Top Balancing "How to"

smoothJoey

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Source is the "Top Balance Tutorial" on page 1 of this thread. Section 3 (https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/)
You mean this "3.Set the power supply constant current to .2 C or less. 3.1.While the power supply is disconnected from the batteries and turned off, short the leads together." ?

Using "home office" as I am just testing that things are "working right" and the app is reading accurate. My cells have now evened out with a 0.014v difference, and they show as "yellow" at 3.24-3.31. These were top balanced, and topped off prior to setting up in series 3 days ago. So for them to already be at that range (60-70% based on this page: https://diysolarforum.com/threads/lifepo4-voltage-chart.3156/) seems a little "off" for these cells having been JUST balanced...so not sure if batteries or app...
Before you do anything else verify your bms cell voltages with your dvom.
If they don't agree then you have problems that will be made worse if you discharge the pack.
 

Just John

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When you say bypass bms do you mean charging directly to the negative terminal? IE... put the PS to the C- when charging green arrow and not red
Positive goes to the battery positive. Negative should go to the BMS C- connection. That means the charge goes through the BMS. Do not bypass the BMS and use the battery positive and negative.
 

Draconius

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You mean this "3.Set the power supply constant current to .2 C or less. 3.1.While the power supply is disconnected from the batteries and turned off, short the leads together." ?


Before you do anything else verify your bms cell voltages with your dvom.
If they don't agree then you have problems that will be made worse if you discharge the pack.
Here are my 4 cells tested on the terminals and the whole pack.

Cell 2 I have the balance lead on the NEGATIVE of the Positive/Negative series. Should I move this to the Positive terminal? Per Will's BMS setup, he said it can go on any terminal of the bus load.

CellDMMBMS
13.3013.300
23.2943.280
33.2933.294
43.3003.301
Pack13.1613.2
 

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Just John

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Here are my 4 cells tested on the terminals and the whole pack.

CellDMMBMS
13.3013.300
23.2903.280
33.2933.294
43.3003.301
Pack13.1613.2
When you say you top balanced the cells, did you actually follow the steps of connecting in parallel and charging to 3.65v, or are you just trying to get to that step? The step you are describing is "how to get your cells close enough to top balance".

The BMS reading of capacity is not accurate until you have done a full cycle, discharge then charge.
 

Draconius

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When you say you top balanced the cells, did you actually follow the steps of connecting in parallel and charging to 3.65v, or are you just trying to get to that step? The step you are describing is "how to get your cells close enough to top balance".

The BMS reading of capacity is not accurate until you have done a full cycle, discharge then charge.
I did a full parallel top balance, amp's read 0.0, disconnected. Let sit for 18 hours and one cell discharged down faster than the other two. you and smooth joey (I think it was him :p) suggested I top up that one battery and then go into series. That one cell is now my cell 3 in the configuration.

I'm not overly concerned about the capacity, more than the cell voltages I am seeing for a pack that was top balanced 4 days ago
 

Just John

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I did a full parallel top balance, amp's read 0.0, disconnected. Let sit for 18 hours and one cell discharged down faster than the other two. you and smooth joey (I think it was him :p) suggested I top up that one battery and then go into series. That one cell is now my cell 3 in the configuration.

I'm not overly concerned about the capacity, more than the cell voltages I am seeing for a pack that was top balanced 4 days ago

OK, now I get it. Yes, always charge through the BMS, that's why it is there.
That one cell would seem a problem, so keep an eye on it.

Not sure how you intend to use these, is it for backup, or normal everyday charge/discharge?
No need to charge above 3.4v per cell in any case, some people think 3.65v, but really that is only for a top balance. Do not charge to 3.65v on a normal basis. Usually people set balance to start at 3.4v, and charge to 3.45v. For normal cells without excessive discharge, the limited balance current will do a good enough job with those settings. That would be 13.8v for a 4 cell pack. If they stay in balance, I wouldn't charge above 13.4v if they are used for "backup" and not cycled daily. Even for backup, I'd try and cycle at least once a month.
 

