# CURSES! My MN20 exploded in my M6 turbo head last night



## js (Nov 12, 2007)

Alas,

My most prized lamp assembly, my old-style MN20, exploded last night in my SF M6 Millennium Turbo head, which of course, ruined it.

I got this MN20 just before SureFire went out of stock on MN20's for many months. It was one of the last old style MN20's made, I suspect. It was not purple, but black with white "MN20" lettering. It had a couple of hours or so of runtime on it, so I thought for sure I was in the clear. I was shocked when it popped. And this, of course, ruined my Turbo Head. Grrrrrr!

Now I have to send the head back to SF for repair or replacement. Again. This is the 2nd time this has happened to me. The first time wasn't as surprising as it was the first time I had used the particular MN20 that came with my M6, and it obviously had a flaw, and blew up within a minute of turn on. But this MN20 which exploded had more than 2 hours of runtime on it. And it was totally clean and clear--no finger prints or oil or anything. I'm totally sure of that.

Anyway, I still do have one last old style MN20, a purple one, and I ran it last night in the spoiled turbo head (after emptying the debris out of it and letting the gas dissipate) and it ran fine for two or three minutes. Which is good. But so what? Doesn't mean it also won't explode after an hour or two of running, too.

I think from now on I will not run the old style MN20's in my M6 anymore. The newer MN20's may be a bit less white (slightly lower CCT) but at least they aren't so prone to explosion.

Sad. Very sad. My favorite LA, my favorite beam. No more. What a bummer. And I was already somewhat depressed.


----------



## Kiessling (Nov 12, 2007)

Uh ... thanx for reassuring me :green:
Is there a problem with older MN20 lamps (I got one or two)? And ... can the whole head explode and glass sahrds fly all over me? 
bernie


----------



## js (Nov 12, 2007)

Kiessling said:


> Uh ... thanx for reassuring me :green:
> Is there a problem with older MN20 lamps (I got one or two)? And ... can the whole head explode and glass sahrds fly all over me?
> bernie



LOL!

Yes, there is a problem with the older MN20 lamps. All of the purple bodied ones are older, and *some* of the all black ones are older, and from what I can tell, these older ones, before the redesign, are prone to exploding. Hence the reason for the redesign.

However, NO, if your lamp explodes, your Millennium Turbo Head will contain the explosion entirely, and will not itself explode. Relatively safe, just depressing and upsetting is all.


----------



## Kiessling (Nov 12, 2007)

Just out of curiosity ... how loud is the bang? Like armageddon or more like a mouse sneezing?

And how do I recognize the old from the new version?


----------



## js (Nov 12, 2007)

Kiessling said:


> Just out of curiosity ... how loud is the bang? Like armageddon or more like a mouse sneezing?
> 
> And how do I recognize the old from the new version?



It's just a little POP with maybe a few PLINK's (glass shards hitting inside of lens). It's not loud at all.

As for telling the old from the new, check out this thread:  Old MN20 vs. new MN20 .... But the upshot is that the new style MN20's have 14 winding turns on the filament coil, whereas the older ones have 12.

And, of course, if you have a purple bodied MN20, it's definitely old style.


----------



## UKSFighter (Nov 12, 2007)

I've had a new MN20 pop already as well. Same experience, not too much head damage but I need to send it back to Surefire. It happened just after the new ones were released.


----------



## js (Nov 12, 2007)

tacticalsupply.com said:


> I've had a new MN20 pop already as well. Same experience, not too much head damage but I need to send it back to Surefire. It happened just after the new ones were released.



Darn! Really? Darn. Is this common, I wonder?

You know, if I was right when I was talking out of my *** in the "old vs. new MN20" thread linked above, then decreasing the CCT was a second order effect compared to the SIZE OF THE ENVELOPE. The MN20 is a small small envelope lamp. Smaller than the Welch Allyn 01160, and yet almost the same power output. So, (talking out of my ***), I would think (all bow before my ever so important opinion) that the thing to do would have been to leave the filament exactly the same and MAKE THE ENVELOPE LARGER. This would have lowered the efficiency, though. (But so did lowering the CCT).

But, fortunately, I don't have that high an opinion of my own opinion, and chose to assume that SureFire knows way more about lamps than I do.

So, I'm hoping that new style MN20 explosions are RARE. (fingers crossed). I mean, explosions WILL happen occasionally with any high output, high efficiency halogen lamp design. So one event does not a pattern make.

I'd love to hear from anyone else who had a NEW style MN20 explode.

Also, please note that if you get finger oil on the envelope, all bets are off. Or rather, a betting man would place money on an explosion. Probably everyone knows this, but just in case, I thought it would be good to post it for the record.


