Need Advice on Mag 3C Build for Runtime

Hey guys,

Seeing some members commented on the short runtime for the Tad's customs 2C Mag I saw on ebay, I'd like to get a bit of advice on what I have in mind as a budget build.

Mag 3C+Maglite 6cell Xenon bi-pin bulb+2 3500mAh 18650s

That's it. What I am after is longer runtime, I realize I don't need the output of G4 Halogens.

Anything more I need to change(aside from maybe a glass lens someday) ?

I'm also wondering what kind of runtime I'd get from such a setup. I'm feeling I would enjoy this a lot more than my usual boring stock Surefires.


Thanks a lot!

That's what I run in my 3C. Coated lens, Xenon 6D bulb, Sanyo 20700 batteries and resistance fixes. Makes it a really long running light with decent and actually quite impressive output.

Interesting! This is the first I've seen 20700 and 21700 batteries. They have much higher capacities than 18650s. I'm curious if the 21700 would fit. Seeing how a C cell is 26mm I would think so.

Some quick math: (I know not all the capacity is useful because the batteries can't fully discharge but this should be a good guesstimate, maybe a better electrically versed member could help me out)

6 x D cells have around 18,000 mah capacity and the run time on a 6D is 11 hours. (Per mag and experience)

2 x 21700s have 5,000 mah capacity so estimated run time would be 3 hours. Maybe a little less.

I've not had much luck with long run time Incan/LiIon setups. D and C cells may not put out a ton of volts and they may be big and clunky but they're hard to beat as far as capacity goes. Heck even NiMH Ds have 75% the capacity of a good alkaline.

I have a Surefire G2 with a 3.7V drop incan and a light miser switch and even on 1/4 power I get maybe an hour of run time out of the light. It's putting out 10 lumens at 1/4 power and has 1 x 16650 with 2,500 mah capacity. So you can kind of see even if you were to run it on 2 x 21700s you could get 4 hours at 10 lumens, not exactly spectacular.

EDIT: I calculated my battery capacities incorrectly and fixed. I forgot cells in series don't add their capacities.

Thank you for the responses!

1.5 hours, not spectacular either eh. So even the best 18650s will probably provide less than an hour, quite disappointing. Oh well.
Any idea how much current that bulb (Mag Xenon 6 cell bi pin) pulls?

Xenon Mag 6D bulb is rated 7.2 Volts 800 mA. Runtime with alkalines is subjective because voltage steadily declines with only your tolerance on how dim you can stand before you say 'thats enough'. For me, it was about 3-4 hours. Remember, the dimmer the bulb the lower the drain on the batteries so the dimmer part of the runtime will be much more than the bright part. So the With two Sanyo 21700 B batteries you have a fully useable 4000mAh, so run-time at least 4 Hours, but as they are unprotected you need to be mindful of letting the light over-discharge. Protected 18650 cells will also fit and may be a safer option if you are lending the light out or it may be used and left on - the protection adds a little to the length which helps. These are typically around 3000 mAh, so just over 3 hours running. I pad my 20700's out with two bands of electrical tape built up to make the batteries a good fit. For 18650 you can do this, or add some tube to take up the size a bit.

Thank you very much Minimoog.

3 hours (or a bit less) is just about right for what I want.
I will go for protected 18650s for peace of mind.

RobertMM said:

Thank you very much Minimoog.

3 hours (or a bit less) is just about right for what I want.
I will go for protected 18650s for peace of mind.

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Its a nice setup. Of course you can go brighter but the 6D bulb is a nice balance between runtime and brightness. If you use the Bi pin Xenon lamp, its worth taking time to center it in the reflector as if it is a little off the beam suffers. Easy to do, just move it a tiny bit in its holder and try until you get the best beam. The old PR kryptons were always self centering, but bi-pin bulbs are a little bit more finicky.

Minimoog said:

Its a nice setup. Of course you can go brighter but the 6D bulb is a nice balance between runtime and brightness. If you use the Bi pin Xenon lamp, its worth taking time to center it in the reflector as if it is a little off the beam suffers. Easy to do, just move it a tiny bit in its holder and try until you get the best beam. The old PR kryptons were always self centering, but bi-pin bulbs are a little bit more finicky.

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Thank you for the advice.

I have had a Mag 4D once that I upgraded to a Mag bi pin bulb, so I am already a bit familiar with the "centering" process.
Then again, I sprayed the reflector back then with a quick blast of clear spray paint to make it slightly OP so I had a beautiful beam as a result.

I was out with my 3C Mag fitted with 6D bulb last night. Perfect for walking and long run time means no worries about being left in the dark.

One tip is if you get one of the Fivemega LOP reflectors that are a bit deeper than usual and also have a smaller opening for the bulb you get a really notable improvement in output and beam quality. I'm sorry but I can't remember what they were called but they add about 1 inch to the length of the head and come in different colours for the visible bit - I have a red and a gold and they really set off black Mags. I have one on my 2C Mag using 2 x 18650 plus Magring and one on my 4D running 11 AA Eneloops and 1166 bulb and makes me appreciate the lights all the more.

Minimoog said:

Its a nice setup. Of course you can go brighter but the 6D bulb is a nice balance between runtime and brightness. If you use the Bi pin Xenon lamp, its worth taking time to center it in the reflector as if it is a little off the beam suffers. Easy to do, just move it a tiny bit in its holder and try until you get the best beam. The old PR kryptons were always self centering, but bi-pin bulbs are a little bit more finicky.

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I really don't like the new bi-pin bulbs for this reason - I can never seem to get them centered well enough to get a decent beam. The old PR krypton bulbs suck, but the old xenon PR based are great if you can find 'em!

For run time with a 6 cell xenon running on 6 eneloops (2000 mAh) in series I get about 2 hrs. A pair of 3400 mAh 18650's should run for roughly 1.7X longer or 3.4 hrs. BTW if the cells are in series, you add the Voltage but NOT the Amp hrs.