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

Mine arrived from KD yesterday. I haven’t taken the driver out yet, but the rest appears to be the same as in the OP pictures.
Only notable difference is the led is on a thicker 25mm aluminium star.

The beam is nice & uniform, & well focused. I like the UI; H-L-off. Hidden strobe.

Happy with this light - even in stock form it’s up there with some of my better modded lights.

Will be taking some measurements in stock form before modding, for comparison :slight_smile:

:beer: :beer:

must……not…….order……

It’s really big Gords.

……………… ahhhhhhhhhhhhhhhh. I can’t visit this thread anymore!

Nice pics btw janko.hrasko.

Sorry guys, this probably won’t help much… :wink:

Couldn’t leave this poor light lying around in pieces anymore…so I did a quick mod/assembly with the DrJones MOKKADRV 7135 driver and a XML2 U2-1D from IntlOutdoor.

To say I’m delighted with the combination is a major understatement! :slight_smile:

Ok so step one was to PM DrJones and get some suggestions on which one of his momentary switch firmware options would work best for this light. I had been eyeing the MOKKADRV and he basically confirmed that this setup would work well in the light. I liked the quick access to High and Low and strobe through a double click, plus programmability should you need to change things around.

I also wanted an extra mode that I could dedicate to moonlight so I asked him to add a fourth output mode, no problem :slight_smile:

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When the driver arrived I stacked some extra 7135s.
I think in the end I added 2x 380mah chips and 6x 350mah chips (basically using up loose and spare chips I had around) onto the 8x 380mah nanjg board. Total should be 5.9A, which should be just about right for an XML2 on copper.


Here’s the stacked DrJones driver mounted onto the original driver with all the components removed. It’s a mess since I was in a bit of a hurry but it works well. The driver is grounded/mounted/soldered to some copper tabs which also help remove heat from the 7135s when they are in regulation. I have yet to run extended tests with the light to make sure this is working properly without the chips throttling back because of heat, but I think it will do just fine.

The little red wire is the control wire for the momentary switch which is soldered to the first star on the back of the nanjg board. Instructions on DrJones site were easy to follow and simple to understand.


I was going to stick a thermal pad on the underside of the driver to transfer a little more heat into the contact board but then I forgot to add it before I soldered the tabs in place. Shouldn’t make much of a difference anyway, but it would have been better than air. :slight_smile:

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For the emitter I decided to try one of those new XM-L2 U2-1D from intl-outdoor. I was keen to see what that tint would look like, since in theory it should offer a really nice balance between the 1A and 1C bins without being overly blue/purple or too green, and potentially with all the emitters being very tightly grouped near/on the BB line. Expectations were high but a potential dedome was on the cards if I didn’t like the tint.


I also drilled and tapped some holes to screw the emitter pcb down tightly.
Reason for this is I hate dealing with thermal adhesives and I’m not going to risk a badly pressed down emitter going smokey and potentially destroying a reflector as nice as this one! Has happened to me more than once when focusing HD2010s.

Since this is a bit of a temporary solution I didn’t go all out and add the press fit aluminium slug to the back of the emitter board as I had intended.
janko.hrasko’s method of inverting the emitter shelf also didn’t work well on my sample because I have rather deep machining marks on the back of my emitter shelf that were too deep to remove by sanding alone. Seems someone got a little too aggressive with a dremel to remove whatever needed to be removed, and unfortunately they’re right underneath the center of where the pcb would mount. :frowning:
I did however add some thick copper wire coil between the bottom of the shelf and the emitter shelf rim, so that at least I could tighter the shelf against this and get a bit more pressure on those crappy threads when the shelf is in the focused position. This works ok but it’s a definite bottle neck in the thermal path and needs to be addressed in the future.

When my lux meter finally gets here I’ll do a runtime/output/temperature test of this setup to see the extent of the thermal sag and then again after I beef up the heatsinking to see if there is any measurable improvement.

Then I lightly lapped/sanded the emitter shelf and the back of the noctigon, just enough to remove the slight edge burrs, nothing extreme. Between the pcb and emitter shelf I added a small amount of Arctic Alumina thermal paste and screwed it down tightly.

On top of the pcb I soldered thin copper strips to the contact pads and then soldered 20Awg emitter wires to these strips to get as flat a setup as possible.
I also had to file down the tops of the countersunk screws that I used to hold the pcb down.
For a centering ring I went back to the stock one but sanded it down considerably, this is a good way to find your ideal focus point. Just take small amounts off the bottom of the ring and keep reassembling and checking until you get it just right :slight_smile:

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First tailcap measurement with stock springs showed just 4.41A, way lower than the 5.9A I was expecting. So those springs had to go, they’re really flimsy and this shows just how much voltage is lost to them even at only around 2A across each one. I swapped them for some chunky gold plated springs from cnqualitygoods and even without copper braiding the reading immediately jumped to 5.85A, that’s more like it. Again I was in a hurry so I didn’t braid them yet but the added thickness and better pressure from these new springs made a huge difference.

Right so now I have a HD2010 XML U2-1C on copper doing ~5.8A on a fresh cell and a Big Head XM-L2 U2-1D on copper doing 5.85A on fresh cells.

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Let the battle commence…

J) :exmark: :open_mouth: 8) :arrow: :bigsmile:

…battle over…HD2010 is dead in the water! :wink:

HD2010 on left and BigHead modded as above on right. Both lights are drawing basically the exact same current and picture taken about 5s into turn on, so any thermal sag isn’t factored in.
I’ve also since taken a little more off the centering ring to get a slightly tighter focus on the bighead light and the hotspot is now even more defined and slightly smaller/more intense again.

It’s really no competition and at distance the throw advantage of the bighead is even more pronounced, it’s currently raining so I can’t take any beamshots outside but this comparison should give you some idea of the output.

And the 1D tint is fantastic, very neutral (in a CW sense) far less green than 1Cs and warm enough so there’s no hint of being too blue as all the 1As I’ve seen are. On top of this it looks to have considerably better colour rendering than all my other cool white xmls/2s with reds that pop quite a bit more than the old XML 1C. Frankly it puts it to absolute shame in every way. It’s a really fantastic premium looking cool white tint so the dome is staying right where it is. I have plenty of nasty blue 1As that can get decapitated instead :slight_smile:

Next delight is the UI from the DrJones MOKKADRV driver, it’s superbly well thought out and feels really premium. From off a simple quick click gives you High, a second click turns the light off again. A longer press from off gets your straight to your lowest setting, in my case that’s a nightvision preserving Moonlight mode. Holding the button longer when on in either mode, starts stepping through the modes, first ascending and then after getting to high descending back through the modes. A quick double click at any time gets you to strobe, which is quite fast almost like the old HD2010 strobe. Superb.
Of course everything is programmable and custom mode levels are even permanently storable via eeprom write so you don’t lose them when swapping batteries. Very pleased with it all and the light is just a joy to use now.

Ok that’s it for now :slight_smile:

Thanks for sharing your mod Linus. Looks like a real winner.

HD-who now?

VERY nice job there, Linus!

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.