Balance Start Voltage for LiFePO4 explained. Why you should not start too early... 🔋⚡
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- Опубліковано 28 вер 2024
- Still no word from JK about the new BMS... what better could we do than a quick tutorial about how and when to balance LiFePO4 batteries. I often see that users are setting the balance start voltage too low. They think it's better to start earlier to give the balancer more time to do its job. Especially when using the passive balancer of the BMS, we tend to panic and balance early.
However, this will achieve the exact opposite of the desired outcome of balancing: already low voltage cells are getting discharged even further.
I have my whiteboard out and explain quickly what is happening. Only until the JK developer team has the new firmware ready. Who knows, how long this will take though...
This video is by no means an comprehensive guide on how to balance. but it gives you a good starting point. There is a lot more too it, like current, deviation, voltage, system design and including all these factors would not made it an easy to understand tutorial. Also, all systems are different and there is no settings which fits all, while the balance start voltage will work for all balancers.
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Andy, most BMSes look at cell voltage deviation as well as balance threshold voltage. The lowest cell will never be pulled down because it's used for the deviation calculation.
My thoughts! Start @ 3.45V ans Charge to 3.55V with Float set to 3.4V. Works perfectly for me. Starting at the top knee an then falling back to the start again after balancing.
Yes that is correct. I didn't go down that rabbit hole as it makes this all more complicated and does not really change the start voltage.
@@OffGridGarageAustralia So if you leave a Passive Balancer connected and you are not charging will it run all the cells down ?
I bought the voltage relay and heltek 5a balancers for my 16s packs with JBD BMS. Best thing I ever did. Start balancer at 3.45v, been running this way since two weeks after your video on the voltage relay..several months at this point. Within each pack they is never more than a .009 Delta. Amazing.
Fantastic! Thanks a lot for sharing!
Good explanation. I still keep the balance atart voltage at 3.41 because to smoothen the highest cells down early and omit high peaking od the cells. With this I can keep the maximum cell voltage below
If it is an active balancer, you can start at 3.41V.
It's just a guideline what I showed in the video.
1. some BMS do have active balancer built in.
2. most active balancer works with cell difference/deviation and then you can have a low start voltage for balancing and the balance only starts when the cells have a deviation > x Volt . Then it's better to have a low start voltage for balancing, specially if you never balance before, it can take over a month for 1A to balance it.
Good, easy and obvious explanation 🙂 This means the balance-start-voltage depends on the aimed battery voltage alltogether! It doesn't make any sense to start balancing earlier!
Hi Andy, please check how the JK BMS does its active balancing.
You set a balance start voltage (highest cell needs to hit that voltage) and a maximum difference between highest and lowest cell.
You can set the balance start voltage to 3.45V on these, and the difference to 5mV.
What happens if we set the charger to 14V (4 times 3.5V) then?
Once the first cell hits 3.45V, the JKBMS discharges only the highest cell (!!) and charges only the lowest cell (!!). This means no unnecessary discharging of the cells „in the middle“. We are already in the area where we can balance LiFePO4 (as you said at 11:55). So it is a good idea to start balancing before we hit the final voltage per cell, as long as we have a strategy like the active balancer in the JKBMS has. Believe me, I have watched mine for hours already. I start balancing at 3.425V in my 4s battery.
Greetings from Germany :)
Yes, tested and shown here many times. There is also a video explaining all the settings: ua-cam.com/video/xTKiOvJ_ejg/v-deo.html
@@OffGridGarageAustralia
Thanks for the reply. I just wanted to emphasize it is in fact a good idea to start balancing a little bit earlier on the JK BMS, since it will only deplete the highest and only charge the lowest cell. As long as you only do that in the steep part of the charging curve before the max voltage you should be fine. You can start balancing then even if the full pack did not reach the final voltage yet.
@@OffGridGarageAustralia
@@OffGridGarageAustralia
@@OffGridGarageAustralia
what about discharging the highest cell and put the energy to the lowest cell?
That's active balancing not passive balancing as shown in Andy's example.
@@vonasi2 My English not is the best, so, maybe I misunderstood something.
@@vonasi2could you be so kind and explain how passive balancing works? And how that is “discharging” the most discharged cell, cause that makes no sense at all, that means the cells will never be balanced :-))) right? I mean, discharging ALL the cells in the same time, that means discharging, not balancing :-)))
@@NoiseSHomePassive balancing works by discharging the cell it is balancing. It removes excess charge on cells which are approaching the top of the curve earlier than other cells in the pack) This is a left-over convention from the use of say packs made from 18650 cells where capacity was maybe 1500mah and balancing works at 0.1c (1/10th of battery potential current flow) versus these bigger cells of 300,000mAh (200 times larger current capacity)
In Andy's example, the stated balance threshold of 3.40v, would mean that all of the cells are higher and will trigger balancing. So, yes all cells will begin "discharge" balancing.
If you're charging with say 17 Amps at that point and balance current is a measley 70mA, then I guess this will counteract this early beginning. However if balancing continues after 100% charge (let's say 3.45v) and is still set to 3.40v, it will discharge those cells back down under the desired charge voltage of 3.45v or whatever. If some sort of over voltage protect is set to 3.45v it may take until 3.40v or under to "recover" and remove that protection state and begin charging again.
The point is to set your balance trigger to meet two states:
1) Is somewhere in the steep end portion of the charge curve
2) Is not lower than the lowest "fully charged" voltage level (let's use float voltage).
I think Andy may have shot himself in the foot by over-simplifying his example (by not discussing cell differential and Bulk/Absorb/Float voltage levels and so on)
@@NoiseSHome Passive balancing has resistors that shunt a certain amount of current . So if the bms turn on the passive resistor for a specific cell , it shunts ( heats up) the small amount of current that most passive balance bms can do - like 80 to 150 ma. So the passive balancer only works well with smaller charge currents . Your question is how do the low cells come up ? Ideally the bms only turns on the passive balance resistors for he high cells, and then this lets the low cell continue to charge. So if the cell balancing is only at the ma value of it's resistor then that cell does not charge. The cells that do not have the balance resistor turned on continue to charge.
I'd add another point to Andy's logical explanation:
Before the chargecurrent doesn't decrease to a very low value close to the balancers capabilities, balancing just doesn't have any big sense.
On the other hand: When coming close to the end of the chargecurve - say 3,55V, it makes sense to lower the chargecurrent to an amount close to the balancers current. In the case of a 2A JK lets say 3-4A, later 2A. Otherwise giving it more, one cell might skyrocket until at 3,65V the BMS shuts down over and over again.
When the chargecurrent is not to much higher than the balancers current, the latter one can catch up and do its job in balancing the cells before the BMS reached OVP.
Perfect, thank you, I 100% agree!
I am in the need to get a few BMS( smart ones) for a off-grid build and was waiting for the new one that Andy just showed and tested but it’s look that i need to wait longer to fix the issues with it
On the other and i need a simpel liable smart BMS where you can set the charge current on different level where you talk about it,what BMS can i buy or what kind of BMS could you recommend it’s for 48v
@@marcvandaele1878 i've got an offgrid-system, too. Very happy with my 2A JK-BMS. I'd recommend going for JK. It's got all the bells and whistles necessary especially a capable active balancer fully configurable out of the box.
