Is it true?

Batteries, Chargers, and Battery Management Systems.
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desmond007
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Is it true?

Post by desmond007 » Jul 24, 2017 8:10 am

Hi

As long as I remember about battery charging technology I knew that CC/CV is the safest charging technique for charging Li-ion batteries. Now I suddenly read about this. https://qnovo.com/why-is-charging-with-cccv-bad/
A company named qnovo who built some technology for big guys like Sony, Intel, Qualcomm etc claiming that cccv actually bad and damages the battery and its capacity, cycle life etc.

Are their claims true or false?

Then what other charging methods we can use to charge our packs?

Please tell us your views.

Also, the guys in battery University claim that CC/CV is the only method for charging Li-ion cells. http://batteryuniversity.com/learn/arti ... y_chargers
Of all chargers, the Li-ion charger is the most simplistic. No trickery applies to improve battery performance and longevity. Only the CCCV method works.


About CC/CV method if I'm not wrong (if yes correct me please) first constant current applies to empty cells with lower voltage, then, when it's full about 80% current drops and voltage rises to 4.2v and cuts off, right? Then whats the traffic collision of ions inside batteries they are claiming is all about?

zackclark70
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Re: Is it true?

Post by zackclark70 » Jul 24, 2017 8:13 am

my stupidly expensive rc charger will charge at the set amps until it hits 4.2v then taper off until its 10% of the set amps and stops so its CC then CV cant see what that would harm them

( nowdays i have it set to 4.1v as the last 0.1v is less than 1% of the charge but takes life away from the battery )

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Re: Is it true?

Post by chessir » Jul 24, 2017 9:33 am

I likewise stop at 4.10 since credible literature claims most damage/stress when cells are charged and discharged between 4.1 and above.However, some have suggested very sporadic charge to 4.2 but why I don't know.
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Philaphlous
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Re: Is it true?

Post by Philaphlous » Jul 24, 2017 1:48 pm

The problem with my cc charger is that some cells boost to a higher voltage under the charging current than the rest...this then leads to a premature...bms cutoff and the batteries don't actually top off. My charger pushes around 125w till cutoff and doesn't cut down the current as it gets closer to a full battery. Crappy charger but I guess it pumps energy in and that's about it.

desmond007
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Re: Is it true?

Post by desmond007 » Jul 24, 2017 2:08 pm

Yes, i also will undercharge the battery to 80/90% to prolong life cycle, but my question is does CC/CV actually hurts the battery? If somone undercharge the battery to suppose 90% using CC/CV charger, will it actually damage the cell?

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Re: Is it true?

Post by zackclark70 » Jul 24, 2017 2:15 pm

desmond007 wrote:Yes, i also will undercharge the battery to 80/90% to prolong life cycle, but my question is does CC/CV actually hurts the battery? If somone undercharge the battery to suppose 90% using CC/CV charger, will it actually damage the cell?
cc-cv wont harm a battery its probably the the most effective way of charging to a high soc without risk of damage when you have a higher cell count

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Re: Is it true?

Post by DVDRW » Jul 24, 2017 3:45 pm

And does charging at very low current shortens battery life?
Like 0.04C ~25 hour.

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fechter
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Re: Is it true?

Post by fechter » Jul 24, 2017 4:19 pm

I tried to read the article. If CCCV charging is bad, then what do they think is better? I didn't find that but maybe it's in there with the other irrelevant information. The BS detector was going off in any case. If there was a better way to charge, it would be widely adopted by EV, cell phone and laptop computer companies.
"One test is worth a thousand opinions"

redilast
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Re: Is it true?

Post by redilast » Jul 24, 2017 5:22 pm

fechter wrote:I tried to read the article. If CCCV charging is bad, then what do they think is better? I didn't find that but maybe it's in there with the other irrelevant information. The BS detector was going off in any case. If there was a better way to charge, it would be widely adopted by EV, cell phone and laptop computer companies.
They already do as far as I am aware. Or at least their fast charging algorithms are different than normal CC/CV. Here is the super charging of a Tesla.

