P91 explosion, May 10th

[Paladin]

We were about 2/3's of the way thru our evening walk, and I was marveling at how much area a P91 driven by 2x18650 was illuminating. Some campers were calling out to us, and I was lighting up the area trying to determine where they were. The P91 went orange, then died completely and I chalked it up to one of the cells cutting out.

This morning I pulled the cells, and found them both at 4.1 vDC open circuit. Then I noticed all the bits of glass inside the M2 bezel. Arrggh, my first bulb explosion. IIRC the P91 had well under an hours run time on it, and when recieved many months ago the lamp part had seemed to not be glued solidly in place inside the reflector. Since I was overdriving the lamp I can accept the loss, and don't feel a call to Surefire to whine is in order.

Does bulb failure when overdriving result in physical destruction of the lamp, or just burn out the filament?

Any suggestions regarding how to clean the cloudy residue from the inside of the pyrex?

Paladin

 

[WildChild]

Re: P91 explosion lest night

Shouldn't overdriving just kill the filament? Exploding bulb sounds like a weak envelope, given the pressure in the bulb.

 

[Aussie Cheese]

Re: P91 explosion lest night

such failures are usually due to structural defects in the glass, either from micro fractures during potting or more likely oils and grit transferred from the skin.

 

[thermal guy]

Re: P91 explosion last night

Can't the p91 take up to 9volts? Two 18650 should be less than that.

 

[pbs357]

Re: P91 explosion last night

Can't the p91 take up to 9volts? Two 18650 should be less than that.

Yeah, the P91 is designed for 9volts, 3 x cr123. With 2 x 18650 you'd only get 2 x 4.2v hot off the charger at most. 8.4v would be no problem so I think it may have been caused to oils on the bulb or other defect - the P91 can get hot enough to slightly melt/distort plastic and lexan lenses.

 

[dudemar]

Re: P91 explosion last night

I agree with the others, it's likely there were oils on your bulb. Next time try soaking one end of a q-tip with rubbing alcohol and generously wipe down the bulb with it.

 

[mdocod]

Re: P91 explosion last night

9 volts will instaflash a P91, or if not on the first try, the second or third try.

The P91 is a ~6.6V bulb being driven as hard as ~7.6V on a pair of 18650s. It is overdriven quite heavily, but exploding glass usually means imperfection. Whether or not it would have exploded on primaries is hard to know.

 

[Cydonia]

Re: P91 explosion last night

I agree with the others, it's likely there were oils on your bulb. Next time try soaking one end of a q-tip with rubbing alcohol and generously wipe down the bulb with it.

There needs to be a sticky up top telling people to clean their bulbs with alcohol after handling. I bet an awful lot of people don't know this is absolutely necessary.

 

[thermal guy]

Re: P91 explosion last night

9 volts will instaflash a P91, or if not on the first try, the second or third try.

The P91 is a ~6.6V bulb being driven as hard as ~7.6V on a pair of 18650s. It is overdriven quite heavily, but exploding glass usually means imperfection. Whether or not it would have exploded on primaries is hard to know.

S/F list the p91 as an option for the 9p.I think you might mean the P61.

 

[paulr]

Re: P91 explosion last night

123's have some internal resistance at high currents so they really do deliver just 6.8 volts (or whatever) to a P91. The P91 relies on that voltage sag. A fully charged 18650 is about 4.2 volts so two of them is 8.4 volts with very little sag. Result: P91 goes poof.

 

[thermal guy]

Re: P91 explosion last night

Wow never knew that! learn something new every day so with 3 X123 in my 9P I'm only getting 6.8 vt to my malkoff? sorry to go OT.

 

[pbs357]

Re: P91 explosion last night

Double wow! I've always seen 2 x 3.7v as acceptable for the P90 and P91 lamps. Good to know.

 

[Icebreak]

Re: P91 explosion last night

Paladin -

Can you post a pic? I'd like to add it to the Race to Failure thread if that's OK.

To get those tungsten and halogen oxides off the Pyrex run very warm water from a tap. Wet the window. Put a drop of Dawn dishwashing (not machine but hand) liquid on the window. Gently swirl a finger or thumb in it to lift the residue up. Then put the window back in to the flow of tap water. What you are wanting to do is create a stream of soap and water that lifts the residue not scrub the residue. Finish it out with your favorite cleaner... binocular/ scope/camera/eyeglasses etc.

Hope that helped.

