50C capable 18650s or 21700s - do they exist?

325addict

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I have a discussion with someone on the Makita Facebook group: he argues a li-ion cell like an 18650 or 21700 can easily supply 50C. He tells me I don't understand ANYTHING from batteries at all, because I tell him you won't find such a cell. Now who is right: the guy telling me 50C capable 18650s and/or 21700s do exist, or am I right?

Let's assume he is right: a BL1860B battery contains 10 cells 18650 in 5S/2P configuration. Each cell has a capacity of 3Ah, which means each cell could supply 150 Amps(!)
But, because there are two cells in parallel each time, the total battery will be able to supply 300 Amps.
This means, an 18V battery equipped with these cells would be able to supply 5400 Watts.

Now some known facts from another Makita battery, also consisting of 10 pieces 18650s: this one is able to supply, if I remember correctly, 1150 Watts. This one features "third generation cells" or whatever marketing threw at it, and seems to have BETTER cells than used in the above mentioned BL1860B. This one is a 36V / 2.5Ah battery. Same 90Wh capacity.

Now the questions:

1. Do 50C capable 18650s or 21700s indeed exist? And by that, I mean the CONTINUOUS current, not what they may be able to deliver 0.5 second or so.
2. Can anyone point me out to a datasheet of such a battery?

It would be too good to be true if someone finds those cells. But IF someone finds them, I stand corrected!!
 
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bigburly912

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I don't know what you all are talking about. I use them to power my flux capacitor and have since 1985.
 

john61ct

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Do the math.

First off rated capacity is calculated at very low current to get a bigger number

Take off like 20-30% if mAh capacity maxing out the C-rate

So trying to go so high a rate even if it did shpply that rate, there is only 30-40sec worth of energy to supply.

Plus voltage sag would get down to below 3Vpc within the first couple seconds, ESIR would shoot through the roof most of the energy going to wasted and stressful heat generation.

Which in turn that rate would murder cycle lifespan anyway.

So even if you could, would be stupid to try.
 

orbital

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The highest quality Lithium Polymer batteries can do 50C easily, even at 6S voltage (25V)

..I do know that's not your question though.
 

Hooked on Fenix

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I've seen 21700s that are rated 35 amps (45 amps without temperature cutoff). Close to 50 amps, not 50C which would be 4-5 times higher.
 

turbodog

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I don't have to time to look at datasheets, but will point out the following:

1. 50C means discharge in 1.2 minutes, not counting depressed capacity due to massive current
2. 1.2 minutes means massive heat & cell venting
3. 50C means huge voltage drop
4. 50C may be possible for a brief time (like 5 seconds), but due to safety concerns you will not find it in published specs
5. published specs reflect safe charge/discharge data
6. 50C would _probably_ generate enough heat to melt the cell's negative casing, positive terminal, and all separators & insulation
 

turbodog

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The highest quality Lithium Polymer batteries can do 50C easily, even at 6S voltage (25V)

..I do know that's not your question though.


Allow me to post off topic reply to your off topic post...

I feel that lipo cells are like nuclear power. We developed it BEFORE we figured out how to make it safe!
 

sbj

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One of the strongest cells known to me Sony VTC5a is specified with 14C constant discharge current. But even at 12C (= 30A) it heats up to just under 80 degrees, which is the maximum permitted temperature. The maximum possible continuous current with LiIo batteries seems to be in this range.

https://lygte-info.dk/review/batteries2012/Sony%20US18650VTC5A%202600mAh%20(Green)%20UK.html
 

orbital

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Allow me to post off topic reply to your off topic post...

I feel that lipo cells are like nuclear power. We developed it BEFORE we figured out how to make it safe!

+

I have lots of them in different voltages & have used them very hard for 8 years now = Never had an issue in any way.
Just use the balance lead to make sure all cells are rather close in voltage when charging.

What brand are you using turbodog???
 

orbital

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Also, I store mine 'balanced' at approx. 3.8V each cell (not on any silly trickle charge, that will ruin them) no bag or anything like that.

..my Li-Ions' I just keep ready at full voltage.
 
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