This is my first post and about my second flashlight. I bought my first without knowing anything about high power LED flashlights. It was an Ultrafire zoomie, but after reading BLF a lot I quickly learned that the Convoy series provides much better quality while remaining firmly in the budget territory. So I bought a Convoy S8 Cree XM-L2 U2-1A AMC7135*8 and I love it. It is a well built light. Worlds lie between *fire and Convoy. I ordered it with 8 of the 7135 chips, fully knowing that the small EDC form factor will have a hard time with heat. This is what I want to talk about in this post.
The S8 has excellent thermal transfer, the heat sinks get warm almost instantly after switching to high. After 10 minutes the fins are too hot to touch, but the tail half of the flashlight is only warm and still comfortable to hold. I haven’t tried running it on high beyond 10 minutes as I’m not sure what would happen and would like to hear some voices form more experienced members first.
- Safety first: I realize that a lot of the “venting with flame” fear is probably overdone, and also that dangerous situations are almost always a result of overcharging, but nonetheless: Is there a reasonable chance that the heat produced by the LED will overheat the cell and cause a lithium fire? Would the solder joints desolder themselves first and naturally shut the light down? I use Panasonic NCR18650B 3400mAh with protection circuit from FastTech, so the flashlight would run for more than 10 minutes on high if I would let it.
- What other dangers are there if this light it put on high and forgotten about? I’m guessing it might start a fire if the burning hot aluminium host touches something easily flammable. I have yet to really measure the actual heat sink temperature though and yet to decide whether I want to test-run it beyond 10 minutes.
I am fully aware that running with this heat will reduce the lifetime of the emitter. I am fine with that, a new one is just a couple bucks. Will it permanently reduce brightness of the emitter or is the emitter the same amount of lumens until it dies? I don’t mean the reduction in brightness while running at higher temperatures, this part is clear from the CREE specification PDFs. I mean if the emitter will be dimmer even from a cold start if it is driven to great heat frequently?
I’m a software engineer and I have the USB programmer for the Atmel chip on the nanjg 105c and the SOIC clip already ordered. I am currently considering writing a custom firmware (or rather stand on the shoulders of giants and just modify the open source ones that are out there) that provides a safety switch off or switch down for overdriven EDCs with not enough heat sinks on them. Unfortunately the Atmel chip on the nanjg 105c does not have an internal temperatue sensor, so it would have to be purely time based, eg after 10 minutes on high the light would automatically switch to low. If the user then decides that temperature is under control (for example in winter when outside) a single quick tap would return the light to high output mode.
Many of us have asked these questions , and have decided to order lots of flashlights in case we burn a few up .
Seriously , though , a fantastically bright , supremely efficient new emitter is always just around the corner , so even if you reduce the life of an LED , you will probably replace it with a better emitter before it is noticeably dimmer .
As far as my experience goes with over heating leds its all been without a direct thermal path, ie regular aluminum mpcb’s and yes once they hit the temperature that the solder melts, thats pretty much what happens, the led comes off the mpcb. That said it hasn’t happend very often, and there is a risk of shorting when it melts, and I have no experience with shorted nanjg’s.
I have had one LED desolder itself (more accurate: the leads fell off the PCB, because the lead-based solder has a lower melting temperature than the lead-free solder used by manufacturers) but it had almost no heatsinking at all.
My UF980L is direct drive on high, so about 4.5A amps. After ~20minutes it got dimmer but was too hot to touch. Didnt burn anything though, so I dont mind. It takes a lot more to burn wood or similar than it takes to "burn" your skin.
But I have a rather tiny 18650 flashlight (Xeno S3A) with a 3.4A driver in it. Its made by DrJones and steps down from 100% to 40% after 2minutes, and thats about perfect. It gets too hot to touch the head in about a minute but you can still hold the tail. Running more than 2minutes on high would hurt.
