FM3 w/ 2x9AA = burnt 1185

vacuum3d

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Since I haven't heard anyone else complaining, I assume my situation is unique.
I don't know if I'm unlucky, or am I just lame (may be a bit of both), but all three potted WA1185 that I got from Fivemega got burnt while using the FM3 with 2x9AA Lenmar2000.
burnt_1185s.JPG

The bulb on the left is a good bulb for reference. The three on the right are all burned.

Let me clarify, they got burnt, but would still light up dimly. Here's what happened...

Bulb #1) 2x9AA rested fully charged cells, installed the bulb, blinding bright for 5 seconds, then turned dim.

Bulb #2) Not knowing any better, screwed in another 1185 in the same setup. Turned it on, bright, bright light. Had fun with it for about 10 minutes. Put it by the bed side and went to sleep. Woke up the next morning. Turned on the light. Dim! Looked at the bulb. It was burned?! I couldn't tell whether turning it on in the morning caused the burn.

Bulb #3) Recharged and rested the batteries for a day. Put in my last 1185. Turned it on. No problem. Played with it intermittently for two days. Total run time roughly 30 minutes. Stored the flashlight away and went on vacation for two weeks. Came back from vacation. Before turning on the flashlight, this time I looked at the bulb first. It looked burned?! Turned it on. Sure enough, it was dim. I couldn't believe it. It got burned while the light was turned off and resting. That's probably the same thing that happened to Bulb #2.

Could someone explain the above phenomenon? I don't think it was caused by the voltage. Everytime I burned a bulb I measured the voltage. It was never above 11.5, more like around 10.8. The problem wouldn't have been caused by the potting job, would it? I ordered 10 bulbs from the current WA GB, but at this burn rate, that won't last me a week. Please help /ubbthreads/images/graemlins/bowdown.gif

ernest
 

KevinL

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/ubbthreads/images/graemlins/huh.gif /ubbthreads/images/graemlins/ooo.gif *gasp*

If I may be so bold..

I think I may know why. When a bulb fires up cold it sucks huge amounts of current. On a normal group of 9AA NiMH, the current draw in turn causes a voltage sag, which is enough to bring the voltage down to safe levels, thus I can fire a 1185 on a 13.8V pack straight off the charger (9 NiMH) without causing catastrophic failure. There are some who have done this on more powerful cells than mine, and toasted bulb, reflector, Borofloat lens and all.

However, FiveMega's adapter is a cutting edge piece of work that stacks two groups of 9AAs in parallel, thus enabling them to deliver 2X the amount of current. Even a rested pack would be in the region of 12+ volts and due to the lack of voltage sag this would be enough to cause serious harm to a 9.6V rated bulb (the 1185).

This is why some lamps cannot be run on the Surefire M6, even though it is technically a 9V platform, it's 2 parallel groups of 9V.

If I were you I'd back it off to 7 or 8 NiMH per channel and use dummy spacers to take up the slack. It would be a crying shame to destroy the last bulb.
 

lasercrazy

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So you're running the fm body with the 18aa adapter. That is an odd thing to see, I'd think it would just flash if it was going. Could you have gotten a bad batch of bulbs?
 

xpitxbullx

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My Fivemega Fat Mag85 runs great with Rayovac IC-3 batteries and no problems with my bulbs. I always rest them for a couple hours.
 

vacuum3d

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Kevin, your guess sounds logical. I guess I'd have to try it when I get my bulbs from the WA GB.

lasercrazy, the thought of a bad batch of bulbs crossed my mind, but my gut tells me that's probably not it. I couldn't see any imperfection on them.

pitbull, I'm assuming you're using 2x9AA as well, right? I'm interested to hear whether anyone else using 2x9AA have seen my problem.

What really puzzled me is that when I turned off the light after Bulb#3, I looked at it and it was fine. Coming home after two weeks and looked at again, the bulb was burned. How could that be? Some ghost playing with my light at night?


ernest
 

xpitxbullx

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If the bulb was fine after you turned it off, left it off, then looked at it 2 weeks later, then it sounds like there must have been SOME power still going to the bulb. Perhaps you have a short somewhere giving just enough current to the bulb at such a low voltage to cause the gases to solidify or frost the glass. But, of course, the filament will remain intact. Without enough 'working' gas to power the bulb to full strength, you will get a weak light output.

Leave the batteries in. Remove the bulb. Make sure the switch is off. Test for voltage with a multimeter at the pedistal. This may give you your answer. If you get any type of voltage reading, you will need to fix your switch.
 

vacuum3d

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I'll test it tonight. However, this doesn't explain how the first bulb got burned. I was watching it go from bright to dim in 5 seconds.

ernest
 

Ginseng

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<font color="red">You overdrove your bulbs.</font> In fact, I'd say you were VERY lucky that you did not have an explosion as several of us have experienced. I have seen this happen in the "MoMag" which is WA01185 on 10xAA nimh. The other times, the bulbs blew up, damaging the lens, reflector and depositing that tungsten dust all over the inside of the head.

I would guess that the reason the bulb does not show the smoky residue right away is that the capsule has to cool down somewhat to enable the sublimated tungsten to redeposit. Although some redeposition occurs right away and you see that manifested as dimming.

Running parallel sets of cells is fine but I would drop back to 8-cells per series. This will still give you superlative voltage under load and great runtime. Running 2P9S is just asking for trouble. In a word, DON'T DO IT.

Wilkey
 

vacuum3d

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/ubbthreads/images/graemlins/frown.gif
I thought the 18cell battery holder by FM is designed for the 1185. I guess I'll have to acquire some dummy AA. Thank you for your expert opinions.

ernest
 

snakebite

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do you see any cracks?
looks like they leaked air.could be bad bulbs or you got lucky and they didnt grenade.
 

xpitxbullx

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Perhaps my Rayovac IC-3's have a higher internal resistance because I run my 2P9AA fine for 5-15 minute intervals.

Ginseng, do you think thats the case or have I been just lucky?
 

Ginseng

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Pit,

I have never tested the IC-3s so I can't say how they perform under load. What capacity are they? Vac was using 2000mAh, which are powerful enough in a single stack so in a 2P9S (two parallel strings of 9 cells in series), they just push it over the edge.

I would say that you might want to try it on 2P8S and see how it looks. If it's bright enough for your general use, then stick with it and get a few more hours of bulb life. If you need to smack down, then go with the 2P9S. I would say that 2P9S of the new 2500mAh cells might not be a bad thing.

Wilkey
 

lasercrazy

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I'm running mine on 18 ansmann 2300mah batteries and have yet to have the bulb either do that or explode.
 

xpitxbullx

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I can't do a parallel voltage reading yet but under load, the amps for 2P9S with Rayovac IC-3's 2 days off the charger is 3.25A
 

lasercrazy

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I just had my bulb do that, /ubbthreads/images/graemlins/wink.gif now where do I get dummy AA batteries?
 

Ginseng

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Lase,

You can get blanks somewhere, but most folks make it up with either bolts, aluminum screen door hardware or my preferred method, small diameter copper pipe and pipe caps.

Wilkey
 

lasercrazy

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I decided to try and run my bulb into the ground and the glass on it is all deformed. It's still running, the glass is glowing red and looks like it's about to have a meltdown. /ubbthreads/images/graemlins/wink.gif
 

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