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balancing
#1
Sorry if this is a stupid question.
But my mother told me: the only stupid question is the question never asked!

Can anybody please explain what balancing is, in simple english please!

What is it purpose and for what.

My packs will be running between 3.1v and 3.9 volt (80%????)
All my cells in my packs are above 92% soh.
I have batrium, 72 longmons.(more coming as needed)
I have only packs and nothing connected, i just want to understand, why what and how.

Thanks in advance, sorry if this is a stupid question, but i would like to know
Still learning English. Learning Li ion and solar technology.

4200 cells in packs Exclamation above 2500mah and 90%soh.
1500 waiting for testing.

Saving for 3 times phoenix inverter 48/3000 230v to gain also 380v
3 chargers?

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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#2
An overly simplistic explanation, but essentially all you need to know is that balancing is the process designed to ensure all cells within a multi cell battery maintain identical states of charge.
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#3
Think of each parallel set of cells are water tanks of a set volume.

During charging, it's possible for 1 tank to get a little higher in volume, or little lower, than the others. Balancing will start to bleed off the capacity of the fuller tank until the others catchup, or all the others until the slower one catches up.
The end goal of balancing is so that all packs (tanks) have the same capacity (volume) at the same time at the end of charge.
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#4
Suppose you have a 14s1p battery, and start off with all cells at the same voltage (3.9V) and keep cycling them between 3.1v ~ 3.9 volt (in total 43.4v ~ 54.6v)

Suppose half of the cells have a self discharge rate just a little quicker than the others, so that eventually, those "bad" half of your cells will be cycling at 3.0v ~ 3.8v. Since the inverter/charger is set to keep the total voltage between 43.4 ~ 54.6, the "good" cells will now be cycling between 3.2v ~ 4.0v. Not a big issue.

Suppose you keep doing that. After a long time, you end up with a battery where half the cells cycle between 2.5v ~ 3.2v (not so good) and the other half cycles between 3.7v ~ 4.5v (definitely not good, unless your aim is to start a fire).

The aim of balancing is to keep the voltage of all cells at the same level, usually by discharging "good" cells to match the "bad" cells.
Most super cheap BMS start to balance only when a cell reaches 4.2?v. If your top voltage is going to be 3.9v/cell, then you need a BMS with configurable balancing function.
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#5
For those that like to charge their packs right up to the top - balancing becomes critical because some may be at 4.1v while others are at 4.2v and the 4.2v packs can be pushed over into 4.3v kind of thing as the 4.1v continue to charge up to 4.2v. A closely balanced battery becomes more critical if you insist on 'max charge'.

On a different note - I have read many times that a properly balanced pack will make it 'more efficient' and 'have more power'? But maybe all folks mean by that is that a finely balanced battery can be charge higher etc. Do you folks know what people are thinking of when they say things like this?

Experience so far... using Batrium... I have 42packs and after a bit of adjustment (adding a few cells to weak ones) they are running 30mv-70mv max difference thru the daily charge/discharge cycle with no balancing for several months at a time. My system's hi is 4.03v/cell and low is 3.46v/cell. So it looks like a finely tuned battery does not need constant balancing BUT its nice to be able to balance them as they age or when doing maintenance to add/adjust packs. Batrium works really well for 'day 2' operations as a resource to identify things that need maintenance and then adjust things when adding new packs etc. I hope to have this battery for 10-15years... to get my money back! so long term is a key part of my thinking.
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#6
(08-10-2019, 12:38 AM)OffGridInTheCity Wrote: On a different note - I have read many times that a properly balanced pack will make it 'more efficient' and 'have more power'? But maybe all folks mean by that is that a finely balanced battery can be charge higher etc. Do you folks know what people are thinking of when they say things like this?

I would imagine this means that there isn't a lot of power wasted trying to bring the high pack(s) down. So you take 100% of your solar (or other alt energy) and dump into your batteries, and then you can pull out 95+% or so (there's always a little loss in storage/retrieval) instead of 88% or less. (%'s are just estimates and not hard set)

Another way would be, the battery could be fully charged in, for example, 5 hours, so by 2pm or so they are good and topped off. Whereas a battery that needs constant balancing, it might take 8hrs or more to do the job. This equates to lost power, and time. And more importantly, if you have overcast weather, can drastically effect how fast/efficient you can charge the batteries.
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#7
A properly balanced pack gives you more usable capacity.

Or rather, an unbalanced battery reduces the usable capacity, because the BMS will cut off discharge as soon as the lowest cell drops to a little under 3.0v, and also cut off charging when the highest cell reaches a little over 4.2v. (values configurable with a decent BMS)

Also, the cells that repeatedly touch those extremes will over time degrade at a faster rate, possibly exacerbating the problem.
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#8
Thank you all for those answers.
It makes the balancing act/part very clear.

Is this also the reason that your packs must be at the same capacity?
For instance 13 of them are 300A and one is 250A.
If one pack(barrel) is 250A and its full,it will be flooded, so the other packs will never reach there full state?
Or they are all full but because one barrel can not hold more than 250A the others will not increase to 300A?

Or is it more when you reach the depleted state of that 250a pack?
Won't they balance like fluid in barrels? this would be my guess.

I think that i am missing the point on the same capacity per pack, and it is a completely different story.

Thanks in advance.
Still learning English. Learning Li ion and solar technology.

4200 cells in packs Exclamation above 2500mah and 90%soh.
1500 waiting for testing.

Saving for 3 times phoenix inverter 48/3000 230v to gain also 380v
3 chargers?

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
Reply
#9
Its Ah not A.... A = Current and Ah = capacity...

No they wont balance when in series. Only oin paralell.

The reason you top balance is that you dont want them to overcharge. So lets say you got 250 250 and 300 and top balance.

What happens is when you drain you will end up with 0 0 and 50.. But when charged up again all is full.
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#10
If barrels = cells

The bypass voltage equals a hole drilled into the side of the barrel (at the point you deem it to be full)

If you dont slow down the rate of filling the barrel, at the point when it starts spilling fluid via the hole, you'll be wasting fluid (energy) and risking an over filled barrel.
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