Hello BLF,
Wishing everyone a happy 2022 filled with fulfilling days, health, and joy. 
To begin the new year, I purchased the Manker MK38 flashlight and would like to share some of my initial thoughts with the community. I'm expecting many people to create their own standard reviews soon with runtimes, brightness measurements, UX overviews and so on.. that's not what I will be doing; instead, I'm hoping to share a slightly different perspective from a more engineering point of view.
The Manker MK38 is one of the new 'soda-can' flashlights of an emerging class, powered by three 21700 cells (either integrated or separate), with a claimed output luminosity of around 40,000 lumens. The MK38 was released towards the end of 2021, and appears to be a direct competitor to the Acebeam X50 (which was released in mid 2021).
These two flashlights have a very similar form factor and are both powered by essentially a 3S 21700 battery pack. They both claim about the same output, and their brightest configuration uses eight XHP70.2 LEDs. They are both offered in 6500K and 5000K variants, as well as other LEDs (such as the SFT40 for the MK38 with more throw, and the GeTain FC-40 for the X50 for higher CRI).
There are lots of people out there who conduct flashlight reviews from a general point of view, talking about the general construction, UX, runtimes, and so on. I'd like to do things a little differently so I'll be focusing a bit less of the general aspects of the flashlight such as runtime, brightness measurements, charging rate etc, and instead look at it from a more engineering and EE point of view. This will take some time since it will require disassembly of the flashlight - I will update this page as it progresses.
The MK38 I purchased is the one in a very nice off-white / light grey micro-arc oxidation finish. I also chose the more expensive option with a XHP70.2 5000K, and the built-in battery pack with USB-C charging. I will be taking the flashlight apart including the charging and battery module.
The flashlight can be purchased here: http://www.mankerlight.com/manker-mk38-satellite-multi-purpose-handheld-searchlight-power-by-3x-21700-batteries/ .
I purchased this flashlight with my own money so I do not have any affiliates or disclosures to make. This was a very expensive flashlight, so I hope this write-up is useful to you all!
First Impressions
The first impressions of the flashlight are very good. It comes in a nice box with good foam padding, as well as an instruction manual, a 60W USB C charger and cable, and a wrist-lanyard (which seems.. much too insufficient for a flashlight of this size.. a shoulder strap would have been more appropriate). It also comes with a carrying handle which has two e-switch buttons and two small fans.
I will be comparing this flashlight with a Zebralight SC700d as a reference, since it's a bright flashlight which many people here are familiar with. I do not own any other 'soda-can' flashlights so I cannot compare with any of them. It would be nice to compare this with the original Emisar Meteor M43 just to see how things have evolved over the years.
The SC700d weighs 158g with a 21700 battery, and the Manker MK38 weighs 890g with the included battery back, charging base, and carrying handle. While physically compact, this makes the flashlight fairly heavy, though it feels balanced with the carrying handle. There is lots of space for the fingers even when wearing bulky gloves, and the ribs on the handle definitely make it much more secure to hold (esp. with gloves). I couldn't help but think that this flashlight would do well with a shoulder strap, and a DIY version seems possible with the inclusion of the 1/4-20 threaded tripod mount. That said, the tripod mount hole is a little shallow, and may require a small washer/spacer - I tested this with one of my tripods and the hole is just not quite deep enough.
The white finish is bound to get dirty when in use, but I think that's ok. It's a tool after-all and is meant to be used (despite the packaging saying proudly, 'More than just a tool'). The finishing seems excellent and the construction and machining feel solid. I would love to see other flashlights adopt this finish. I raised this up with Fireflies and they said they would consider it for future flashlights.
Subjectively, I am also a fan of the aesthetics, and I prefer its look compared to the Acebeam X50, even though the Acebeam seems to have much more effective cooling fins. I appreciate the industrial design of the MK38 and I'd love to see Manker build some other (smaller) flashlights in the future with a similar design language. It has a storm-trooper feel to it.
I was impressed with how the the e-switch buttons are integrated into the handle (which the X50 lacks), allowing easy control of the two small fans as well as the main switch. The effectiveness of the fans is questionable since they do not provide much airflow, and they are merely blowing air around the channels around the front of the flashlight (I struggle to call them fins). That said, I'm sure they will provide some sort of improvement since I can indeed feel the airflow, and there is likely some Coanda effect in play.
Regardless, the flashlight is large enough and LEDs efficient enough that the MK38 is likely be able to sustain several thousand lumens until the battery runs out. Manker claims 9000 sustained lumens with the fan on, and 5500 without. Given the similar form factor and specs to the X50, and that the X50 has been verified by other reviewers to sustain about 6000 lumens, the claims seem plausible.
