High power flooders - postmortem

Hi all. A while back I posted a concern that I seemed to be having trouble getting high power LED flooders to work well: Originally, I couldn't get a ThruNite TN36UT to run in turbo mode at all on two different sets of ThruNite 3400mAh cells, and I also got nothing out of a replacement NiWalker MM15MB. Switching to some higher-current cells (a selection from LG, Samsung, Efest and Panasonic - only the last being protected) the MM15MB gave me a run time of about a minute at turbo and twenty minutes on "high" before turning off, which wasn't really what I signed up for. I posted a thread to ask what was up; this is a follow-up.

Having sourced a replacement TN36UT (now I have cells that I'm more confident in), I got about 10 minutes' run time on turbo before the lights went out - still way below the 80-odd minutes reported in some reviews, more so than I'd expect for the difference between a 3400mAh cell and a 2500mAh cell. I also have some TN30s, because I spotted a special offer and thought I may have some 3400mAh cells that might otherwise go wasting. (Recall: I'm trying to portably light dim locations that have white ceilings with a portable uplighter.) They work, but they're much less floody and bright than their big brother.

I finally have news to report: Out of paranoia, I also sourced a new 18650 charger (a D4 from Nitecore) to supplement my Foxnovo F-4 (the non-S version, without the LCD). On the previous thread, NoNotAgain suggested that I check the cell voltages. Which I didn't get around to doing earlier. Silly me, I thought nobody could mess up making a charger...

So I took a set of "fully-charged" (three solid bars) 18650s off my Foxnovo charger and stuck them on the Nitecore one. Which reported 3.58V, one bar of charging progress, and spent a significant additional time pumping them up to somewhere nearer 4.2V.

With the Nitecore's idea of a fully-charged set of cells, I tried my MM15MB again. Turbo ran for at least five minutes, after which (while the power indicator LED had turned red) it was still running and the flashlight was uncomfortable to touch; this is much closer to the behaviour I expected, and I had to go to work before continuing the experiment. I'm reasonably confident of getting a longer run-time out of the TN36UT as well, and might even discover that my ThruNite 18650s are perfectly capable of running these flashlights after all (and don't need to be relegated to the TN30s). I also got some 18650-based fans to point at them, which has proven to me that everything powered by an 18650 is a bit scary (they would double as hair driers) and will hopefully keep at least the TN36UT (which has fins) reasonably cool.

On the plus side, I seem to have solved my lighting problem. Apart from anything else, pointed at a white ceiling, the TN36UT puts out enough illumination that it makes negligible difference to the room illumination whether or not I have the main room ceiling light turned on; scarily, this is also true in my kitchen, which has a set of six pretty reasonable LED spotlights. I've not run them side by side, but the MM15MB is in the same brightness range, with a bit more of a hotspot.

But I did just spend a lot of money over-fixing a problem caused by a $15 charger. So grr. I'll be posting an unfavourable Amazon review.

Sharing the story so others can learn from my mistakes!

Incidentally, one additional use of a flashlight to add to the pile: I cooked some pancakes on Tuesday, and was going to fire up my laptop to do some work, but happened to play with the TN36UT on turbo first. There was a weird swirling to the air that I couldn't see under my normal dim room lights: the area immediately in front of the flashlight looked like a thrower's beam shot. Turns out, I'd mildly burnt the pancakes. I decided not to suck a load of smoke into my laptop's fan, and delayed until the next day. (The same test now shows my room to be a bit dusty, but no longer full of smoke.) So, my TN36UT is now a smoke detector. Which will entirely justify its purchase to my wife, I'm sure...

Thanks again for everyone's assistance. Especially the one bit I didn't listen to!

Glad to hear you got your problem solved. As you learned it's always best to get a good reputable charger such as the Nitecore or Xtar to begin with. I always prefer to get a charger with an lcd screen and voltage read out so I can actually see what the battery is doing vs using a blind charger with just led indicators. It's best to still check the batteries on a DMM every now and then just to verify the charger is accurate.

Also, the cells you have that are unprotected, how many times and how long did you use them for before getting the Nitecore? The reason I ask is because if they weren't being charged fully (4.2v) than there is a good chance they may have been discharged below 3V which is typically considered the lowest safe voltage a lithium battery should be discharged to. I'm sure the lights have a low voltage protection but it's something to keep in my mind.

Thanks, Tac. I'd carelessly assumed that chargers were a known technology (as I hope they are for NiMH cells) and that it wasn't possible to mess one up. I live and learn.

I've only used the cells briefly - although a couple of sets hit the flashlight cut-off. If I can hit 25 minutes of uninterrupted turbo, or a couple of hours on high, I'm happy to swap them out at that point. Both the MM15MB and the TN36UT's internal indicators suggest that the cells were okay after the cut-off, it's just that the drain for turbo instantly tripped them below the monitoring voltage. I'll confirm on the Nitecore charger the next time I run some to the flashlight's cut-off voltage and see where we are, but I'm expecting more than 3V. Worth checking so I know how paranoid to be, though - you're right.

Fluppeteer said:

Thanks, Tac. I'd carelessly assumed that chargers were a known technology (as I hope they are for NiMH cells) and that it wasn't possible to mess one up. I live and learn.

