December 27, 20241 yr 1 hour ago, Youda said: Well, cells themselves are pretty cheap, as one 25Ah LFP pouch cell costs just around 25 USD. Just remember that finding a cell with the same dimensions on the market might be a bit challenging, of course. But the main problem is that the Pylontech repair will be quite a messy work: There are three cell packs in the US2000, each one sealed in plastic. Internal wiring of the each cell pack is 5S2P. You can't replace just one swollen cell, but at least the two that are connected in parallel. Chances are that some other pairs in the pack(s) will be swollen too. Chances are that all three cell packs will contain swollen cells. You have to carefully cut open everything, diagnose, unsolder/solder, and re-pack the cells tight, in order for them to fit back in. Not to mention that you have to precharge all the cells in the battery to the same voltage, as the internal balancer is not powerful enough to solve bigger voltage differences. IMHO, much easier approach would be to buy US2000 with a dead BMS board and just swap a swollen cell pack for the salvaged one. It's important to keep in mind that the cells are swelling for a reason: Overcharge, undercharge, overheat, etc. If you do not remove root cause of the failure, there's no point in fixing the batteries as they will get killed again. Most of the time it's like this: one or two cells are extremely swollen, while the rest of them is starting to swell too. A case of 29 perfect cells sitting in a box with the one that's looking like a balloon is .....unrealistic. Personally, I run a lot of Pylontechs too. Should they start to die, I will go for something with prismatic cells inside, as swapping a prismatic cell with the screw terminals is "a piece of cake" when compared to brain surgery skills needed for the Pylontech. @Youda Thanks for your point of view. Yes prismatic cells will be a best approach but it is quite difficult to find cells that fit in the case. Googleled everywhere and actually found only the standard size that does not fit in the case.
December 27, 20241 yr Also worth noting that most of the prismatic cells have aluminum case with just a thin blue coat (EVE for example). Therefore, it's best to put some kind of separator between the cells. Which consumes another space. Given how crammed the US2000 is using those 30 x 25Ah cells, it's obvious that you won't be able to fit 30 x 25Ah or 15 x 50Ah prismatic cells in that space
December 27, 20241 yr 21 minutes ago, Youda said: Also worth noting that most of the prismatic cells have aluminum case with just a thin blue coat (EVE for example). Therefore, it's best to put some kind of separator between the cells. Which consumes another space. Given how crammed the US2000 is using those 30 x 25Ah cells, it's obvious that you won't be able to fit 30 x 25Ah or 15 x 50Ah prismatic cells in that space @Youda ah shit.😥 Maybe i can use LFP round cells for fitting in the case :https://a.aliexpress.com/_EHQTDHA Or modify the wiring for using batteries outside of the casing 😐
January 12, 20251 yr On 2024/12/27 at 10:30 AM, Youda said: No, samotné články jsou docela levné, protože jeden 25Ah LFP pouzdrový článek stojí jen kolem 25 USD. Pamatujte, že najít na trhu buňku se stejnými rozměry může být samozřejmě trochu náročné. Ale hlavním problémem je, že oprava Pylontech bude docela chaotická práce: V US2000 jsou tři balíčky článků, každý zatavený v plastu. Vnitřní kabeláž každé sady článků je 5S2P. Nelze nahradit jen jednu oteklou buňku, ale alespoň ty dvě, které jsou zapojeny paralelně. Je pravděpodobné, že některé další páry ve smečce (smečkách) budou také oteklé. Je pravděpodobné, že všechny tři balíčky buněk budou obsahovat oteklé buňky. Musíte vše pečlivě rozříznout, diagnostikovat, odpájet/pájet a znovu pevně zabalit články, aby se do nich vešly. Nemluvě o tom, že musíte předbíjet všechny články v baterii na stejné napětí, jelikož vnitřní balancer není dostatečně výkonný, aby řešil větší rozdíly napětí. IMHO mnohem jednodušším přístupem by bylo koupit US2000 s mrtvou deskou BMS a jen vyměnit oteklý balíček buněk