Draconius

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OK, now I get it. Yes, always charge through the BMS, that's why it is there.
That one cell would seem a problem, so keep an eye on it.

Not sure how you intend to use these, is it for backup, or normal everyday charge/discharge?
No need to charge above 3.4v per cell in any case, some people think 3.65v, but really that is only for a top balance. Do not charge to 3.65v on a normal basis. Usually people set balance to start at 3.4v, and charge to 3.45v. For normal cells without excessive discharge, the limited balance current will do a good enough job with those settings. That would be 13.8v for a 4 cell pack. If they stay in balance, I wouldn't charge above 13.4v if they are used for "backup" and not cycled daily. Even for backup, I'd try and cycle at least once a month.
You sir are awesome!

The BMS has setting shows
Overvoltage 3.65 (release 3.5v)
Undervoltage 2.5v (release 3.0v)
Pack overvoltage 14.6v (release 14.0v)
Pack undervoltage 12.0v (release 12.0v)
Balance turn-on voltage 3.4v (precision 0.015v)
Single Full voltage 3.4v
Single cut-off 3.0v
Balance enable: True
Charge balance: True
Load check: True.

Pack will be used in my camper van about every 2 weeks so not backup power, but also not discharging every day.

Should I be changing the balance turn-on voltage to a lower number or leave as is based on usage? Or are these not even the right settings? Xiaoxiang v3.1.1026
 

Just John

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You sir are awesome!

The BMS has setting shows
Overvoltage 3.65 (release 3.5v)
Undervoltage 2.5v (release 3.0v)
Pack overvoltage 14.6v (release 14.0v)
Pack undervoltage 12.0v (release 12.0v)
Balance turn-on voltage 3.4v (precision 0.015v)
Single Full voltage 3.4v
Single cut-off 3.0v
Balance enable: True
Charge balance: True
Load check: True.

Pack will be used in my camper van about every 2 weeks so not backup power, but also not discharging every day.

Should I be changing the balance turn-on voltage to a lower number or leave as is based on usage? Or are these not even the right settings? Xiaoxiang v3.1.1026
I would leave it as is, and see how it does. Those are very reasonable settings.
 

Draconius

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I would leave it as is, and see how it does. Those are very reasonable settings.
Thank you!!

Running til about 5pm with this 180w load and will see what it says amp wise. Then will hook up my PS at 13.8v and charge it up via battery pack + and BMS C-. :)
 

smoothJoey

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Thank you!!

Running til about 5pm with this 180w load and will see what it says amp wise. Then will hook up my PS at 13.8v and charge it up via battery pack + and BMS C-. :)
Suggest you draw the battery down until your weakest cell starts to diverge significantly.
Say 50mv delta or 12.00 volts whichever comes first.
That will tell you where your low voltage cutoff should be.
Then charge to 14.2 and see how well your cells hold together.

Your cells are already behaving in an unusual way.
Typically cells settle to between 3.45 and 3.55 volts after top balance.
Yours seem to have hit stasis at 3.3 volts.
That is as weird as a Koolaid sandwich.
 

Draconius

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Suggest you draw the battery down until your weakest cell starts to diverge significantly.
Say 50mv delta or 12.00 volts whichever comes first.
That will tell you where your low voltage cutoff should be.
Then charge to 14.2 and see how well your cells hold together.

Your cells are already behaving in an unusual way.
Typically cells settle to between 3.45 and 3.55 volts after top balance.
Yours seem to have hit stasis at 3.3 volts.
That is as weird as a Koolaid sandwich.
Noooooooo. :( not what I wanted to potentially hear.

I'm hoping maybe it's just me jumping the gun too darn early and not letting the pack behave. It has been stationary at this 3.29-3.3v range for awhile now. The BMS is estimating 22.1ah already used, so about 19% of the pack used.

