4C Maglite - MT-G2 build research / questions

I have (2) 4C Maglites, the xenon type. I am looking to build them into MT-G2's as security lights. My wife works as a security guard, and nights are not uncommon. I need a good balance between output, and runtime. I was thinking about 1000 OTF lumen's, give or take a bit. I was hoping (3)x 26650 would work, but am unsure if the diameter of the cells might be a bit large. I do not think protected cells will work, as they are a bit long. Unless, of course, I have the tail mod done. If not the 26's, then perhaps the 18650's. Duracell C's x 4 measure about 196mm give or take just a smidge... Thinking a tail spring mod might be in order...? Honestly I would kinda prefer protected cells. I am new to Li-on type cells, how "bad" would unprotected KingKongs or some other GOOD type cell be in real world practice?

-- I bought a couple of these reflectors to play with: http://www.ledil.com/node/2/p/5694 ,, I figure that a set hotspot is probably preferable when a 1000 OTF output is default, so it being adjustable is not very important to me. I like the combination of good spill, and good throw.

-- I also got a couple borofloat lenses, mostly because I wanted to replace the poly with glass of some kind. I figured the Borofloat would be about as tough as it gets.

-- I am considering the b3Flex as a driver. I am wondering a 9V emitter would work or not. With voltage sag, and a bit of run time, probably not?

-- This is the emitter I am looking at, right at the moment: http://www.mtnelectronics.com/opencart/index.php?route=product/product&product_id=71

-- As far as a switch goes...Old Lumens had posted a Momentary Mod for the existing Mag... Guessing that might be the way to go?

-- Will need a heat sink.

Suggestions, and ideas on how best to proceed are very much welcomed. Nothing is really set in stone.



Welcome to the forum. There are links to many different mods on the DIY page Here for lots of ideas if you’re just beginning the process but it sounds like you’re on a good track. Any way you slice it there will be a fair amount of work involved. I’d go with protected cells when running them in series like that.

Gonna be tough to set up, but doable. No need to worry about the switch, just do spring bypasses everywhere you find a spring and it’ll handle whatever you throw at it. I have a 1D with Triple XM-L2 in direct drive and it handles over 15A. Original factory side-switch. So you should be fine staying with that.

You could easily run 2 of the high capacity 18650 cells, since you’re not requiring mega amps for whopping output the Panasonic NCR18650B should work well for you. It’s not sensitive to being paired up so that shouldn’t be a problem, and with 3400mAh you should get some decent runtime at 3A or so, which will give you in excess of your desired power level. (probably around 1300 lumens, I have an MT-G2 in a chopped AA MiniMag, running as a mule, making 1345 OTF from 2 tiny 14250 IMR cells at 3A)

So I’d just do the Zener mod on a Qlite, run 2 cells with sleeved adapters and a filler to take up any additional length. (I’ve had good success with a nylon or plastic rod bored to accept a 5/16” aluminum rod in the correct length for the power transmission)

That would give you 3 solid modes, decent runtime (around an hour on high) and if you make sure to include some decent heat-sink you shouldn’t have any issues. With some heat-sink making good contact with the big Mag head, should work out pretty good.

Edit: Oh yeah, onlinemetals.com now offers USPS flat rate shipping, so you can get a nice chunk of copper for around $14 shipped. :slight_smile: (I have one coming, 1” long x 1.375” diameter)
EditII: Spring bypasses won’t be needed at 3A, but they’ll help it run more efficiently. That great big honkin spring in the tailcap really needs it :wink:

Thanks guys. I appreciate the help. I am new to this, so I am taking it a step at a time. Still need to decide on a Solder Station as well....


The Hakko 888 station created a monster over here! I can solder! :slight_smile:


I can see this becoming a hobby ... ;)


I am up to 50+ lights. Cells for them all. Extra cells. Chargers. Extra chargers. Parts. Extra parts and even the supplies to build my own drivers now.

Get that station, watch your skills skyrocket, and give your wife the credit card. Or hide.

A really good way to get your feet wet is with a bare host from Mtnelectronics. RMM has a thread that is rarely off the front page and can set you up with led, driver, cells and chargers. My favorite is the Convoy M1. Same for Calvin at Illumination Supply but different selection. You would learn a ton about modding if you were to follow the second annual scratch made light contest kicking off next month. It runs for 3 months and will be loads of fun. There’s still time to sign up and it’s free to join. Free to watch as well.

Very nice DIY host, much better than anticipated. Brass contacts, brass pill, everything about it is well done and easy to complete with your choice of driver and emitter. A copper SinkPAD or Noctigon will solder to the brass pill for utmost thermal transfer or you can just use a dab of thermal compound.

Definitely a good place to start.

Three cells (the longest I know of, the Moli 26700s) are about 0.450" longer than four alkaline C cells, you can pretty easily get that much extra space in the tailcap with a different spring. Shorter cells will make it easier still.

If you are starting with new King Kongs and take the following precautions, you should be fine using unprotected cells:

  • Check cell voltage before loading charged and again when unloading discharged cells. If they are coming out of the light with similar voltages, that's reasonable assurance that they are discharging in unison. I put the cell is the highest voltage in the tail as that position seems to drain faster. I don't know what a safe variance is. I keep my cells withing .04 volts of each other.
  • Don't discharge the cells below 3volts or the manufacture's recommendation if lower. Doing so repeatedly will make the cells dangerous.

If a cell comes out lower or higher than the others, it's time to discharge test the cells and mark their capacities on the wrappers. You should only use cells with similar capacities together in series.

Best of luck. Sounds like it's going to be a great light.

It's going to be difficult to get only 1000 lumens out of a MTG2...

Out of context, that would be a strange statement…

I've never had a C cell Mag, what's the tube ID in front of the switch? That'll determine the max driver OD. The new DRY driver would be a good choice for 3 cells/1 MTG2 but I don't think there's gonna be room for it.

Tube ID is constant all the way. The tail cap opening is a bit wider at the threads before it narrows. If you want to pump it up check out Malkoff bezels and tail strikes.

The 5A driver from RMM would fit and work with mtg and 3 cells but if your willing to pay the price it’s hard to beat the Bflex for quality and it’s very thin and rated up to 3A but programmable for lower max. It also has programmable voltage monitoring. You just have to be patient with setting up the UI as it’s tedious. Simple in operation once that’s done though. If you’re going to run it at 1A you might consider the Maxflex with 5 x XML-2. Same UI but a greater selection of tints available

As for the 1000 Lumens... I only say that by way of wanting a more reasonable run time. If it is more, so be it. As long as it has at least the same general run time available as the Xenon Incan it started out as with good old Duracell's.

I will have to check the ID... Now you have me curious. I will be away from comp for most of the rest of the day, so it will be later this evening.

I will have to look at the M1, I am not 100% wed to the idea it *has* to be a Mag... :) Decisions, decisions!

Thanks for the warm welcome everyone!


M1 is a single 18650 light, to get a MTG2 working requires using two smaller & much lower capacity 18350 cells. They do work, but not really comparable to 2/3 26650s.

Will probably go ahead and use the 2 Mag's since I already have them. Still need to actually measure the bore to see what I might need to do battery wise.

A good driver choice for an mtg and 2-3 cells at 2.8A would be the driver Match used in the 4M and Triple Nichia from KD. It has been produced and copied by just about every vendor known to man.