M3T w/ LeefBody question

[cmaylodm]

So I got my M3T today (love it!) but I would like to be able to run the MN16 on some Li-Ions. Should I keep the sick M3 body and get a cell extender to run 2x17670, or get a LeefBody and run 2x18650? I think the LeefBody is a bit too plain for my tastes, but I can't resist the runtime of 18650s. Plus, I think the combat grip might be a little awkward with the extender. Any suggestions?

 

[Strauss]

I too like the greater runtime with the 18650 body....but I think I would prefer keeping the beautiful M3 body. If you still wanted that grip-ring style on the end, pick up the detonater extender for a few more bucks. My MN16 ran beautifully off 2x17670's....nice and white and ~30min of runtime. Single-click power-up everytime.

Or you could just buy both

 

[SunStar]

I have run the MN-16 on both 17670's and 18650's. In my experience there is only a few minutes difference in run time. However the 17670's are a little over burdened with MN16 requiring multiple clicks mid way through the run cycle - not something I would recommend for hard use in the woods if light is needed "when light is needed". The 18650's handle the load much better with a single click throughout the run cycle but I'm only getting 4-5 minutes additional run time. I've verified this with multiple battery sets and 2 lamps. I am, however getting additional runtime to 55 minutes using the new MN20 / 18650's.

 

[Strauss]

Thats weird. What kind of 17670 cells were you using?

I have never had any start-up problems using AW's protected 17670's...one click every time :huh2:

 

[nzgunnie]

you can also get the leef grip for the 18650 body.

 

[SunStar]

Thats weird. What kind of 17670 cells were you using?

I have never had any start-up problems using AW's protected 17670's...one click every time :huh2:

The 17670's work fine on a single click initially. But after 20 min of run, the 2x, 4x, 6x... etc. begins. I can get over 40 minutes total run from 17670's but it's too frustrating beyond 20 minutes for me if I use the light momentarily. I have got the same result using both AW and PILA batteries. The 18650's however, are a single click to the end.

 

[Strauss]

Hmmm, I guess the only times I ever run my cells down that far is if I have the light constant-on. With momentary use, I charge my cells once a week or so.

 

[cmaylodm]

SunStar, what is your opinion of the MN20 compared to the MN16?

 

[SunStar]

Well, the new MN20 is somewhat "detuned" from its previous version. I find the new MN20 / (2) 18650's to be very similar to the output of the MN60 / (4) primaries. The MN16 when driven on Li-ion 18650's is whiter and overall has a significantly brighter hotspot than the MN20. In my side by side analysis, the MN16 / (2) 18650's will also out throw (slightly but noticeable) both the MN20 and MN60.

I have noticed that after about 7 hours of runtime on one of the MN16's I've tested, the lamp is starting to darken on the inside. There is no noticeable decline in output but I am unsure as to what this means in terms of overall lamp life. I am also unsure if this is characteristic of this particular lamp or if this is characteristic of the MN16 design.

The color temperature of the MN16 / 18650 set-up is just right to me - it's very white and output is very flat through out the run cycle diminishing to the equivalent output of the MN60 / 4 primaries after 40 minutes of run time. Shut down occurs around 45 minutes on protected cells. The MN20 will run out to 55 min. on protected 18650's with only slight dimming out to 50 minutes.

Both lamps are nice. The MN16 will deliver far more than 225 lumens on 18650's and is my personal favorite for output, throw and color temperature. However, based on my observatons, I believe the MN20 will provide longer lamp life and will give an extra 10 minutes of very useful runtime each cycle.

 

[Dave.]

Great post SunStar, thanks for the comparisons. That's probably the most tricky part of the Surefire lamp line-up and it's great to get some firsthand experience of the reality behind the dry lamp specs. :thumbsup:

It's taken me ages to cotton on to the fact that voltage ratings on lamps aren't quite as straight forward as they first appear. I'd always taken them to be fairly rigid: stump up the specified voltage or the lamp wont perform correctly. To little and it will be too dim, too much and it will fry. Turns out that's far from the case a lot of the time.

