Convoy M21C-U

1lumen selects and reviews products personally. We may earn affiliate commissions through our links, which help support our testing.

Specifications

Brand / Model	Convoy M21C-U
LED	CREE XHP70.2
Lumens	[unspecified]
Beam intensity	[unspecified]
Battery config.	1*21700
Material	Aluminum
Modes	4+ramping
Blinkies	Strobe, SOS
Reflector	Smooth
Waterproof	N/A
Review date	October 2020

Convoy is where I began my journey of enthusiast flashlights. Once I discovered that one could build a flashlight, I knew I had to. And that’s where Convoy fits in – in addition to making several nice, no-nonsense flashlights, Simon (the owner of Convoy) also makes hosts available that we could use to build our own custom lights.  It was that offering that really got me into the never-ending world of high output flashlights.

After closely following Convoy for the past few years, I began to drift away from them. Why? Well, I realized just how flexible e-switch flashlights can be. And unfortunately, very few of the Convoy offerings used e-switches, nearly all were solely tailcap mechanical switch based. Sure, there were a few such as the M3 (kinda chunky for my tastes) and S9 (with its strange, small square side switch) but none really to my liking.

Then finally, the Convoy M21C-U hit the market. It promised high output (Cree XHP70.2) and a compact form factor (single 21700) along with an e-switch driver in a sleek-looking package. Was this the Convoy I had been waiting for?  It sure looked like it!

Package quality.

I’m never really sure what to expect with packaging from Convoy. Sometimes you get a nice looking, Convoy-branded, sturdy white box with foam inserts, such as you would get with an H1 headlamp or some of the nicer S2+ lights.  And then there are those times when I get an M1 or C8 with a simple bubble sleeve and a paperboard box.  The M21C-U was kinda in between those two ends of the spectrum. It arrived in a sturdy brown box with foam inserts. Not the sleek, branded packaging, but not flimsy either.

Inside this box was:

• Convoy M21C-U flashlight

Yeah, that’s it. No lanyard, no manual, no spare o-rings, no nonsense. Just the flashlight. I was a bit shocked by just how little was in the box, but that’s sometimes Convoy’s M.O. I can’t recall the last time I really cared about a lanyard or spare o-rings. A manual would have been nice, but that’s what we have the internet for, right?

The Convoy M21C-U feels extremely comfortable in hand. It feels really well balanced, and the placement of the side e-switch matches up nicely with how the tube is grasped. Something about the dimensions just feels right for a powerful flashlight.

The head has flat areas on five sides that help visually taper the head as well as provide anti-roll features. The tailcap is quite flat, it can tailstand easily. That tailcap also has holes that a lanyard, should you choose to provide one, can be threaded through.

My sample came in beautiful Titanium colored anodizing. I feel like I’ve mentioned this a couple of times lately, but I’m kind of tired of black flashlights. I feel like we’re starting to see a few more colors show up, be they Desert Tan, Olive Drab, Cyan, etc. And this flawless Titanium anodizing provides a good visual distinction without being too flashy. The head is adorned with a smooth stainless steel bezel. Like most other Convoys, the M21C-U has solid square-cut threads that are smooth; anodized on the tail end, and non-anodized towards the head. There isn’t really knurling, per se, but the tail is cut with some rings and channels that provide a decent amount of grip. The side switch button is surrounded by a stainless ring that pairs nicely with that stainless bezel.

The Convoy M21C-U comes with a Cree XHP70.2 LED. In typical Convoy fashion, it comes with several CCT options including 6500K, 5000K, 4000K, and 3000K. My particular sample is 5000K, my favored temperature. The powerful emitter is nestled in a smooth reflector. I usually don’t fuss over reflector styles that much, but many would call into question using a smooth reflector with an XHP LED because of the potential for tint shift and “donut holes” (a dark spot in the middle of the beam). I’m pleased to say that I don’t actually notice any donut hole effect, part of that is likely due to this being the XHP70.2 version which has the dies closer and completely coated in a layer of phosphor. There is certainly a small bit of tint shift when white wall hunting, but I did not notice it’s presence when using the M21C-U outdoors. To be honest, I’ve seen much worse. There is a single, faint ring outside of the main spill area because of the stainless steel bezel. I’m a fan of the stainless bezel though – it gives the light a nice, distinguished look so I’ll gladly overlook that ring.