One thing to keep in mind, though, is that each BMS-battery-combo acts standalone. So the Solarcharger can't know if there are big differences between the batteries. It'll do the job.
Andy's new JK on the other hand might be a gamechanger in that particular regard.
I think it works the opposite way. The longer into the charging process you wait with the balancing, the higher the risk is for an OVP, because there is no mechanism to lower the highest cell. The balance process itself doesn't increase the risk of an OVP, instead it does the total opposite, it lowers this risk by constantly discharging the highest cell. This is true no matter if you start it early or late. So I'd say it is a good idea to start the balancing as early as possible, as soon as you hit the steep part of the voltage curve where the voltage is proportional to the SOC.
I agree with you that a small balance current of 2 A might not make much of a difference to a high charge current. So the actual effect of early balancing might be very small. But it is still better than nothing. My main point is that starting balancing early has no negative effect, and can only have positive effects.
If you have problems with the BMS balancing your cells, I think that setting the absorption voltage a little lower than normal has a much bigger effect than changing the Balancing Start Voltage in the BMS. Then you get a much smaller charge current at the end of the charge cycle, like you mentioned, and this will make the job of the BMS much easier.
There's some confusion in this explanation. If your target is 14.2v you don't want to start balancing at that point. You do want to start before that. The first explanation was kind of correct because @ 13.8v (3.45v/cell) is around the point the cells start running away from each other (they are starting to climb out of the flat). I've watched this closely with my 12v set ups and it's pretty consistent that when the first cell reaches 3.43v the deviation starts to increase quite quickly. 3.43 or 3.45 there's very little difference. But if the target voltage is 3.55, you certainly want to start balancing @ 3.43/3.45 because this is the voltage range where you can clearly identify that the one cell (which is actually the weakest almost always- not the strongest) is becoming close to fully charged, You want to start discharging that cell as the others increase. There's no benefit in waiting until one cell is @3.55 volts to start discharging it. If you have cell #1 @3.45v and the other 3 cells are at 3.33 for example, you can be sure that cell #1 is running away and can start balancing that cell. To make that assumption below 3.45v has no benefits which is where Andy is correct.
If you got an active balancer that is strong enough to carry the capacity discrepancy of the weakest vs the strongest cell as a diversion energy transfer during both charging and discharging it will effectively be able to divert the energy that is either too much or missing at the weakest cell and get it from or push it to the strongest cell(s). This should in theory wear the stronger cell(s) faster (as their currents are higher) and spare the weaker cell.. over time bringing all cells to a more common level and remove the discrepancy.
@@joansparky4439 If you have an active balancer like the Neey that is strong. Set the start voltage to 3.45v and forget about it. You won't even be watching this video probably. But If you are charging with 100amps and set the balancer to only start at the target voltage you're going to go into a start stop scenario immediately.
@ AussieAustrian
Yeah, if the cell difference (weak/strong) requires the energy diversion to exceed what the active balancer is capable of diverting the weak cell will hit the boundaries quickly, leading to start/stop cycles (just like in a passive balancer or without a balancer at all).
But I think if the strong active balancer technology becomes economical enough we won't be talking so much about matched cells anymore, which is a good thing IMHO as it allows for cheaper packs to be built.
Right now the JK's use just one capacitor to run around and move energy between the cells. If they could build those with two or 4 of those energy movers for the bigger BMS this would be good I think.
why one? i for example have 4 'weak' cells from 8.
It will just target the highest voltage cell that is running away. In your case you have 4 “weakl cells. So in your case it will shave charge off the highest voltage cell, charge the capacitor and send it to the lowest voltage cell. This will make one of your other 3 higher in voltage. It will then pick the highest voltage of those three and do it again.
Hello Andy i live in Montréal canada thank you so much for you good expérience i change all my daly bms to jk 200am on my système now i have using this for 280 day it very good bms. Thank you
Wow, that's a big upgrade. I'm not sure if I would have done it or just add some active balancers to the Dalys.
However, JK is definitely the better BMS...
00:09:30 but the balancer will Kick in only if your battery is above a certain cell deviation, right?
Yes, that is a second trigger. For this video, I wanted to keep it simple. There is far more to it. I may make a 2nd part...
Off topic: I would like to ask if the video about Victron integration into Home Assistant will be coming soon? Thank you
It will come, yes.... Soon, I don't know. I guess, I could... It's very specific though.
THANK YOU! I needed this.😁
Thank you.
I don't know how your balancer works, but mine doesn't start balancing until both the "Start Voltage" & "Delta Voltage" parameters are met. First, a cell's voltage must be above the "Start Voltage" and then the highest cell voltage must be more than the lowest cell voltage by the "Delta Voltage". Then and only then will the balancer balance any cell who's voltage exceeds both these settings and only the cells that do exceed these parameters will be balanced. Your way will only balance when your cells reach their maximum voltage. Due to the flat voltage curve it doesn't make sense to start balancing until the cells reach the knee and the voltage starts to rise quickly.
An active capacitive balancer will be acting to bring all cells to the same voltage. The amount of charge moved between the cells is tiny for the flat portion of the LiFePO4 curve, charge transfer only increases when voltage imballance increases. There is a small loss associated with an active balancer but if you battery is big this is of no concern. Conclusion you can start an active capacitive balancer early. Or even leave it running all the time!
The active capacitive balancer will have undervoltage lockout to enter a low power sleep mode. However you do not want to trigger/rely upon this as it is likely set below 2.5V
Is there anything wrong with the above?
Andy, if BMS-only (no active balancer), I am seeing high .050 Delta voltage (and higher) around 3.3v. I was seeing even higher Delta over .15v last week. The battery bank is about 2 years old (48, 100ah CALB cells in a 6P8S configuration with a DALY 500amp BMS). Having started balancing at 3.3v at .2 Delta, the pack reaches about 3.4v with .25v Delta during Equalization. I have ordered a 1a smart active balancer to add to the system. I may boost balancing start voltage now that the cells are reaching lower Delta.
Is the chemical "goop" that you speak of inside of the cell called the electrolyte?
What happens when you have four 100ah batteries with each battery having its own BMS? I am enjoying your channel. Thanks much for your contribution with all the knowledge shared with your subs.
4s configuration to be clear with aEG4 3000W EHV. All in one inverter solar charge controller.
Each 12V set up will drift away by time. Probably not so quickly. Check them every now and then.
One design change that would make sense for passive balancers...... Note, I said "would", is to have ALL the resistors in a parallel series configuration to maximise the current without burning up or causing deamination to the PCB, and then have the Fets switch in the cells as needed to burn off the most energy possible, This would mean that each cell can be balanced individually, I do suppose it would make the BMS's more expensive, and would require a software rewrite..... But, hey ho...... I suppose that is just me that thinks in this way...... Thanks Andy.
Yeah, making the passive balancer stronger would solve a lot of issues. I don't mind burning off the energy at this point. The battery is full anyway at this stage and energy is free of course...
It may cause other issues though if the heat of these passive balancer becomes a problem. Tight spaces and enclosures for example.
So active balancing makes kind of sense.
Hm i think you are wrong. Neey starts at this voltage but does Not discharge any of the low cells.
He always discharge the high and Charge the low. Never the less How big the voltage is over the Start voltage. And this is a good thing
Andy was mostly talking about the passive balancers in most bms , not active balancers like he Neey.