za ten zachráněný. Je důležité mít na paměti, že buňky bobtnají z nějakého důvodu: Přebití, podbití, přehřátí atd. Pokud neodstraníte hlavní příčinu poruchy, nemá smysl baterie opravovat, protože se znovu zabijí. Většinou je to tak: jedna nebo dvě buňky jsou extrémně oteklé, zatímco zbytek začíná také otékat. Případ 29 dokonalých buněk sedících v krabici s tou, která vypadá jako balón, je .....nerealistický. Osobně také provozuji mnoho Pylontechů. Pokud by začali umírat, půjdu pro něco s prizmatickými buňkami uvnitř, protože výměna prizmatické buňky se šroubovacími svorkami je „hrací úlovek“ ve srovnání se schopnostmi operace mozku potřebnými pro Pylontech. These are my photos - problem - US2000+. I can confirm that my cells are behaving exactly the same, swollen cells gradually appear with different batteries. The number of cycles is up to 1000. I had a total of 9 batteries - 2 are already dead. Connection to PIP-5048MK via their communication and 4x converter, battery connected correctly according to Youd. So I wouldn't see the problem with the HW connection... Unfortunately, I bought them second-hand, so no complaints. I repaired one battery twice with a new cell about a year ago (similar in size but slightly thicker (I then had to adjust the cabinet) but I have it back in the workshop and I will diagnose what is going on in it... Edited January 12, 20251 yr by moravan30
January 12, 20251 yr 28 minutes ago, moravan30 said: These are my photos - problem - US2000+. I can confirm that my cells are behaving exactly the same, swollen cells gradually appear with different batteries. The number of cycles is up to 1000. I had a total of 9 batteries - 2 are already dead. Connection to PIP-5048MK via their communication and 4x converter, battery connected correctly according to Youd. So I wouldn't see the problem with the HW connection... Unfortunately, I bought them second-hand, so no complaints. I repaired one battery twice with a new cell about a year ago (similar in size but slightly thicker (I then had to adjust the cabinet) but I have it back in the workshop and I will diagnose what is going on in it... Thanks for the pictures and information. Mine has swollen only after 440 cycles and 6 years of usage. Theses batteries are not a good investment 😫
January 12, 20251 yr 3 minutes ago, fhocorp said: Thanks for the pictures and information. Mine has swollen only after 440 cycles and 6 years of usage. Theses batteries are not a good investment 😫 Many people have no problems at all with them and pylontech seem good at warranty replacement. It's often an inverter problem that causes the problem.
January 12, 20251 yr Problem with Pylontech is that even when the data communication from BMS to the inverter is working, the BMS tells the inverter to charge till 53,5V. (=3,57V per cell). Add the facts that: 1) The voltage is not distributed perfectly among the cells. Some will be At 3,4V while the others will be at 3,6V already. It is a job for the balancer to level the cells. 2) Pylontech balancer is quite weak, unable to burn amps of current. 3) Inverters like to overshoot voltage when AC load fluctuates. The result is constant stress and hidden overcharging, as discussed in the Victron threads many times. On the Victron side this was fixed by firmware tweaks, luckily. But when comes to Axperts, the problem is even more dangerous as it is not solved in the official firmwares, AFAIK. IMHO, the first step on the road to hell is that one of the cells gets damaged by that hidden overcharge. Then a chain reaction starts as all other cells become stressed even more. From that point there's no way back. It does not make sense to replace the cells if all other parts of the system will stay configured the same, as the damage will appear again. From my experience, for the longevity, the best is to ignore charging voltage value that BMS is announcing and set 52,6V instead. Based on the setup it might be +-0,2V but definitelly not 53,5V. Shame is, the batteries that already experienced the stress for weeks or months cannot be saved as some of the cells started to swell already.
