When your battery pack becomes out of balance, most BMS will not do a whole lot to fix it. Here I show one simple technique to manually balance a battery pack.
This is partially true. The reason why passive balancers don't work is if you charge with a high enough current your BMS will never be able to counter the cell groups that are high from reaching 4.25V when balancing starts at 4.18V. If your BMS balance current is 60mA (quite common) then charging at 10A is going to drag the high cells up to 4.25V way faster than your low cells could ever catch up. Your low cells are seeing 10A at 3.5V and your high cells are seeing 10A until they reach 4.18A at which point they are seeing 9.940A so the time it takes them to go from 4.18V to cell overvoltage at a 60mA reduced rate is nearly the same as it would be for the full charge rate. In this scenario you can A. Keep charging fast and not see your cells get closed to balanced until you do a dozen or more cycles B. Lower the charge current and give that 60mA balance current a chance at making a difference I don't think this is really explained anywhere. One dedicated slow charge could significantly bring your pack back into balance and allow you to continue fast charging after that so long as you're happy with the delta v. If I had a pack that was 400+ millivolts out of balance and had no way of charging single groups, I just had a charger rated for the voltage of my battery with adjustable current I would do a 1A or even lower charge cycle and see if it can get me in the realm of 100 millivolt difference. At that point you're not leaving too much capacity on the table when you continue to use it 100 millivolts out of balance and that should correct itself over the next handful of cycles.
makes sense! thank you for the detailed reply. I'm going to give this a try. although I'm still surprised that a relatively feature-rich BMS like ANT or Daly doesn't have an active balance built-in. I know Daly sells active balancers - I have one and it works great - but this really should be the default cell balancing method on any medium-grade BMS & up
Sir pls answer this question of mine...im desperate for an answer I have an 8S LiFePO4 battery pack for my ebike project which I tried to charge using my suspicious lithium battery charger. The charger applied a voltage slightly higher than the battery voltage at any moment to charge it along with 1.5 A of current. For example, if the battery was at 26.2 V the charger applied 26.5 V and 1.5 A, and the voltage increased in the same proportion as the battery voltage increased. This was constant current charging. The thing is, the charger cut off the charging while my battery was only 85-90% charged(26.6V) and never intiated the constant voltage charge. I just read somewhere that I need a charger which applies a constant voltage of 29.4 V to fully charge a 24 V LiFePO4 battery. Did I damage my battery by charging it through a charger that doesn't fully charge my battery and give out constant 29.4 V? I may be just paranoid but it could be a serious thing. Can I continue using this charger in the long term which never initiates the CV charging? I'm fine with not utilising the remaining 10% SOC. I just want to make sure this kind of undercharging and this charger doesn't harm my battery in any way. And what I'm more concerned for is that i also heard that many bms' tend to start balancing the battery when it reaches a certain VOLTAGE (full charge voltage), if this is true..... doesn't it mean that my battery can become unbalanced in the long run as the bms may never balance the cells? Can charging an 8S LiFePO4 battery pack using a charger that never initiates constant voltage charging and doesn't fully charge the battery to 100% cause damage to the battery, and can this lead to cell imbalance if the BMS only balances the cells at full charge voltage?
@@electricalA.K. do you have a BMS installed on your battery pack? If yes, it is most likely that your cells are already out of balance and the reason your pack is not charging full is not because of the charger but because one of your cell groups is reaching max voltage, and the BMS is cutting off charging to prevent damage to the cell (overcharge protection). Thus, you have one cell at full charge and the rest remain not fully charged so your total pack voltage is less. You can check the charger voltage at the terminals before you connect it to your battery pack. If it is what the total pack voltage should be, what I described above is most likely the issue. If the voltage at the charger terminals is lower than what the fully-charged voltage should be, the problem is that the charger voltage is too low - depending on the charger you may be able to adjust this by opening it up and twisting a potentiometer
@@GaiusGarage sir i had checked if the problem existed with the battery or the charger.... Turns out that the charger cuts off the charge at 90% SOC (i monitored the voltage and current while the charging process was going on) . My question now is, the battery is new and no cells should be out of balance, so can the battery get unbalanced in the long run because many bms start the balancing process when the battery nears full charge voltage, which my charger will never reach. And second question is, the lifepo4 8s resting full charge voltage is supposed to be 27.2v(100% soc) while my seller lists it to be 26.5v on their website(which is 85-90% soc which is what I'm reaching) what is going on here? Why is the voltage listed by the seller lower than the actual full charge voltage
It’s a good tip. Sometimes that works but I find that usually when the cells are that far out of balance it’s for a reason. I’d recommend people be extremely cautious doing this and never walk away from it while charging.