Length:

• Length: 163 mm / 6.4 inches
• Head diameter: 55 mm / 2.2 inches
• Body diameter: 28 mm / 1.1 inches

Weight: 

• Without cells: 275 grams / 9.7 oz
• With cells: 343 grams / 12.1 oz (with Sofirn 4000 mAh 21700)

Size comparison with other flashlights

Image 1: Convoy line-up, left to right: Convoy T2, S2+, S2, M1, C8, M21C-U, L2

Image 2 and 3: Mid-large Convoy lights, left to right: Convoy C8, Convoy M21C-U and Convoy L2

Image 4 and 5: Other comp with a flashlight thrower, left to right: Emisar D1S, Convoy M21C-U

The Convoy M21C-U uses a 22 mm driver held in place by a retaining ring. The tail spring has a bypass from the factory; the driver contact is a tall brass post. Official specs say the driver puts out 4.8 amps to a 6 volt LED. It is one of the first, if not the first, Convoy flashlight to offer a ramping firmware. And overall, the firmware is relatively full-featured.

Modes: Ramping or 4 modes (1% – 10% – 30% – 100%)

From OFF:

• Press and Hold: turn on in moonlight (0.2% brightness)
• Single-click: turn on in last used mode (or ramp position)
• Double-click: turbo
• Triple-click: strobe
• 4x click: tactical mode (4x click again to exit)
• 5x click: voltage readout (in volts pause tenths)
• 6x click: switch between ramping and stepped modes
• 10x click: lock (10x click again to unlock)

From ON:

• Press and Hold: ramp up
• Single click: turn off
• Double click: turbo
• Triple click: strobe

Tactical Mode:

• The tactical mode on the M21C-U is a momentary turbo mode; holding down the button will provide instant access to turbo and releasing it will turn the flashlight back off.

Mode memory:

• Yes, mode memory is present

Strobe/blinkies

• Strobe mode is present and accessed via a triple click whether the light is on or off

Lock-out mode: 

• Lock-out is enabled (or disabled) with 10 clicks from off. It will be confirmed with a double blink. If you press the button while the light is locked out, it will blink at you. There is no momentary action.

PWM

• No PWM was detected

Additional info: I really like that this light offers both ramping (default) and stepped modes. This enables the end-user to customize it to their liking. I normally like ramping quite a bit, but I feel like the ramp is a bit too fast in the lower end and too slow in the upper end. It’s almost as if the ramp was programmed to increase linearly instead of exponentially. And one thing I feel like the UI is missing… once you activate moonlight mode by holding down from off, your only option is to turn the light off again. I really wish there was an option to start low, then ramp up.

I had a spare Sofirn 4000 mAh “40A” 21700 flat-top battery that I am using the in M21C-U. It fits comfortably.  There is very little side-to-side wiggle room; not enough to allow the battery to rattle. It appears that there is a couple mm of length to spare.  So longer 21700 cells might fit but have not been tested.

There is a low voltage protection present. In the turbo runtime test, protection kicked in around 3.11 volts. For the high mode runtime test, protection kicked in around 2.97 V.

For current measurements, an ANENG AN8008 multimeter and UNI-T UT210E clamp meter were used.  Lux was measured by a UNI-T UT383 BT at 10 meters. Lumens were measured in a homemade lumen tube using a TSL2591 sensor, calibrated against several known lights. Temperature was monitored with an MLX90614 IR temperature sensor.

Amp measurements  

• Standby: 45 uA 
• Low: 58 mA
• Med: 631 mA
• High: 1.83 A
• Turbo: 7.44 A @ 0 sec, 7.30 A @ 30 sec

Turbo current draw was done with the battery at 4.10 V.  Assuming Simon is correct with 4.8 A to the LED (sounds plausible based on the lumen output), the LED is probably using 6.09 V (link), then efficiency = power out / power in = (6.09 * 4.8) / (4.10 * 7.44) = 96% efficiency. I don’t necessarily believe that to be exactly correct (too many assumptions!) but if it’s anywhere near that… awesome!

Runtime graph

I performed two runtime tests.  One on turbo mode, and another on high (30%, stepped level 3 of 4).

• Turbo started out at 3811 lumens and dropped to 3691 lumens by 30 seconds
• Between 4 and 5 minutes, it ramped down to 1409 lumens
• It stay at 1409 lumens until it dropped to 37 lumens at 92 minutes into the test
• The High mode test start out around 1375 lumens and stayed there until dropping down to 38 lumens at 117 minutes into the test
• Temperature seems well controlled.  It maxed out at 52°C in the turbo test and 50°C in the high test

Lumen measurements (for each mode)

• Low: 39
• Medium: 484
• High: 1375
• Turbo: 3811 @ 0 seconds
• Turbo: 3691 @ 30 seconds

Throw numbers: 

• 315 lux at 10 m
• 31,500 cd
• Throw: 355 m / 388 yd

Outdoor beam shots are taken at 25m (82ft) using a Pixel 3 set to ISO 200 with ½ second exposure time

• Convoy M21C-U
• Olight Odin
• Manker MC13
• Brinyte PT18pro and PT28
• Convoy XP-L HI
• Sofirn SP33 V3

Disclaimer: This flashlight was sent to me for review at no cost, by Convoy. I have not been paid to review, nor have I been holding back on problems or defects.