The Neey is an active balancer that works across all cells. It opens the charging circuitry (of the balancer, not the battery pack!) To all cells to charge the capacitor(s). Then it disconnects the charge circuitry and opens the discharge circuitry to all cells to charge lower level cells. So, it effectively does what you say. The Neey also considers voltage differential between cells I believe, so it won't activate until there is a significant difference between cells.
There are "active" balancers which move charge between neighbouring cells until it reaches the lowest cell. These work differently in that they will try to move charge from a higher cell to a lower cell. If your trigger level is too low, then all cells could be considered to be high cells (because they are all above that trigger). These are usually inductive balancing in nature vs capacitive.
Then there is passive balancing. Which just discharges cells which are above the trigger level. Usually cells have individual detection and discharge circuitry, so they are never in an All-Discharging state because of a single cell exceeding the trigger. But in Andy's example of 3.40v all of the cells do exceed that trigger so they will all have discharge circuit enabled.
The examples may have been over-simplified for the discussion. It gets pretty complex, and I think Andy may have been trying to avoid that complexity.
@@LarryKapp1 okay i haven't noticed this
Yes, the NEEY or other active balancer will not discharge the low voltage cells, correct. This was more to demonstrate when to start balancing. And this does not change if passive or active balancing.
Hi Andy, why cant i set my calibrating voltage to more than 13.52v? I am using the jk bms on a x4 cell, 60Ah battery.
On my two amp JK balance BMS I raised the balance trigger voltage too 0.020 because my cells seem to be quite a bit different size in amp hour. Even though they're perfectly balanced at the top if I start charging quickly the lower amp hour cell starts to raise higher in voltage than the other cells. This would cause the balancer to create imbalances if I did a tighter threshold.
So, balancing is primarily taking place during the absorption phase of the charge cycle. Starting just before the CC goes into absorption and then continuing thru absorption, correct?
That begs another question: if our cells drift a bit more than we are comfortable with and we have a relatively "weak" passive balancer (Overkill) should we not increase our absorption time so the balancer has more time to try and bring the voltages closer together?
Yes, correct. Once we hit the CV phase, we start balancing as this is out of the flat part and cells start showing their true voltage.
By increasing the absorption time, you definitely give the balancer more time. That's exactly the test I'm doing right now with the battery shelf...
If you have a few cells getting too high, you can try increasing the time and see how it goes. I had no success with that method as the balance current is just too small in these balancers.
Hello Andy, thank you for the clear explanation, now i got it for sure. Just 1 question, when you say " your desire voltage" does it mean the bulk voltage or floating voltage, because in our inverter, when reach the bulk voltage the inverter immediately switch to floating voltage which is far lower than 55.2v.
Bulk charging does not have a voltage, bulk has a max charge current.
In addition, LiFePo4 do not use bulk, absorption and float, so asking for float voltage is also irrelevant..
LiFePo4 uses CC/CV charge profile. Constant Current = Bulk, Constant Voltage = absorption.
After CV is done, the charger is supposed to turn off, Victron has solved this my setting the float charge voltage bellow the rest voltage of the LiFePo4 battery..
So the answer to what "your desired voltage", it is the voltage defined in CV part of the charge, or Absorption Voltage for Lead Acid...
Desired voltage = Bulk/Absorption voltage.
If your inverter does not have any absorption time, maybe set the float voltage close to the Bulk voltage to allow the balancer to work. Otherwise it will never balance.
Heya, aperantly it is difficult to learn people/companies differant chemistrichs with a differant charge curf
Practically genius. Thank you!
true that is the correct way to balance,
but as far as i know (correct me if I am outdated);
1. the NEEY smart balancer starts balancing when the average is above the set value, so the fewer rogue cells you have, the lower the average, and sometimes balancing will never start.
2. capacitor balancers rely on the value of the first cell to start or stop balancing, so if the first cell is lower than the other cells, it could lead to the balancer never balancing.
Thanks for your questions:
1. The NEEY will turn on balancing if ONE of the cells hits the set threshold and turn off once ALL of the cells are under the stop voltage. This is with the latest gen4 hardware and software on the balancer. It is not using the average voltage for that as in previous version of the NEEY. Watch this video here where I tested this in all details: ua-cam.com/video/jpG3siEzll8/v-deo.html
2. Capacitive balancers balance all the time, so there is no start or stop voltage. However, they have a low voltage disconnect when cell1 goes under 2.7V to stop further discharging the battery.
More about this in the next video.
@@OffGridGarageAustralia
1. ah yes the newest 4th Gen NEEY doesn't rely on the average anymore, I have couple of dozen 3rd gen, that is why I set my balancing a bit lower, I personally like the the JK Active balancers more, you set the config once, and store it, when it is connected again, it is ready, no need to change anything or activate it, the NEEY on the other hand, turns off when disconnected and you need to manually enable it again. that is why i use NEEY for my batteries since I can intervene, and i use JK Active balancers for remote batteries and client batteries.
2. as for the capacitive balancers I ordered a big quantity last year and customized the starting voltage to be higher, but was a bit disappointed after receiving them and noticing that the first cell's voltage is used to start and stop
Thank you Andy, now I have it kapiert.
I have a JK BMS B2A8S20P and I have two questions as I practice these things.
1) I can only find bluetooth control on the device - and it keeps me very firmly at home, even though the battery is in a fire safe place. All my other devices are in my real remote control via the wifi hotspot, such as the EcoFlow power station and various smart sockets. How can I also connect this bms device to my wifi router so that I can control it when I have to leave the house?
2) I have a few solar panels in the yard and a small 320W MPPT controller. If I want to charge this LiFePO4 battery with the current produced by the solar panels, is it necessary to find the exact settings for the charge controller software, or is it enough that the BMS device knows how to control the cells and the MPPT controller does not let the voltage get too high?
Thank you!
Thanks for your questions.
1) You can connect you JK-BMS to Home assistant with this project and control it form anywhere. I will show and test this on my channel in January. github.com/Uksa007/esphome-jk-bms-can#readme
2) You need to set the charging parameters in the MPPT and cannot rely on the BMS for that reason. The BMS is a safety device which triggers if the MPPT is faulty. MPPT charges, BMS protects.
It's a bit like making a short and trip the breaker every time you want to turn off your lights.
@@OffGridGarageAustralia I looked at the documentation you linked, but I don't really understand everything. That's why I'm waiting for January like a child lollipops :) Thanks for your thoughtfulness, Andy!
Andy, ... I have four 100 aH sealed 12V batteries (LiFePO4) ... connected in parallel ... can I top balance these or reach top balance? None of the batteries has/have a bluetooth to the BMS and I had them way before I started watching your show. I haven't made my own yet. Great video.
Very difficult as you don't know what the single cell voltages are. You can only charge them to a voltage until the BMS turns off. You know then, this is you maximum charge voltage for this battery. If they still balance at this point, you don't know.
That makes sense,,, thank you,.pat@@OffGridGarageAustralia
I guess this would come down to the implementation.
In case of a passive balancer it might just connect all of the batteries for balancing.
But if the start voltage only turns on the active balancer so it can balance only the cells with enough deviation, then starting just a little earlier should not be a problem as long as you avoid the flat part of the voltage curve.
I left the deviation setting out here as it complicates things, but you're right, the balancer may not run with the examples I brought up.
