Weird Fenix L2D-CE behavior.

Hi guys. A few days ago, I was playing with my L2D and decided to do a roof bounce test. The flashlight was at medium level and when I put it down on the table to tailstand, it changed modes to low. It did slightly 'knock' the surface when I put it down so investigating, I realized that was the cause for the mode change. I repeated the results with a vertical drop onto the table of of about 1/2 to 3/4 inch. The mode change also occured from high to low but not from turbo to strobe.

I tried repeating the mode change by quickly tapping the switch with the flashlight on but it did not happen. It however did happen if I tapped the front of the light (resting it down face down,) and with a slightly greater force if I hit the side of the light against a table. I must stress that I'm not abusing the light, it's just a light tap which causes this mode change.

Have anyone else experienced this behavior? Can someone try to repeat these results with their own light?

The batteries in the light at the time were amondotech's enduro rechargeables.

Thanks.

The changes of level in Fenix flashlights happen through a brief cut of the power. This cut is normally achieved through the tail switch but may well happen when the top of the battery leaves briefly the contact in the head or there is a break of the contact between the two batteries. The latter is IMHO what happens in your L2D when you tap it against a hard surface. In turbo mode you tighten the head and consequently load a bit more the spring and thus the contact is stronger.

PS: if you stretch a bit the spring in the tailcap it is likely it will not happen anymore

I thought about that and realized that if it was a cut in power similar to depressing the tailswitch, wouldn't the level change from low to medium or from medium to high instread of from medium/high to low?

I've noticed the same thing with mine, just didn't bother to post about it. Figure its some sort of design issue, and no amount of posting would fix it for me!

Not sure if the batteries are falling backwards or just moving side to side and hitting some grime or something.

As Bowler noted, when this occurs the light does not act the same as it would if you had tapped the switch it goes right to low. I have a few overly complex theories, and one simple one (Ockham's razor?).

The light when cycled through turbo goes back to low despite what mode it was in before turbo was activated. So is the "putting the light onto a table for candle mode" bouncing the head down and very very briefly activating the turbo mode? Seems reasonable, however, I've unscrewed the head a couple turns and still had it act this way so I'm not convinced this simple theory is correct.

The more complex theories have to do with the batteries bouncing, and providing a rapid oscillation of on/off voltages, and having the light electronics do some kinda reset, or some other funky thing internally.

Kilovolt said:

The changes of level in Fenix flashlights happen through a brief cut of the power. This cut is normally achieved through the tail switch but may well happen when the top of the battery leaves briefly the contact in the head or there is a break of the contact between the two batteries. The latter is IMHO what happens in your L2D when you tap it against a hard surface. In turbo mode you tighten the head and consequently load a bit more the spring and thus the contact is stronger.

PS: if you stretch a bit the spring in the tailcap it is likely it will not happen anymore

Click to expand...

Even with the head unscrewed enough, so the turbo mode contact won't be able to touch the body, this glitch happens. I also noticed it. When bumping the light like this, the positive contact of the battery disconnect from the contact in the head for a very small length of time. This makes the circuit reset itself...

Since "digitally" controlled UI has been included in these lights, glitches and bugs can happens. I just find it funny and it doesn't affect much at all the normal functioning of the light. I dream about the day a light will output blue light when a bug happens! Flashlight BSOD

PegAir said:

The more complex theories have to do with the batteries bouncing, and providing a rapid oscillation of on/off voltages, and having the light electronics do some kinda reset, or some other funky thing internally.

Click to expand...

WildChild said:

When bumping the light like this, the positive contact of the battery disconnect from the contact in the head for a very small length of time. This makes the circuit reset itself...

Click to expand...

It does seem very likely that the circuit is resetting at least in mode 1 but, it sill is very hard for me to believe that the battery is disconnecting since the taps to reset is often very light. I also tested this theory by quickly tapping the switch to turn off then on the light for a split second (too fast for the level to go up but fast enough for the light to flick off) but the glitch did not reoccure. :shrug:

Maybe we wouldn't be able to figure it out but I'm glad that there are other flashoholics in here who's picky/observant enough to discover the glitch as well.

BTW WildChild, I'd love if the glitch caused the light to continually brighten from nothing to brightest back to nothing again!

This same behavior was reported a bit after the lights first came out. I don't believe there was ever a 'fix' reported other than to follow the premise of this old joke:

A man goes to the doctor to report a pain in his arm. The doctor says "Does it hurt when you do this" and he holds up his am. The man says "Yes", and the doctor says "Well, don't do that" (cue rim shot).

Sorry.

Yeah, I've never noticed this in real use, but WildChild suggested I try it myself.. Put it on Medium and tap it on something. Sure enough, it reset to low.

So the only real life situation I can think of is dropping the light. Maybe if you're holding the light and doing something like climbing a hillside and the light bumps a tree/rock as you climb..

