the easy way to keep your cells balanced is...active balancing

[Diysolar123]

so I have some aliexpress express cells and of course even after top balancing they quickly like to get out of balance...
neither the daly or overkill solar BMS in "balance" mode does anything useful.

with cells out of balance by about 130mv I let the bms do its balance thing for a few days.
watching the overkill app constantly declare its "balancing" and absolutely nothing was changing.
The BMS was in "balance" mode and not closed...but watching the current flow the method it uses to balance is, well, mostly useless.

So I had an active balancer (hw version 1.3) that I had from ebay for $35 and decided to plug it in.
I use the xiaox bms app to turn OFF bms balancing.
plug in the active balancer...
poof...magic... balancing actually starts to happen, I can literaly see on the BMS app that cells are balancing!!!
within a few hours 130mv delta has turned into a 60mv delta...
within 24hours the BMS app is showing a voltage diff of 0.006V... yep, thats 6mv!!

I unplug the mppsolar from the wall and let things run on battery for short time, plug back into the grid, cells stay nicely balanced (<10mv).

I was waffling on using active balancing for a bit, now I am sold on these devices. No settings, you just plug it in and it works.
fyi I have my mppsolar set to 27.2V charging/float...all my cells are now in the range of 3.398 to 3.404.

 

[snoobler]

I've personally seen capacity imbalances of less than 0.3% wreak havoc on voltages, and these commodity cells self-discharge at different rates.

 

[Diysolar123]

I've personally seen capacity imbalances of less than 0.3% wreak havoc on voltages, and these commodity cells self-discharge at different rates.

so could you expand on "wreak havoc"???

 

[snoobler]

Balance 8P cells to 3.65V.
Let sit 10 days.
8S cells and charge. Within 30 seconds, peak cell at 3.8V and low cell at 3.36V. Got that high because the Chargery delay was set to 5 seconds.

No cell needed more than 6 minutes of individual 10A charging to hit 3.65V again. After that, they were fine.

10A for 6 minutes is 1Ah. 1Ah/280Ah = 0.36%. All cells required < 6 minutes, so I rounded down to 0.3%.

 

[Diysolar123]

perhaps some confusion, I did not mean you use these in place of a BMS or as part of your initial cell top balance.
This is for the "normal" day-to-day imbalances that will happen; relying on the BMS that says it can balance has, at least for me with both a smart daly and an overkill bms, shown that they cannot really balance anything at all.

I just did a current check on each of the active balance leads and with the total pack delta of 6mv I see a draw of around 10ma on the balancer(it has a nice bright led, sigh)...so that constant LED is a secret load that bypasses the BMS hehe

it seems to not be doing anything harmful at all, if fact, its just nicely sitting there now that the cells have been balanced (with that constant LED current draw).

I always have my BMS disconnect set to 3.65V post balance and I have my 8S set to 27.2v; no cell should ever reach 3.65 but that has nothing to do with an active balancer which is the point of the thread. The BMS should promptly disconnect when any high or low limit is hit.
I am sold on this approach now and have already ordered another active balancer (same model).
I will turn off the useless BMS balancing, get an active balancer, and let it nicely handle the small cell variances that will always happen.

also I always make my balance cables as a "Y" so I have an extra connection to all cells to plug(or unplug) things like an active balancer or a calibrated isdt battgo to take a quick look at voltages.

 

[snoobler]

Sorry. My comments were directed at systems using only a BMS based passive balancing, DALY, Overkill, etc.

I plan to use active balance on my NMC bank that is finally coming together. Batrium on order.

 

[Sky-HHI]

I started using an active balancer on my used BYD 24v battery pack which kept the battery balanced and helped increase the capacity. I now have one on my new 280 ah ,24v battery pack. They work great and keep the battery well balanced. My active balancers have capacitors which move power from the high cell to the lowest cell, this way no power is burned off with passive balancer resistors. I have left the bms balance on but should turn it off as the active balancer does the job. I also have a mpp solar set at 27.2 charging and float works great, from the Off-Grid Garage guy.

 

[WhiteHot]

Which active balancer are you using?

 

[Sky-HHI]

I use a Heltec Capacitor Active Balancer from amazon or aliexpress. Be careful when you use a capacitor active balancer , make sure you pre-charge the capacitors before you hook it up to your battery, I use a resistor on the negative lead to pre-charge the capacitors before I connect up the negative lead to the battery. With my first balancer I forgot to do that and I burned up one of the capacitor.

 

[curiouscarbon]

I use a Heltec Capacitor Active Balancer from amazon or aliexpress. Be careful when you use a capacitor active balancer , make sure you pre-charge the capacitors before you hook it up to your battery, I use a resistor on the negative lead to pre-charge the capacitors before I connect up the negative lead to the battery. With my first balancer I forgot to do that and I burned up one of the capacitor.

thanks for mentioning this

 

[Horsefly]

I've been messing with both the Heltec Capacitor Active Balancer that @DouglasHHI mentioned, as well as the QNBBM active balancer. I've done a variety of experiments. I aggressively charged and discharged my little 8S test pack far beyond the knees, where cell voltage tends to become unbalanced. I've also intentionally discharged one cell by hooking it up to one of the little 300W capacity testers for a while, so that it was 100mV off from the other cells in the middle of the charge curve. In all cases, both the QNBBM and the Heltec did a good job of bringing the cells back in balance. Sometimes it took a while, but it worked. Anyway, I too am pretty much sold on active balancing.