I would still not set the start balance earlier.
@@OffGridGarageAustralia I'm doing all of this reasoning in theory, but don't you run the risk of the balancer comstantly turning off and on as the charger backs off or even shuts down completely?
I suspect that at these margins the charger may effect cell voltage measurements just a little to much,, especially as balancing also loses some energy as heat.
Or is this all taken care of by the other BMS settings and margins in the balancer itself?
thaks andy, again, very helpfull.
Thank you.
Hi Andy, should I switch of the BMS balancer of the Pace BMS (by setting a high start voltage) when I have a 4A Neey balancer in parallel?
The BMS balancer can stay on, it does not matter, it is so small, no impact.
Andy love your video's and have learned al lot.I have a 12v 100amp lifepo4 battery, which has a build in bms . Buit it will only charge to 13.6v. Could it be that my charger cuts of to soon? And voltage drops?( charches with 14.4v) or do i have bad cells.
May it help if i charge the battery with a power supply on like 14.2v and low amps? I use three of these batteries at my campsite for off grid
Mart
Hey Mart, measure the charger voltage without battery. to this voltage it will charge your battery. If the battery stops charging before that voltage, most likely on cell is out of balance and the BMS protects it from overcharging.
If you don't have access to the BMS via Bluetooth, you can use a power supply and charge close to the voltage when it cuts off. Leave it there overnight in hope the balancer will do its job. Increase the voltage very slowly in the morning and see if you can already charge a bit higher. Some BMS don't balance if there is no charge current.
I really like that you also see bitcoin miner as part of your critical loads. Can you please tell us a bit more about your bitcoin setup?
There will be a video coming soon'ish...
New video lets goooooooooooooooo
Ok this makes sense to me if I was using individual cells that I could check the voltage of each cell. But I am using sealed Drop-in Lifepo4 batteries (2 x 12.8v 100 ah )and have no way to check the voltage of each cell . How do I balance the cells in each of these batteries??
Thank you
Thank you Andy, always a pleasure to watch your videos. I am trying to find the optimum settings for my new svolt battery / inverter with built in pace bms. One of the cells constantly reach 3.65v while others remain fairly equal within a few mv. . Is it bad for a cell to reach 3.65v often during bulk charge, or can I utilize the function of "forcing" the bms to stay into balance mode as long as no current is drawn. (It is difficult in a production system to not draw current, which gets worse in my country with electricity so called load shedding - e. g. today we will be without electricity for another 8 hours BUT with lots of sun) My supplier suggests 3.5v bulk charge and 3.4v float. Should balance threshold be ok at 3.45v?
-Chris
Thanks for your question Chris.
If you have access to the batteries, the fastest way is to temporary connect an active balancer to the battery and let it do a perfect top balance.
3.5V as charging Voltage is fine if you let the cells absorb for maybe 20-30min afterwards. That will fully charge them. Under such normal charging, none of the cells should reach 3.65V and trigger the BMS to turn off.
Float, I would set a bit lower to 3.35V. 3.4V is a bit to high.
You can start balancing at 3.45V, no problem.
Target voltage/cells in series makes sense for higher target voltages. Does the same formula apply for lower target voltages? Say your target voltage was 54 for a 16s pack, is 3.38V what you would recommend for balance start threshold?
Is balancing really only that you discharge the cells over a specified voltage? I though you took current from high cells and pushed that as extra into low cells.
You described active balancing and not the passive balancing as shown in Andy's example.
Both, active and passive balancing should start at this voltage. This was the main point of the video.
@ OffGridGarageAustralia
Passive balancing gives the weakest cell the leading role, thus late to balancing is preferable as that is the only point in the charge curve where it's easy to decide.
Active balancing allows for the weakest cell(s) to be supported by the strongest cell(s) and thus allows for higher capacity in less well matched battery banks. Early balancing is preferable for those applications as it spares the weaker cells and wears the stronger cells more, bringing the cells in the bank to a closer match. But this requires the balancer to be able to divert as much energy as the difference is between the weakest and the strongest cells during dis/charge to work - otherwise we're back to passive balancing.
i don't see any logic in this video as this is not how modern balancers work . just because you set the balance voltage to 3.4v does not mean the bms will constantly discharge this cell until it reaches 3.4V . by your logic if i set balance voltage to 3V and my pack is currently at 3.6v per cell the balancer will start discharging the pack - this is not the case . balancers should work only when there is a voltage deviation between cells
3.42V is the ideal balance start voltage. You have to start early to not overshoot 3.65V
Ahm, no... It's not that easy.
Just to be curious - what bitcoin-miner are you running?
Super interesting, that it can be run out of solar-power!! :D
It's an old T15 I'm testing... I'll make a video and tell you the story.
Andy, as per your video from a year ago on Daly balancing, you for the Daly active balancer you found the lowest cell had to be above the set starting voltage of 3.3V for balancing to start, that is, all cells must be over 3.3V default to start active balancing. And for the Daly passive balancer in the BMS it is set to start at 3.2V Daly default, but some cells might be higher e.g. 3.4V, and I'm not sure if all cells or highest cells need to be over 3.2V. So what pack charge (absorption) voltage would you target for the Daly, say, 24V system? I am thinking keeping my setting at 3.45V*8= 27.6, or moving the setting up to 28.4, the higher number due to your recent testing videos of getting your passive balancing to work better for battery shelf. If today's video is correct, raising the setting on the Daly from 3.3V to 3.45V may mean that balancing never starts at all😮 because I've notice once absorption voltage is reached the charge current basically tapers rapidly to zero (within one hour) and the voltage is held steady at the target.
That could depend on what Daly BMS/balancer you are using. I have seen them acting differently. But you can test this and the app will show you if the balancer is turned on, so you can check if on cell or all cells need to be above the threshold.
27.6V seems to be a good absorption voltage. As you said, the current will go down quickly and the balancer should start if ONE cell goes over the 3.4V you have set. If the balancer waits for all cells, it is total garbage anyway. At 27.6V you goal is 3.45V for every cell, The balancer catches the ones which are above that, nothing else. and if you cells are all at 3.45V, the balancer will not start at all, correct.
Thank you for taking the time to share your experience in practice. You mention top balancing due to the cell charge curve, and if I follow Stuart's circuit logic correctly, an active capacitive balancer will equalise by averaging the eg 4 cells by switching them from series to momentary parallel connection. You mentioned in your video that your video today applies to both active and passive balancing. I don't know how passive balancing works but I might guess it is resistive burning away of cell capacity by choosing the highest one or two cell at a time. This will result in loss of charge over time and the balancer will stay on until the set balancer voltage is reached, this all cells are slowly brought down even if it is one at a time. Perhaps in practice only the highest cells will come down before the battery pack is discharged via usage anyway. Whereas the active balancer will top balance by averaging, bring cells above the resultant average down and the cells below up to average. Actually, it is more precisely an RC capacitive resistance (switching) circuit so resistive losses too will bring all down all cells somewhat. So active balancing may be able to occur slightly below the highest target charge voltage if it's still high enough in the charge S curve. Also, the RC capacitive balancing logic will have its own curve which would work faster at higher cell deviations. Without knowing all the circuit vakues I would like you have suggested simply have to test and see. Thanks again
Good points today.
Thank you, very basic stuff. We will dig deeper in part two...