yes, this is a good point (that I should have mentioned). Internal resistance is the name of the game here and I actually ordered a meter to measure this. I dont necessarily think these low cells have exceptionally high internal resistance -- probably more due to repeated use and negligence with respect to balancing, but it is most likely higher since these cells were more stressed.
its for a reason, but that reason may very well be a variation in self discharge rate. i have a pack from a bike, 48v, 13s4p, LG MJ1 (i think). After manual balancing, all is fine and dandy, cells all have 4,2 volts and they also discharge at very similar rates. but after 1/2 year of storage, the little shit is out of balance again. now if you look at individual cell groups, theres nothing really frightening about 1 group discharging 20% in half a year while the other discharges maybe 25%. its chemistry after all.. but the stupid pack has no balancing at all and that leaves me with a really big and stupid problem of always having to deal with this disbalance. switching BMSs is possible, but not very sexy when your pack is for a retail bike and you have a battery case that can show state of charge with LEDs.
Hi! Have you tried calibrating the volt meter on your charger using the adjustment screws on the back of the display (using x small needle nose pliers works best) ? I calibrated mine recently and it hasn’t drifted so far.
Oh also what gauge / mm size are the jumper cables you’re using in the breadboard?
6 месяцев назад
Hvala za tale prispevek, sedaj je veliko stvari bolj jasnih, tudi jaz sem videl da celice niso uravnotežene, in sem kupil nov BMS, ki je naredil isto kot stari izklopil polnilnik pri 39v in ugasnil baterijski sklop pri 38v. Sedaj vem kako bom uravnotežil vsako skupino celic posebej in si naredil na ohišju vtiče, da ne bo treba razdirati ohišja. Hvala😎😎👍👍👍
Interesting video and good tips. I notice though that the plugs on balance chargers (and battery BMS) are larger format than what I have on my E- Bike battery. The battery shut down when I left the charger on it overnight. I was hoping to test the voltage of the cell groups, but I cant find anything that is the correct size to plug into the battery pack.
i am currently trying kind of the same with a 10s but im discharging and hoping the bounce back up and level out hopefully avoiding any cell drop (this is a 16ah 10s 1p polimer pouches so taking a while )done it with 4 of the cells so far and there all now sitting at 3.64 ,will let you know how it goes after i charge it all back up as a pack with the 42v see if they keep balance ,great video by the way thankyou
Each cell group is a collection of individuals 18650 cells all connected in parallel, so while their capacity added together, their voltage is the same as one individual cell, which is 4.2V. Therefore I am charging each cell group to 4.2V
Each cell group is a collection of 18650 cells all connected in parallel, so while their capacity added together, their voltage is the same as one individual cell, which is 4.2V. Therefore I am charging each cell group to 4.2V
@@GaiusGarageyou know what’s really scarry about these larger packs that consist parallel series interconnected batteries. Each of your “cell groups” that you aim to balance right, what really ticks my nerves are within those cell groups are many individual batteries that only god knows how far apart they are from eachtoher 😂 I get anxiety just thinking about the fires that are waiting for us down the road
I have this problem where all my cells are full charge except 1 group wired in parallel are flat. Taking a battery rated at 288wh and turning it to a 50wh battery, testing it on a known load and measuring. I assumed that series might have a bad cell so disassembled that series from the pack to test each cell and they all behave the same. I should have just attempted to balance them in the pack before I disassembled. I got my cart before the horse here. Now I have to rewire them into the pack when I finish charging these cells 1 by 1. Im a novice not an expert, but like to learn. Also dont have nickel tab or a spot welder, so I beat a wire winding from a toroidal coil into a sheet and pretinned it, since ill be soldering...I tested calcium lime and rust, known as CLR as a cleaning agent as a soldering acid and it actually allowed solder flow when tinning that toroidal coil copper sheet, but I had that copper pretty clean.
