A, (the default is 30 A, if it's the model I'm thinking of, same as mine) then the premature float bug should not have happened. You can get a little more run time without affecting battery longevity by using patched firmware and correctly setting up KettleKomp™. (It won't work out of the box, it has to be set up. Just follow the instructions; it's not very hard. ) This feature will compensate for the battery internal resistance to a degree, so that a fixed voltage like 50.0 won't be as badly affected by high loads. The latest patched firmware for Axpert MKS PF0.8 models is 73.00e. So try the patched firmware and/or reducing setting 29 (low DC cutoff voltage), but be aware that reducing setting 29 will reduce the life expectancy of your battery. It is possible of course that your battery is faulty and/or junk. Check the individual battery module voltages; they should agree within a few tenths of a volt. Any that are reading under 12.0 V rested no load are dangerously low on charge. It may be that you'll need some sort of battery balancer. A car battery charger can be used to charge battery modules, but unless it's a powerful car charger, it will take many hours or days to charge one module, let alone a pair of modules in parallel. Did your battery modules stand around for months before installation? Even new, some may be months old, and sellers rarely check if they need charging. Hopefully, it's just that a few of them are out of balance, and some patience with a car charger will bring them back to balance. Note however that lead acid battery modules don't take kindly to being low on charge for extended periods of time, so it's possible that some of them may be ruined, and need to be replaced. I hope it's good news when you investigate. Arandoza and Beat 2 Quote
Bean Posted May 2, 2022 Author Posted May 2, 2022 Thanks so much for your insight @Arandoza and @Coulomb! After more testing today, what you have said now actually makes sense to me. I generally have about 300W running continually and that then climbs when we use a kettle or a toaster or the microwave. We have 2 fridges and a water cooler that are on the inverter and I think when power changes over to the inverter, those draw too much for the 48v 400ah gel batteries to handle, hence the super fast drop off (at least that is how I understand it after your explanations?). Today I shut off the fridge circuits and turned the mains off. The inverter dropped from 54.4V to 52.2V and stabilised. Hovered between 52.2V and 52.3V for over an hour. I then turned the fridge circuits back on and the system dropped to 50.0V where it stabilised at 50.2V and sat for another hour before I turned he mains back on. With the fridges running, my max load is only about 800-900W (add laptops and 3 Smart TVs and a few LED lamps). I see my only solution being 1 of 2 things: - I remove the fridge circuits off the inverters and back to mains; - I place a time delay relay on the fridge circuits so they each come on 2-3 mins after everything has switched over and stabilised on the inverter. I’m not even sure if this is possible? Thanks again for the help. Much appreciated! Quote
Beat Posted May 3, 2022 Posted May 3, 2022 I agree with Coulomb that your voltage settings are too high. Since you are running the system as an UPS only, the most time the batteries are in floating mode. That keeps them charged and in condition. In the rare events of black outs you want to make maximum use of the battery capacity. Allow to discharge to 20 - 30% SOC. Quote
Irocmaster Posted May 3, 2022 Posted May 3, 2022 Hi Bean set your battery cutoff to 46V this is a ups setup and you are not cycling the batteries daily. Quote
Bean Posted May 3, 2022 Author Posted May 3, 2022 @Beat& @Irocmaster - Thanks for your input. Anything that can help me figure this out is appreciated! Irocmaster 1 Quote
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