January 12, 20251 yr 51 minutes ago, Youda said: Problem with Pylontech is that even when the data communication from BMS to the inverter is working, the BMS tells the inverter to charge till 53,5V. (=3,57V per cell). Add the facts that: 1) The voltage is not distributed perfectly among the cells. Some will be At 3,4V while the others will be at 3,6V already. It is a job for the balancer to level the cells. 2) Pylontech balancer is quite weak, unable to burn amps of current. 3) Inverters like to overshoot voltage when AC load fluctuates. The result is constant stress and hidden overcharging, as discussed in the Victron threads many times. On the Victron side this was fixed by firmware tweaks, luckily. But when comes to Axperts, the problem is even more dangerous as it is not solved in the official firmwares, AFAIK. IMHO, the first step on the road to hell is that one of the cells gets damaged by that hidden overcharge. Then a chain reaction starts as all other cells become stressed even more. From that point there's no way back. It does not make sense to replace the cells if all other parts of the system will stay configured the same, as the damage will appear again. From my experience, for the longevity, the best is to ignore charging voltage value that BMS is announcing and set 52,6V instead. Based on the setup it might be +-0,2V but definitelly not 53,5V. Shame is, the batteries that already experienced the stress for weeks or months cannot be saved as some of the cells started to swell already. Ok @Youda. In the next year i will have second hand US2000B, for working with my axpert max 8Kw i will use the USER profile without BMS connection and the voltages you tell for saving the end of life of the batteries (they are not swollen at this time). The BMS of the batteries will only be connected to Solar Assistant for monitoring purposes. Best Regards
January 14, 20251 yr On 2025/01/12 at 11:54 PM, Youda said: Problem with Pylontech is that even when the data communication from BMS to the inverter is working, the BMS tells the inverter to charge till 53,5V. (=3,57V per cell). Add the facts that: 1) The voltage is not distributed perfectly among the cells. Some will be At 3,4V while the others will be at 3,6V already. It is a job for the balancer to level the cells. 2) Pylontech balancer is quite weak, unable to burn amps of current. 3) Inverters like to overshoot voltage when AC load fluctuates. The result is constant stress and hidden overcharging, as discussed in the Victron threads many times. On the Victron side this was fixed by firmware tweaks, luckily. But when comes to Axperts, the problem is even more dangerous as it is not solved in the official firmwares, AFAIK. IMHO, the first step on the road to hell is that one of the cells gets damaged by that hidden overcharge. Then a chain reaction starts as all other cells become stressed even more. From that point there's no way back. It does not make sense to replace the cells if all other parts of the system will stay configured the same, as the damage will appear again. From my experience, for the longevity, the best is to ignore charging voltage value that BMS is announcing and set 52,6V instead. Based on the setup it might be +-0,2V but definitelly not 53,5V. Shame is, the batteries that already experienced the stress for weeks or months cannot be saved as some of the cells started to swell already. On 2024/12/27 at 10:30 AM, Youda said: What you write makes sense, but a friend has had the same configuration with his parents for 5 years. The battery controls only via the PIP-5048MK inverter. During the summer, the batteries are full most of the time before the day (they are older people - low consumption) they have 6 x US2000. Yesterday he checked all of them - visually on the back sides and has no problem. Isn't it rather a matter of battery firmware? I would also like to know your opinion on how long it takes for the cell to swell after damage from overcharging. My point is that I bought the batteries used and I don't know how the previous user used them (he had an older Axpert inverter), I discovered the swelling after less than a year in the condition they are in the photos. Edited January 14, 20251 yr by moravan30
January 14, 20251 yr 1 hour ago, moravan30 said: Isn't it rather a matter of battery firmware? Pylontech firmware is not actively modulating charging current, nor voltage. It just passes through whatever the inverters sends down the wires. And the inverter (when BMS communication is established) is sending whatever BMS asks for. All the Pylontech US firmware versions, that I've tried, asked for 53 250mV (53,25V). Since some of the inverters are not able to set charging current in such a fine steps, they will charge to the nearest possible value, that is 53,3V or even 53,5V. It would be nice to have a Pylontech firmware that would ask for a charge voltage of 52,6V but it is nonexistent. (if you exclude the option to hack BMS protection values via RS232 console and throwing your warranty out of the window). Why some setups experience swelling while the others don't: Depends much more on the inverter. How precise and fast it is, how much it overshoots. Depends on the wiring quality and battery bank capacity. Larger banks are capable of surviving more abuse. Smaller banks degrade faster. Depends on the varying AC loads. Big AC loads that are being turned ON and OFF quickly are the worst, as the energy from the PV panels is already in the inverter and when the load is suddenly OFF, that energy spike has to go somewhere. Most of the time, it goes to the grid (for hybrids) or to the batteries (for off grid). One example of such a nasty load is induction cookstove. Can't tell you how much time of abuse it will take before the batteries starts to swell as I am trying not to abuse mine, charging them to 52,6V or 52,7V and they are fine so far. Even the ones that I bought in 2018 are still working like a charm.