I still don't know *why* this is the case though, perhaps someone would be kind enough to enlighten me on this. Why is it that a cell or set of cells with a voltage quite far under the one specified for a lamp can still run it perfectly well, and even in some cases much better than a different cell/set of cells with the "correct" voltage? Is there any way to know when this is the case, and when it isn't?

Electricity is a strange beast...

 

[defusion]

Great post SunStar, thanks for the comparisons. That's probably the most tricky part of the Surefire lamp line-up and it's great to get some firsthand experience of the reality behind the dry lamp specs. :thumbsup:

It's taken me ages to cotton on to the fact that voltage ratings on lamps aren't quite as straight forward as they first appear. I'd always taken them to be fairly rigid: stump up the specified voltage or the lamp wont perform correctly. To little and it will be too dim, too much and it will fry. Turns out that's far from the case a lot of the time.

I still don't know *why* this is the case though, perhaps someone would be kind enough to enlighten me on this. Why is it that a cell or set of cells with a voltage quite far under the one specified for a lamp can still run it perfectly well, and even in some cases much better than a different cell/set of cells with the "correct" voltage? Is there any way to know when this is the case, and when it isn't?

Electricity is a strange beast...

well, my highschool teacher compared it to cargotrucks.
volts are the amoun of cargo per truck, amps are the trucks.
using more trucks with less stuff in them you can still get the same amount of stuff at the unloading dock.

so amps go up if volts go down, so a lamp rated at 9v pulling 2 amps = 18watts, but if you run it at 6v (usually ~7.4, but 6 for this example), it would have to pull 3 amps to get the same amount of watts. 9*2 = 18, 6*3 = 18 aswell.

so basicaly, it's that watts that count for output (ofcourse there are still limits as to how low you can go with voltages, and also it's better to keep closer to the optimal voltage, as higher voltage usually means higher efficiency (if same wattage))
the problem becomes that with lower voltages you need to run the batteries at higher amperages. This is often the limitating factor as to how high you can go. Batteries can only pull so much (usually around 2 times their capacity (refered to as 2C), so a 1AH battery can pull 2amps max safely (for 0.5 hours, 1AH means 1amps for 1 hour, so double the amps means half the hours)

 

[cmaylodm]

Why is it that a cell or set of cells with a voltage quite far under the one specified for a lamp can still run it perfectly well, and even in some cases much better than a different cell/set of cells with the "correct" voltage?

I think it's because lithium primary cells sag more than Li-Ion cells do, so 3 primaries (9V) sag to the level that 2 Li-Ion cells (7.2V) provide.

the problem becomes that with lower voltages you need to run the batteries at higher amperages.

Lowering the voltage will also lower the current (V=IR) as the resistance of the filament remains the same. Lower voltage batteries will not output more current to keep the power constant, at least not in an unregulated light. However, the current draw of the bulb should be less than/equal to the maximum discharge rate of the batteries (2C in the case of Li-Ion)

 

[Dave.]

Ah, thank you Defusion, now that does ring a bell! I seem to remember our analogy was a waterwheel but same thing. Wonder if I still have my highschool physics notes kicking about somewhere...

I hadn't cottoned on to the fact that the thing missing from the equation was Power, so now I see what was throwing me off: all the lamps being rated by Voltage and not Wattage. Curious...

I can see why they have done it that way, given Voltage is the most critical in normal applications where batteries are involved, but it is rather an over-simplification. Why not give the Wattage too? From what I can tell that is the thing that will remain the most constant for the lamp.

For instance, I have a Surefire P90 here and all it says is "9V Lamp" on it. That's really not enough to know what sort of a lamp it is. Thanks to this incredibly helpful post though I know it draws 1.18 Amps on a pair of 17500 Li-Ions. So that's 1.18A on 7.4V, which is about 8.7 Watts. Huh, I think it all makes sense now!

I suppose though the reason they dont put Wattage on various different lamps is because it would end up being a misleading rating, given various types of lamps perform quite differently... very efficient lamps would appear to have low output as we are used to Wattage being directly linked to output in domestic lighting. Argh, victims of our own over-simplification on all fronts!!

Thank you though Defusion for knocking that bit of knowledge back into place for me.