How closely do cells need capacity matched?

Short_Shot

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Oh and regarding bottom balance, I must have missed that and I do agree there.

Not that anyone should just blindly accept what I agree with as true of course, but that people should read the alternatives and seek to understand before choosing a course of action.

The only problem I have with bottom balancing is the rare situation with used cells where the capacity can vary by enough that you trip the overvoltage protection even with a fairly low series charge voltage. This would get annoying pretty quickly.

I'm actually debating switching to a bottom balance for my camper though since I rarely ever charge it past 13.6v anyways and they're close enough that it shouldn't be a problem. Future usage will dictate that choice later on.
 

toms

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It's the parallel part that he's so hot against doing, and while I understand the reasons why one would want to avoid it and the reasons why one CAN avoid it in certain situations the simple fact remains that some scenarios still require one to achieve top balance as quickly as possible before putting it into service.

His insistence that he personally doesn't need it and therefore nobody else should either is asinine.

My advice is that there are risks involved in assembling your cells multiple times, as well as risks in connecting a cheap charger to multiple cells with no overvolt protection, as well as risks with holding cells high in the voltage knee for extended periods.

Thankfully enough people have actually taken the time to think about what they are trying to achieve, and are getting the results they require without taking unnecessary risks.

Once again, give me one scenario where parallel top balancing is the best way to achieve the end goal.
 

Short_Shot

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Once again, give me one scenario where parallel top balancing is the best way to achieve the end goal.
To get full capacity on the first cycle for testing and warranty purposes, or simply because you want full capacity right out of the gate but that's hardly a pressing concern.

While you're right that good matched cells won't have much imbalance, bulk or used cells often very much do have significant soc imbalance that will have a negative effect on pack capacity until balance is reached.

And I've explained two methods to provide overvolt protection while doing so.
Convenient that you keep ignoring it entirely and continuing to pretend it can't be done though.


Is also been pretty well established that holding the cells at that high knee for one parallel balance cycle isn't going to do squat to the cells on its own unless you're there for weeks or months at a time - and if you're doing so many cells that it takes that long you can probably afford a larger and better power supply anyways, and regardless the time is drastically decreased with a series charge first.

The only remaining point of contention is the multiple assembly thing. Of course you are correct that it's best to minimize mechanical interaction but once together, once apart, and once together isn't exactly high volume opportunities for failure.
 
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toms

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To get full capacity on the first cycle for testing and warranty purposes, or simply because you want full capacity right out of the gate but that's hardly a pressing concern.

This takes a lot longer than topping cells in place after the highest cell has reached HVD. No advantage to parallel top balancing here.

If you want to capacity test your cells then get a capacity tester and do the cells individually. I don’t get how parallel top balancing helps with capacity testing at all.

And I've explained two methods to provide overvolt protection while doing so.
Convenient that you keep ignoring it entirely and continuing to pretend it can't be done though.

Sure you can, same with topping a cell in series configuration. No advantage to parallel top balancing here.

Is also been pretty well established that holding the cells at that high knee for one parallel balance cycle isn't going to do squat to the cells on its own unless you're there for weeks or months at a time.

If you say so. There are many studies showing holding these cells high in the knee voltage promotes dendrite growth. The rebuttal is the studies don’t specifically mention a time frame. If you are comfortable with only damaging your cells a tiny bit then OK. Why do it if there is a better alternative though?

The only remaining point of contention is the multiple assembly thing. Of course you are correct that it's best to minimize mechanical interaction but once together, once apart, and once together isn't exactly high volume opportunities for failure.

Sure, if there was no other way it would be low risk. What we are seeing over and over on these forums is a combination of all the low risks associated with parallel top balancing coming together to destroy a lot of cells.
 
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