TY, i in winter have clouds about 4+ months, i (pavyziu(jealous), sun), ( we are on different sides of the earth)...☀
Yes, we are...
I dont get it. With passive balancing i do agree...
But not with active balancing.
With active balancing you should start right at the knee, so the cell charged most wil be drained over to the cell with least energy.
Then all cells will be charged faster to desired voltage.
If you wait to long the cell with the most energy will be banging on the max voltage to long.
Or am i lost here?
If you charge to 3.55V per cell and start discharging/balancing a cell at 3.47V makes no sense. Your target/goal is 3.55V per cell, so let them charge until this voltage before start discharging.
A too high balance start voltage would increase the risk that a high V cell reaches the BMS's cell overvoltage before the balancer had enough time to bring that cell down or other cells up. So the BMS could turn off charging, but your battery is not at 100% SOC yet.
There is a difference between discharging and moving power between the cells.
I did try your setup, and ending up with one cell with less power in one cell.
I have a jk BMS.
Andy, make us a graphical flow chart of when to use what type of balancing start and stop voltages. Seems to me this is not cut and dry with one method.
The start voltage should be very straight forward. Divide your charge voltage by the amount of cells in series.
Thank You. That makes since. I changed mine again. I am starting winter and I know I will have to use the grid. I am setting my inverters to save enough for 24 hours of power grid being down in reserve. 20kw of 56kw. I think 40% isn't enough since I do not go lower than 48 volts and I do not go over 56 volts. I will try 45% which is 52.1 volts rested. does that sound right? Winter where I am sucks for Solar. 11.2kw of panels is about 1/2 of what I need and I could also double my batteries to get me close to off grid.
Good idea to keep the battery at a certain level to cater for these days when you need it.
I don't think 45% will have a certain voltage though. That is impossible to pinpoint with LiFePO4 batteries. You have to rely on the BMS or shunt for this purpose.
@@OffGridGarageAustralia I been watching and its not perfect but I have a chart and its real close. The BMS isn't connected to inverters so I have to tell them when the batteries get to a certain voltage switch to grid. I have taking them down to 46 volts so the BMS is more accurate. When doing so I have about 20kw from 52.1 to 48 volts. I double check with BMS which I have 4 JK's
anyone knows is it enough to use 1A balancer with 48v18a LFP? using for ebike 35-45amps, daily charged.
Oops, I'm doing it all wrong. I have my balance voltage set to 3.2V and diff set to 20mV. So far the cell variation stays around 1 or 2mV.
At 3.2V, all cells look balanced. You cannot tell if they have the same SOC.
I dont fully understand this video. If you have 4 cells getting charged, say at 3.38v, 3.40v, 3.39v & 3.37v, (aiming for 3.45v) and the balancing starts at 3.4v, then the one reaching 3.4v first will get held at that voltage. The next one hitting 3.4v will also get held at that voltage. Same with the third one, then the majority of the current is being taken by the lowest voltage cell. When it hits 3.4v, the cells 'balancing' current will effectively be overwhelmed by the larger charging current , but the highest voltage cell at each instance going forward, will always be dragged back a little, thus helping to keep them in unison during the final bit of charging between 3.4v and 3.45v. ***Furthermore, my BMS has a function to balance in storage mode. Now, when the loads are light and sun plentiful, the cells go into storage mode whilst 'floating'....so i'm wondering if the balancing at these low currents could be accomplished during this phase??? ***
IMHO, a smart balancer will work "all the time " when you want a low deviation such as 1mV. If you are happy with a 10mV deviation then the balancer will just finish the job and stop. It ill not start balancing just because balancing is enabled at, say, 3.2V. It will wait for a deviation higher than 10mV. I guess I am telling you to stop balancing to 1mV and try 10mV or even 20mV instead.
Looking forward to your reaction and to learn more.
I guess there is a difference between (dumb) active balancers and smart active balancers. The dumb ones cannot be configured and they start working when the first cell is above a certain voltage and are then working continuously until the first cell voltage falls below. The smart ones can be configured to be enabled when the voltage of the first cell is high enough. In addition, they start balancing only when there is a deviation above, say 10mV (configured) , and this does not happen in the flat area of the curve.
I guess a smart active balancer is the way to go.
i am also developing BMS and as far as i can tell, if there is no active balancing i go with history-based balancing at LFP.
Also balancing here is not from a certain cell voltage threshold. We only balance the highest. 216s is the biggest LFP setup which runs fine.
Balancer would not balance at all if the threshold of 5 or 10mV cell difference is not exceedec, it doesnt matter when you start, you just shouldnt balance below the run off curve in the flat area. 3.42V is ideal.
I'm wondering if there is any real capacity difference between charging to 3.45V and 3.55 or 3.65 if they're all followed by absorption and float (at a lower voltage).
Andy did a video on what the capacity differences are at the different voltages. It isn't a lot of difference at the voltages you talk about.
That's the video: ua-cam.com/video/pijPu7t-akM/v-deo.html
Thanks, Larry.
So how do you balance the battery only joking Andy I watch your channel mate lol
OK, here is the explanation again. Just for you:
just kidding...😂
With seplos bms the neey should start at the overvoltage warning value
Depends on how you set the warning levels...
@@OffGridGarageAustralia with victron in offgrid like yours you have totaly other settings. But most users have an on grid System and then there is the best solution to let All settings like Standard just put the Pack overvoltage protection a little bit lower.
56.6V (3.55V) i think is best
Overvoltage warning at 56V (3.5)
And here there should be the Start voltage. So the neey starts balancing at 3.5V when the battery is Charged with only 10A to reach the Charge voltage. Just a user experience
Hi Andy, I don't think you are right. Once the balancing target is reached, the algorithm will decide which cell needs a correction. On passive balancing systems, a resistor will drain the cells with higher voltage. On active balancing systems, the energy of the highest cells will charge capacitors that will charge the lowest cells. Peppe from Napoli.
This is about balance start voltage not how balancers work, Peppe.
Thanks!
Thanks a lot for your ongoing support, Sree! 🙏
Pylontech battery US5000 has fifteen packs per unit.
Yes, and they still charge you the same price as other do for a 16s battery😂
Thanks a bunch. This is why I am subscribed. You hit the point and very educational. I have it balancer at 3.45. why would someone want to set the balancer at 3.55? Capacity? Use Application?
In the last few videos on passive balancing, Andy discussed that this higher start point gives the balancer a better voltage differential between cells and therefore will result in balance current being higher. At this point in the curve you see bigger differences in discrete cell levels, and this is where balancing is 1) required and 2) most effective (ie higher balancing current). But he has shown that the passive balancing schemes continue to struggle to bring a pack into balance when the charging current is larger by orders of magnitude than the balancing current.
@@CollinBaillie If solar charge controllers could limit their charging current to a smaller amount at a setpoint voltage that would be great for balancing. But it doesn't seem like any can do that.
Yes, there is much more to it: the deviation setting of the balancer as well as the actual charge current at time of balancing. Charging with 100A and the JK balancer can do 2A balancing, does make much sense and difference.
Unfortunately, most systems cannot be fine tuned that the actual MPPT is slowing down when hitting CV.
more ac coupling with more biger ongrid inverters pls
It's the off-grid garage, so no AC coupling or ongrid inverters 😊
Id love to see an entire 16s1p electromechanically disconnected from loads during charging and reconfigure to a 1s16p to have a completely charged battery then physically switch back for loads.
