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21700 comparison: constant current/power, and flashlights

toobadorz

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Here I would like to share with you my experiment results, most likely the 21700 cell discharge curves with constant current, constant power, and their performance on different flashlights. This should give you some clear idea regarding which cell to use under which circumstances.

More than half of the tested 21700's are Samsung ones, so for each discharge configuration, I make a single plot for the Samsung 21700's and another plot for the selected Samsung ones vs. the other brands. For the 20A and 60W discharge, since they are way too high for most of the cells, a single plot is enough.

Note that:
  • Samsung has revisions to existing cell models, and sometimes a new version can perform noticeably better. For example, a 50E version 2 (=50E2) performs much better than the first version, while the 50E version 3 (=50E3) performs similarly to the version 2. So here I include the old 50E and 48G, for your comparison with the newer 50E3 and 48G2.
  • The 40T version 2 (=40T2) also exists, but I see no difference when comparing it with the 40T version 1, so here I only put the 40T version 1 curves.
  • 48X is known as a specially upgraded version of 48G. It has a pretty long cycle life and performs better than 48G. But note that I only tested the 48X version 2 (=48X2), and I don't know the difference between version 1 and 2. A snapshot of the official document:48X.png
  • 50S is the most powerful high capacity 21700 known right now (2020/12). It is rated as 20A continuous discharge (without temperature cut), 35A non-continuous discharge (with 80℃ temperature cut).
  • Although that Tesla 21700 is made by Panasonic and its performance seems reasonably good, I personally won't recommend it, because its positive end is usually made of aluminum, not quite robust, and is recessed. So an additional top will usually be soldered on to such a cell with laser by some 3rd party, to make it useable in flashlight and be able to be sold in the retail market. But that introduces some risks: the cell is thus more vulnerable to shock/heat/etc and may be prone to leak. A few pictures demonstrating the leakage (they are shared by someone else): [1] [2] [3]
  • I didn't include some cell models like MuRata/Sony US21700VTC6A, LG INR21700 M50L, etc, maybe I'll do that in the future...

Here are my discharge curves:

10A

S10A.png
T10A.png

15A

S15A.png
T15A.png

20A

T20A.png

20W

S20W.png
T20W.png

30W

S30W.png
T30W.png

40W

S40W.png
T40W.png

50W

S50W.png
T50W.png

60W

T60W.png

Here are the performance comparisons of some selected cells, on some flashlights. It may be a bit difficult to correlate the discharge curves of a cell with its real performance in a flashlight, and that's why I conduct these tests.

The steps I did to obtain these curves for each cell model:
  • Put a fully charged cell into the flashlight, and switch to the maximum output of that flashlight. A fan is on to provide additional cooling and extended turbo runtime.
  • Switch off the flashlight once the thermal step-down behavior is observed.
  • Cool the flashlight for quite a while, until it's fully cooled. Then switch to the maximum output of that flashlight again. That's why there are many "spikes" in the curves. Note that the flashlight can also step-down due to low voltage, that's why you see some "stages" in the curves.
  • When the flashlight shows a low voltage warning, switch to the next highest output level, and so on.
So such kind of curve is essentially the most demanding situation you can have on a flashlight, and the flashlight output curves with different cells in this situation can greatly help you decide which cell to use.

EC65TURBO-35HI.png
EC65TURBO-NICHIA.png
T36TURBO.png

For these regulated ACEBEAM flashlights, its output can be maintained as long as the temperature limit is not exceeded and the cell voltage is high enough.

That bundled ACEBEAM 21700 performs poorly because it's made from LG M50 or M50T (much weaker than most of the other choices, as seen in my discharge curves), and the protection circuit introduces also more resistance, making it even worse. This is also the situation commonly encountered with a branded/bundled 21700 with a protection circuit. They are usually made from one of the worse cells but rather expensive.

