Quote:
Originally Posted by CaptainRivet
Just saw this.
You are sure thats the issue?
Active or passive balancing?
At voltage level did you stop charging daily, 3,55V?
It depends how and when balancing starts with the REC, if done from 3,45 volt on and you go to 3,55 then it might not be enough time but if it done from 3,30V or continous then it should be.
There is a ongoing discussion if a active balance can work properly and eg Dacian, the developer of the electrodacus BMS states it cannot and thats why he implemented a passive one.
If thats right I have not enough experience about that to judge, still learning here....
Interesting article from Eric Bertscher from Nordkyn design when terminating the charge:
https://nordkyndesign.com/charging-m...battery-banks/ |
I see no argument that active balancing can’t be used.
Firstly cell Imbalance is it the end of the world. If you implement cell level monitoring ( and every
lithium system should be cell monitored then all that happens is the charge terminates on the first cell to reach the designated charge cutoff parameters.
Now in most cases cell imbalance where fractional C usage is deployed ( typical of
boats ) you will see imbalances of 5-10 % all this means is you have slightly less energy available then the theocratical Ah number suggests. So your 500Ah system might now be a 475Ah. Given you should have built in some capacity
headroom anyway , big deal , so what.
In my experience cell imbalance tends to remain fairly static over time. So it’s not rust things get progressively worse.
Balancing is sometimes presented as somehow “ drawing off charge “ to reduce the voltage to a balance , this is not right. What ( top) balancing is in fact is diverting charge
current away from the cell that has reached charge stop so as to allow the other cells to continue to charge to their charge stop points.
With active or passive top balancing , therefore you need to have two conditions , (a) the charge
current at the start of balance must be within the allowable range of the balance load. And (b) there has to be enough time to achieve the balance.
So if we have say 25aH imbalance and a 1A balance load , then it will take 25 hours at 1A
charging so the charging process must have this time available. This can be problematic on
boats.
Secondly most top balancing is made nonsense of by the
battery continuing to supply loads while charging , because in many cases ( low capacity mains chargers or falling sunlight ) the load currents exceed the available charge currents and a discharge cycle begins , top balancing is useless here
Active and passive balancers ( in terms of terminology , these terms are used in the
electronics industry to simply mean the load type ) do the same thing they provide a load which diverts charge current away from the out of balance cell either
lost as heat for passive balancers or converted into charge current for active balancers.
The other issue is of course that the
battery charging current at the time of a cell reaching its charge stop point may be to high to engage the balance load. If your charge current is 2A and you balance load can only handle 1A , and you reach a cell charge stop point , you are now forced to stop charging the whole bank irrespective of whether you can balance it or not.
I’m coming to the conclusion that cell based charging is actually the best way to handle
lithium recharging. Ie a dedicated isolated boost converter dedicated to each cell. All 12v nominal charges sources are paralleled into the cell
charger and the BMS has one
charger per cell to control and NO balancing is every necessary as each cell is dealt with individually
I really think the issues we have are largely brought about by trying to shoehorn lithium into a overall charging system designed for a different battery technology entirely.
In my opinion in process passive balancing , ie diverting current from cells charging slower is a travesty of engineering
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