Single cell 18650, 3500 mAh, can it last at least 2 hours hike?

Wawona · Jan 29, 2020

Hi,

Searching results show some similar post How long does a 18650 battery last? The answers are quite technical. Here I am looking for more practical answers. I need the light to last for 1 to 2 hours to complete a hike/walk/run in the evening (it's dark at 5pm in winter!). My main focus is safety (finish the hike and not having the flashlight burning because of mis-use or crappy battery)

I buy on eBay. The flashlight ($5, uses 1x 18650 cell) or headlamp ($10, uses 2x 18650). There is a choice of LED type T6, L2, V6. The product description says light power can be set on bright, medium, low, blinking.

Let's take an example:

battery Samsung INR-18650-35E, 3500mAh
flashlight using one 18650 cell
one LED of type L2

Question 1: How long the light would last on "brightest position"? And how long on the "dimmer" position?

Question 2: Does the energy consumption vary significantly depending on the type of LED? For example, would a V6 LED exhaust the battery faster than a T6?

Question 3: Let's assume I use the light until the battery doesn't have enough energy to give a strong enough light. Would that kill the battery? I have heard we should avoid to let the voltage to drop to too low on a Li-Ion battery. Hope that the battery will not be too dead because those are pretty expensive. I do have a good charger though (Nitecore new i2).

Thanks in advance for any help.

lightfooted · Jan 30, 2020

Hmmm, let me focus first on question 3: Assuming your light does not have built in low voltage protection and the cell itself has no protection circuit then yes, it could potentially kill the cell. Especially if the LED is directly connected to the cell and no control circuitry is used. If there is more than one output level (and it's not using simple resistors to obtain those levels) usually that means there is some kind of circuitry in between which will usually require some amount of power to function and thus provide a marginal cut off which may or may not be above the 2.6-2.8 volt threshold considered safe for most Li-Ion cells.

Understand, doing this once won't necessarily kill the cell but it will diminish it's life even if only a small amount. Repeatedly doing this is what causes the problems and can lead to a "vent with flame" situation. Most quality cells will simply not hold a decent charge after repeated abuse however since it is abuse the cell was not designed to tolerate...anything can happen. The catch is that most charging systems are not designed to charge a cell below this threshold and so you will simply be unable to restore it to a usable charge.

As for cost...well I haven't found quality Li-Ion cells to be all that expensive. Unprotected IMR or INR chemistry cells can be had for less than $10 USD each from many sources. Protected cells aren't much more expensive except if you buy branded ones from any of the larger flashlight manufacturers. Even then they generally come warrantied from the seller (i.e. Olight, Surefire, Klarus) and you could likely get some compensation if there is a failure of the cell.

Personally I have both kinds as I still have many of the cells I first bought when I started getting more into this hobby. I now know better and am more comfortable with the use of these cells and have upgraded to unprotected cells as I do prefer not having the additional failure point along with the internals of the lights themselves. All of the lights I use them in have their own protection built into the control circuitry. I also have the equipment to check these cells regularly to ensure that they are in fact still "safe".

lightfooted · Jan 30, 2020

Question 2: Yes. V6 is a bin designation for the latest XP-L from Cree I believe and you certainly can look it up on their website to find the official specs, most of them can and often are, driven out of spec to obtain "Lumen War" numbers...or at least the appearance of them. However it is more or less the reverse of what you think.

The older LEDs tend to draw more current from the power source and deliver less output than their newer siblings. The goal is to achieve more lumens for less power. This is what the LED manufacturers are striving for, not just super-luminescence of stellar proportions. The V6 led is roughly 20% (or so) more efficient in use than the older T6. However the T6 is also a different package too (slightly larger) so I'm not sure a direct comparison is entirely fair. With older LEDs there is usually an even greater difference in operational requirements.

lightfooted · Jan 30, 2020

Question 1: Without having the lights to measure how much current is being drawn from the battery in each mode, it's not something we can know. While one would normally expect that the lower output is using less power, in some flashlights of questionable manufacture I have seen reports of the lower modes being less efficient due to the method of controlling the power. It should at least last noticeably longer on the "dimmer' position.

Generally, you can make an assumption of roughly one hour for every one amp of charge in the cell. Most LEDs are capable of being driven at that in at least one mode. For some they produce around 400 lumens for that amount of power...but it's not a guarantee. Older ones will produce significantly less.

peter yetman · Jan 30, 2020

There's no definative answer to Question #1, unless you know how much current the light is drawing. You can find this out by using a DMM.
Let's assume that on high the thing is drawing 3 amps. The formula to use is battery capacity/draw)0.8 = runtime in minutes
So (3500/3000)0.8= 56mins

Bearing in mind that you are using a cheap cell that probably has its capacity overrated (they all do, usless you buy carefully) this is optimistic.

You say your main focus is safety. To achieve this you need to spend a bit more money and buy a light and cell from a reputable manufacturer and source.
A cheap light and cell WILL let you down, at least. And at worse, may cause damage by overheating. I wouldn't put one in my pocket.
If you want to find something safer than the one that you have go to the "Recommend me a light" area on here and fill in the form to get some suggestions.
https://www.candlepowerforums.com/vb/forumdisplay.php?135-Recommend-Me-a-Light-For

Sorry if I sound grumpy, but a cheap light is a false economy.
P

Wawona · Jan 30, 2020

lightfooted said:
Hmmm, let me focus first on question 3: Assuming your light does not have built in low voltage protection and the cell itself has no protection circuit then yes, it could potentially kill the cell. Especially if the LED is directly connected to the cell and no control circuitry is used. If there is more than one output level (and it's not using simple resistors to obtain those levels) usually that means there is some kind of circuitry in between which will usually require some amount of power to function and thus provide a marginal cut off which may or may not be above the 2.6-2.8 volt threshold considered safe for most Li-Ion cells.