One thing that struck me immediately was the glass lens covering the beautiful 8-up orange peel reflector. This lens has what appears to be a very effective anti-reflective coating, so much so that reflections are difficult to see, and it almost looks like there is no glass. Manker claims that the lens "Utilizes dual-sided AR coated, 99% transmittance toughened glass lens" - and I believe them, it's a nice detail.
Manker claims "Integrated precision digital optics technology provides extreme reflector performance", but I have no idea how this reflector is 'digital'! Maybe because it has 8 cavities and 8 is a digit! Jokes aside, the reflector appears to be very nice and I especially like its compact size (for 8 XHP70.2 LEDs).
The LEDs in my MK38 are XHP70.2 LEDs with a 5000K colour temperature. I contacted Manker directly to request which specific LED they used, but they seemed hesitant to provide the actual part number. Comparing with my Zebralight SC700d, I'm quite sure it's the 70CRI variant since it has a slightly poorer colour rendering of reds.
Interestingly, I also asked Acebeam about their X50, and they claimed that they were using 90CRI XHP70.2 LEDs in their flashlight. This seems a little suspect to me given that both the MK38 and X50 have about the same claimed brightness and are likely being driven at close to the same power level. The 90 CRI LED is much less efficient and I would expect something closer to high 20,000 lumens if it were the case. Note: Acebeam claims that their 6500K version is CRI 70 and the 5000K version is CRI 90, in a chat conversation I had with them.
While I do not have equipment to measure the brightness of the flashlight, I can say that it is immense, making the quoted 40,000 lumens believable.
In the above beamshot, I have both flashlights at the same distance illuminating the room, with the camera set on a fixed exposure. The middle photograph shows the SC700d at 3000 lumens, and the right most shows the MK38 on turbo, with the middle of the photo saturated. I'll definitely have more beamshots coming soon.
So whether the flashlight is 40,000 lumens, or somewhat less at 30,000, I can't say for sure at the moment. Regardless of the actual numbers, the MK38 is overwhelmingly bright indoors, and my initial estimates put the driving power around 350W, depending on the exact LED used, and maybe less if the top-bin LEDs are used and the output is less than advertised.
It was a foggy day, so it was perfect to light up the sky with the MK38. The beam is fairly floody with a bright central spot - the SFT-40 version should throw a lot better.
Next, let's move on to the insides. I'm expecting to find a really big inductor (or inductor array) inside, with discrete fets and a standard switch-mode controller IC with current sense feedback similar to my Lume drivers. For the charger, I'm expecting a simple USB type-C port controller with PD support, together with a bi-directional buck booster IC with integrated battery charging such as the SC8915. I'm hoping to see if it's done properly with cell balancing and such, but unfortunately I'm not expecting it to be.
Carrying 'Fandle'
The MK38 comes with a very nicely machined handle and comes in the same gorgeous finish as the rest of the flashlight.
The handle attaches via a large custom screw. Manker provides a simple tool to help screw this in. Other option they could have done is to have use a large Hex or Torx screw, and have a hole through the handle to allow the use of a screwdriver. However, the implementation is decent enough. A nice touch is that the screw acts as a plug for the hole should the user want to remove the handle. An O-ring around the screw provides water-proofing.
The handle interfaces with the flashlight via 4 gold popo-pins. This seems reliable enough, but the pogo-pins are exposed if the handle is removed from the flashlight and needs to be treated with care. Manker has tried hard to ensure water-proofing and added an O-ring around the port.
In future updates, I hope to look at the effectiveness of the two small centrifugal fans on the handle. These provide a small but noticeable airflow around the head of the flashlight and I suspect that they may be more effective than initially meets the eye, so don't dismiss it too quickly!... It will be interesting to compare this implementation vs. the Acebeam X50, which has much deeper fins, but no fan.
Battery Charger and Powerbank
Caveat - please do not disassemble your flashlight; it will likely void your warranty of a very expensive product. I am a electrical engineer and I do these kinds of things as a job so I (hopefully) know what I'm doing and I can fix something if I mess up. I'm doing this with the hope of sharing some knowledge with the community.
Manker offers the MK38 in two different models - one with an integrated battery pack and charger / powerbank, and another one which uses three individual 21700 cells. Due to the huge power that this flashlight draws (over 100W PER cell), personally I think that using raw batteries can be a dangerous choice and creates limitations with the reliability of the overall performance of the flashlight.
The one I have is this powerbank version, and it differs from the individual-battery version since the tail now houses the charging electronics. Let's unscrew this back module and see what we uncover..
The insides are revealed. I was fairly impressed with the overall quality of this charger / powerbank unit.
The system is housed on a single PCB with a very nice matte-black finish - I don't see many of these in mass-produced consumer electronics because it's expensive - some engineer is taking pride in their work!