I just took the 10s3p 18650 pack out of an old scooter and was surprised to find there was no balance plug on it. The pack has an XT30 connector and an extra plug with 2 wires, a black and red, which is probably for a thermistor to measure battery temp. The entire pack is 3.51v. Not per cell, but the entire pack, so it's toast. I am going to rebuild the pack and I am thinking of adding a balance plug and using a hobby charger to balance charge the new pack. Is this a good idea? I've never messed with scooters. I only work with FPV drones.
@@GaiusGarage I thought maybe I could wire it as two 5s packs and make a series plug to turn the two 5s packs into a 10s pack. I also bought a BMS that has a 10s balance plug. I don't know much about BMS but I assume it balance charges the pack?
@@CarbonGlassMan the BMS balance charge feature is not so great on most generic BMS's so a balance charger would be much better. but it's more complicated to use two 5s balance chargers to charge the pack. you're probably better off keeping it as a 10s pack and adding an active balancer alongside the BMS. the balancer will keeps the cells balanced and the BMS will provide all the protection features
I use lipo balance charger with modular ebike packs I run in series when ebiking and disconnect down to 2s packs for charging ... Got tired of 5x BMS failing!!
Thanks, you solved my big question whether BMS with balance feature can actually balance a battery pack....So the answer is no. I was also trying to manual balance a 10S4P pack using a imax b6 charger and charging 1s each time starting from 1s upto 10S but this was not successful too :( (Charging was like stopped at 3.65 V ). Any ideas ? Now i m trying to discharge seperately cells that are higher to others P.S. Voltage difference is like 0,2-0,3V, not damaged cells
Are you trying to charge Lithium Iron Phosphate? What setting are you using on the iMax B6? Charging each group up to a certain voltage is the best way to do it (or discharge the few high ones if that's how it works out better for you). There will be some slight voltage drop after you remove the charger, I don't consider a cell at its resting voltage until its been off a charger for at least an hour but realistically most of the movement happens within the first 10 minutes of the cell coming off the charger or load.
The original sense wires of a BOSCH batterypack are very thin, they only function as a detection of the voltages of the groups, nothing more, one group is full , the load current stops globally, also in the case of one group is undervoltage, the BOSCH stops with working.
So let's say my drill battery is unbalance and it consists of 8 batterys can I just charge them all up individually to the same voltage ? Great video 👍🏻
@@nothingbutthetruth7900 a drill battery should have a good active balance function on the BMS. it shouldn't really be too much out of balance unless the cells have been very stressed and some are degraded. balancing them may not solve the problem as they will just become unbalanced again after a few cycles
@@GaiusGarage thank u so much for taking the time to reply bro👍🏻just doing some drill refurb rebuilds and very new to this and tbh lithium scares me a bit 🤣as watched videos way to much of them exploding so when I'm working on them it's like I've got a bomb suit in terms of safety precautions 🤣👍🏻
@@GaiusGarage also will let's say there are a few a bit out will the BMS sort that out without me having to take off and charge to the same as others 🤔
I just manually top balanced my 13s5p lithium ion battery because like most i stored it for a few months at 80% instead of fully charging it once a week. In order for the BMS to maintain top balance, a few conditions must be met: 1. Battery bricks must still be related well matched in internal resistance so one brick is not artificially surged up to OVP. 2. The charger should only charge at 0.25c and taper at the top so that the differential voltage caused by different IR of each brick is minimal. 3. The charger must not exceed 4.21v/cell open voltage. 4. The pack must be initially too balanced such that at peak charger voltage no cells are pushed up to OVP level (normally 4.25v). Once these conditions are met it should be understood that the ONLY time balance maintenance can be done by the BMS is when at least one brick is between 4.20-4.25v, and normally this is done by leaving the charger on for at least an hour after the light turns green. If you unplug it as soon as the light turns green and use it right away, ZERO balancing maintenance is done. I also tried to manually balance a 5s1p pack for a cordless tool but the charger does not taper so it never allows it to balance. It surges up to OVP, closes the port, subsides below balance voltage but not down to release voltage (
I'm trying to learn about balancing, as I'm a novice in these things, but couldn't understand what you are saying, shame you coudn't have made it simpler for us novices, and use less acronyms. Thanks anyway for your imput
@@imho7250 Thanks, I keep watching your videos on balancing, and reading the description, also I keep reading your post on this video, hoping each time I will understand more, I’m using your information as a reference, so thanks for that. No doubt I will have more questions. I think it’s essential that if anyone uses an lithium iron battery they need to understand how to keep it balanced, from a safety point of view
And this is where Active balancer equalizers come in . I would go with 10A balancer . They now also have traditional BMS protection functions like overcurrent protection ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-5tHeT72xxtE.html
yes for sure! what I still don't get is why active balancing is not a basic feature of a BMS - is it just a cost issue? I wasn't even aware that active balancers have BMS protection features - some that Ive seen did not - is it overvoltage protection too or just overcurrent?
