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Top balancing dilemma ....

Stupid Monkey

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Dec 14, 2019
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So finally got my BLS Cells - 24pc of 150ah and I've started the top balance.

Cells ship at 65% charge right? so each cell needs ~50ahhr of charge, 24 cells, 1200ah

i've a 10A charger, but raising 3.3 - 3.4V its started at 1A, so by the time that stage drops to 0A assume average 0.5A at every stage (3.4-3.5 next stage etc) thats 2400hrs, or 100 days .....

Have I calculated wrong? What would you do ?
 

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Gone to 3.6v getting 2.81A so lets assume 1.5A average ... only a month to top balance ?
 
Your math is sound. I had the same issue with 64 50Ah cells using a 10A charger. Feels like it takes forever! I just kept telling myself the longer it takes, the more remaining capacity the cells have.
 
After reading this, I'm glad I got that 50A charger unit, hope to heck it works as advertised.
Lucky it shipped, they are now a bit back ordered.
The Grey One 3-15V up to 50A (link underneath image)

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I use a 65amp charger that cuts off at 13.6v, i charge through a dali BMS as a safety precaution. once amps have dropped to 0 at 13.6v i switch to my 6amp balance charger. with a 200ah battery it takes about 24-30hrs for it to complete a balance charge from that point.
 
I use a 65amp charger that cuts off at 13.6v, i charge through a dali BMS as a safety precaution. once amps have dropped to 0 at 13.6v i switch to my 6amp balance charger. with a 200ah battery it takes about 24-30hrs for it to complete a balance charge from that point.
Charging individual cells is not quite the same, The charger I posted, which I am waiting on, is intended to charge Cells, not complete packs as such, I suppose you could do so for a 12V pack, In my instance, my Inverter/Charger & SCC can easily handle charging a pack. As you pointed out, doing a full on pack can take serious time, might even call it painful. I'll be doing what @Stupid Monkey is doing but with 280AH cells when they get here and then again with the 174AH cells I already have in a pack, which I have to redo again and split into two 24V /8 Cell / 175AH packs.
 
I'm thinking of charging for maybe 10 days - I'm charging at 0.00138888C now, 3.65V 5 amps

And seeing what voltage that is at, maybe just then assembling the battery and letting the BMS top balance the pack at much higher C rate.
 
So a week in and I'm still charging at a little over 5 amps (and noticed Will had the same Longwei power supply in his latest "tools" video - just a side note)

I'm now on 3.35v ......

Thought I'd cheat and swap then to the 6P4S they will be used in and charge at 14v for a bit .... BUT, I F***ED UP .... set power supply to 14v, connected black to black ... but when red touched big spark and blew power supply .... cells seem fine, voltage unchanged, but reverse voltage (as on these BLS cells the +ve is black) thats done the power supply in.

Time to assemble in the van and let the charger/BMS finish the job.
 

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ok ... so 2 months on and with work off the cards for now I've got back onto this.

Now located in the camper-truck, and with BMS (temporarily) attached currently charging at 15A ....get full and top balance via the BMS. looking good, everything 3.37v

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Back in "patience required " mode...... cell 1 drops to 3.499, clicks back to charge @15A, soon hits 3.65 even with 1A balancing and cutoff.

In that cycle the other cells gain 0.001v


Kinda wish I'd spent £5 on an extra balancer

... or fixed the power supply so I could trickle charge this top balance rather than use the victron charger on half power.
 

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Do you have a charger that can run at 3.5 and 3.6v ? If so run them all in parallel to balance them out together.
 
Well its tomorrow, and the BMS balancing is useless ....

first into balancing at
9:40pm 3.516 3.440 3.425 3.420 for the 4 packs this was the most balanced the battery has been, despite several cycles of drop to 3.499, charge while burning off cell 1 according to the BMS get to 3.65v after about a minute and drop back down to a more out-of-balance state and hour later and repeat ..... tried to record around same rest voltage to be able to compare.

9:40pm 3.516 3.440 3.425 3.420
10.00pm 3.535 3.380 3.361 3.365
11.00pm 3.534 3.356 3.346 3.348
12.45am 3.535 3.348 3.341 3.341
02.10am 3.502 3.343 3.337 3.338 - this one i waitied till it almost dropped to charge voltage
07.00am 3.590 3.345 3.375 3.337
11.00am 3.556 3.341 3.374 3.335 (now)

So it seems I'll need to manually drain cell pack 1 to balance myself - the BMS wont do it.
 
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