Trouble balancing battery

[eMark]

99.99% of the hobby balance chargers out there use the exact same passive bleeding | resistive method as do most of the BMSs.

Realize what you are attempting to communicate, but your exaggeration can easily give the wrong impression to others than what you intend to communicate. The PRIMARY task of a TRUE Balance Charger is charging (increasing the parallel cell voltages while balance charging) NOT "passive bleeding / resistive method" as with only 99.99% of BMSs :wink:

Whichever Lipo/Li-ion Balance Charger i use it's a TRUE balance charger as the parallel cell voltage increases as its PRIMARY task of increasing the cell voltages to the users desired level. Thus TRUE balance charging can never be achieved with a typical BMS "passive bleeding | resistive method".

IFWR i want to exactly equalize the parallel cell voltages (which practically isn't necessary), of my two 5S5P packs (10S5P battery) i use the following multi-purpose stand-alone discharge balancer. Even then it can take an hour to exactly equalize parallel group voltages that are already within 0.05v of each other ... so it's use isn't all that necessary when using a balance charger to begin with that equalizes the parallel group voltages within 0.05 volts of each other, if not closer ...



Because i still have a couple Lipos like new (3S 2200mAh & 3S2P 4400mAh) i can take them with me when etriking in case i need to charge my phone or bike light or easily separate and check voltages of the two 5S5P packs of my 10S5P battery. The USB and phone charge port is located on the right side. You press the middle button to see options such as "Start Charge" (actually discharge :wink: ). Very legible readout shows which parallel group(s) are too high and when all parallel cell groups are at same exact voltage and will then stop (shutdown). Instruction manual ... https://www.isdt.co/down/pdf/BG-8S_en.pdf ... the top photo is how the readout appears before pressing the "Start Balance" button and when pressing the "Start Balance" button whatever parallel group of cells having a higher voltage (slowly being discharged) appear in a redish brown color. After a minute the screen shuts down, but the discharge balancing is still activated. Press the middle button again whenever you want to see the cell voltages. As long the small blue light at the middle top is blinking it is discharge balancing even when the screen is off. It uses a XT60 connector.

Your generally low opinion of BMS as balancing devices is not warranted, plenty of them are out there that perform perfectly well in that role.

Apparently you didn't read my concluding advice in my previous post ... so will paste again ...

Bottomline is that a BMS is still a good idea if only for protection(BPS)

 

[john61ct]

Many of the protective functions people use a BMS for, can be implemented without a BMS.

Plenty of BMS do no protective function at all, only balance. Some allow balancing at the midpoint, or the bottom of SoC.

A BMS that balances well, does so much better and faster than that charger.

Many other chargers do a great job balance charging, much better and faster than that charger.

Most generalizations are overly so.

 

[DjSpaceGhost]

Some people would use such a profile

hold 4.1Vpc until trailing amps drop to zero

as a benchmark standard prior to running a timed CC Load cap test.

But only once a year, or every 100 cycles, not frequently.

I would caution to just try not do make it a habit.

Fact is you really won't be giving up much **actual usable** capacity / range

by just doing CC-only, don't hold that 57.6V for any Absorb/CV time, just "charge to and stop" for normal usage charge cycles.

Depending on the C-rate, likely getting to 98-99% SoC with that, and can just use a reliable HVC to terminate charging automatically.

Such a profile will be inherently less stressful, so you could also bump the voltage up closer to 4.2Vpc and shorten charge time a bit.

Thanks. I will be doing exactly what you said (CC to terminal voltage with no absorb ) going forward . Makes more sense.

 

[eMark]

I've used many of the "cheap" style with good results. For badly out of balance packs I use a single cell charger to bring up the low cells. I found some solid strand copper wire that fits nicely into the BMS plug. One the cells were balanced, they have done nicely for years. The balancing function is pretty useless but having the protection against over and under voltage is important.

First balanced my two 5S5P packs (Samsung 30Q) with only 1mv difference between the 5 P-groups of each 5S5P pack with the joined 10S5P at 37.5v. Then charged the 10S5P battery with my 2.5amp bulk charger set to 40.6v (via 10S5P discharge connection). Then separated again into two 5S5P packs and measured the P-group voltages (via P-group balance lead wire connections) of each 5S5P pack. Only 8mv min-max difference between the 5 P-group cell voltages on one of the 5S5P pack and only 7mv difference between the min-max 5 P-group cell voltages on other 5S5P pack (no cell balancing during bulk charging).

It took 25 minutes to balance each of the two 5S5P P-group cell voltages to within 1mv min-max difference beginning with a 15mv-16mv difference in the P-groups using the ISDT BG-8S (discharge balancing). Resulting in 37.5v for the 10S5P battery before bulk charging to 40.6v. After bulk charging to 40.6v there was an average P-group cell voltage difference between the two 5S5P packs of 7mv & 8mv. The 5P-group min-max cell difference in the two 5S5P packs was 4.056v min to 4.064v max in my 10S5P battery. Being a former QC medical technician i'm a stickler for getting the best performance. Being retired i have the time to experiment and track results for doing whatever it takes to prolong cycle life longevity. Hopefully my 10S5P battery will serve me well for at least 5 years while enjoying the ride and keeping track of cycle life performance along the way.

Not only is BMS discharge balancing "pretty useless" with a pack of first-rate quality cells with occasional balance charging of my two 5S5P packs. Even moreso when my 10S5P battery is never discharged below 34v or charged above 40.6v ( assuming it's never abused along the way :thumb: ).

Probably should mention that the above test is with a new 10S5P Vruzend pack with brand name quality cells. So the above test is the best that this 10S5P battery will ever see again as it very slowly ages and little by little the cells become unbalanced. Thus the importance of balance charging to equalize cell voltages AMAP. Some may consider my passion for cycle life longevity too extreme, but if a $120 car battery is good for 60 months there shouldn't be any reason why my 10S5P battery shouldn't serve me with many miles of enjoyable riding for a minimum of at least 5 years ... with TLC :thumb:

 

[john61ct]

That's all good there!