18650. Need help with one simple question.

[Rafael Jimenez]

When you are using your 2x18650 AW 3100 Li-ion flashlight, how do you know when it is time to recharge?

 

[mvyrmnd]

They're protected, so one or both of them will cut out and break the circuit. You'll know they're flat when your light turns off.

 

[moderator007]

You can measure the voltage with a DMM. When one cell reaches 3.5v or below at rest (measured out of the light individually) time to charge. Here's a capacity versus voltage chart for li-ions. This is a general guide for li-ions. They are several of this charts floating around here, but there all quite similiar.

 

[Rafael Jimenez]

What about when the flashlight is in use? If you whait for it to turn off, will it hurt the battery?

 

[Redhans]

Each cell has a protection circuit that kicks when the cell has been drained down to something like 2.8v. At that point, the cells will no longer discharge and you must recharge them. The flashlight itself has a voltage range at which it operates. For a 2x18650 light, I think it would typically be about 2.8-8.4v. The flashlight will turn off when the cells have been drained to this point as well. These values represent the maximum possible drain that can be put on a battery, and the battery will not be damaged by being discharged to 2.8v.

From what I have read here it is not a good idea to purposely engage the protection circuit on the cell, so you will need to determine which has the lower threshold: the power cell or the flashlight. If the flashlight driver cuts off at a voltage higher than the cell protection, then you can use the flashlight until it shuts down without the cell protection circuit kicking in. If the low end of the flashlight driver voltage range is less than the power cell protection circuit voltage cutoff, then it is probably a good idea to stop using your flashlight before it shuts down from the protection circuit kicking in.

Here is an easy scenario: my battery has circuits that kicks in at 2.8v. My 2-cell flashlight operates at 3.0-8.4v. Therefore, my flashlight will shut off before my battery protection circuits do. I can simply run my light until it shuts down without stressing the batteries.

Here is the tough scenario: I own a 1-cell flashlight that operates in the range of 2.8-4.2v. In this light, the protection circuit of my power cell may kick in at 2.8v before the flashlight driver shuts down. In this latter case, I would need to think about when to stop using my light because I do not want to be chronically tripping protection circuits on my cells. I timed this light to burn completely through 1 cell in 60 minutes. From then on, I will only use the power cell in that flashlight for like 57 minutes to avoid the shutdown. One could also measure the voltage with a multimeter periodically and this is probably the easiest way to keep track of this sort of thing.

There are some with far greater experience than I who could probably direct you to a more satisfying answer. I simply share with you information that I have gathered from my own search of this forum.

Redhans

 

[Vesper]

Yea, you shouldn't let your battery drain to the point of your prot circuit kicking in. It's more of a safety net than an indicator that it's time to recharge. Get in the habit of topping off your li-ion cells regularly.

LiIon Battery Charge Status
4.2V – 100%
4.1V – 87%
4.0V – 75%
3.9V – 55%
3.8V – 30%
3.5V – 0%

Try to keep them above 3.8. It's much better for the longevity of your cell.

 

[Rafael Jimenez]

Ok, I will see what happens when I go to low. Maybe there could be a sign in the beam intensity?

With NmHd its easy to know when they are low, because they stop generating heat on high power.

Thanks.

 

[mvyrmnd]

Remember, folks, that the 2.8v cutoff happens while under load. When the circuit is cut, they will return to 3.2V open circuit, which is a perfectly save place to be.

 

[moderator007]

What about when the flashlight is in use? If you whait for it to turn off, will it hurt the battery?

This very thing has happened to me plenty of times. From what I have also read here it's not a good idea to let the pcb kick. But that does depend on a few things like the battery sag at a certain current draw. In a high current draw light the battery will sag in voltage quite a bit. Once the pcb kicks in a high current draw light and you take the battery out and measure the voltage usually the battery will bounce back up in voltage when measured at rest. Should be close to the 3.5 or 3.4v. The pcb voltage is reading the voltage under a load. In a low current draw light the battery would be drained much lower before the pcb kicks. If the the pcb does kick. Charge the battery up as soon as possible, as I have read this can cause irreversible cell damage if left drained for extended amounts of time.
If your using the light for a purpose I wouldn't really worry about it if the light is needed at the time. The more you use it you will learn about what its run time will be. Then you can charge the batteries up knowing their about to go dead. Most lights will begin to dim as the batteries are depleted. This is a good indication they need charged. Measuring with a DMM will let you know how much of the battery capacity you are using like a fuel guage on a car. You wouldn't want to set out on a big trip with 1/4 of tank. So you would natural stop and filler up.