January 14, 20251 yr 41 minutes ago, Youda said: Pylontech firmware is not actively modulating charging current, nor voltage. It just passes through whatever the inverters sends down the wires. And the inverter (when BMS communication is established) is sending whatever BMS asks for. All the Pylontech US firmware versions, that I've tried, asked for 53 250mV (53,25V). Since some of the inverters are not able to set charging current in such a fine steps, they will charge to the nearest possible value, that is 53,3V or even 53,5V. It would be nice to have a Pylontech firmware that would ask for a charge voltage of 52,6V but it is nonexistent. (if you exclude the option to hack BMS protection values via RS232 console and throwing your warranty out of the window). Why some setups experience swelling while the others don't: Depends much more on the inverter. How precise and fast it is, how much it overshoots. Depends on the wiring quality and battery bank capacity. Larger banks are capable of surviving more abuse. Smaller banks degrade faster. Depends on the varying AC loads. Big AC loads that are being turned ON and OFF quickly are the worst, as the energy from the PV panels is already in the inverter and when the load is suddenly OFF, that energy spike has to go somewhere. Most of the time, it goes to the grid (for hybrids) or to the batteries (for off grid). One example of such a nasty load is induction cookstove. Can't tell you how much time of abuse it will take before the batteries starts to swell as I am trying not to abuse mine, charging them to 52,6V or 52,7V and they are fine so far. Even the ones that I bought in 2018 are still working like a charm. I don't agree 100% with your statement about modulating charging current and voltage. I can see the behaviour of my bank connected to an Axpert with Batteryview and I can see how charging current is varying across each battery module. I never see voltages of 53v either. You can see on the attached pictures that inverter is supplying 23amp at 51volt and some batteries are taking just 2amp while others are taking 7-8 amp. Last picture shows full charge status just reached. If the batteris are communicating with each other and with the inverter, the BMS' can effectively manage charging. In my opinion, it seems that some pylontechs have a premature failing rate that could be related to manufacturing defects and not to the way they are used. I had a faulty unit after 2 year use and it was replaced under warranty. It was connected and used exactly the same way as the other 5 units so, why did the others show no issues? .
January 14, 20251 yr 2 minutes ago, Mauritius B said: I can see the behaviour of my bank connected to an Axpert with Batteryview and I can see how charging current is varying across each battery module. This is normal. As the cells in a module are reaching full charge, their ability to receive charge drops gradually. Therefore the charging current drops too. For example, here's the charging current of 8xUS3000 in one of my stacks: The gradual drop of the current is caused by the cells, it's not something that BMS or Inverter does. For each battery in the stack this curve will be slightly shifted in time. That's because each battery has a slightly different charge, therefore slightly different ablility to receive current. Exactly as shown on your BV screenshots. You can observe this even by just looking at the LED bars of the individual batteries - some of them will be fully charged already (LED bar goes off) while the others will still being charged (LED bar with one blinking LED). Once again, it's pretty normal that you see a different amps for each battery in the stack and the BMS/Inverter has nothing to do with that. Yes, the BMS IS able to tell the inverter what to do, but the charging information is sent for the whole stack, not for individual batteries. For example, this is the info, that BMS sends via CAN BUS during charging of the above mentioned stack of 8 batteries: charge with 300A max charge with 120A max charge with 100A max charge with 90A max charge with 0A max 24 minutes ago, Mauritius B said: In my opinion, it seems that some pylontechs have a premature failing rate that could be related to manufacturing defects and not to the way they are used. I had a faulty unit after 2 year use and it was replaced under warranty. It was connected and used exactly the same way as the other 5 units so, why did the others show no issues? Yes, some of the batteries might experience manufacturing defects, resulting in premature damage. That's what warranty is for. But the examples shown in this thread, where 10+ batteries "blown" at once are not that case.