Image

And compared to a traditional CC/CV curve:

Image

I didn't read the article yet but as far as I know is the bad thing about CC/CV is during the end of the CC phase when the cell voltage is high and the current is high, it is bad for the cell especially if charging at higher rates like 1C for example. 1C at the end of the CC phase before CV phase transition you are at max current and max voltage at the same time. It's better for the cell to have the current be gradually decreased at around 4v instead of 4.20v. But at low rates like C/10 or C/20 charge rates, CC/CV is probably just fine. At higher rates its bad.

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Re: Is it true?

Post by zackclark70 » Jul 24, 2017 5:37 pm

fechter wrote:I tried to read the article. If CCCV charging is bad, then what do they think is better? I didn't find that but maybe it's in there with the other irrelevant information. The BS detector was going off in any case. If there was a better way to charge, it would be widely adopted by EV, cell phone and laptop computer companies.
There is only a limited amount of ways you can push power into a battery lower current will extend life so fast charging should only be used when needed if you have 6h use a slow charger if you have 1h use a fast charger

i have to say the 20ah amp20 lifepo4 cells i have are awesome i have had them 5 years and they have over 600 cycles of 60% or more DOD and still hold over 18AH at a 2c discharge (All charges were at 1C to 3.5v cc-cv )

i also have a few 5ah 20c lipo bricks with 250+ cycles over 4 years and they still hold 4.5ah at a 4c discharge they sag a bit but they have done well as they have been charged at 2C to 4.1v

to be honest i think we are getting to the point that shelf life will be a bigger problem than cycle life on any good sized battery pack i have 60 mile+ range on my bike so it only gets charged 2 times a week or when i want to do a long ride

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fechter
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Re: Is it true?

Post by fechter » Jul 24, 2017 10:27 pm

OK, I can believe the Tesla guys. But those are some extreme charge rates. I usually charge at around 0.5c or less. I agree what happens to the cells after they've been charged (storage conditions) becomes more important at lower charge rates.

Charging to a lower CV voltage we know is good for calendar life.

I'd love to see some data from this guy's charge profile, but the way the article was written just had BS all over it.
"One test is worth a thousand opinions"

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dogman dan
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Re: Is it true?

Post by dogman dan » Jul 25, 2017 6:32 am

It does make some sense to me to lower the amps above 80% charged. Especially if your charger is jamming like mad below that. Fast as possible quick charge from empty, followed by a slower finish when you park overnight. Makes sense to a dumbass like me.

But bear in mind, I have an ag degree, not EE. I am sure though, that for the prices we like to pay to charge a bicycle, we just get a set amps output till shut off or constant current voltage is reached. I thought it was the battery itself getting full, that caused the observable slow down in amps flowing as the charge gets above 90% full, not the cheap ass king pan charger. I thought Lithium chargers did not do constant current anyway. Don't they just shut off instead? Some will turn on again after a bms drains the high cells, and some just stay shut off till you unplug/ replug.


Am I wrong? Do they switch to CC at the end, before shutoff/ green light?

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fechter
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Re: Is it true?

Post by fechter » Jul 25, 2017 8:20 am

dogman dan wrote:
Am I wrong? Do they switch to CC at the end, before shutoff/ green light?
Normally the charger runs CC until the pack voltage matches the charger voltage. At this point, the current starts to taper down and it's running CV mode until the current gets down to some predetermined set point and the charger shuts off completely.

I can totally believe cells could be damaged by excessive charge current. What's "excessive" depends on a lot of factors.
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dogman dan
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Re: Is it true?

Post by dogman dan » Jul 27, 2017 6:08 am

I had a more simplistic view of it. Back to the old water analogy,,, if you had a bucket full, and a bucket empty, and a hose connecting them at the bottom,, the flow slows down as the levels get closer to the same.

I thought a similar thing went on as the voltages got closer to the same. I thought the lithium chargers, cheap ones anyway, just ran CV till they shut off at green light .

The lead chargers would go to CC when the light turned green.

I guess a cheap kingpan charger is a bit smarter than I thought. So if they do go to CC in the last %, that should help a bms keep up, discharging that high cell at the top of the charge.

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Re: Is it true?

Post by amberwolf » Jul 27, 2017 1:44 pm

dogman dan wrote: So if they do go to CC in the last %, that should help a bms keep up, discharging that high cell at the top of the charge.
"CV" in the last segment. ;)

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