XT45TURBO.png
NS03TURBO.png

These two flashlights utilize FET (direct-driven) in their turbo. In this situation, a cell performs well as long as it can hold high voltage for some short period (i.e., non-continuous discharge). Actually the newer high capacity Samsung cells (50S/48X2/50G2/50E3, etc, not all tested here) all perform well in such a situation, their output is usually close to 30T/40T in a short period, as long as the current drawn is not horribly high.


That's all, thanks for reading.
 
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Flummi

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Vielen Dank für das Bereitstellen Deiner Messungen! Super! :daumenhoch:
Sieht so aus, als sei die Samsung 50S der neue (Allround-) Leistungsträger.

...aber derzeit noch schwer zu bekommen. Darf ich nach Deiner Quelle fragen?
 
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toobadorz

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29 Juli 2016
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Acebeam
Vielen Dank für das Bereitstellen Deiner Messungen! Super! :daumenhoch:
Sieht so aus, als sei die Samsung 50S der neue (Allround-) Leistungsträger.

...aber derzeit noch schwer zu bekommen. Darf ich nach Deiner Quelle fragen?
Sure. After learning the existence of this 50S cell (from some friend who works in a related industry), I kept my eye on it and asked vendors like Vapcell and EVVA several times, about once per week, so in the end I was able to purchase some pieces from Vapcell two months ago, before their limited units (only few boxes I think) were all sold out. Mine are the very first batch Vapcell got and they are not re-wrapped as T50... Vapcell easily got that batch sold out before even re-wrappingo_O

(Sorry I can only reply in English, I know very little about German and I use the Google Translate to read the posts)
 

Flummi

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Dankeschön. 21700er sind noch spannend, da tut sich noch etwas, wie die 50S es zeigen. 18650er haben wohl ihren Zenit schon vor Jahren erreicht. Ich bin mal gespannt, wann es die 50S bei unseren bekannten Anbietern zu erwerben gibt.
 
  • Danke
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ayoto

Flashaholic
12 Januar 2020
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Ich habe mir vor paar Wochen 2 Stück T50 bestellt, eigentlich nur für die Convoy M21B mit einer SST-40 und für die NS43 mit drei SST-40 (nicht Turbobetrieb geplant), damit ich auf dem Fahrrad eine längere Ausdauer habe. Leider scheint Vapcell die noch nicht losgeschickt zu haben. :S

Allerdings scheint sie sich auch für stärkere Lampen wie eine Fireflies E07, oder vielleicht sogar für eine FW21 pro zu eignen. Wobei wir da über 50 Watt im Turbo sind.

Bisher war für mich der P42 der beste Akku, vor allem in Hinblick auf die Laufzeiten im Vergleich zur etwas geringeren Helligkeit bei voller Spannung. Wobei nebenbei der Vorteil entsteht, dass die etwas geringe Helligkeit durch weniger Hitze länger gehalten wird. Aber irgendwann möchte man auch mal / immer wieder die volle Leistung abrufen. :flooder:

Heute mit einem 30T (in FW21 pro) gemerkt, dass mit abnehmenden Füllstand dann relativ schnell die Turbohelligkeit abnimmt, für den kleinen Vorteil der etwas höheren Helligkeit mit vollem Akku. Ein paar Tage vorher war ich mit dem 40T in der FW21 pro unterwegs, da ist auch später noch eine recht gute Helligkeit im Turbo rausgekommen - was mit den tollen Messungen hier bestätigt wird. :thumbup:


@toobadorz thank you very much for your many efforts and that you publish your results here. You don't often find such good information.

I have so far mainly Molicell P42 in use and have ordered the Vapcell T50. As I consider the first and now the second have the best balance between brightness when the battery is full, power when the voltage drops and total burn time.

Thanks for your test results.

Something great @andreas0401 does with his reviews of flashlights, for example the Astrolux EC03, where he tests the lumens that still come out at the respective state of charge of the battery.
 
  • Danke
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