Means no using it while its charging. It would be like... Electrical OCD lol.
Rabbit hole alert. What if you have a cell that's got considerably more self-discharge than the others. Then maybe you need an extra cell deviation set point. One that says hey, if the cells get extra far apart even though it's below the normal balance start point go ahead and start actively balancing, taking power from the others and putting into this problematic cell. That way as you're state of charge moves around on the cloudy month somewhere between 10 & 90% that low cell will actually trigger some balancing so it doesn't get ridiculously far behind. Because otherwise they'll be no balancing done because you never reached full the whole month. And that little two amp active balance won't be able to keep up when your system is ramming 200 amps into your battery up to the full mark quickly on the first sunny day of the summer.
Math 🧮 😊
Simple.
🐸🐸🐸
🥈
+
Andy
You Told Us Earlier That Start Balance at 3.4 Volts
WTF
Now You Sy 3.45 Volts
I Think Someone should make up THERE Mind!!!!
Don't you think?
My settings are the same as yours but 1/2 because of 24 volts
It depends on your system design and what your charger settings are.
many "ifs and buts"...
And depends...
.... Erster... 😀🍻
Liebe Grüße aus Unterfranken!
Ganz toll, du bist der Held!🎉
He's actually fourth 😂 But Hello👋
Sorry but it would not be a wise decision for a poor man to buy a wealthy man a beer.
I agree. I'm not wealthy.
Are you a freeloader? 😂
@@OffGridGarageAustralia 🤣😂🤣. If you're not wealthy I'm fred flinstone. Wealth and poor are in the eyes of the beholder. To be wealthy is when one is not struggling to get basic needs. To be poor is when one is struggling to get basic needs. I'm not tike you assume, I'm not a freeloader type person , I'm a disabled type person. Nice try though lol. A freeloader is a scammer trying to get people to buy what is not worth having. The definition might fit you better. 🤣😂🤣👍🤟👌
The problem is that in my case (the boat and solar panels) I am charging my banks with relatively low current - like, 0.1C. And at 0.1C the charge curve is drastically different from 1C and even 0.5C. That is, the battery is fully charged at much lower voltage, something like 3.4 volts per cell (i.e. we get 100% SOC much earlier). In this case I will bever get to the balancing voltage of 3.5 volts simple because at these currents it will mean overcharging the battery. Maybe in this case, setting it to something like 3.5 volts will make sense?
at about 7 mins, what kind of $20 balancer does that! why would it balance all 4 cells as you rightly say when only one has gone above 3.45? you just need to dump energy from the 3.48 into the 3.42 (like the jk bms would)
did i ever mention that I think the jk is the only bms worth buying....
That was just an example to explain the basic balancing function.
Yes, JK is still the top!
@@OffGridGarageAustralia it's addictive, now I have nearly 8kw so need a pure sine inverter so I can run the induction cooker....
THANKS Andy, as always, a big 👍👍. Right on the money.
Years ago I had a slow balancer on my 400A LFP caravan battery, and couldn’t set a start voltage so it was always “balancing”, and can absolutely confirm your findings.
Since I fitted the JK in the van, with balancing set to start at 3.45v, it’s all been PERFECT. I typically see just a few millivolts difference between cells.
I think jk BMS default of 3V is much smarter, and a cell deviation of .005. Cause what will happen is you will trigger over voltage protect just because one cell hit it when others are lower, thus battery never gets fully charged quickly then
Other issue is let's say you discharge to 10%, could take days or weeks to get battery back to 100% if many cloudy days, it should be balancing overnight so we don't start next day again with to much deviation
Are you sure the ‘balance start voltage’ is the voltage over which all cells will be discharged and not the voltage over which ONLY the highest cells will be discharged?
This is correct for active balancers!
@@ClausMallorcaso you say that “passive balancing” is just a stupid all cells linear fix current discharging?!? This makes no sense at all. On the other hand, on software we see that at a time, the BMS is balancing 2 cells: the strongest and the weakest.
All the time. And this is not done by discharging both, that would be nonsense and we clearly see that the weakest is charging when the strongest is discharging…
@@NoiseSHome Most bms have a differential setting that has to be met to start balancing. So for example if 20mv differential is set in bms, no balancing will happen at all until the cell deviation is above 20mv. If one cell is 20 mv above all the other cells - the high cell will balance ( bypass resistor turns on ) but the other cells will keep charging to whatever the charge setpoint is . If the low cells raise voltage, and the high cell drops , the deviation turns off balancing below 20mv differential.
Some BMS boards also require all cells to be above the trigger level. It comes down to the manufacturer's implementation. Simple balance board or BMS boards will simply have an analogue circuit (ie not smart ["computer" controlled], and component variance means that the trigger levels will differ slightly, and generally fades in or out instead of a sharp turn on or turn off) for each cell which has a set voltage level where a limit is over ridden (or exceeded) and the discharge path is enabled. This is the most basic of balance mechanisms.
My example was charging to 13.8V but starting balancing at 3.4V. This would then discharge all cells with a passive balancer.
Hi I have a 280AH battery pack 16s which JKBMS do you recommend me must take into account that I also have the NEEEEEEEY 4th and a 5kw voltronic inverter Thank you but it is imperative that it must communicate with inverter ! Thank you your videos as well as being constructive, they are also funny ;o)
You have a JK and a NEEY??? Are your cells that much out of balance that one AB cannot handle it?
You can make any JK BMS talk to your inverter...
At 6:25 - This is factually incorrect. No BMS that I have ever worked with will ever discharge "all" the cells at once. BMS units will only ever discharge from the highest cells. Most BMS units look at deviation from the average and only discharge from cells that are above the average cell voltage. So if the battery is at 13.8v the avg cell voltage = 3.45. So even if the balance start voltage is at 3.4v, the BMS will not discharge any cells above 3.45v because 3.45 is the avg cell voltage.
Not saying there aren't some crappy low end BMS units out there that might behave this way... But I haven't seen one first hand.
I have built numerous packs and I always use 3.4v as my balance start voltage and have never had an issue with that because the BMS is smart enough not to pull down the lower voltage cells.
I have packs that charge to 58v (3.625v per cell) and I start balancing at 3.4v without issue.
Then at 10:30 you also state that this "rule" applies regardless of whether you're using active or passive, which is obviously not true. An active balancer always pulls from the highest cells and pushes that energy into the lowest cells. It's literally impossible for an active balance to "pull from all cells" at the same time because then where does that energy go? Active balancers just transfer energy from cell to cell, so if they pull from all cells where does that energy get transferred "to"?
I think the Daly does it and balances all cells if they are over the set threshold. Shown here on the channel...
Because of the variance between batteries, I balance all the time, both during discharge and charge. After 7 years of fulltime use and a delta of 6 milliamps and 95 percent of beginning capacity I'll take my method over yours when you seem to have a constant problem with delta drift. My BMS is original to the system with zero problems.
That totally depends on your charge voltage and target. If you don't charge high enough, you will never see a delta with your cells. Also chemistry is important as I explained.