----------



## LED61 (Nov 12, 2007)

WOW!! I'm sorry about that Jim, well look at the bright side--NEW TURBO HEAD FROM SF!!!!

Scary though, maybe that's why SF new MN20's aren't as white as the old ones.


----------



## Brozneo (Nov 13, 2007)

So what makes these lamps explode rather than just burning out??


----------



## js (Nov 13, 2007)

Brozneo,

An explosion occurs when the envelope fails. A burn out occurs when the filament turns liquid at one or more points and partially vaporizes, thus stopping the flow of current, thus stopping the heating, thus cooling the tungsten, thus stopping the output of light. This happens almost always at turn-on, because the filament is cold, and massive currents go through it, so if there is a thin spot, it will be differentially heated up a lot faster than the rest of the filament, and then !POOF! an instaflash occurs.

Icebreak started a thread called  A race to failure: Halogen process, filament temp and envelope glass. which has been exploring these issues. Initially I discounted the notion that overdriving increased explosion risk significantly (although, I always agreed that it did increase it somewhat). My theory was that overdriving would increase risk of instaflash and shorten lamp life, but that explosions were almost always just due to envelope failures, weak points in the glass, fingerprints, etc. As the evidence has mounted up, however, I think that it is clear that overdriving will increase the risk of explosion, especially in some kinds of lamps.

I've overdriven the heck out of my ring-potted WA lamps, and they've never exploded, only just burned out, but these are basically just bare bi-pins surrounded by potting, like in a TigerLight or SL lamp module.

The PR-base potted WA lamps, however are another story! They've been exploding left and right around here. I theorize that this is because one lead must be bent backwards, which has a chance of weakening the pinch.

As for how SureFire's LA are potted, and whether or not a lamp lead is bent in the process, I don't know.

I think the verdict is still up in the air, but, I currently believe that as long as the envelope integrity is not compromised, an overdriven lamp, by the odds, should burn out or instaflash and NOT explode, except as a rare occurrence. For what it's worth.


----------



## LED61 (Nov 13, 2007)

Jim, would you consider an overdriven MN21 less likely to explode because of the much larger envelope size, even at twice the output than the MN20 ?


----------



## js (Nov 13, 2007)

LED61,

Yes. Not just the larger envelope size (at least twice the volume), but also thicker glass and more spherical shape (better for spreading internal pressure evenly), vs. the conical, tall and narrow shape of the MN20.

But still . . . I know what level you're driving your MN21 to. hehe. Pretty intense, LED61 !!! I wouldn't rule out an explosion in your case, that's for sure. But that has to be one amazing light when overdriving the MN21 like you are. Wow. Stunning, I bet, right?


----------



## LED61 (Nov 13, 2007)

He He, yeah you´re right Jim, simply amazing, sometime I´ll head up to NY and let you try it!!

Now, so far, in fact, last Sunday night, I did eleven one minute runs with one minute cool downs in between--no problem at all. Any more and I think heat would start darkening the envelope. Eleven minutes is all that Will´s pack is giving me now and since it works so beautifully I haven´t dared change the batteries for the ones you graciously gave to me. I take care of them though, giving them slow 200 mah charge once a month.


----------



## Brozneo (Nov 13, 2007)

js said:


> I've overdriven the heck out of my ring-potted WA lamps, and they've never exploded, only just burned out, but these are basically just bare bi-pins surrounded by potting, like in a TigerLight or SL lamp module.


 
Thanks for that explanation!

And the above has happened to me quite a bit, but no explosions! Touch wood!


----------



## 325addict (Jul 6, 2010)

So some people still prefer that old, exploding MN20?

Then.... GET IT:



It's the old purple one... brand new!


Timmo.


----------



## cm_mtb (Jul 6, 2010)

Why did you revive two old threads just to post that link?


----------



## Steve in SoCal (Jul 7, 2010)

Some new in box old stock surefire stuff has been for sale on Ebay lately and its a fair warning to remind folks that some of these old Mn20s are stinkers. I recently had one that started melting after only a couple minutes of runtime.


----------



## cy (Jul 7, 2010)

what an old thread... got me looking at an old purple NM20 that burnt up... good thing it didn't blow up


----------



## 325addict (Jul 7, 2010)

I did so because it seems, some people want them badly and there were just two days left... better twice than not at all, was my thought. Indeed, these threads are very old (didn't notice that at that moment...)

I wouldn't buy them, with all we know now 

Timmo.

EDIT: I'm sorry I broke rule 9. Although I KNEW about the cross- and double-posting, I just did it in a hurry, just forgot that these nearly the same replies would be seen as a double post. It won't happen again!


----------