Your comment makes me feel like I'm gonna probably need to trigger the dispute process then in AliExpress...test it in my van while camping next week and if need, refund. :(
 

smoothJoey

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Noooooooo. :( not what I wanted to potentially hear.
What will be, will be.
I'm hoping maybe it's just me jumping the gun too darn early and not letting the pack behave.
No clue what you are driving at here.
It has been stationary at this 3.29-3.3v range for awhile now. The BMS is estimating 22.1ah already used, so about 19% of the pack used.
The bms capacity estimates can and are mostly likely wildly inaccurate until you get a couple of cycles done.
Your comment makes me feel like I'm gonna probably need to trigger the dispute process then in AliExpress...test it in my van while camping next week and if need, refund. :(
All the more reason to test it without delay.
Up to you.
Your comments make me think I've wasted my time.
 

Draconius

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What will be, will be.

No clue what you are driving at here.

The bms capacity estimates can and are mostly likely wildly inaccurate until you get a couple of cycles done.

All the more reason to test it without delay.
Up to you.
Your comments make me think I've wasted my time.
My apologies if you feel you wasted your time. I think otherwise. I'm new to this and if there is something funky, I'd rather find out now vs past any serviceable window. :/

I'm taking all your imputs VERY seriously. My comment of me jumping the gun was that any "oddity" is what triggers my "am I screwed" stance. Top Balance, my pack was stagnant but my PS went weird. Your and Just John's responses made me seek a new PS. I'm learning...my apologies. :(
 

Gazoo

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Texas
Your comments make me think I've wasted my time.
No you have not wasted your time :) I know Draconius is eager to learn as I have had several PM conversations with him.

The only thing I would add, and maybe you mentioned it some where, is if attempting balancing, then set the charger to a low current once 3.4 volts is reached. As you know once the cell reaches 3.4 volts it doesn't take long to get to 3.65 volts. So the longer the cells can balance when in the area between 3.4 volts and 3.65 volts the better.
 

Draconius

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No you have not wasted your time :) I know Draconius is eager to learn as I have had several PM conversations with him.

The only thing I would add, and maybe you mentioned it some where, is if attempting balancing, then set the charger to a low current once 3.4 volts is reached. As you know once the cell reaches 3.4 volts it doesn't take long to get to 3.65 volts. So the longer the cells can balance when in the area between 3.4 volts and 3.65 volts the better.
Thank you sir! I am a sponge right now and there are stories of AliExpress of sell and ditch and I just don't want to be out $450. :p

I left home with the pack at about 23ah (per bms). I might be building packs for some friends, so knowing the tell tale signs and what not have been INSANELY educational. I even had the pack doing weird readings and after someonely else having issues about terminal nuts not being tight, I double checked and lo and behold...one of my studs was loose.
 

Horsefly

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This should be good for getting some amps into those bigger packs
Everyone has to decide for themselves, but I'm not sure I would want to trust a relatively cheap buck converter to maintain a precise voltage in CV mode. This unit also isn't capable of that much power. It says 50A, but it also says it can only sustain 600W (skeptical me, but I think that means it can sustain 400W). That's actually only 12V @ 50A, which isn't that useful for even a 4S pack. Anyway, I would probably pass on that buck converter.
 

LVLAaron

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I'm rocking two of these. One on each end of the parallel bus bars.


Drok stuff seems to be very good and more accurate than most cheap stuff we find on the chinese markets.
 

crozen

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Firstly, when i got these cells, i put them in series and charged them. I was surprised that the cell 1 triggered BMS on 3.65v when the 3 others were 3.43v.
So i charged them separately to 3.62v (not in parallel), didn't dismantle series. Cell1 was 99% already full. All the 3 cells took about 50Ah (5 hours charging with 10A per cell). Finally, every cells had same voltage and normally the same capacity.
6 hours later, i put a load, small load of 3.5A. About 13 hours later, BMS triggered on cell 1 at 2.5v when the others were 3.26v

There is no bulging, no difference.
I got a load battery capacity tester. Here are the result. As expected, Liitokala sent me a cell which is half the capacity compared to the other 3 cells, 50Ah instead of 100Ah.
I contacted them, let's see their answers.
 

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crozen

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Liitokala's anwser is "our batteries are sent out after strict inspection, and the capacity of the batteries is in accordance with the description".
No refund.
Never trust again them, they are scammer.
 
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