I've only used the cells briefly - although a couple of sets hit the flashlight cut-off. If I can hit 25 minutes of uninterrupted turbo, or a couple of hours on high, I'm happy to swap them out at that point. Both the MM15MB and the TN36UT's internal indicators suggest that the cells were okay after the cut-off, it's just that the drain for turbo instantly tripped them below the monitoring voltage. I'll confirm on the Nitecore charger the next time I run some to the flashlight's cut-off voltage and see where we are, but I'm expecting more than 3V. Worth checking so I know how paranoid to be, though - you're right.

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Sounds like a good plan. I do hope you are planning to use those fans to keep the lights cool while running them at such high levels for so long. If not, the lights won't last long and will more than likely fry the circuitry.

I'd consider a voltmeter an essential piece of kit for multicell lithium flashlights. I always check voltages before I load up.

Rob

Rob: Now I know. I wonder where I put my multimeter?

Tac: The fans were indeed for cooling the lights. Although everything is, I believe, supposed to be thermally regulated. I'm keen not to rely on that more than I have to, anyway. I'd really like someone to make a TN36UT with a CPU fan bolted on the back of the heat sink, sucking air in through the cells and blowing out the sides - it can't pull that much power, and wouldn't add that much to the size. I'm assuming waterproofing isn't a priority in this case, of course. One advantage of the MM15MB is that it'll run with the back off the case - that reduces the heat sink size (though increases the exposed area), but reassures me that the cells aren't cooking. With the TN36UT, they're sealed in the furnace. Even if the thermal regulation was coping, the light would drop off as it throttled back, so I'm motivated to get some airflow. I admit that I hadn't bothered so much for the initial tests, but then I was periodically touching the light (and to an extent using blood flow as liquid cooling, with alternating hands) and ensured it didn't max out. I'd not let it turn on in a bag...

Fluppeteer said:

Rob: Now I know. I wonder where I put my multimeter?

Tac: The fans were indeed for cooling the lights. Although everything is, I believe, supposed to be thermally regulated. I'm keen not to rely on that more than I have to, anyway. I'd really like someone to make a TN36UT with a CPU fan bolted on the back of the heat sink, sucking air in through the cells and blowing out the sides - it can't pull that much power, and wouldn't add that much to the size. I'm assuming waterproofing isn't a priority in this case, of course. One advantage of the MM15MB is that it'll run with the back off the case - that reduces the heat sink size (though increases the exposed area), but reassures me that the cells aren't cooking. With the TN36UT, they're sealed in the furnace. Even if the thermal regulation was coping, the light would drop off as it throttled back, so I'm motivated to get some airflow. I admit that I hadn't bothered so much for the initial tests, but then I was periodically touching the light (and to an extent using blood flow as liquid cooling, with alternating hands) and ensured it didn't max out. I'd not let it turn on in a bag...

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They are thermally regulated but as you said, that just steps down the output. I'm like you in that I would like to see a light with active cooling. Olight appears to actually have that on a prototype light introduced at Shot show, I believe it is the x12.

Fluppeteer said:

Thanks, Tac. I'd carelessly assumed that chargers were a known technology (as I hope they are for NiMH cells) and that it wasn't possible to mess one up. I live and learn.

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Sorry to break the news, but NiMH chargers have problems of their own. CPF member HKJ has done a number of reviews of NiMH chargers. You can search for his reviews to learn which ones are the good ones.

Oh dear. Wouldn't it be nice if we lived in a world where things that aren't that complicated basically worked? (I have a feeling that this route will lead me into ranting about patents, so I'll just subsume that thought into my general grumpiness...)

I thought I'd report back on what happened when I tried running some cells "flat" using my big flooders. I haven't dug out my multimeter, so I'm relying on the Nitecore charger's report on the voltages.

I tried:

My MM15MB, running a set of fully-charged Samsung INR 18650-25R (green) 2500mAhs. I got about an hour of run-time attempting turbo mode, but the light frequently stepped down (and I do mean stepped) to a lower setting (I assume "high") because of thermals. Even with a fan blowing hard right at it, the case got extremely hot, and I couldn't stop it having to throttle down - I guess this is the curse of a small case with no cooling fins. I periodically turned it off to cool (when it was throttled back), then resumed on turbo mode again once it had cooled down. On removal, once the flashlight refused to run with them, the cells were showing 3.57V. I guess that's why I got almost no run time out of my other charger - it was barely taking them above the cut-out voltage. In "high" mode the fan kept the MM15MB very cold to the touch - it was only turbo that overwhelmed it, but it won't toggle back up. I'm tempted to try sticking it in an ice bath and see whether it keeps running or turbo!

My TN36UT, running a set of EEfest IMR 18650 2500mAhs. Again, I got about an hour of run-time on turbo, but without manually toggling things and without the digital stop-down to "high" mode (though it clearly did throttle back). It stayed warm, but possibly not quite as much so as the MM15MB; I guess the larger head and fins helped. On removal, the charger reported 3.03V on one cell and (worryingly) a bit more - around 3.1V - on the others. So I seem to be getting some genuine run time, and it seems that it's pretty much exhausting the cells before dying (hopefully just before getting to the damage stage). I feel slightly better about buying the TN36UT having seen this behaviour, and it should fit my needs, if it doesn't cook the cells too fast. (Both flashlights are extremely effective hand warmers on turbo.)

I've yet to try my 3400mAh Thrunites, but I'll give them a go soon. Fingers crossed they can provide the current after all, if charged sufficiently.

I've no idea whether this information is of news to anyone, but I did the experiment, and figured someone might care about the results.