Top Balancing...Do I need to go to 3.650V?

LivingTheDream said:

@MisterSandals do you you think it's worthwhile trying to match these cells?

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MisterSandals said:

Let me back up and reiterate that we want to match based on capacity; putting the lowest capacity cells in one battery and the highest capacity cells in the other.
Other than capacity testing all of your cells individually (which i have never done nor do i have a capacity tester), the next best is to watch which cells run away at charge and discharge extremes.

Batch #1:
Earlier I mentioned "positions 3,4,8 and possibly 6 that are different (lower capacity)."
What cell labels are those now? Those are the lower capacity ones in your first batch.

I have been working on a theory as others have also suggested, that "the lower capacity cells self-discharge faster". Is this reflected in your table above? (i cannot tell where cells 3,4,8 and 6 fall into your new labels). Are they cells C,D,F and H?
From your table it looks like B,C,F and H are the fasted discharge cells.

Please confirm labels and how they relate to original numbers.


Batch #2
Lets try to match those with the lower capacity cells in your second batch (presumable I - P labeled above).
The only data we have are the surface charge dissipations over the periods in your table, correct?

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LivingTheDream said:

The cells that you were eluding to (3,4,8,6) are from the second batch. So they are now labeled K,L,N,P.

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MisterSandals said:

That’s a couple more data points. If these were the low capacity cells, they did not show faster surface charge loss. (Dang for my theory!)

I would keep these 4 together and migrate any other low capacity cells to this group (and high capacity away) as you discover them.

What is your plan?

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DerpsyDoodler said:

Do you expect them to be sitting 5 days in between charge/discharge cycles?

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LivingTheDream said:

No, I'll be hooking them up to 1620w of solar on the RV. From what I can see, I'll need to set the parameters on the charge controller to keep them between 20-90%. At least that's what I think I remember reading.

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smoothJoey said:

You need to charge into the high knee on a regular basis to maintain the top balance.
How regular depends on the cells and the bms balancing capacity.

A charge voltage >=3.45 volts will get your batteries better than 99% full.

I suggest your bandwidth managment target be 99%-15%.

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LivingTheDream said:

Good to know. I thought I remembered hearing that for RV usage, you didn't want to go that high. However, I don't recall at all where I read that on here or who said it.

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