January 14, 20251 yr 1 hour ago, Youda said: This is normal. As the cells in a module are reaching full charge, their ability to receive charge drops gradually. Therefore the charging current drops too. For example, here's the charging current of 8xUS3000 in one of my stacks: The gradual drop of the current is caused by the cells, it's not something that BMS or Inverter does. For each battery in the stack this curve will be slightly shifted in time. That's because each battery has a slightly different charge, therefore slightly different ablility to receive current. Exactly as shown on your BV screenshots. You can observe this even by just looking at the LED bars of the individual batteries - some of them will be fully charged already (LED bar goes off) while the others will still being charged (LED bar with one blinking LED). Once again, it's pretty normal that you see a different amps for each battery in the stack and the BMS/Inverter has nothing to do with that. Yes, the BMS IS able to tell the inverter what to do, but the charging information is sent for the whole stack, not for individual batteries. For example, this is the info, that BMS sends via CAN BUS during charging of the above mentioned stack of 8 batteries: charge with 300A max charge with 120A max charge with 100A max charge with 90A max charge with 0A max Yes, some of the batteries might experience manufacturing defects, resulting in premature damage. That's what warranty is for. But the examples shown in this thread, where 10+ batteries "blown" at once are not that case. Again, I am not 100% in agreement. If the inverter is able to send 53,5volt to the stack as you stated, the cells remaining at 52,6v should be still getting charge current but it is not the case because the BMS on each pylon has already stopped the charging process. You can see on my 3rd picture that 4 batteries are showing 100% charge, 0amps and 52,6v. Status is idle. 2 of them were still finishing the charging process with low current. Module #2 is actually higher in voltage (52.671v) than the rest but still charging 0.265amp. The panels were still able to produce 1.5kw but such power was not delivered nor used. The charging information is not sent from inverter to stack. The stack is informing the inverter about the maximum current it can accept based on the number of battery modules connected and their ratings. If you check the picture from watchpower screen, you can see 23amps sent to the stack and each battery module taking a defined amount of current that is not related to battery module voltage. Module 1 has 51.955v and it is taking 8.391amps while module 2 has 51.952v and it is taking 7.816amp from the bus. Higher voltage does not take lower current so, cells are not limiting the charging current. The BMS does. Maybe the manufacturing defect is not on the cells/pouches but on the BMS hardware/firmware when 10 pouches are swollen, but in my opinion it is not a problem of BMS capabilities to manage the charge.
January 14, 20251 yr Author I can confirm that a busbar for my installation of 20 x US2000b + US2000C is installed in the trunking as per initial pics provided and dispute that no bus bar is causing the batteries not to charge to the same voltages (They differ between 0..2v at most on the busbar but all 4 inverters charging to all 4 battery banks x5 US2000b/US2000C mixed as per recommended Pylontech Parallel setup). These batteries have bad cells on a lot of them. Please see my post of the 2 x US2000C installation and ONE of the TWO Batteries in Parallel swollen on a single inverter. The other US2000C on this installation runs flawless and no errors and no swollen cells and these only had 200 cycles and installed the same time. If overvoltage occurred I am sure both batteries would have been damaged, same as with my 20 x US2000b+US2000C mixed installation of which some of the batteries warranties was not honored and I had to fork out an additional R 60k for replacements. The 2 x US2000C in parallel installation were also set since date of installation to 52.2v Float and 52.4v Absorb after Pylontech recommended settings change from 2017-2021 from the initial 53.2v Float/Absorb recommendations to a lower voltage and charge state still indicates 100%. Hence a -1.1v offset to ensure if inverter overvolts there is no overvolt on batteries (Even though Pylontech market their products for overvolt protection). I have been waiting for more than 6 weeks for the 1 x Swollen US2000C to be replaced, apparently no stock of US2000b Plus or US2000C in the country. Still monitoring 2 x problematic US2000b's after firmware upgrade to send in for replacement. All log files on all swollen batteries indicated no overvoltage from inverters, just internal cell issues HV/OV/UV randomly. I opted to rather read the log files myself and send it to Pylontech CN and they have sent me firmware to run and check if issues improve. Obviously swollen cells/gasses already built-up will remain so will be sending in these for replacement after communicating with Pylontech international. I do not have trust that these batteries can do 3000 cycles and my DOD was always 40% max and rare cases 90% when power was off for more than 3 days due to major municipal issues.