 

[nzgunnie]

Re: P91 explosion last night

Wow never knew that! learn something new every day so with 3 X123 in my 9P I'm only getting 6.8 vt to my malkoff? sorry to go OT.

No, to your malkoff you'll be getting a lot more than 6.8v because the malkoff draws what? 750mAh? So the voltage sag at this level of current draw is minimal.

The P91 draws 2.5A, so there is a lot of voltage sag under this much higher load.

 

[Paladin]

Re: P91 explosion last night

My digital camera takes lousy macro shots. The glass residue consisted entirely of very small, almost coffee grounds size pieces. I read the "race to failure" thread and in my case the glass envelope did not fracture, it simply disintegrated.

There is a small possibility of oil contamination, as IIRC when the P91 was sent to me it was loose in the carton and had a packing peanut wedged against the reflector. I know not to touch the lamp, but I also never cleaned the lamp personally. FWIW when I was installing fiber optics systems we always used 91% isopropyl alcohol to clean connections and Rx/Tx ports.

Paladin

 

[Double_A]

Re: P91 explosion last night

I had an exploding lamp explode in my M6 with about 10 minutes of runtime on the lamp and an hour of runtime on a brand new M6.

Surefire sent me a couple replacement lamps AND a new head as the bits of glass were imbedded in the reflector. The replacement head was a black M500 head from a Weapons light so I have a Natural HAIII M6 with a Blk HAIII head.

I had "already" known about the problems with oils on quartz glass and scrupulously followed procedures.

Surefire told me they had reports of a bad batch of lamps.

I also had a P91 melt the polycarbonate lens of my 9P. I purchased a replacement lens for the 9P....and one of the newfangled lock-out tail-caps that they were newly releasing.

 

[leukos]

Re: P91 explosion last night

Double wow! I've always seen 2 x 3.7v as acceptable for the P90 and P91 lamps. Good to know.

2x3.7V Li-ions with the P90 is an acceptable combination: SF's LOLA's are engineered for higher voltages than their HOLA counterparts. The instaflashes and explosions tend to occur more with SF's HOLA's like the P91 when used with Li-ions.

 

[Icebreak]

Re: P91 explosion last night

Disintegrated. Ah. I've seen a few Welch Allyns do that. Like some others, I'm leaning more toward a flawed-from-the-factory lamp, especially considering that you know the cleaning drill. It's possible it would have been fine on primaries but like mdcod mentioned; it's hard to know. I think that when we overdrive lamps, imperfections in the lamp assemblies are more likely to reveal themselves. In this case it could have been the envelope but another long shot possibility is the potting to envelope interface. Since the lamp was loose it could be that the thermal path was not optimal. I tend to think that the flawed LA scenario happens more often than the fingerprint oil problem. I'm not at all discounting it as a possibility I just think it happens less often than convention has indicated. I clean my lamps and sometimes when I'm experimenting they still explode. I've purposely rubbed my fingers on lamps and watched (with safety glasses on and torch angeled away) the oil just smoke off.

I'll bet your P91 looked bright and white when it was running.

For others reading along, mdcod's compatibility chart shows: SF P91: 20W, 360 - 215 lumen in 43 minutes on two 18650s so this is a known good combination. He has cautioned us that lamp life will be reduced.

 

[Crenshaw]

Re: P91 explosion last night

There needs to be a sticky up top telling people to clean their bulbs with alcohol after handling. I bet an awful lot of people don't know this is absolutely necessary.

im one of those awful people! thanks for the heads up....

Crenshaw

 

[blinder switch]

Re: P91 explosion last night

My digital camera takes lousy macro shots. The glass residue consisted entirely of very small, almost coffee grounds size pieces. I read the "race to failure" thread and in my case the glass envelope did not fracture, it simply disintegrated.

There is a small possibility of oil contamination, as IIRC when the P91 was sent to me it was loose in the carton and had a packing peanut wedged against the reflector. I know not to touch the lamp, but I also never cleaned the lamp personally. FWIW when I was installing fiber optics systems we always used 91% isopropyl alcohol to clean connections and Rx/Tx ports.

Paladin

......................................................................................
Paladin-

I'm not trying to be a wise *** or anything, but I am wondering what company, or maybe an individual, would send you a P91 like that. Every one of the P91's I have ever received were enclosed in a little clear bag and stapled shut twice with the SF logo and thick paper, or maybe it's thin cardboard. Just Curious.

And as you already knew, SureFire clearly states to not touch the lamp. I would think that most people would know, like you did, to handle the lamp correctly.

Thanks for the report.:thinking: