Teardown and Mod Thread of Courui XML2 Aka "Big Head 3x18650 Side-Switch Thrower"

Ok guys, so just when I thought I’d leave this light aside for a while another package arrived and I had to get stuck in again. Only a small mod this time but it’s probably put the biggest smile on my face so far.

I decided to take a little gamble a while back before I had the light and ordered a 73mm lens from flashlightlens.com thinking if I was lucky it might just fit this light.
This is a multicoated Acrylic (yuck plastic! :P) lens but the specs are pretty damn convincing so I thought I’d give it a go.
I couldn’t find any other glass AR lenses of the right size and was pretty keen to try this type of material and give the coating a closer look. I mean I’ve been wearing AR coated acrylic glasses for years and the coating can take a beating, so how bad can it be.

So anyway I got this lens today and replaced the stock uncoated glass one tonight, thankfully it’s a perfect fit. Being Acrylic a bit of sanding down wouldn’t have been out of the question but it fitted right in…and…all I can say is WOW! This is a very impressive piece of kit, the coating is incredibly anti reflective totally on par with the coating on some very high quality acrylic lenses in my eyeglasses.

Comparing side by side with my other AR coated glass flashlight lenses, one from cnqualitygoods and another in the BTU shocker (different coatings with BTU lens being superior) this acrylic lens puts both to shame. It’s also quite stunning with it’s reddish sheen.

Here cnqualitygoods AR lens in HD2010 (Top) and Bighead Acrylic below. I may have overexposed just a tad but it should be obvious that the Acrylic lens reflects much less of the filament bulbs intensity, the difference is even more apparent in person.

The HD2010 lens isn’t the best AR coating I’ve see but it still puts an uncoated glass lens in it’s place.
The Acrylic lens is really spectacular in this regard, most dimmer light sources just don’t register in the lens at all so it gives a spectacularly unhindered view into the reflector.

With the light on there are clear positives but also one negative point to report.
The biggest benefit I noticed right away with this lens is far less prominent beam artifacts due to internal reflections. The main one that plagued this light is a fairly noticeable ring artefact around the central hotspot just past the fringes of the corona. I figured this might be due to rogue photons bouncing off the uncoated glass lens and that seemed to be the case since the AR coating on this new lens has almost completely removed it. And what little there is left is much softer and really dim so it’s hard to spot now, BIG improvement.

There is also less light spilling out of the sides of the beam close to the reflector, this used to be quite obvious in a bright ring projected at around 120degress all around and now it’s very faint and tinted slightly red.


Note the reddish sidespill compared with the very blue sidespill of the cnqualitygoods lens. Both look pretty cool and distinctive and on the bighead that ring is massively dimmer than it was before.

On the downside.
Looking at the light when it’s on, the lens is very slightly more “milky” than a perfectly clean glass lens. This is probably just the material itself absorbing and scattering a small amount of the light as it passes through but it’s really no worse than the general standard of “clean” glass lenses we tend to get. Even if there is a tiny bit of oil or impurities on or in the glass it starts looking very similar.

It’s just a shame because this is the only thing not truly spectacular about the lens and it would be amazing if it was as clear when on as it is when off…but it seems there’s always a tradeoff. :slight_smile:
In any case going by the specs for this lens material and the 97% transmission figure I’d be happy to say that the light being lost through internal reflections on the stock lens is probably far more significant than what is being swallowed up by this one because of it’s material composition. That combined with the much cleaner beam profile and just damn gorgeous appearance I’m giving this lens a full thumbs up! :slight_smile:


I’ll just file this under flashlight porn shall I? :wink:

A bit of an unknown is how durable this coating will be, it’s certainly more prone to “blueing” when touched with anything oily (similar to a photographic lens coating) and is probably less hard wearing than an equivalent glass coating but this remains to be seen. I’ll treat it with a bit more care than I normally would but hopefully it holds up well in general use.
If someone finds a quality glass AR lens for this light then that may still be the better option, but overall I’m really pleased with this upgrade to my light.

Small but important Safety Note for this light!

Check the machining of the inside of the battery carrier/body.
Mine had some sharp edges on the pedestals between the battery “tubes” which I’ve just noticed had been rubbbing and cutting into the shrinkwrap on my batteries quite a bit.
This is obviously bad but could also be very dangerous especially with protected batteries where the battery positive is carried along the side of the cell to the protection circuit, only covered by very thin shrink wrap and just fractions of a millimeter away from the negative shell underneath!

Check it and if you have sharp edges there or anywhere else in the body of the light sand them down!!

100% scaling:

Got round to doing an extended runtime test taking tailcap current and head temperature over 50mins, just to see how the batteries hold up and how the output drops over time.

I did the test with the light lying on it’s side on a wooden table. Tailcap readings were taken using my trusty tunigy watt meter. It’s precise and has very heavy leads so it doesn’t affect the readings much if at all, but it’s a little granular in it’s readings so you’ll see some stair stepping in the current readings that is solely because of the meter.

The temperature readings I took with an IR temp “gun” aimed at the same spot on the heatsink/pill section of the body just opposite the switch location. There’s a few kinks in the readings which I put down to being slightly off with my aim but it should give a good idea of the heat you can expect from this light running at these output levels.

On the current side I was quite surprised to see how quickly these cells, 3x Kinoko IMR 2250mah 18650s dropped out of regulation, they were only able to maintain the 5.85A maximum for just over 5mins after which the decline was fairly steep and then it started leveling off again some near 4.5A. Some quality higher capacity cells are probably better suited to this light, offering better extended output levels if not maintaining regulation much longer. But I think these lower capacity cells are somewhat of a handicap especially considering the relatively low amp draw per cell. That said it’s still very bright even at 4A and will still give a higher driven HD2010 a run for it’s money even 50mins into the run so this light puts out a lot of light for a relatively long time with this battery setup.

Batteries read 3.62v after this run and were only around 40degress warm.

The temperature rise is pretty standard stuff, the heatsink portion of the light body rises quickly despite the crappy thermal pathway from the emitter shelf to the body. The battery tube also a warms quickly but lags slightly behind the heatsink while the head section takes longest to reach temperature equilibrium.
In this test setup the light quickly becomes too hot to hold (<50degrees C), which happens at around 15mins, and keep in mind the main heatsink and hottest part of the light is the part containing the switch and something you will be holding on to tightly. So despite the battery tube being cooler for longer it doesn’t really matter much, you will feel the heat before the batteries begin to sag.

There wasn’t much of a thermal runaway though, because even in this uncooled environment with no body contact to coduct away heat the light never reached really dangerous temperatures, maximum recorded temperature at the heatsink was 55.5degrees and at that stage (around 30mins into the run) the batteries had sagged to such a point that the current was down to 4.5A and the temperature began to drop thereafter.

So I guess the body of the light can dissipate enough heat to keep temperatures under control with the led driven to a regulated 4.5A for extended use.

Again it’s a whole different story when the light is held in the hand and used outdoors so make of this what you will.

I really wish I could have also taken some lux measurements to see if the output stayed in line with the current drop or if thermal sag is a major factor because of the limited thermal path from emitter shelf to body. But unfortunately my fasttech order with the lightmeter is still MIA :frowning:

Higher capacity cells are likely to have higher internal resistance, so at best the runtime at full current will be the same. Series cells and a buck driver is the only true solution, short of that any improvements will be minor.

Thanks for the graph an info.. Its nice to see.

The output decline is no surprise. Just look at XM-L2 Vf charts and battery discharge graphs.

Output would have been better with NCR18650B.

LG D1 (4,35V) would have rocked.

Using the typical IMR, Samsung 20R and such cells are pretty much a waste if good (average) output is the goal in this light..

If you are planning on rebuilding the pill, it would be sweet if you did it after you have gotten a light meter. Tempereture and light output before and after modification would be very interesting to see! (assuming you use the same cells)

Yeah you’re probably right, just looked at the discharge curves comparing the Kinokos and an efest high capacity 3400mah cell and the extra capacity is only really evident once the cell gets to below 3.4v. Was hoping there might be a slower voltage drop in the initial part of the discharge but they seem very similar at 2A.

edit:
oh yep great comparison thanks, so there’s some small benefit but its not a major difference as comfy says. I don’t have any of those cells at the moment but I’d still be interested in doing this exact test again when I get some and see how the current graph is affected by the slightly higher voltages.

Hmm those pink LGs look very interesting for this light. I never fancied the extra hassle of charging nonstandard cells but that higher voltage seems to offer a serious edge in a light like this. Might have to try them out after all.

Your heat tests looks like confirming janko.hrasko’s thoughts on the heatsinking of the light. Up to 5A and without modification (ie. adding heatsink mass), the default setup works to keep the heat away. That is great news for me because I cannot seem to find a solid copper rod at all here. So, looks like I will have to go with plan B which is to solder in some FT copper heatsinks to the underside of the shelf LED.

Also, with both my lights, they were rattling a bit on the reflector side of things. So, I believe if the shelf LED was to be turned the other way around, again, as suggested by janko.hrasko, then it would put that extra bit of height needed to stop the rattling.

Final thoughts on the light. At stock, it is a thrower and a half. It doesn’t beat my modded Big Head K8 (de-domed Noctigon XM-L2 U2 1A, 2.8A, single cell) for throw and brightness, but it does give it a run for its money. The PWM, as far as my eyes can see, it is high enough for me not to notice.

About modding it. I still have my other soldering iron and some other bits and pieces. I’ll start doing the little things first before getting stuck into the driver. Oh, and all the Noctigons I ordered from Int’l Outdoor recently - all but one of them has been de-domed successfully with petrol. It worked a treat.

Well I wouldn’t use my test to show that the thermal path is anything but adequate. The led didn’t burn up and the light did eventually get hot but that’s about all you can say about it unless you take some output measurements and see if there is any thermal sag affecting output. ~20Watts is a fair chunk of heat to get rid of quickly.

For all we know the emitter shelf could be 40degrees hotter than the body temperature of the light, struggling to transfer the heat into the body fast enough and the led would be even hotter again, losing output as the temperature rises. There’s a big (or maybe small depending on who you ask:P) difference between what might be called adequate heatsinking and a truly effective thermal path. And each bottleneck along the way causes the temperature on the other side to rise above the ideal which is obviously not what we want.

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I will definitely repeat this test once I have a lux meter and then again after I beef up the thermal pathway behind the emitter shelf. I’m very curious if I’ll see any measurable improvement or better stability in the output.

I imagine the key part of the test will be to monitor the output during the regulated 5mins at the start and I’d be very surprised if the stock emitter shelf thread contact isn’t hampering the output in some measurable way.

Rattling doesn’t sound good that’s for sure, I’d be wary of running the lights for too long before checking into what is loose. Sounds like the reflector isn’t pressing down on the emitter shelf which is them rattling in the threads. Provided the star is glued down that’s not a huge issue but who knows how these lights are assembled half the time. Could be using just thermal paste and then pressure is critical, again I’ve said it before but I’d hate to see one of these reflectors destroyed through a badly heatsinked emitter going smokey! It’s a sad sight and by the time you notice that your reflector is filled with white smoke it’s already too late… :frowning:

Check the back side of your emitter shelf, wonder if the machining/dremeling marks are only this deep on mine or if they all have it to some extent. I couldn’t flip the shelf as suggested because of this but you may have better luck.

Have you focused up the reflector yet? The improvement from stock was pretty drastic on mine, I’m sure you’ll be in for a pleasant surprise once you have those photons going where they should be! :slight_smile:

I don’t know what is the lowest price you can get for this Courui at the moment but now DX carries it with $38.80 .

Recent experiences with testing a couple of XM-L2 U2 1D's leads me to believe it's under-performing for a U2. Want to do true head to head testing to be sure, but I'd say it's output it comparable to a T6 from what I've seen so far. Wonder if anyone else has seen similar results.

If this is true (speculation so far), your big head would do even better with a U2 1A.

I’ve seen this light advertised on various sites as XM-L2 T6 and XM-L2 U2. I guess there’s no way to tell what it really is.
Maybe I should just swap in a XM-L2 U2 1A in my mod just to be sure. Although I’m going to try pushing it at 7A, so maybe I should keep the unknown emitter just in case she blows.

Interesting, I don’t have any way of testing that myself so if you do some detailed testing that would be good.

Mine is definitely quite warm compared to all my other cool whites so I’d expect to see a slightly lower overall output compared to the bluer 1As and greenish 1Cs.
Love the tint though and it’s plenty bright for me, 1As for me are only really an option for dedoming.

Ouchy, Tom is talking about the led I used to replace the stock one. The stock led is most likely a T6 and the one in mine looked like a 1B/1C tint. Replacing it with a known u2 emitter on copper is a must if you’re aiming for 7A.

Yes, I got I think like 3 1D's installed now, and definitely a slight rosy tint in the spill, compared to a 1A or 1C, but I do like it - agree with your impressions of the tint. I bought 10 1D's bare at a good price ($4 each) from Hank a while back, and got lots of bare SinkPAD's and Noctigons.

The rattling does not seem to fully stop when the LED shelf is overturned. So what I have done is used around 4 layers of kapton tape on the underside of the reflector. Add to that, the slightly thicker Noctigon plus the wires, it should stop the rattling. I did a test fit, sans the wire, plus half turned the shelf so that it wasn’t fully tightened, and this did result in the head to stop rattling. I am hoping the half turn would be equivalent to the 18G wire I will be using to wire it up.

Focusing the emitter is something I have not been able to do just yet. However, I will be positioning the LED as far into the reflector as much as possible.

Have you seen my build thread on this light? The underside of the shelf was also badly scratched up. About 30 minutes worth of lapping fixed it right up.

Before:

After:

[quote=Rod911]

Cool, yeah those scratches were really deep on mine, in the middle the gouges where about a millimeter deep and I didn’t feel like removing that much material from an already very thin shelf. I guess it all depends on how heavy handed the dremeling is on each individual shelf.

I may still lap it smooth when I get round to upgrading the heatsinking since then it won’t matter that the shelf is a little thinner, probably wouldn’t matter now either but hey… :stuck_out_tongue:

Oh but adding extra layers of kapton tape to the underside of the reflector seems counter productive to me. Since that will hamper how low you can sink the reflector over the emitter for focusing. If you can’t bottom out the shelf even when it’s upside down then I’d say it’s not worth sacrificing your ability to focus the emitter.

The stock centering ring is WAY too tall, so I’d take that down first to the point where when everything is tightened up you have the emitter in perfect focus, then see how much you need to shim the emitter shelf to get some pressure on those threads. Do you have some copper pieces/plate you could use to make shims between the bottom of the emitter shelf and the body?
I coiled some copper wire to act as a spacer but that’s obviously not a good solution, just lets me tighten the shelf threads up.

I just drilled a big hole right through the middle. That took care of the scratches.

If the heat still has to go through the stock threads it really won't matter much what the plate's made of or what's added to it.