January 14, 20251 yr 1 hour ago, Mauritius B said: Maybe the manufacturing defect is not on the cells/pouches but on the BMS hardware/firmware when 10 pouches are swollen, but in my opinion it is not a problem of BMS capabilities to manage the charge. Totally agree on that ! As my opinion the BMS is quite good for regular use but some settings could be improved. For example, when a cell/pouches beging to swelling, it internal resistance should be higher than the normal values (and also the other cells/pouches), why the BMS couldn't modify the charging current and voltage based on this behaviour ? This measurement could be added for the BMS for calculating the SOH of the battery. If the BMS detect that most of the cells have too much internal resistance, i should step down the SOH of the battery. The SOH of the battery will never be only based on the past events.
January 14, 20251 yr 2 hours ago, Mauritius B said: Again, I am not 100% in agreement. If the inverter is able to send 53,5volt to the stack as you stated, the cells remaining at 52,6v should be still getting charge current but it is not the case because the BMS on each pylon has already stopped the charging process. You can see on my 3rd picture that 4 batteries are showing 100% charge, 0amps and 52,6v. Status is idle. 2 of them were still finishing the charging process with low current. Module #2 is actually higher in voltage (52.671v) than the rest but still charging 0.265amp. The panels were still able to produce 1.5kw but such power was not delivered nor used. The charging information is not sent from inverter to stack. The stack is informing the inverter about the maximum current it can accept based on the number of battery modules connected and their ratings. If you check the picture from watchpower screen, you can see 23amps sent to the stack and each battery module taking a defined amount of current that is not related to battery module voltage. Module 1 has 51.955v and it is taking 8.391amps while module 2 has 51.952v and it is taking 7.816amp from the bus. Higher voltage does not take lower current so, cells are not limiting the charging current. The BMS does. Maybe the manufacturing defect is not on the cells/pouches but on the BMS hardware/firmware when 10 pouches are swollen, but in my opinion it is not a problem of BMS capabilities to manage the charge. The BMS in the Pylontech does not limit the charging current UNLESS the pack has gone overvoltage, cell over temp, cell over volt etc.. The BMS has no current limiting facility other than on or off and requests to the inverter. The different pack currents are due to the slight differences in eg manufacture of the cells, age, usage and temperature etc. Edited January 14, 20251 yr by Tinbum
January 14, 20251 yr 1 hour ago, Mauritius B said: If the inverter is able to send 53,5volt to the stack as you stated, the cells remaining at 52,6v should be still getting charge current but it is not the case because the BMS on each pylon has already stopped the charging process. Technically the inverter is not sending voltage, but it's sending current. It's so called "CC mode". The current is being split between all the batteries based on their internal resistance, interconnection resistance and willingness to accept charge that changes with SOC of the individual cells. For the same voltage, different batteries will have different charging current. The 53,5V is the voltage value that the inverter is looking for to stop sending current (stop charging). Some of the events that signalize end of charging (CC mode) and transfer to the CV mode: If the battery reports 53,5V the inverter stops charging, even if the cells would still accept current. If the cells stops accepting current, the charging is finished. This might occur even before the cells reach 53,5V. If the BMS reports 100% SOC, inverter will stop charging. If the BMS reports "Advise Charge = 0A", inverter will stop charging. If the BMS reports one of the many possible Errors and Alarms, inverter will stop charging. Most of the time CMOS will be activated by the BMS, so even if the inverter would still continue with the charging, the actual current will be zero amps. Pylontech BMS is really doing nothing to the current that is flowing from the inverter. It has two protective MOSFETs (DMOS and CMOS), that are being operated in the ON/OFF state based on alarms. No analog current modulation feature is in the BMS.