I wonder if you put it on Turbo and bopped it, would it go into strobe? That'd stink.

Derek Dean said:

This same behavior was reported a bit after the lights first came out. I don't believe there was ever a 'fix' reported other than to follow the premise of this old joke:

A man goes to the doctor to report a pain in his arm. The doctor says "Does it hurt when you do this" and he holds up his am. The man says "Yes", and the doctor says "Well, don't do that" (cue rim shot).

Click to expand...

Good one, couldn't agree more! :wave:

Real world use - not a problem.

Repeatedly "drop-testing" on hard surface - maybe a problem.

LOL Dean, that was good

Derek Dean said:

This same behavior was reported a bit after the lights first came out. I don't believe there was ever a 'fix' reported other than to follow the premise of this old joke:

A man goes to the doctor to report a pain in his arm. The doctor says "Does it hurt when you do this" and he holds up his am. The man says "Yes", and the doctor says "Well, don't do that" (cue rim shot).

Sorry.

Click to expand...

Ha. Got a weak laugh out of me at 9:59 A.M.

Daughter and wife are still in bed.

Khaytsus said:

So the only real life situation I can think of is dropping the light. Maybe if you're holding the light and doing something like climbing a hillside and the light bumps a tree/rock as you climb..

Click to expand...

An unfortunate real-life situation: using L2D-CE as bicycle headlight.
The design flaw discussed above effectively limits bike-mounted L2D-CE to Low and Turbo modes only. Bike vibrations quickly turn Medium and High modes directly back to Low mode.
Details:
My main L2D-CE use is as my bike headlight (there's a huge price/size/performance advantage of Fenix lights vs. bike-specific headlights). I keep it attached to my bike handlebars with a $5 TwoFish LockBlock (an elegantly simple mount made of shaped rubber and velcro straps), which absorbs some (but far from all) of the road vibrations.
I cannot use the L2D-CE in medium mode or high mode. Road vibrations will, sooner or later, reset to much-less-visible, less-safe, low mode. Because of this, I generally keep the light on Turbo whenever I ride(stays in Turbo despire vibration, as in above posts). When I need more than 2 hours of night riding (or even, say, 1 hour of night riding if batteries are at half), I must conserve and use Medium or High mode when I can, but this requires checking light every so often ("has it gone into Low?"), plus tapping through modes with attention on light output while riding, which can be dangerously distracting while one should be checking for traffic and obstacles.

So: any mod/fix I can make to my light to help prevent this? Is this an _unavoidable_ consequence of Fenix's patented twist-head-to-select-mode-cluster feature? Does this feature mean any shove forward of batteries from vibration will simulate a "twist to (Turbo/flash) position, then immediate twist back to General (L/M/H/SOS) poistion",
and thus a shift to low?
Perhaps battery-liner sleeves would solve this??

Cheers,

Bazzers

Interesting. I also use my L2D as a bike light in a Lockblock, but I've always run it in turbo. I didn't know the other modes posed a problem.

How about replacing the rather flimsy stock spring with a stouter one? The springs in Fenix lights are wimpy.

You could first try stretching out the stock spring a bit. This isn't the proper way to increase spring power. Ideally, you should replace it, but sometimes a little stretching provides enough extra oomph to solve an issue.

As you suggested, a liner would snug up the batteries. The increased friction, particularly in combination with a heavier spring, might solve the problem.

bazzers said:

An unfortunate real-life situation: using L2D-CE as bicycle headlight.
The design flaw discussed above effectively limits bike-mounted L2D-CE to Low and Turbo modes only. Bike vibrations quickly turn Medium and High modes directly back to Low mode.

Click to expand...

Wow, yes you're right. That does suck. I have a bike mount too which I've intended to use the Fenix on when I need to and I hadn't thought of that aspect.

Maybe someone can test something... I don't have anything on hand to I don't think. Put some sort of plastic washer or such in the head so the head can be screwed down completely yet not go into turbo mode and see if that fixes it.

If you sometimes need turbo mode while on the bike, this isn't a good solution, but I don't see that being a problem.

I think if I really start using the bike at night more, I'll get a P3D and RC123's to go with it. But I wonder if the P3D has the same bounce-reset problem. I should read back through this thread some more.

Glad you brought this up, I hadn't considered it even though I'm looking forward to trying out the P2D on the bike.

I noticed this 'feature' (not 'problem') when Fenix first came out. Whenever I needed a lite quickly, I would simply depress the head assembly inward while holding the lite in my hand. For the duration of holding the head assembly inward, the lite would remain on. Modes will change likewise if desired. This is a great feature in my opinion because when you need a quick lite you DON'T have to screw in the head as long as your fingers are positioned as to not completely block out the beam of lite.