Unfortunately I still haven’t received my USB programmer because the current shipping delays due to the Lithium-ion postal crack down, so I couldn’t start coding yet. Most of the responses in this thread seem to conclude that something else would fail before the cell is in danger so there might not be a point to my idea anyway. That may very well be true, but I’m not entirely convinced yet. I run my flashlight on protected Panasonic NCR18650Bs. Part of the warning on the cell reads “DO NOT HEAT ABOVE 212F, OR SHORT CIRCUIT”. That is exactly 100C, so a very round number and probably(?) chosen by the manufacturer to be a safe distance from where the cell would really start to be in trouble. Anybody have any hard data about Lithium-ions and heat? Whenever you heard about problems it is either due to a punctured or an overcharged unprotected cell, but I haven’t heard about heat problem yet.
I did some more testing with my Convoy S8 AMC7135*8 on high mode, tailstanding ceiling bounce. I took a Bosch PTD1 IR Thermometer and measured every minute at the heat transfer fins of the S8. This was meant to be a rough test and as such the environment wasn’t controlled, just a regular room and my measurement point most likely moved several millimeters each time, but was always somewhere in the middle of the fins.
00:00 33.0C (Flashlight was warmed up from holding it in hand)
01:00 41.5C
02:00 44.2C
03:00 51.2C
04:00 52.9C
05:00 54.7C
06:00 59.2C
07:00 61.4C
08:00 61.1C
09:00 64.0C
10:00 66.7C
11:00 66.5C
12:00 68.8C
13:00 69.5C
14:00 71.6C
15:00 72.4C
16:00 72.5C
17:00 73.7C (Test aborted because the S8 could not tailstand anymore)
The funny thing is that I had to abort the test because the S8 just fell over. The silicone switch had expanded and the S8 could not tailstand anymore. I took a pair of oven gloves and took the battery out and measured 63.2C on the middle of the cell pointing the thermometer where the warning text about 100C is written. Toughts?
I only have my knowledge from using these lights. As others have already pointed out, after a while you will have backups :-) so I rarely try to measure temperatures.
However I have a Sipik SK68 from about 2008 . I have used IMR cells in that nearly always. And that little bugger can get hot like nothing else I own. Literally too hot to handle. I used it for a work light for more than 3 years before changing it to a 18650 based light. And given the rather ridiculous low runtime on 14500 IMR's I had 4 cells with me every morning going to work. 1 in the light and 3 in a case + a ordinary AA. It is not often that I have resorted to the ordinary AA but it has happened at least a half dozen times. And I always recharged at least 2 cells every day. That gives someting like 35 minutes a day in average for about 500 days (I am a sailor doing 1/1 rotation so I get half my life on board and half my life at home). Or roughly 280 hours. And that little bugger is still working as bright as the day I got it! At least as far as I can tell by eye. And it has been tailstanding for a full battery to be come depleted several times in a row, inside a boiler firing chamber that is about 60°C when we enter. We wear gloves when going in there so changing batteries did not hurt me.
Now the tail switch is gone bad in that one so it flickers. But the led and driver are fine. So I relax about these things. In fact I never think about them other than when I burn myself on a light. Or answering this thread. Which made me think a good bit about it.
Hi - just an fyi, I'm a software engineer too and though I programmed many micros over the years, I preferred to use the excellent starting point Dr Jones provided - the source code for luxdrv. I've been programming drivers for almost a year now -- the USB programmer from Fasttech works great.
Be careful with those protected Panasonic's from FastTech - the protection circuit is an unknown and has failed for at least one user - The KeepPower circuit boards are superior from all the reviews and experiences I've read up on.
Another option would be to use another controller with built in temperature sensor or so like tiny85…
Maybe you have to bend the legs a bit because they are wider soics but if you are really concerned it could work.
Has anyone tried to put a lion cell in an oven and test what happens if it will get really hot…that would be interesting
The Tiny25 is available in the narrow SO-8 package and has a temp sensor. Beware of some slight register differences with the Tiny13… particularly in the ADC setup registers for selecting the badgap reference…
