December 20, 20223 yr Just get a BMS with active balancing and forget about top balancing. Just connect up and charge.
December 21, 20223 yr @GreenMan I've connected the power supply as you described. @DeonBez thanks for links. I set the power supply to 3.4V, cells voltage is now 3.35V, current 0.29V. What worries is that cells are not getting close to 3.4V regardless of whether I set power supply to 3.4V or 3.6V. What could be preventing cells from reaching 3.4V-3.6V?
December 21, 20223 yr 42 minutes ago, Tim003 said: I set the power supply to 3.4V, cells voltage is now 3.35V, current 0.29V ¿que? current is measured in Ampere, do you mean 0.29Ampere current? what is the PSU capable of current wise? the Voltage should reach 3.4V once the cells have enough energy in them that supports that Voltage level... which, depending the on the current provided and the Ah capacity of the cells can take days... I didn't check from the 1st posting, but if you have 16 cells in parallel, each at 100Ah, that's 1600Ah, now if you're charging at lets call it 0.3A, that's 0.3Ah, assuming the cells are at 70% (could be more, could be less, who knows for sure) they can then expect to have another 480Ah shoved down their connections before being 100% full, lets go for 90%, that would be 320Ah and at 0.3Ah, well, another 1000-odd hours to go?
December 21, 20223 yr 11 minutes ago, Kalahari Meerkat said: ¿que? current is measured in Ampere, do you mean 0.29Ampere current? what is the PSU capable of current wise? the Voltage should reach 3.4V once the cells have enough energy in them that supports that Voltage level... which, depending the on the current provided and the Ah capacity of the cells can take days... I didn't check from the 1st posting, but if you have 16 cells in parallel, each at 100Ah, that's 1600Ah, now if you're charging at lets call it 0.3A, that's 0.3Ah, assuming the cells are at 70% (could be more, could be less, who knows for sure) they can then expect to have another 480Ah shoved down their connections before being 100% full, lets go for 90%, that would be 320Ah and at 0.3Ah, well, another 1000-odd hours to go? Yes, I meant 0.29A. I set the power supply to 3.4V 10A connected to 8x 120Ah cells. I've been charging for 4 days now, current was high and continued dropping but cells voltage is steady around 3.35V. I expected the cells to increase to the set value of 3.4V or previously set value of 3.6V.
December 21, 20223 yr 30 minutes ago, Tim003 said: Yes, I meant 0.29A. I set the power supply to 3.4V 10A connected to 8x 120Ah cells. I've been charging for 4 days now, current was high and continued dropping but cells voltage is steady around 3.35V. I expected the cells to increase to the set value of 3.4V or previously set value of 3.6V. The voltage will remain around 3.4 volt for very long. You have indicated the current is low. If they were like at 50% SOC and charged at 1A it will take quite a bit over 60hrs. At some stage the 3.4V will go up fast when close to 100%.
December 21, 20223 yr 6 minutes ago, Scorp007 said: At some stage the 3.4V will go up fast when close to 100%. What if the cells reach 3.4V and current is 0A, would that imply that they are now balanced?
December 21, 20223 yr 15 minutes ago, Tim003 said: What if the cells reach 3.4V and current is 0A, would that imply that they are now balanced? Yes it would. Personally I would take them to 3.45V though.
December 21, 20223 yr 1 hour ago, Chris_S said: Yes it would. Personally I would take them to 3.45V though. I'd go for 3.55V at this stage, since all are in parallel that would be fine and below the 3.6V limit, what ideally you'd want to do is actually get the PSU set to 3.6V, your bulk charge Voltage, but once the cells, reach, say 3.5V, stop the charging you're probably at 95+% at that stage... 3 hours ago, Tim003 said: I set the power supply to 3.4V, cells voltage is now 3.35V, current 0.29V. There's the issue, with 3.4V bulk charge Voltage it will take forever to reach 3.4V, you need to charge with 3.6V or 3.5-oddV, if you're afraid of getting too close to the limit, but either way, monitor the cells' actual Voltage, you will find if you crank up the PSU to try and deliver 3.6V, the current to the cells will climb (faster charge rate, since the actual vs the charging Voltage is rather larger than it is now) and you will get more energy into the cells quicker, without doing damage, unless you let the cells get to 3.6V or higher, of course...
December 21, 20223 yr Another easy oversight: most cheap PSUs come with thin cables. Ensure thick enough cables for the 10A and good connections on both the PSU and battery sides. The stop charge current is normally 5% of the capacity so for the 960Ah pack charging at 10A is very low. Top balancing at 10A in parallel up to 3.65V will definitely not damage the cells or cause run away. Edited December 23, 20223 yr by DeonBez
December 22, 20223 yr On 2022/12/21 at 11:12 AM, Kalahari Meerkat said: There's the issue, with 3.4V bulk charge Voltage it will take forever to reach 3.4V, you need to charge with 3.6V or 3.5-oddV, if you're afraid of getting too close to the limit, but either way, monitor the cells' actual Voltage, you will find if you crank up the PSU to try and deliver 3.6V, the current to the cells will climb (faster charge rate, since the actual vs the charging Voltage is rather larger than it is now) and you will get more energy into the cells quicker, without doing damage, unless you let the cells get to 3.6V or higher, of course... Thanks, I did exactly this, I adjusted the voltage while connected to the batteries and current went up. The cells were briefly unattended and reached 3.7V, this scared me but I read that they can reach 4.2V before damage can occur. Now they are at 3.632V, perfectly balanced. Next would be to do capacity test. Do I need a BMS for the test? The reason I'm asking is because the capacity tester I have can limit low voltage discharge.