Since my (short by methodically analyzed) experience is more like yours, please share with us the exact precise settings in your inverter AND in your BMS - talking here about voltage settings. Also, geographical are would be great. More important would be to know the setup in terms of inverter, batteries and panels to understand at what SOC your battery stay during winter/summer time. For example, if your battery will charge most of the time at 80%, that would keep all the cells at the same voltage (but not necessarily at the same real energy reserve stored in every cell). Also, what batteries are, in therms of brand and source. Are they certified?
As a side note, my chinese uncertified cells have the tendency to self-balance, without BMS and equalization, which is weird.
But true.
This all only applies to passive balancing BMS, not the active type like the JK's, which support the weakest cell and instead wears the strongest cell at all times.
Active balancers like this in theory even allow for the FULL capacity of each cell to be used (even if they differ), surpassing top-balancing, as the BMS is supporting weaker cells with stronger cells during charging and discharging.. this naturally needs a BMS whose balancing current is at least as large as what the maximum dis/charge-current one has got in the pack times the difference between the worst cells. Say the difference is 30% between best and worst cell and the max current is to be 10A, then the BMS active balancer needs to be able to balance 3A.. which means the strongest cell is delivering 13A while the weakest delivers 7A.
The overall concept is then heading into the direction of not needing to top-balance a pack at all once the BMS balancer is strong enough to deal with any mismatched cells - it's simply balancing all the time anytime. Economically the whole thing lives from the price difference of a strong active balancing BMS vs what a well matched battery pack costs compared to a not so well matched pack.
In IT they use the term JBOD for Just A Bunch Of Disks to create a larger volume.. maybe once strong active balancing BMS become widespread and economical enough we'll be talking about JBOB in the future and don't care about matched cells for a battery pack anymore.. because the balancer is able to cope with very unmatched packs due to being able to let the strong cells work for the weak ones.
Simply having a stronger balancer might cover some serious defects... Another useful future BMS function could be intelligent sensors that notice weird behaviours and flag this to the user... Like changes in cell drifting behaviour...
Fully agree, at active balancers which only discharge the strongest cell to load the equalization capacitors it is better to start earlier to keep the cells in balance. When it comes to passive balancers Andy is 100% right.
@ kirkdis
I think Andy is just not realizing that cells with all the same voltages at the top is just a way to make passive balancing work (and it looks "tidy").
Active balancing doesn't care about looks, it just tries to get the job done of getting a bit more out of the battery (driving individual cells differently), which naturally must lead to the top balance being off when it comes back up on recharge - because it purposefully balanced it further down and anywhere in between.
Active balancers simply do not keep the "tidy" top balance intact.. there is no need for it really. They re-balance all the time anyway.
And if they are strong enough and the balancing current is capable to divert enough energy (the diff between the strongest vs the weakest cells(s)) the battery will actually be in (soc) balance 100% of the time, not just at the top.
As much as I love Andy and his channel, in my situation I found this not to be the best advice. Using JK BMS and solar charged batteries, I found 2 things that makes my situation maybe different:
1) There are days (especially in winter, or during rainy days) when my battery does not reach full charge. It could be many days in a row, when my battery reaches anywhere between 50-80% charge and then discharges (down to 10%). In this situation I would be many days/cycles without any balancing.
2) From my observation my JK BMS does not behave like mentioned in the video. The JK BMS takes the highest voltage cell to charge the lowest voltage cell. Does not touch any other. Furthermore, the deviation settings help, so if the batteries are within 5mV it does not kicks in anyway.
@@tomsydney2430Same here except I use 10mV delta to start the balancing. While the cells at the flat curve (10-90% SoC) there is so little voltage difference between them the balancing do not happens.
Andy, might you be able to mention the Miner, and how much wealth it's producing?
At some stage I will...
@@OffGridGarageAustralia Thanks.
💙👊😎
The weaker cells have the higher votage and higher resistance. Not the other way around.
Weaker cells means their voltage and SOC is lower, hence they don't get balanced.
Andy, balance start voltage is not the same as target voltage, and the BMS has no target voltage for the cells. In your example you say that if we set the balance start voltage to 3.4 V, then the BMS will drain all the cells down to 3.4 V. No, that is not what will happen. The BMS will be in balance mode as long as one or more of the cells are 3.4 V (or higher) AND the delta is more than 10 mV (or whatever you set it to). It takes from the cell with the highest voltage and inserts into the cell with the lowest voltage, and repeats. There is no target voltage the BMS tries to reach. If the delta is 9 mV and all cells are above 3.4 V it will still stop.
That's not quite what I said. In my example, we are charging to 13.8V which is 3.45V per cell if full balanced. Setting the balancer to 3.4V, makes it discharging/balancing any cell above that 3.4V, even you try to charge to 3.45V.
@@OffGridGarageAustralia No, this will not happen, because the BMS only balances two cells at a time, and it stops balancing as soon as the delta is lower than 10 mV, no matter if the cell voltages have not yet come down below the starting voltage. An active BMS doesn't eat up any charge from the cells, it just moves the charge between cells. So if you say that it will lower the voltage of all cells, you need to explain where all this charge ends up. As heat? No, this is not how it works. And active BMS doesn't have a power resistor it can use to burn up energy.
Here is what the BMS does when it balances: The cell with the highest voltage is discharged into a supercapacitor, and that energy is charged into the cell with the lowest voltage. Then the BMS measures the voltages of all the cells again, and repeats the procedure. It could be the same two cells this time, or two different cells. So in your video at 6:20, the 3.45 V cells will be left completely untouched by the BMS, because they are neither the lowest or the highest cells, and will never be. The BMS only does balancing as long as two conditions are true at the same time: A) one or more cells are above the starting voltage, and B) the difference between the lowest and highest cell is more than 10 mV. In your example, condition B will happen before the BMS has any reason to touch the 3.45 V cells.
This is also why starting early with the balancing (setting a low starting voltage) does not have any negative effect on the balancing. It will end up exactly the same as starting late, except it will get the pack balanced slightly earlier, because it would have had more time to do it. There is probably very little time difference though, because the charge current is so much higher than the balance current.
That's exactly it is. I have it at 3.0 Volts and it works perfectly.
@@jonaugust69 Thanks for confirming this.
this time everything turned out very complicated, I'll pretend I didn't see it 😅
Hahaha, and it is soooo easy!
active ballancers solve everythink. BMS passive balancing 60-150mA is bad joke for 280Ah cells.. active ballancers have 0-5 amps if disbalance is small current is small, same for big disbalance = big ballancing current and active ballancers run all the time supporting poor cells and after time we have minimum disbalance, maximum lifetime and max usable capacity.
Wouldn’t a battery bank balance itself over time by just parallel connecting the batteries together? For example, if I fully charge my 3 - 24V 200Ah batteries separately (600Ah total) then parallel connect them set for 2 to 3 days or more. Would they not balance?
Ooooh man you opened a can of worms.Getting ready to test that with 4 Enerkey 10 amp active balancers on my channel
Yes, I know. There were so many emails and questions around this so I thought a simple rule to when starting balancing will help...
I guess, there will be a part 2 😁
Can you parallel multiple MPPT chargers to one battery?
And when yes, can you also connect to the same solar panels to increase charging current? Or only different panels to one battery?
You can parallel as many MPPTs as you like and connect them all to your battery. Each MPPT can only have dedicated solar panels connected to it. The panels cannot be shared amongst the MPPTs.