Since the Heltec Capacitor model is so much cheaper than the QNBBM, I would tend to favor it.

 

[Steve_S]

I run 24V, all of my battery packs have a QNBBM-8S Active Balancer on them and they work quite well to keep everything nicely balanced.
Passive Balancing is essentially useless on large capacity LFP as it only burns off hi voltage cells at low power by dissipation. There have been some recent imrovement's on Active Balancers by Known Good vendors like Heltec & QNBBM (deligreen :-( ).

A NOTE: Be certain that the Active Balancer you select has enough capacity to handle the Size of your cells ! As Active Balancers transfer power between cells, the larger capacity cell balancing has to work more.

I have done extensive cycle tests & thrash testing of my packs with the QNBBMs and they take it all quite well. Thrash Tests included full C-Rate charge & discharge runs as well as other stress tests.

Charge Setting Note: (I use a Midnite Solar Classic SCC)
Absorb: 28.2 for 15 minutes
Equalize: OFF
Float 27.9V
MIn Volts: 22.0 Max Volts: 28.7
Rebulk Voltage: 27.7
End Amps: 14A
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

* Active Balancing + Float:
I've found that once the battery packs are "full" and in float mode, they barely take any input but as the Active balancers are working and levelling, the float allows for everything to fully top off evenly, all cells within all packs are between 6-10mv once float has been running for an hour. This is what I have observed with my packs.

Hope it helps, Good Luck

 

[Javalord1]

perhaps some confusion, I did not mean you use these in place of a BMS or as part of your initial cell top balance.
This is for the "normal" day-to-day imbalances that will happen; relying on the BMS that says it can balance has, at least for me with both a smart daly and an overkill bms, shown that they cannot really balance anything at all.

I just did a current check on each of the active balance leads and with the total pack delta of 6mv I see a draw of around 10ma on the balancer(it has a nice bright led, sigh)...so that constant LED is a secret load that bypasses the BMS hehe

it seems to not be doing anything harmful at all, if fact, its just nicely sitting there now that the cells have been balanced (with that constant LED current draw).

I always have my BMS disconnect set to 3.65V post balance and I have my 8S set to 27.2v; no cell should ever reach 3.65 but that has nothing to do with an active balancer which is the point of the thread. The BMS should promptly disconnect when any high or low limit is hit.
I am sold on this approach now and have already ordered another active balancer (same model).
I will turn off the useless BMS balancing, get an active balancer, and let it nicely handle the small cell variances that will always happen.

also I always make my balance cables as a "Y" so I have an extra connection to all cells to plug(or unplug) things like an active balancer or a calibrated isdt battgo to take a quick look at voltages.

Hello 123! Would you kindly share what active balancers you are using? My new set up is 2P 16S. Thanks! J

 

[Javalord1]

I started using an active balancer on my used BYD 24v battery pack which kept the battery balanced and helped increase the capacity. I now have one on my new 280 ah ,24v battery pack. They work great and keep the battery well balanced. My active balancers have capacitors which move power from the high cell to the lowest cell, this way no power is burned off with passive balancer resistors. I have left the bms balance on but should turn it off as the active balancer does the job. I also have a mpp solar set at 27.2 charging and float works great, from the Off-Grid Garage guy.

Hi Sky, may I ask what brand and link of active balancer are you using? Thanks! J

 

[Boondock Saint]

Hey java . . whats the temps where you are in ID this week? (I'm fleeing northerly)

That's a nice 48v system you gots there btw.

 

[Javalord1]

Hey java . . whats the temps where you are in ID this week? (I'm fleeing northerly)

That's a nice 48v system you gots there btw.

Thanks! Not bad... 90 Friday, then hi 80s for a week. Nights go cool to the 60s. Come to Idaho! J

 

[Boondock Saint]

I have a buddy I met when we worked at MSFT and he moved to Sandpoint, Cocolalla, then Coeur d'Alene area. I was planing on going through there to show him my beastly RV build anyways.

 

[Javalord1]

I have a buddy I met when we worked at MSFT and he moved to Sandpoint, Cocolalla, then Coeur d'Alene area. I was planing on going through there to show him my beastly RV build anyways.

It's beautiful there... We are in the SW corner, 40 miles from Boise.

 

[Boondock Saint]

As a Dev you can work remotely, but ya, I figured as much.

My buddy has tried to convince me for years to move to there, but I'm spoiled with no state taxes etc. People are buying up ID like hotcakes, sight unseen.

Anyhoo, back to the tasks at hand, so much to do about active balancers.

 

[Sky-HHI]

Heltec active balancer