noob top balancing - over charged my cells to 4.2v

[Horsefly]

I know that sustained low current charging in the upper knee causes cell degradation - it is well published. As there is no reason to go there - i think it’s a bad idea.

Fair enough. Your position seems honest. I don't even know how to search for these well published papers about this topic. Do you have a couple you can point me to?

Here's the thing. We are probably both right, to a point.

My interpretation of what you were saying was that charging at 3.65V was fine right up until the current dropped to 0.05C, and at that point immediately it was a huge problem. My guess is that it isn't some step function at 0.05C, so I don't think that is what you meant. It's probably a more linear thing. There is probably some harm being caused at 0.06C, and that may even be the same as the harm caused at 0.04C.

I dunno. I don't have a clue. The specs seem to say that cells are rated for 3500 cycles (or whatever) when charged to 3.65V until 0.05C, and then discharged to 2.5V. That's one cycle. I've not seen anything that suggests if you only charge until the current drops to 0.07C you will get 4000 cycles, or that if you charge until you get to 0.03C you will only get 2000 cycles.

I really do want to learn, and appreciate your experience. If you can point me to anything that would help me be smarter, I would be forever thankful!

 

[toms]

Sure, this thread has been taken off topic, i’ll PM you.

 

[Short_Shot]

As has been said many times - parallel top balancing is a bad idea full stop.

Thankfully even on this forum where parallel top balancing has a weird cult following - a lot of people are realising this.

Said by who and for what reason?

Citation needed.

It works fine as long as youre not a doorknob and set the voltage to 3.65 AFTER hooking everything up.

"You'll damage the higher charged cell by holding it at 3.65v".

Fine. Set it to 3.5v first and get everything to the same 3.5v soc for as long as you please, then top it off. The curve is steep enough there to minimize the effects. If holding it there is a problem then many RV power systems are damaging batteries every day by running at 14 to 14.2v

Not perfect enough for you?

If we are using a 50 dollar Chinese power supply we probably aren't that worried about perfection.

I think if you're trying for best case then absolutely go for it.

But if you're just tossing this into a camper then I doubt you'll have significant enough degradation to care. If the difference is 3000 cycles vs 2800 cycles there are other things you can do that'll more than make up the difference, like simply not using 100% capacity.

 

[Gazoo]

It works fine as long as youre not a doorknob and set the voltage to 3.65 AFTER hooking everything up.

Not quite sure if you meant AFTER. The voltage of the power supply is supposed to be set to 3.65 volts before connecting to the cells. If you were referring to something else then you have my apologies.

I think most of us agree if there is any damage it's so small it can't be measured. It only took apx. 4 hours for my eight 280ah cells to finish top balancing once my power supply went into absorb mode and the current started to drop, and I was charging at 12 amps. I think a cell would have to be held at 3.65 volts for a much longer time before damage would be evident.

As far as the variation of SOC goes, Andy from Off-Grid Garage posted a video showing how fast current would pass from a high cell to a low cell. In most cases there isn't a high variation in SOC between the cells from what I have seen, and not enough for current to flow once the cells are connected in parallel, but there is enough variation to justify parallel top balancing.

I had a round with toms before...lol. But as I recall he was agreeable to the fact there is much data missing and the chemistry has improved over the years. He has his methods and I have mine, but I do like the idea of a HVD since we have seen too many people over charge their cells.

 

[Short_Shot]

Not quite sure if you meant AFTER. The voltage of the power supply is supposed to be set to 3.65 volts before connecting to the cells. If you were referring to something else then you have my apologies.

I did mean after. As in "doing it after would make you a dingus", and it should be set before hooking it up.

That would be the incorrect method. Poor wording on my part. Was half asleep.

 

[Gazoo]

I did mean after. As in "doing it after would make you a dingus", and it should be set before hooking it up.

That would be the incorrect method. Poor wording on my part. Was half asleep.

I get it now. Sorry I misread your meaning.

 

[Short_Shot]

I get it now. Sorry I misread your meaning.

Nah that one is on me lol

 

[Smokin]

You Can't Type Yourself Smart
" Jack Rickard"

 

[xNYCMarc]

You Can't Type Yourself Smart
" Jack Rickard"

I bought my first cells from Jack Rickard. RIP Jack. (The grey cells in the picture are the cells I bought from him 6 years ago. I've abused these cells and they are still going strong!)