January 14, 20251 yr Also, it is important to understand that physically, there is nothing like 100% SOC for the cell. A LFP cell is just like an air-filled birthday party balloon: When is the balloon 100% full? Is it the state when you blow another air molecule into it and it pops? If so, how does it depend on the balloon's temperature? If that 100% full mark is somewhere lower, where more additional molecules would safely fit inside, can I blow some more air into the balloon? How much? The "curse" of LFP is that they are so energy efficient that you can damage them even with just 1mA of charging current, if applied for a long time. With Lead-Acid batteries that would be absolutely no problem, but LFP stores lithium ions in the hard 3D lattice. If there's no more space for incoming ions, the lattice will crush and gas-mix of O2+CO2+phosphate will be produced. And that is the reason, why some cells are swollen. Either they had manufacturing defect (most of the time it's the the separator failure), or something was hitting them with just a few miliamps of current for a long time, so the lattice started to break. Yes, it would be great to have a BMS that can perform sophisticated monitoring of the cells, but in reality all the BMS-es are just measuring temperature, voltage, current and doing time-based integration of Coulombs in order to "guess" SOC. But keep in mind that more complicated electronic device is, more likely will it fail. Not to mention that it will cost more, consume more energy and produce more heat. While the Pylontech BMS is far from being perfect, the solution is not to improve and over-engineer the BMS itself, but to configure whole solar system in a way that the margin between "balloon full" and "balloon popped" states will be reasonably wide and safe.
January 15, 20251 yr 10 hours ago, JT1 said: they have sent me firmware to run and check if issues improve @JT1 can you share to us the firmware file and version they provided ? Best Regards
January 15, 20251 yr 15 hours ago, Youda said: Some of the events that signalize end of charging (CC mode) and transfer to the CV mode: If the battery reports 53,5V the inverter stops charging, even if the cells would still accept current. If the cells stops accepting current, the charging is finished. This might occur even before the cells reach 53,5V. If the BMS reports 100% SOC, inverter will stop charging. Will the BMS will be doing the first two checks here, so it sending a 100% SOC to the inverter means that it has detected one of the two conditions that you mention. Just a question. Another little piece of information I can file away.
January 15, 20251 yr 17 hours ago, Youda said: Technically the inverter is not sending voltage, but it's sending current. It's so called "CC mode". The current is being split between all the batteries based on their internal resistance, interconnection resistance and willingness to accept charge that changes with SOC of the individual cells. For the same voltage, different batteries will have different charging current. The 53,5V is the voltage value that the inverter is looking for to stop sending current (stop charging). Some of the events that signalize end of charging (CC mode) and transfer to the CV mode: If the battery reports 53,5V the inverter stops charging, even if the cells would still accept current. Not the case. My batteries have 52.6v and they are not charging anymore. If the cells stops accepting current, the charging is finished. This might occur even before the cells reach 53,5V. Chemically and physically speaking this is not possible. The cell is not able to reject the current whenever the charging voltage is higher than cell voltage. That is why BMS cuts current when cells are charged, even if inverter is still trying to charge the battery. If the BMS reports 100% SOC, inverter will stop charging. True for some inverters only. Axperts usually show "warning 69" when they are trying to charge the battery but it doesn't accept the charge because it has reached 100% SOC and BMS has stopped charging process. If the BMS reports "Advise Charge = 0A", inverter will stop charging. This confirms that BMS has the control over charging process. Why not using it? If the BMS reports one of the many possible Errors and Alarms, inverter will stop charging. Most of the time CMOS will be activated by the BMS, so even if the inverter would still continue with the charging, the actual current will be zero amps. Emergency situations should not be considered in a normal operation analysis. Pylontech BMS is really doing nothing to the current that is flowing from the inverter. It has two protective MOSFETs (DMOS and CMOS), that are being operated in the ON/OFF state based on alarms. No analog