@@GaiusGarage The new balancers coming out have almost the same features as any other BMS . I don't think it's cost issue . In my opinion it's innovation or figuring out news ways of managing battery packs . Standard BMS usually burns of the difference with the help of resistors , but that's really old tech which believe it or only now is being phased out . Now we start to see BMS systems which will act like active balancer equalizer but only balance at the top . An active balancer equalizer on the other hand will transfer energy from cell to cell even with great voltage differences between the cells
@@Ray88G yeah I guess its why I found it so surprising - given falling the cost of electronics and R&D for PCB design its odd that most BMS's are just bleeding off charge through resistors - whats the overhead for developing a more sophisticated method. But I guess its just supply catching up to demand
switch it out for what is the question. there are essentially no BMSs that are appropriately sized and priced for a small battery pack like this and have active balancing built-in. they all use a passive balance method, which may as well do nothing. there are now active balancers on the market that you use together with a BMS but now you have to have both wired to your battery pack and fit inside your case. I think it's good to keep a BMS, mostly for overcharge protection, but for balancing, it's probably best to keep a balance connector accessible to check and balance charge the pack periodically
@@GaiusGarage to be honest I was hoping there would be a high end BMS that would do a better job balancing, but I haven't researched it. Maybe I would be better off just building my own.
So what I’m about to say is still a passive solution so takes a long time - my battery has now been balancing for about 7 days and we’re not quite done yet. It’s as ANT brand BMS with bluetooth and I just set the protect param/cell high recover and balance control/balance start voltage to 3.9 (default is 4.1). This passive discharges at 100mA so it’s not quick but it shoud get there ! When I started last week one cell was at 3.8 while the others were at 4.15 and now it’s closer at 3.85/3.94. It’s a pain in the butt, but I’d rather not take my battery apart all the time (same case as is the video) given the small screws that bit into plastic.
@@k20nutz there are more expensive BMSs out there like Batrium, which do have active balancing but it would not be cost-effective for a small battery pack like this and wouldnt even fit in the case. if you can design your own, hats off to you! Ive thought about this as well but would need to seriously up my EE game for a project like that
@@salunderscorepark I have an ANT BMS as well for a large battery pack and had a similar difference in cell voltages (4.1 vs. 3.8) and I did the same as you-- lowered the balance threshold and increased the high cell cut off to 4.25, and recover to 4.15. Then you can leave it plugged in to the charger and the BMS will keep cutting off charging when the high cell reaching its limit, then the balancing should bleed off some of the extra charge to the lower cells, then repeat -- for *days* ... and still not balanced. I finally ended up using a hobby Lipo balance charger to balance charge 4 cells groups at a time until I had the entire 20s pack balanced. BMS balancing is practically useless.. you either need to use an active balancer permanently wired to the battery or keep a balance connector available for intermittent balance charging. what a pain!
@@MikeCaskey they have them on Amazon but maybe be a bit cheaper on Aliexpress. the Daly brand active balancers are pretty good. you can use their app to monitor cell voltages
The BMS may or may not have the Cell Balancing option built-in. If you bought a BMS, *without* the Cell Balancing option then *obviously* the BMS will not balance the cells. Isn't this just common sense?
The BMS is still useful for protection features and absolutely necessary for charging. You need something in place to cut off charging current if one of the cells over-volted or over-heating to prevent a fire. these scenarios are even more likely if your pack is out of balance.