The key components are the Injoinic IP2716 USB-C Power delivery controller with source-sink capability, hooked up to a Southchip SC8902 bi-directional buck-boost converter with integrated 1-4S battery charging. A 7150 SOT-89 LDO provides 5V power to the Injoinic VSYS. The batteries are wired in a 3S configuration. My initial measurements with a USB-C PD charger show a roughly 33 to 37W input charging power (when battery is about half full), which is in-line with the claims made by Manker (1.5hr charge time to 90%). IMO this quick charge and power-bank function is a significant benefit, and could be worth the price over the individual-battery variant. Manker also provides a no-brand '60W' USB C charger but I haven't used it yet (because it does look a little cheap, and improperly engineered power supplies always worry me!); charging has been done instead with an Anker 60W USB PD charger.
Overall, I'm glad to see that this seems like fairly standard and decent implementation with no major corners cut*. The above photo shoes the charging PCB with all the components on the top layer; there are no components on the bottom layer, other than two pads which the battery wires are soldered to.
* - note this is just based on an initial visual inspection; I haven't made any effort to analyze the actual EE design.
PCB quality looks unexpectedly good and assembly looks decent. The USB C connector is of the waterproof variety, and also features an o-ring to seal it from the outside, in addition to the rubber flap.
However, there are some areas of concern at first inspection. First, I would have preferred to see would be some silastic (or other dampening method) around the larger components like the large inductor and tantalum caps, which could potentially shear off on a hard impact or vibration. I hope that Manker addresses this since it could be a point of failure for a product that presumably is meant to take some abuse in the field. I'm going to call it out now since I'm expecting that there are going to be people who have some failures with their charging system since that big inductor is just asking to be sheared off its pads.
I would also have preferred to see two LEDs on the board for better charge indication (there is only one red LED, which indicates both charge and discharge modes; the LED turns off when fully charged and I would like to have seen a blue or green LED turn on instead).
I did not see any cell balancing circuitry on the board, nor any heat-sinking. The 30W charging rate is fairly high, and personally I would have gone the extra mile to add some thermal pads on some of the components to use the body of the flashlight as a heatsink. Based on a quick soldering test on the wire pads, the PCB looks like it has some internal copper layers (I'm guessing a 4 layer board), so thermal management should be OK in practical situations. I'm going to assume here (for now) that Manker have done their homework. The overall layout of the board seems decent as well.
Taking off the back module, we can see the battery pack. It's a custom-made 3S 21700 pack, with a claimed rating of 10.8V / 4200mAh. Given that it needs to be able to support >=35A continuous discharge, my guess is that it is made up of three Molicel INR-21700-P42A - one of the best performance high-drain 21700 cells on the market. It is shrink-wrapped and padded with foam, and looks reasonably well constructed - we will take it apart at a future time. The two flexible silicone wires connect to the charge/powerbank board and seem adequate for the purpose. The entire weight of the battery only held by the PCB though (and 3 screws), and that could be another point of failure during a hard axial impact.
Ideally I'd like to see some sort of active charge balancing inside, but I'm not holding my breath for it. They could also have been carefully matched in the factory, and the hope is for the electrodes to be properly tab welded together; personally if I were to design this flashlight, I'd make sure the cells have a balancing circuit, and do away with the individual cell variant from a safety point of view (though this is probably not a discussion I want to have since a 40,000 lumen flashlight is inherently dangerous :P.. )
One safety point though - this 3S battery pack is extremely powerful. If something were to happen on the charger (or driver) PCB and a short were to occur, there is no safety mechanism and you could have the entire battery shorted, causing a huge fire hazard. I'd like to have seen a fuse somewhere. Personally, I'll be adding a small fuse to this section, maybe on the PCB or in-line with the battery wire. In the event of some short, the fuse will blow.. Note that it is possible that there is one in the battery pack - I would be very happy if it is indeed there!
Despite some small nitpicks, overall I'm happy with what I see. For an extra $60, you get a battery pack (three P42A cells would have been about $18 by themselves), and a properly designed powerbank and charger implementation (effectively a 12600mAh battery pack). I would have preferred to see a smaller cost delta (say $40), but my guess is, unlike EDC flashlights which sell in much larger volumes, Manker are not going to be selling a huge number of MK38s.
Just the engineering required for the charger electronics alone, battery pack development, material cost, and a different SKU required for the flashlight body, is arguably more than the majority of super-simple AMC7135 flashlights, and makes the $60 cost easier to swallow. They do have to recoup back their engineering and tooling cost afterall.
[ .. continued on the next post .. ]
Its 3x 21700 in series for 12V ( from manual). Driver DD (easiest way)?