 

[Rafael Jimenez]

Thanks for all this advice, as I am new to Li ion. I will try to notice a dim in the intensity and try to guess when I am close to the normal runtime, and this way avoid going to low.
I have a Xtar charger plus the aw protected 2900 and 3100 mAh. And I am using a Malkoff Wildcat or a Hound dog.

 

[treliving]

Could one of you advise me on a website I can go to to buy the AW 18650 Li batteries. I unfortunatelly bought ultra fires and I am not confident in them at all but I can not find what looks like a honest website to purchase AW's at. Thank you for your help.

 

[TEEJ]

Could one of you advise me on a website I can go to to buy the AW 18650 Li batteries. I unfortunatelly bought ultra fires and I am not confident in them at all but I can not find what looks like a honest website to purchase AW's at. Thank you for your help.

I go to the CPF market place and order them directly from there.

 

[treliving]

Thank you.

 

[treliving]

With regards to the charger its self, will any charger rated for the 18650 batteries do the trick or should I get a higher end charger? Sounds like a silly question but I only ask cause I bought a duel charge charger that does 16340 and 18650 batteries. I bought that one from amazon.com because I have a laser pointer that uses 16340 batteries so I figured 1 charger would be better than one for each type of battery.

 

[Rafael Jimenez]

Thanks.

 

[Rafael Jimenez]

Lighthound.com

 

[Rafael Jimenez]

With regards to the charger its self, will any charger rated for the 18650 batteries do the trick or should I get a higher end charger? Sounds like a silly question but I only ask cause I bought a duel charge charger that does 16340 and 18650 batteries. I bought that one from amazon.com because I have a laser pointer that uses 16340 batteries so I figured 1 charger would be better than one for each type of battery.

Xtar sp2 works great and is not expensive to buy. I only use aw protected 2900 or3100 batteries and they seem to be very good and safe to use.

 

[lwknight]

If you are using 2 18650 you probably will not see a beam intensity change.
You will still have over 5 volts even with depleted batteries.

 

[Rafael Jimenez]

If you are using 2 18650 you probably will not see a beam intensity change.
You will still have over 5 volts even with depleted batteries.

If I don't see a change in beam intensity, then what do I do to avoid over discharging?

Maybe check voltage before every other time I use it? Charge if 3.7 or lower?

 

[march.brown]

If I don't see a change in beam intensity, then what do I do to avoid over discharging?

Maybe check voltage before every other time I use it? Charge if 3.7 or lower?

I try to "guess-timate" when the battery reaches 3.8V so I can top them up (or recharge them) ... I try to mentally work out how long the battery has been in use ... I don't like the idea of the light going out just when I need it to be on ... It is so easy just to check the battery volts and charge the cells up when they drop to your preferred voltage minimum ... I always have two or three good spare 18650's at home ready charged ... I used to use Ultrafire 18650's for the first two or three years of getting into torches and they gave me good service ... I still have a couple as spares , but I'm buying 3100mAh protected Panasonics now as replacements and will standardise on them from now on ... If I get three or four years service out of them then I will be happy ... I won't get as long a battry life as some other users as I don't store them in the fridge at 40% charge ... I personally prefer to have my spares ready to go ... Since I will only have three good spares , I don't mind having to buy more cells every three or four years.

The more you use your torches , the better you get at estimating when to charge the batteries ... By estimating when my batteries are at about 3.8V , I know that I have a bit in hand ... At 3.8V there is still about 40% charge left in the battery ... Always carry a couple of AAA or AA torches as every-day carry (just in case) ... I always carry two ITP A3's (one on each keyring) plus an ITP A2 (clipped in my inside pocket) ... As yet , my 18650 torch has never switched itself off , but it is easier to grab one of the ITP's in the dark than it is to try and put in a spare 18650 battery that you have in your pocket.

Good luck.
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