current modulation feature is in the BMS. Some comment on the quote. Technically speaking, in order to produce a current flow it is necessary to create a potential difference between 2 points. If the inverter is creating a voltage of 53,5volt (as you mentioned, it is the charging voltage target) and the battery voltage is around 52v, there will be a current flow from the inverter to the battery due to the difference in potential (voltage) between them. I refer again to the picture where battery modules are resting at 52,6v and no charging current is present. Control modes CC and CV are not relevant for the case as they only define the charging mode that is applied, Constant current or constant voltage. When constant current is applied, the voltage on the battery will rise until it equals charger voltage and the current ceases and in constant voltage mode, the current will be decreasing to cero when charger voltage and battery voltage are the same (no potential difference). In any case, if there is a voltage difference, there is current. How can we explain that batteries on the picture have a voltage of 52,6v, the inverter is producing 53,5v but the charging current is only 0,265amp? According to ohms law, 0.9v (53.5 - 52.6) over a resistance of a few milliohms (typical internal resistance of a battery) should produce dozens of amps. There is something else that is limiting the current across the battery. Based on all the above, it seems that inverter is not always charging at 53.5v because BMS is instructing to do so, or BMS can effectively control charging current. Edited January 15, 20251 yr by Mauritius B
January 15, 20251 yr 5 minutes ago, Mauritius B said: Based on all the above, it seems that inverter is not always charging at 53.5v because BMS is instructing to do so, or BMS can effectively control charging current. The BMS instructs the voltage the inverter charges at. The BMS only controls charging current by instructing the inverter of the max current for the combined pack. It does not restrict the current internally other than 'off' or 'on'.
January 15, 20251 yr 4 hours ago, Bobster. said: Will the BMS will be doing the first two checks here, so it sending a 100% SOC to the inverter means that it has detected one of the two conditions that you mention. AFAIK, in case of Pylontech US, the BMS declares 100% SOC once all the cells are at 3,48V or over and the voltage difference between lowest and highest cell is less than 30mV. Below these values, BMS will appear to stuck at roughly 90% and there will be a small jump to 99 a 100 finaly. Reason is that it's very hard to calculate SOC based on integrating Amps at these stages. Writing this just from my memory, the exact numbers can be extracted using CLI. If you continue charging, the current will be accepted by the battery but the reporeted SOC will be still just 100% (well, sometimes GUI can glitch to 101% but that is an error). This is "balloon full" state for the Pylontech. Anything above is the margin before the "balloon popped".
January 15, 20251 yr 2 hours ago, Mauritius B said: How can we explain that batteries on the picture have a voltage of 52,6v, the inverter is producing 53,5v but the charging current is only 0,265amp? Because it is not. Just try it: Get the batteries to this state of being almost full Wait for the BV to show 52,6V Connect the multimeter to the DC terminals of the inverter and measure the voltage. You will not see 53,5V there. Can you handle this? Edited January 15, 20251 yr by Youda
January 16, 20251 yr 17 hours ago, Youda said: Because it is not. Just try it: Get the batteries to this state of being almost full Wait for the BV to show 52,6V Connect the multimeter to the DC terminals of the inverter and measure the voltage. You will not see 53,5V there. Can you handle this? Yes, it is clear. I am not talking about "almost full" batteries, I am talking about "100%SOC" batteries that went into idle state at 52,6v, so the BMS never requested further charging up to 53,5v from the inverter and I will never be able to measure 53.5v on the terminals. You stated on post "Problem with Pylontech is that even when the data communication from BMS to the inverter is working, the BMS tells the inverter to charge till 53,5V. (=3,57V per cell)" Maybe it is something related to certain firmwares like the ones that you tested from US. Let's agree on the point that BMS in not perfect but, when batteries produced on the same batch (even with consecutive serial numbers) and connected to the same inverter are failing randomly, in my opinion, there is something else than a bad BMS design otherwise, all of them would be failing sooner or later. It is just an opinion.
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