I absolutely agree with top balancing to improve pack capacity.
The smallest cell i’ve ever used is 100ah, the largest is 450ah.
There is no way to determine the SOC imbalance without series charging.
Series charge first, individually top up cells as required. Easiest, fastest, lowest risk method.
The reason people parallel top balance is because they don’t understand how to top up cells in a series pack.
As i said, i have tried and understood both methods - have you?
You talk about large packs, that is where parallel balancing is the worst option!
If you have a 900ah / 48V pack (the largest i’ve assembled), and it is nominally 50% SOC on delivery, how long do you think you’ll be leaving the charger connected?
Also would you recommend leaving tens of thousands of dollars of cells connected to a charge source without a secondary high voltage disconnect in place?
Describe to me a single scenario (ie cell SOC when received) where parallel top balancing will get you to full pack capacity faster than series/individual cell top up.
If you are really in a rush, series charge with a high current active balancer in place.
So. I agree, and disagree. Depending on the individual aspect. You are definitely not wrong on the whole, but I disagree that the issues presented are important enough to go on a crusade against the matter. The issue is you are presenting it as parallel top balancing itself is the problem. Its really not though.
Parallel top balancing is not bad. The only actual issue that can cause damage or a real problem that you are presenting is the chance of overvoltage situation which is a concern, but the method presented doesn't actually eliminate it and might actually make it more likely to occur (bad) while reducing the possible damage to only one cell (good). So... people can do it either way.
The time thing is just an annoyance. Everyone wants faster, but more time wont hurt anything.
Regarding time to parallel top balance, that's a matter of equipment and individual opinion about it being "too long". Taking too long is not itself a "problem", its an annoyance. Get a larger power supply. Or....
Regarding your comment about it being better to series charge then top balance - that's what most of us are doing to skip the wait time. I agree and it works fine. You can still finish it with parallel just the same. However, time taken is an opinion rather than a problem to strictly avoid.
Regarding time spent parallel top balancing
after series charging: if the top-off process takes, say 5 hours per cell, then it will take 20 hours for 4 cells - plus swap time. Unlike the series charge, we aren't saving any time doing them one at a time because the voltage delta is the same and the total power you need to put into it is the same. It also adds time with the disconnect and whatever "extra" time you wait while its sitting there at no current and are away. So once again the "time" argument isn't really a strike against it and your suggestion
increases that time.
Regarding leaving it hooked up without a secondary disconnect - your followup suggestion is to do individual cells and that's the same scenario, but much more work to disconnect and reconnect multiple cells. Insisting on doing them one at a time does nothing to
reduce the odds of power supply failure, but adds time and effort to the process while
increasing the odds of a cheapo power supply biting the dust by introducing more handling to it, and more turning it on and off.
It does however force you to check on it more often, so that's a positive. Not much of an improvement if you are diligent though, but for some this is important.
And at the end of the day your only real reason to avoid it would be solved by having a high voltage disconnect that you can adjust to your preferred cutoff.
Perhaps some enterprising individual will create and sell such a thing with sufficient accuracy to protect the cells, while still remaining fairly inexpensive.
Ideally with just a cheapish voltage monitoring board with a dry contact for the user's choice of higher current relay/contactor. There are a few cheap ones on the market but the accuracy is rather low, usually like +/- 0.1v.
Like this one here.
This can still work of course. You could set it to say 3.55v, and set your power supply there too. Then just the last bit of top balancing would require manual attention. You could likely set it to 3.7v as well, but you still risk just a bit of overvoltage there. However if the power supply has failed it would blow way past that anyways, and 3.7 or 3.8v is way better than 4+