December 22, 20223 yr 5 minutes ago, Tim003 said: that they can reach 4.2V before damage can occur. No, dude, NMC type LiIon batteries can go to 4.2V, but not LiFePO4's, these are only supposed to go up to 3.6V max...
December 22, 20223 yr 1 hour ago, Tim003 said: Thanks, I did exactly this, I adjusted the voltage while connected to the batteries and current went up. The cells were briefly unattended and reached 3.7V, this scared me but I read that they can reach 4.2V before damage can occur. Now they are at 3.632V, perfectly balanced. Next would be to do capacity test. Do I need a BMS for the test? The reason I'm asking is because the capacity tester I have can limit low voltage discharge. Next time you do this please don't adjust voltage while connect to batteries. Too much current on a full battery is asking for big trouble
December 22, 20223 yr 3 hours ago, Kalahari Meerkat said: No, dude, NMC type LiIon batteries can go to 4.2V, but not LiFePO4's, these are only supposed to go up to 3.6V max... 3 hours ago, Kalahari Meerkat said: No, dude, NMC type LiIon batteries can go to 4.2V, but not LiFePO4's, these are only supposed to go up to 3.6V max... This article states Lifepo4 can be safely charged to 4.2V but I wouldn't deliberately do that. https://www.powerstream.com/LLLF.htm Edited December 22, 20223 yr by Tim003 Link
December 22, 20223 yr 3 hours ago, Tim003 said: Next would be to do capacity test. Do I need a BMS for the test? The reason I'm asking is because the capacity tester I have can limit low voltage discharge. Any advice on this?
December 23, 20223 yr 11 hours ago, Tim003 said: This article states Lifepo4 can be safely charged to 4.2V but I wouldn't deliberately do that. in the article they state Quote A LiFePO4 battery can be safely overcharged to 4.2 volts per cell, but higher voltages will start to break down the organic electrolytes. and 4.2V is higher Voltages in the specs of LiFePO4's, unless you are happy that powerstream.com will guarantee your cells for you, I'd stick to the generally stated values, if you want your cells to be with you and working for a few years. As for a capacity test. I'd say wait for the BMS and even then, how do you propose to do this, use the battery and log the power drawn from the battery under normal use, until it is pretty much down to 3V per cell and time to recharge? Or do you want to test just one cell? without specific hardware that can put a constant load and monitor the Voltage at the same time and give you accurate accumulate power reading, its not so easy to get an accurate measurement out of this...
December 23, 20223 yr please check this site. https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom#:~:text=The Pylontech battery requests a charge voltage of 53.2V. and also : https://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery Edited December 23, 20223 yr by alexam3001
December 23, 20223 yr 21 hours ago, Tim003 said: The reason I'm asking is because the capacity tester I have can limit low voltage discharge. What is model / specifications of the capacity tester you are planning to use? I use the EBC-A40L for some time. It works great. Because of the high current capabilities, it also works nice to top balance cells in parallel after charging it to almost full in serie.
December 23, 20223 yr I connected the cells in 12V configuration to an inverter. The load was a heater at 375W. The test lasted for 7.33 hours, voltage dropped from 14.06V to 12.1V. Average current is 31.25A. Approximate capacity is 12V 229Ah. I am happy with the results considering the cells were not fully charged when the test commenced and I did not test all the way to 2.5V/cell. Edited December 23, 20223 yr by Tim003 Incorrect calculation
December 23, 20223 yr 3 hours ago, DeonBez said: What is model / specifications of the capacity tester you are planning to use? I use the EBC-A40L for some time. It works great. Because of the high current capabilities, it also works nice to top balance cells in parallel after charging it to almost full in serie. I have this 150W tester : https://www.amazon.com/MakerHawk-Electronic-Load-Tester-USB/dp/B0BPCN1XMJ Not suitable for high currents.
December 31, 20223 yr Hi All Just experiences from buibuing , I have a 272amp back build in 2021 its over a year performance is fantastic i get at least 14kwh from the pack. Charge voltage is 55v, charge current 100amp, discharge is 100amp aswell ,cut off 50volts, JBD bms with SA. Lishen 272ah cell from Basen Technologies, JBD bms from AliExpress and Active Balancer from Hankzor AliExpress. .  Edited December 31, 20223 yr by Raj35
January 2, 20233 yr Do you run the active balancer permanently or can that BMS switch it on after a certain voltage?
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.