Are there any 1000 lumen range flashlight, that can properly use 2.5V 18650 battery?

[CuriousOne]

A friend of mine has a large stock of unprotected 18650 batteries, with 2.5V cut-off voltage. So he wants to buy flashlight, which will be able to fully utilize their power and won't cut off at 3 volts. Are there any such flashlights? He's not looking to superfancy flashlight, nor for $5 cheap ebay find. Any ideas?

Thanks in advance!

 

[Woods Walker]

A friend of mine has a large stock of unprotected 18650 batteries, with 2.5V cut-off voltage. So he wants to buy flashlight, which will be able to fully utilize their power and won't cut off at 3 volts. Are there any such flashlights? He's not looking to superfancy flashlight, nor for $5 cheap ebay find. Any ideas?

Thanks in advance!

I think ArmyTek cuts off at 2.6 or 2.7 volts and that's about all I would ever do. 2.5 IMHO is too low even 2.6 is.....

 

[Jose Marin]

I think zebra lights cut off at 2.7, if you have flat tops go with the third generatios and if you have button tops go with second generation

 

[ssanasisredna]

A friend of mine has a large stock of unprotected 18650 batteries, with 2.5V cut-off voltage. So he wants to buy flashlight, which will be able to fully utilize their power and won't cut off at 3 volts. Are there any such flashlights? He's not looking to superfancy flashlight, nor for $5 cheap ebay find. Any ideas?

Thanks in advance!

Just keep in mind you are quibbling over 5-10% of the total capacity of the battery at typical discharge currents. That's within the realm of voltage tolerance + current tolerance of most flashlights and less than the jump from one efficiency bin to the next for most LEDs. Point I am trying to make is get a flashlight you actually want to use. There is little practical reason to pick one based on cut-off voltage. That's not remotely a guarantee of maximum run time.

 

[CuriousOne]

Thanks a lot for the suggestions. Let me clarify initial requirements a bit. Flashlight should provide even brightness and all modes functional, till battery is discharged to 2.5V. (For example, I have Jetbeam KO-01 and when battery is going low, but not too much low, "turbo" mode brightness is visibly decreased) And capacity difference between 2.5V and 3.0V discharge is way more than 10-15%. I've personally discharged NCR18650BE to 3V and it gave about 6Wh, while being discharged to 2.5V, it produced about 9Wh. So 33% is not that small amount of power.

 

[Connor]

Your measurement was likely wrong. Take a look at http://lygte-info.dk/pic/Batteries2...ed)/Sanyo NCR18650GA 3500mAh (Red)-Energy.png for example. The capacity available <3,0 V is very small.

 

[Bucur]

Thanks a lot for the suggestions. Let me clarify initial requirements a bit. Flashlight should provide even brightness and all modes functional, till battery is discharged to 2.5V. (For example, I have Jetbeam KO-01 and when battery is going low, but not too much low, "turbo" mode brightness is visibly decreased) And capacity difference between 2.5V and 3.0V discharge is way more than 10-15%. I've personally discharged NCR18650BE to 3V and it gave about 6Wh, while being discharged to 2.5V, it produced about 9Wh. So 33% is not that small amount of power.

The 33% you are talking about is energy but not necessarily power. It should provide 33% more runtime at a certain current rate but I wonder if this current rate would be satisfactory for the current requirements of the flashlight in question. In order to benefit from the energy that is available between 3 and 2.5V, the flashlight should be contented with quite a low current rate.

 

[CuriousOne]

OK, let's back to topic question. Flashlight model, that can still deliver 1000 lumens from 2.5V..

 

[Bucur]

I don't think that a single 18650 battery can supply enough current @ 2.5V to power a 1000 lumen light for a duration that is worthy of note. In other words, I don't think that such a flashlight exists. What is worthy of note varies from person to person, though.

 

[RoJohn L. Sugg]

I think 1000 lumen light need to be powered by two 18650 batteries, for I have such a flashlight.

 

[Tank007torch]

Even with sepcialboost circuit board, the battery cannot last long. So, do not expect too much for such a flashlight.

 

[CuriousOne]

Being an electronics engineer, I don't see any significant troubles in designing driver circuit, which can power up 10 or 20w led from 2.5V power supply. But instead of building own flashlight, I just asked if someone already makes it.

 

[Bucur]

Being an electronics engineer, I don't see any significant troubles in designing driver circuit, which can power up 10 or 20w led from 2.5V power supply. But instead of building own flashlight, I just asked if someone already makes it.

The problem is, if you try to power this circuit (that drives 10 or 20W LEDs) by means of an 18650 battery at 2.5V; the battery would fail in supplying the necessary power.

 

[Lynx_Arc]

Being an electronics engineer, I don't see any significant troubles in designing driver circuit, which can power up 10 or 20w led from 2.5V power supply. But instead of building own flashlight, I just asked if someone already makes it.

If you are an electronics engineer you should do the math. At 2.5v input you probably have to boost the voltage to 4V or more to get 1000 lumens from an LED which is over 50% more voltage which means a boost circuit that is 100% efficient still has to have 50% more current from the already depleted battery. At 1000 lumens if you go with no heat loss and 200 lumens/watt that still is 5 watts to the LED and that means 5w from the battery with NO losses at all that means 2A.
A good engineer can do the math and find charts on batteries online easily and figure out that a 2A load on a 2.5v 18650 will drop it in voltage a good amount (if not drop it like a dead short) and as voltage drops a boost circuit that can regulate will resist the output drop by drawing more and more current from the battery.

Ideally at 1000 lumens you aren't going to get 200 lumens/watt efficiency from LEDs even 3 of them probably won't see more than perhaps 150 lumens/watt which means you need over 6 watts to get there. Boost circuitry and wiring are going to lose at least 10-15% if not more so that means maybe you need 8 watts from the battery. Most likely the battery will cave under a 3A load now to 2v which makes for the need for 4A load and like a death spiral you end up with the battery dropping to low to sustain any light from the LED other than a dim glow in pitch dark. A non regulated boost circuit would probably get you 100-250 lumens perhaps from a 2.5v battery but even at that runtime would be dimming to sub 100 lumen levels before you know it... nothing to compare to the desired 1000 lumen output.

I'm not an electronics engineer but I only have a measly worthless associates degree in electronics.