Came from reddit, please excuse Blaze, he is not well received. If you want to passively balance LiFe cells, I recommend doing so at 3.5v with a constant voltage for several hours. Andy over at OffGridGarage has made some great videos detailing this process. The TLDR of it is that even though the cells may be at the same voltage, unless you absorb charge them (at low current) for several hours, they can still be a few amp hours apart at the same voltage. Also, I would recommend that you get the Bluetooth module for that Daly BMS and adjust your protection parameters to something a bit more conservative for battery longevity.
thanks for the hints and the help. I know most of Andys Videos, he is a great source. I was just confused by this forum entry and thought I can work around top balancing as it takes a while. I think it could also work iff the cells were already matched/balanced by the manufacturer. Regarding the bms I wanted to have a stupid one as I heard that the smart ones are not that reliable. I think I could also tweak the settings of the charge controller to avoid low/high voltage. The BMS is just the safety net.
The mistake here is in thinking that voltage-matched cells means “balanced” cells. It definitely is not the case. As another commenter says, to properly balance cells they need to be top balanced (or bottom balanced, but that seems less practical in use) at 3.5v or more, and allowed to absorb current for a while until all cells are saturated. this absolutely MUST be done before assembling cells in series for use if you want to get maximum capacity from the pack, and not trigger BMS cutoff frequently when charging.
This isn't unusual with LiFePo4 cells because of their really flat voltage curve. Eg you might have 4 cells at 3.2v, but they might be at 60% 40% 50% and 70% state of charge. (there shouldn't be that much variation on a new set from the same supplier, but a top balance makes sure that they're all the same state of charge before putting them in series) The state of charge won't equalize just by putting them in parallel, without bringing them to a full charge or draining them all to a low state of charge. A reliable method is to put them into parallel and then bring them all up to a full charge. For my build I did this with a 20A hobby charger set to LIFE 1S. It took 2 days for mine to charge and top balance.
you need to TOP balance not just balance, if all batteryes are at same low voltage doesn't mean have same charge. you need to put them in parallel and charge at 3.65 volt or at least 3.5 volt after you put in series
I made 3 batteries on similar cells. They are cheap and certainly not top quality. I find bluetooth very helpful because I can see what is happening with the cells. I also use an active balancer, .. I can't imagine a battery without it. He balances targets non-stop and can do it with high current (up to 5 A). The balacer included in the BMS balances only when charging, after exceeding a certain voltage (e.g. 3.4V) and doing it with a very small current (approx. 30mA). Its effectiveness is very low. Use an active balancer once and you will never make a battery without it :)
@@LupoDIY I will add - the balancer in the BMS balances through the loss of voltage on the resistor, and this is a loss of energy. The active balancer transfers energy from the higher cell to the lower one and nothing is wasted :)
@@Radauskas that is true. but it also depends how you discharge the battery. if you discharge and charge with high current, the active balancer might run into problems as it is too slow to balance everything. a good top/bottom balanced system can stay balanced for a long time, even without a balancer (BMS or active). In general, it really depends on the type of load you have.
@@LupoDIY As I wrote earlier - cheap cells do not ensure good voltage equality. In my opinion, an active balancer can help a lot without making anything worse.
@@Radauskas I think there are situations when a active balancer can make things worse, as shown in ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-4iPpn8-Pakk.html ... but for a lot of use cases it is a good solution.
thanks John for the reply and happy that you like it. I fully agree with the balancing, also what I showed than in my next video ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RKIwnFIyiJA.html
thanks Jason. you are right, that is also what I did at the end as shown in the next video ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RKIwnFIyiJA.html
Hey Lupo, Just a thought concerning your Low Temp Charge Cut off Problem: In Case of neither your BMS nor the solar Charge Controller has a Low Temp Cut off and solar ist your only charging source you could probalbly use a simple thermostat Switch Inline in the solar Input to the Charge Controller. Set it to Open at e.g. 5°C and should be o.k.!? I'm not an expert. Just building a first Battery 24v280ah myself for an RV application. My old SCC had No Lithium settings and No LTCP as welll. Ended up buying a Victron model that has one. Good luck with your projekt! Grüße Holger
Hey Holger, thanks for the advice. I also use a victron charge controller which has a low temp charge cut off and I guess I want have the system on during the cold winter times so I should be safe. otherwise I think I would definitely add another safety mechanism as you proposed. cheers, Lupo
your bottom balance voltage 3.27V was too high. Which did not reach to the bottom area yet. Around 2.8~3.0V will be good to bottom balancing area for LiFePO4.
Hey, thanks for the suggestion, you are right, the voltage is to high for bottom balancing. I didn't want to bottom balance it but it is definitely a good option to do so. In ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RKIwnFIyiJA.html I also showed what I did at the end. cheers, Lupo
Why not get a small active balancer, I think they are quite effective. Otherwise just to a top balancing by connecting all cells in parallel. Also you should try out a QUCC BMS with the Bluetooth, they are better than Daly, better tech support and cheaper as well.
thanks for the tip, I will also have a look into the QUCC BMS, I already consider a smart new one to monitor everything. Regarding the active balancer, I guess, it wouldn't have helped as the voltage was on the same level, but as you proposed top balancing is the best solution. I also covered my solution in my next video ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RKIwnFIyiJA.html
I think people understand very well when you explain things. Therefore, I tried to explain it in this video ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RKIwnFIyiJA.html
