Surefire MN21

chillinn

Flashlight Enthusiast
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According to one of my favorite and most consulted posts (by rikvee, last seen Feb. 2016), the MN21 (for M6 KT4) draws 4.9A on 6x CR123A for 20 minutes. Everywhere I have looked says the lamp is 500Lm.

What I was wondering, first of all, is if one 500Lm incan the same as the next? Or is this lamp super intense for 500Lm (whatever that means)? The curious thing about it is that it is 4.9A, which I would expect to mean it puts out a lot more than 500Lm, maybe 3-5 times more, and Surefire cleverly underestimates while other manufacturers lie about lumens, or maybe 500Lm is the average lumens across 6x CR123A discharge profile.

rikvee's post includes a lot of lamps intended for CR123A that also run on similar voltages of Li-ion. Generally,
  • 2x CR123A ~ 1x Li-ion
  • 3x CR123A ~ 2x Li-ion
  • 4x CR123A ~ 2x Li-ion
It's not very linear, and there is no Li-ion configuration listed for MN21.

I have learned here to assume that CR123A drop to 2.5V under load, and extrapolated that figure can be matched to Li-ion nominal voltage (3.6V/3.7V) to match voltages between number of CR123A and number of Li-ion. But CR123A@2.5V under load is probably no longer true at close to 5A, leading me to guess that the MN21 may be nominally 18V but truly 12V, which should run at close to 500Lm on 3x IMR, or 11.1V nominally, though 3x IMR resting voltage adds up 12.6V. But maybe it will not immediately flash on 4x IMR, 14.8V nominal, 16.8V resting, though these lamps seem to be pretty rare, so it would be very good to know beforehand if ever one finds its way to me.

Lastly, B&H kindly leaves up old product pages, including the MN21, but has a second product page for MN21CS. What is that? What's the difference? Specs look the same as MN21.

FWIW, my interest has turned to lamp assemblies since two of Tad's last three G4 sockets sold about a week ago, and I had fully intended to purchase all three in about 3 days. I contacted Tad, and he was kind enough to pull the last G4 socket for me so I don't miss it. Ultimately, I want a total of four lights with a KT4 head, though this will take some time on my budget. Then I'd really like to hook up with some caving photographers, though I'm not going very deep into any cave. Shallow caving photographers, then, might be interested in me and my lights.
 
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Surefire M6 incand does not run by 6 series CR123A
Battery holder is connected 3S/2P for total of 6 CR123A
So nominally 9 volt and since each CR123A can not provide 4.9 or 5 Amps, therefore they had to use two groups of cells and in this case each group carry only 2.4 or 2.5 Amp.

According to
this test load of 2.5 Amp will drop voltage of each primary cell to about 2.2 Volt so MN21 works at 6.6 Volt which is not enough by single Li-Ion and little too much by 2 Li-Ion at 7.4 Volt.
And according to same test current draw of MN20 (2.5 Amp) will drop voltage of each primary cell to about 2.5 Volt so MN20 works at 7.5 Volt which is good enough and safe by 2 series Li-Ion.
Please see
here.
 
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Thanks fivemega. That explains why there's no Li-ion configuration for it in rikvee's post. A second mystery solved, and it is devastating. I never would have known because I'll never own an M6. Just as well that MN21 is rare because I wouldn't be able to drive it with anything. MN20 tho.
 
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I've run a MN21 (very short period) on two LiPo 18500 batteries. It's a safe voltage but I'd imagine a very short runtime (not the best). Better than burning up CR123s 😆.

I've also run MN11 lamps like this.
 
I've run a MN21 (very short period) on two LiPo 18500 batteries. It's a safe voltage but I'd imagine a very short runtime (not the best). Better than burning up CR123s 😆.

I've also run MN11 lamps like this.
Interesting. That gives options. Maybe 30 mins of MN21 on Vapcell IFR26650 55A 2600mAh. Not nothing w/ fivemega's hardware & M6. I'm reconsidering the never owning one. Thanks for posting!
 
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Hey @chillinn dunno if you found this already, but a great thread by @js on M6 lamps and background, what works and why...

 
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I had not, but something I read there is confusing the snot out of me:
In case you're wondering what the reasoning here, I will quickly say that the voltage under load of a battery (and especially CR123A batteries) very much depends on both the state of charge and the draw rate. Draw more current and you have less voltage at the lamp. Draw less current, and you have more voltage. And since the two stacks of 3 CR123A's in the SF M6 share the load equally, they will have half the current draw of what they would have in the M3T driving the MN15, so there will be an increase of voltage applied at the lamp.

Why would two stacks of 9V draw half the current from each stack? Aren't two stacks of cells pretty much the same thing as two cells? Isn't a lamp's entire current applied equally to both cells in a two cell light? This is freaking me out. Voltage is divided among cells, but I thought current was not.
 
I had not, but something I read there is confusing the snot out of me:


Why would two stacks of 9V draw half the current from each stack? Aren't two stacks of cells pretty much the same thing as two cells? Isn't a lamp's entire current applied equally to both cells in a two cell light? This is freaking me out. Voltage is divided among cells, but I thought current was not.
I'm not clear on the specific details of the app here, but are you talking about using a 'battery' (or "stack") of 3 CR123s in series, vs using 2 such batteries' (or "stacks" of cells) which are themselves connected together in parallel with each other?
 
What I was talking about was js' conjecture that two parallel cell sets would split a lamp's current draw in half. It took me a good long while to learn no matter how many cells you've got in series, the same amps apply to each cell. I guess that's the difference between cells in parallel vs. series. I've just never used cells in parallel before, so it's alien to me.
 
What I was talking about was js' conjecture that two parallel cell sets would split a lamp's current draw in half. It took me a good long while to learn no matter how many cells you've got in series, the same amps apply to each cell. I guess that's the difference between cells in parallel vs. series. I've just never used cells in parallel before, so it's alien to me.
I think I get you. Yes, the current flowing / measured at any point of a series circuit will always be equal. The same current flows through each series circuit element. So, with three 3V CR123s connected in series, the same current will be flowing through each cell. The voltage provided by each cell in series is additive though, so the series stack of 3 cells will provide 9 V.

If two such 3-cell strings are connected together in parallel, the voltage of the 2 stacks is not additive, so the voltage across the 2 stacks of 3-cell strings is still 9 V, however the current being drawn by the load will be divided between the 2 parallel stacks, so each stack of 3 cells will be supplying half the current to the load. So while the current flowing through each cell in a given stack is still always equal, the current supplied by each stack will be half as great with 2 parallel stacks as with a single stack.

So since the load current is split between the 2 stacks of cells, each stack will be supplying half the current that would be supplied by a single stack. That means the current provided by each cell will be half as much. If one assumes that the voltage of CR123 cells sags (decreases) under load, that means the voltage sag of each cell under load will be less. That means that under load, the voltage of each parallel stack, which is the same since they're in parallel, will be higher, and that means that under load, your light bulb will see a higher voltage applied with 2 parallel stacks than with a single stack because the voltage 'sag' of each cell will be less.

That may help.....or not:)
 
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If two such 3-cell strings are connected together in parallel, the voltage of the 2 stacks is not additive, so the voltage across the 2 pairs of 3-cell strings is still 9 V
I had it all except for this part. Thanks. Makes me wish I could run some of my single cell lights in parallel to double capacity.
 
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