Understand, doing this once won't necessarily kill the cell but it will diminish it's life even if only a small amount. Repeatedly doing this is what causes the problems and can lead to a "vent with flame" situation. Most quality cells will simply not hold a decent charge after repeated abuse however since it is abuse the cell was not designed to tolerate...anything can happen. The catch is that most charging systems are not designed to charge a cell below this threshold and so you will simply be unable to restore it to a usable charge.

As for cost...well I haven't found quality Li-Ion cells to be all that expensive. Unprotected IMR or INR chemistry cells can be had for less than $10 USD each from many sources. Protected cells aren't much more expensive except if you buy branded ones from any of the larger flashlight manufacturers. Even then they generally come warrantied from the seller (i.e. Olight, Surefire, Klarus) and you could likely get some compensation if there is a failure of the cell.

Personally I have both kinds as I still have many of the cells I first bought when I started getting more into this hobby. I now know better and am more comfortable with the use of these cells and have upgraded to unprotected cells as I do prefer not having the additional failure point along with the internals of the lights themselves. All of the lights I use them in have their own protection built into the control circuitry. I also have the equipment to check these cells regularly to ensure that they are in fact still "safe".

I don't know if it is allowed to post the eBay link in thins forum so you can see how the product looks like. I hope a screenshot is OK: https://imgur.com/958i5FK

This headlamp looks pretty modern. I hope it has the smart electronics to protect the batteries, although I have no idea how to assess this. Maybe common sense. This product seems to be wide spread, I see it on many online stores. If it is of bad quality as to killing the batteries cells, it would be anti-economic to the seller because of the refund.

Can you please give more details about "the equipment to check these cells regularly to ensure that they are in fact still "safe"" ? What is it called, brand name?

Wawona · Jan 30, 2020

peter yetman said:
There's no definative answer to Question #1, unless you know how much current the light is drawing. You can find this out by using a DMM.
Let's assume that on high the thing is drawing 3 amps. The formula to use is battery capacity/draw)0.8 = runtime in minutes
So (3500/3000)0.8= 56mins

Bearing in mind that you are using a cheap cell that probably has its capacity overrated (they all do, usless you buy carefully) this is optimistic.

I was hoping that Samsung INR-18650-35E, 3500mAh would be a good cell. Can you please recommend some brands and model? From the few readings Ive found it was said that IMR and INR chemistry are better suited for flashlight. That why I was just assuming Samsung and INR ans 3500 mAh is good.

Thanks for the formula. What is complicate is to find out the amperage that the LED is operating. I just though that the electronics and LED of the flashlights are all similar. So having an idea of the experience of regular users would give me an idea of what I am going to have. For example if they won't last more than 1 hour, then I would bring backup battery or a backup light.

Oups, made beginners mistake of ordering flashlight + headlamp on eBay. And yet I had review quite a few models to settle on those which seem of better quality. For now it's a $20 lesson. But let's hope that they will work OK. I won't gamble on the 18650 cells however. Will buy brand name.

peter yetman · Jan 30, 2020

As long as they are genuine, the Samsung's are Ok.
P

Wawona · Jan 30, 2020

Got answer to my question 3 via this thread Flashlight with NO low voltage protection

lightfooted · Jan 30, 2020

The reason I referred to "equipment" as such is because you can use a separate multi-meter to measure the voltage of each individual cell or you can buy a charger that has the ability built into it to measure the voltage of each cell. Some flashlights are also capable of measuring the voltage of the cell inside it. There are many ways you could accomplish the same thing all using different types of equipment, hence why I said I have a way of doing so rather than giving you the impression it could only be done one way.

Not sure what answer you got in that thread that you didn't get already....but okay.

Wawona · Jan 31, 2020

Thank you for the info about the various way to assess battery voltage.

lightfooted said:
Not sure what answer you got in that thread that you didn't get already....but okay.

From a novice standpoint, ie. zero experience in LED and in battery. Your answer gave a general idea but not clear enough. Just to place you in the context. I would be still using my $2 flashlight with 3 AAA alkaline if I didn't break the battery cage when I replaced the batteries. But then I discovered the modern LEDs and Li-ion batteries when I ordered a cheap replacement. The new LEDs are so much brighter which led me to learn more about why and how to use.

I get the idea of the light, it's function of features and quality. But the battery is more complicate. Making the right choice is one, but the precaution on how to use and maintain Li-ion batteries is new to me. Especially the concept of cut-off voltage below which the battery is harm. From the Flashlight with NO low voltage protection thread, I learn that it is OK to get away without Low Voltage Protection. Because the light will dim to a low level that you would know before it dips into the "danger" low voltage.

In a week or two, when I will receive all the lights & batteries, I will put the knowledge I learn here in practice and experiment to get used to the equipment. BTW by evening time, I hike on safe trails and for short distance. In the worse case when there is no light, it is still OK to get away with moon light.

thermal guy · Feb 1, 2020

Well first there is a big difference between 1 hour and 2 hours. And if you start out with say 300-400 lumens at first will 50-75 lumens be enough light at the 2 hour mark for you?

Single cell 18650, 3500 mAh, can it last at least 2 hours hike?

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