Well done Andy, thanks for comprehensive recap of cell balancing, Something I've noticed on some cheap no-name and Daly low-dollar passive balancers with fixed parameters commonly used in ebike packs, is that they start at 3.50 volts per cell, but they don't discharge only the cells at a higher charge, but simply discharge all cells to 3.55V or 56.8V on a 16S pack, and cut of all charging current if any cell goes over 3.7 volts. Therefore to balance the cells I pretty much have to charge to 58.4v and disconnect charge voltage until the entire pack discharges to 56.8v and then charge again.
That also means that if you keep a constant charge voltage applied the pack will never fully balance as the passive discharge current is continuously replenished, and balancing only occurs when charge power is manually removed. If load is applied after charging, without leaving any time for all cells to discharge to 3.55v, then cells won't balance either, and I suspect why cheap eBike packs that are left on charge and then disconnected and immediately ridden can develop major imbalances
Pretty crude balancing but functional way of if you understand how it works and charge accordingly
I would not use these cheap BMS where all the settings are fixed. You really don't know what they are doing and have no control over it.
Smart BMS are not expensive any more and you can get them from $40 already with Bluetooth app.
@@OffGridGarageAustralia I would ever use hem on a large storage system either.. Just FYI for people who may have them in eBike or portable power systems as they seem to be common.
For small cheap, potable packs I find them a cheap, compact and adequate for over and under voltage protection, and balancing as long as you understand how they work.
Доброе. Как запустить bms 4s12v если на b- 13.2 v а на p- 9.45 v
Зарядка не помогает / через нагрузку тоже
Замыкание b-p- тоже нет результата.
Подскажите как сделать? Чтобы на p- было 13.2 v .....?
I guess you mixed up some terms. If we talking about balancing on the charge phase, there is no such thing as a discharge (unless your balancer allows you to bypass ALL charging current for a dedicated battery). So if the balancing current is less than the charging current (which is true for almost all cases) all that balancer can do - is distribute a small part of the charging current between the batteries. So if the charging current is 20A and the max balancer current (delta) is 5A you may have as a result, for 4 cells: 25A (for battery with lowest voltage), 15A (for battery with highest voltage) , 20A, 20A. So there is no such thing as "discharge", just one battery with the highest voltage would have less charging current.
No, I didn't mix that up. Balancing while charging is pointless unless you charging current is lower than your balance current. Just as you said.
@ OffGridGarageAustralia
Balancing while charging removes charging energy from the weaker (faster raising) cell and pushes it to the stronger (slower raising) cell.
As long as the cell capacity/capability difference is within the reach of what the active balancer is able to divert from the weaker to the stronger cells, will this ensure that all cells are being loaded appropriately to their capabilities.. the weaker ones are being loaded less while the stronger ones are loaded more (same applies to discharing while active balancing is on). Over time this should get the cells within the pack on equal footing as the wear on the stronger cells is higher.
All this "top-balancing" wisdom is only useful for passive balancers.. active balancers who can divert the energy difference between weak and strong cells make this approach moot and gives us access to 100% capacity of all cells.. not just the 100% of the weakest cell applied to the whole pack that passive balancing is capable off.
I agree with you. Ok, 2 A balancing current is not much compared to 20 A charge current. But it is still better than nothing, and will slightly prevent an OVP. Starting the balancing early (90%+ SOC) will in worst case accomplish nothing, and best case prevent an OVP. My main point is that it has no negative side effects, so why not do it? It will not artificially lower all the cells like Andy claims. I think he is right about many things, but in this case he is wrong.
Another major point is that the charge current will push up the cell voltage and effect the balance start. If the balance start voltage is set too low, high charging current can cause the balancer to start way too early (before the cells are really past 90% SOC).
This is why, by default, the balance start voltage should be at least 3.50V (14.0V in an s4 battery). In otherwords, well into the exponential part of the charge curve. Because the device needs to work properly across the full current and temperature range of the system.
But if you know for absolutely sure that you won't be charging at high currents... say you never charge at more than 0.2C (very common for solar + battery systems). Then you can safely reduce the balance start voltage to 3.45V.
Another factor is the bulk/absorb target that people set. The charge target should always be at least 0.05V (per cell) higher than the balance start voltage. For many reasons not the least of which being measurement error between devices and ensuring a full charge across the whole working temperature range (colder temperatures need higher bulk target voltages, for example).
When we combine all of this together we get a balance start voltage of 3.50V/cell and a charge target of 3.55V/cell as a really good default. And if someone really wants to optimize for low charging currents, a balance start voltage of 3.45V/cell and a charge target of 3.50V/cell is reasonable. I would not go below those parameters, though.
I know a lot of people do and swear by it, but going lower really begins to restrict the operating temperature and current ranges for proper charging operation without really giving much benefit in return. The cells won't really last any longer with lower targets, particularly in cyclical applications such as solar, RV, and boat setups. As long as the charge controller properly goes into a float stage 1-2 hours after absorb with 3.35V to 3.375V/cell for the float stage, the battery will have a great life-span. Even if it is being charged to full every day.
-Matt
Thanks for your comprehensive comment, Matt.
The topic is far deeper than I pointed out in the video. More settings, different setups and designs, charge current, target voltage, absorption time and much more to consider....
Sir show your home and family pls.
Back to basics hey, good, had enough of all the communication stuff. I prefer to work on the K.I.S.S principle. Don't know if I can wait for the new project, nothing sort of popped up in the background that I saw or did it? Keep up the great and informative work, thanks.
We will do a lot of small projects next year. I have some interesting and cool stuff coming up. All very basic... but super useful.
What charge voltage you use from inverter for target 55.2v (3.45 x 16)? On my Growatt Inverters I getting 3.35v on my fully charged batteries from charge voltage of 52v.
Yeah, that's normal because of the voltage drop and the two individual measurements the inverter and BMS take.
You may have to set the inverter to 55.3V/55.4V and see how this goes...
You have also to stop balancing when you discharge, weaker cells with higher resistance overshoot when charging with high currents and drop fast with discharge currents, what would cause imbalancing them again if you don't stop balancing on discharge.
That's another point of not balancing too early. With the simple rule I explained in this video, the balancer would stop as soon as the discharge process kicks in.
Hi Andy, My Daly 1A Balancer is doing fantastic, but with my Poorly Grade F Litokala cells I need a wider spread on the start woltage to stop a runner. Charge to 3.55 balance start at 3.4 I have tried higher but no good with these cells.
Only 52 Days to the Solstice!!! By Christ it is dark in 🏴
Shine on mate
Gaz
Once you top balance to 3.55V, can you go higher to 3.6V and balance the pack there? Turn off the balancer at this stage and do a cycle. The batteries should stay fairly balanced when they come back to 3.55V. Not 100% but it should work at least to the point that none of the cells shoots over 3.65V.
@@OffGridGarageAustralia Hi mate, I have already tweeked it up a bit. Start voltage is now 3.45v charging to 3.6v and all settled and running well with no disconnects.
I will try your higher start voltage but with small poorly cells the upper voltages rise very quickly. I am not sure how these will act once I charge at higher amps.
Just need more sun lol, the Scottish weather has been very dark and unreliable with a handful of brighter days.
Dave 🐔sends his love, he dreams of roaming your garden in Hot and Sunny Australia .
Cheers Gaz