frankvw Posted July 20 Share Posted July 20 As I understand it, the general recommendation is that LiFePO4 batteries in regular use should be charged to about 90%. However, there is also the matter of cell balancing. In this thread a post from @zivva states that: Quote Batteries should reach 100% SOC on a regular basis for cells to be balanced that typically occurs after 3.4V. When only charging to 70%, cells will remain around 3.25V then never be balanced. Expect more & more unbalance in the long run ... I believe (note how I phrase it) that this makes sense, but how often is "regularly"? How frequently should I charge my battery to the point where the charger switches from absorption to float in order to maintain proper cell balancing? // FvW Quote Link to comment Share on other sites More sharing options...
WannabeSolarSparky Posted July 20 Share Posted July 20 I try to do mine every 6 months. But since using the jkbms i noticed they do not really go out of balance TaliaB and zsde 2 Quote Link to comment Share on other sites More sharing options...
Scorp007 Posted July 20 Share Posted July 20 6 hours ago, WannabeSolarSparky said: I try to do mine every 6 months. But since using the jkbms i noticed they do not really go out of balance And I thought with my JK BMS and cells also very close and trying to balance every 3 months was too long between balancing With no LS my battery does not really get used but I do give them a walkies now and again. TaliaB and WannabeSolarSparky 2 Quote Link to comment Share on other sites More sharing options...
zivva Posted July 21 Share Posted July 21 There is no reason to only charge your batteries to 90% instead of 100% ... The less you charge them to the point they get balanced at the end of the charging curve (> 3.5V), the more unbalance you create and the less accurate the SOC gets estimated by the BMS. If you want to improve battery life, you can choose to only use x% of their capacity but cycling from 100% to 40% is better for the reasons given above than from 90% to 30% ... Any cases what matters is cells being in balance at 3.5V (> 99% SOC). Only garbage cells are out of balance @ 3.3V (SOC = 30% to 90%, middle of the flat curve, impossible to be precise) TaliaB and Scorp007 1 1 Quote Link to comment Share on other sites More sharing options...
frankvw Posted July 21 Author Share Posted July 21 4 hours ago, zivva said: There is no reason to only charge your batteries to 90% instead of 100% ... The less you charge them to the point they get balanced at the end of the charging curve (> 3.5V), the more unbalance you create and the less accurate the SOC gets estimated by the BMS. If you want to improve battery life, you can choose to only use x% of their capacity but cycling from 100% to 40% is better for the reasons given above than from 90% to 30% ... Any cases what matters is cells being in balance at 3.5V (> 99% SOC). Only garbage cells are out of balance @ 3.3V (SOC = 30% to 90%, middle of the flat curve, impossible to be precise) OK, I hear what you say. I've got BlueNova batteries which are the best I can afford but not top of the line; especially the BMS is a bit noddy. I don't think they're crap cells but BN definitely bears careful handling if you want to get the most out of them. I'm not discharging below 30%. However I have noticed that (due to varying loads and my MPPT set to apply an adaptive absorption stage duration) the batteries weren't being charged fully (my guess is not over 85%) and if that goes on for too long cells and batteries might require rebalancing. At least that's what the supplier has told me. So right now I'm fiddling with settings to ensure that the batteries at least get a decent absorption stage. Can't hurt... Quote Link to comment Share on other sites More sharing options...
zivva Posted July 21 Share Posted July 21 How would you know your battery is reaching 85% ? It's just a matter of voltage. To reach 100% capacity, you just need to reach +/- 3.5V per cell. Anything between 3.45 & 3.6V will do. Quote Link to comment Share on other sites More sharing options...
frankvw Posted July 23 Author Share Posted July 23 On 2024/07/21 at 1:48 PM, zivva said: How would you know your battery is reaching 85% ? It's just a matter of voltage. To reach 100% capacity, you just need to reach +/- 3.5V per cell. Anything between 3.45 & 3.6V will do. As far as the 85% is concerned, I'm basing that on the default "State of Charge when bulk finished" setting in my Victron Multiplus. Plus, it makes sense: the bulk charging stage ends and the absorption stage begins, as per the datasheet for my battery, at 28.4V, or 3.55V per cell. So I respectfully disagree with you: the cells are not fully charged when they reach 3.55V. Otherwise no absorption cycle would be necessary. Yet it is: During the bulk stage the battery is charged at a constant current until the voltage reaches 3.55V per cell. Then the absorption stage starts at which the battery continues to charge at a constant voltage of 3.55V per cell until the current drops to zero (or close enough as not to matter). So your statement that "To reach 100% capacity, you just need to reach +/- 3.5V per cell" is incorrect. WannabeSolarSparky and Antonio de Sa 2 Quote Link to comment Share on other sites More sharing options...
zivva Posted July 23 Share Posted July 23 If you had a shunt, you would notice that 1 cell reaching 3.5V is charged to +99% of its capacity. BMS typically starts balancing cells @ 3.4V. that was your initial interrogation. There is a reason why most hybrid inverters do not bother with bulk, absorption & float but just charge up to a determined voltage then let the BMS limits current when cells reach OV. This makes barely noticeable difference in achieved capacity. It is demonstrated here : https://lygte-info.dk/info/BatteryLiFePO4Charging UK.html So, I confirm my initial statement Quote Link to comment Share on other sites More sharing options...
frankvw Posted July 23 Author Share Posted July 23 Yes, you're right. Victron have no clue about how batteries work! I really have no idea how they have managed to stay in business for about half a century, most of that time as a leading vendor in that market. But not to worry; I'll forward them your URL so they can ask this blogger in Denmark to explain it to them. Once they do that, I'm sure they'll change the software in their products accordingly. 0012 and zivva 2 Quote Link to comment Share on other sites More sharing options...
zivva Posted July 23 Share Posted July 23 (edited) Those 85% SOC when bulk finished is just the default value on Victron. It is supposed to help the Multi to more accurately calculate the SOC at the end of charging cycle. Assuming one set the proper voltage to that bulk charge. Which is obviously not 3.55V ... https://community.victronenergy.com/questions/823/why-is-my-maximum-soc-stuck-at-85.html You could set bulk @ 3.8V, your Victron would still display 85% SOC when bulk finished with that setting ... Default value meaning ... you can change it & probably should, cause @ 3.55V you're well above 85% SOC ... but 99+ %. Kind of defit the purpose of that 3 stages charging algorithm then. Oups. Or reduce that bulk to 3.35V which is closer to 85% even if Lifepo4 charging curve being flat like pancake, it's hard to get a precise SOC between 3.2V and 3.4V. Why does Victron uses a 3 stages charging algorithm when 1 stage CV does the job ? Probably cause they sell BMS-less Lifepo4 as AGM drop-in replacement ? Or other reasons, don't know, don't care, not concerned. Ask them ... I'm not the one asking questions here. You're welcome ! Edited July 24 by zivva Quote Link to comment Share on other sites More sharing options...
0012 Posted July 24 Share Posted July 24 On 2024/07/23 at 11:33 AM, zivva said: Why does Victron uses a 3 stages charging algorithm when 1 stage CV does the job ? yes, that 3 stage method really is just a hangover from the lead acid era Quote Link to comment Share on other sites More sharing options...
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