Re: ZebraLight SC600
http://www.panasonic.com/industrial/batteries-oem/oem/lithium-ion.aspx
Small capacity (old) ones are speced at 3V cut-off. Newer ones such as the NCR18650 (2900, in production since 2006) have a 2.5V cut-off.
This is the exact same link as i posted.
If you click on the "technical data" tab in the box at the bottom of the page this takes you to the more detailed pdf file i linked to.
The "specifications" pdf files listed on the first page give no data with regard to low voltage cut-offs.
It's also worth noting that although there have been slight improvements in lithium cell technology over the past few years (mainly doe to new polymer designs) the basic chemistry still stays the same.
As long as it does the way this chemistry reacts at low voltages will stay the same.
I use Panasonic 2900's, and I'm GLAD the cutoff is at 2.7V for me, that's the perfect cutoff point. I'm quite comfortable discharging these cells to 2.5 Volts,
as per the manufacturer. Some people are ridiculous. If I wanted to only discharge to 3 V, I'd just swap the cell more frequently. It doesn't matter if you swap the cell out too soon and recharge more often, at 3.8V or 3.5V or whatever.
George,
We all have our own preferences and experiences and many people disagree with those, to label them as "ridiculous" though is firstly dramatic to the point of being out of proportion and secondly kinda funny :wave:
A couple of things.
1/ It is impossible to judge a torches voltage by it's brightness.
In a lab with an extremely patient and attentive user it MAY be possible to notice a drop in brightness on the old type non step down torches.
Out in the real world though with shades, varying shine distances, reflections etc it's almost impossible.
Add to this the new step down function and it's even more difficult.
I have on occasion noticed my old type SC600 cell drop brightness and have swapped cells, this has only been possible out in the real world around 3 times out of 10 though.
2/ It very much DOES matter if you take Lithium chemistry cell voltages down low, both this and leaving them stored fully charged has a dramatic reduction in their usable life cycles.
This is no secret, cell manufactures, assemblers and users have known about this since they have been bought into production.
But if you're stuck in the middle of no-where; in the dark with no access to a fresh cell, having the ability to use the light beyond 3.0V could be the difference between life and death. Or at least between convenience and inconvenience.
Keep it how it is, George!
Couple more things.
Lithium cells do not have a linear discharge rate, after around 3.7v is reached their discharge rate drops dramatically, the lower the voltage the sharper the discharge rate drops, as shown below.
So although your statement
But if you're stuck in the middle of no-where; in the dark with no access to a fresh cell, having the ability to use the light beyond 3.0V could be the difference between life and death
Is no doubt dramatic it does contain enough artistic license to render it impracticable.
In the real world the run time you get from say 3.3v to 2.7v is seconds.
I'd also suggest that if your using a torch in a "life or death" situation you take along a few spare cells :thumbsup:
I couldn't disagree more with this. First off the data sheet you attached in your previous post was too old (2007). The newer cells, as has been stated, have lower cutoff points.
Please see my response to ZL's post above.
As i said we linked to the exact same page.
Second, as the newer cells age, the voltage drop under high current loads get larger. I have a few slightly older AW 2900's that when pulled at the current levels of even this torch would sag below 3.4 volts when they still have PLENTY of life left in them. On high, I wouldn't be surprised if moving from 2.7 to 3.4 volts cut run time by as much as half on these slightly older cells.
No thanks!
Again please see my response to George above.
Your findings do not corroborate the basic chemistry of the cells nor the findings of thousands of Lithium cell uses, manufacturers or distributors over the last 20 years or so.
To substantiate my claim with regards to discharge rates i would like to recommend (very highly) an extremely through and well carried out test here.
http://lygte-info.dk/info/Batteries18650-2011 UK.html
As i say IMO there is absolutely no doubt that 2 things dramatically reduce the usable cell life of lithium cells.
1/ Storing fully charged
2/ Taking the voltage too low
Panasonic clearly state that they consider anything less that 3v detrimental to the cells life, this at 25c which many of our SC600's have no chance at when in high mode.
So unless you enjoy replacing cells every few years or having them expand in your torches i would recommend upping the cut-off to around 3.3v.
Cheers
Mark