Laser pointer doesn't work in cold - batteries?

[sculptor]

Been having problems with my green laser pointer stopping working. Replace batteries, fixed. Few minutes later, dead. Replace batteries, fixed. Few minutes later ... yawn. Put in pocket, and it was working again. I suspect that the batteries stop working in the cold, and get better when warm.

(The laser itself has such low thermal inertia it is a bit hard to tell if its the laser or the batteries).

Anyone seen something similar? Any recommendations on good AAA batteries for cold weather? (The laser lives screwed to the side of the scope as an all-sky finder/pointer, so I can't just keep it toasty warm in my pocket.)

[OneOfOne]

I have similar problems with my 5mW when it is cold. When I turn it on initially, it can be quite hard to see but after 20 seconds or so it suddenly gets a lot brighter. I think after this time the laser has warmed up and the light output increases to the specified level. I haven't actually tried new batteries to fix this problem though, I just put up with it. As I only normally use the laser to initially align the goto with 3 stars it is a fairly minor problem. I just bought a 30 from Sirius for pointing out things to people and they recommended getting a couple of Lithium AAAs. Remains to be seen if the 30 has warmup problems or if the Lithium batteries are affected by the cold, hopefully they work well as they cost $11 for the pair!

[sheeny]

Yep. Sounds familiar. Mine does the same on cold nights. I'm lead to believe that the lasers are a bit touchy about the cold - more so than the batteries. I find keeping it in my pocket to keep it warm between uses works OK.

Al.

[sculptor]

Al has encouraged me to be more scientific. I put the laser (empty), a set of cheap carbon batteries, and my brand new lithium batteries all into the freezer and did the shopping. On return, the laser plus new warm carbon batteries was dead as a dodo, but gradually came good (from the warmth of my hand and/or the batteries) working feebly in about 10 sec, and up to usual power in a minute or so. Conversely, freezing cold batteries worked first up in a warm laser. Conclusion: the laser itself is by far the worst offender. That means I need a way of putting it back in very exactly the same position each time for use for 3-star alignment. (Thinks: mmm. Have an idea....)

By the way, for people who haven't tried using a laser for alignment, it's (pardon the pun) brilliant! No lying in the mud with a cricked neck, no wondering if you've got Algorab or the one next to it, steering is intuitive, and (except in winter or at star parties) it will put your alignment star in the middle of a 0.5 deg low power field. But the cold thing is a pest. Perhaps I can knit it a tea-cosy.

[rogerg]

I'd recommend putting a small dew heater coil around the green laser if you have it mounted. (resistance wire)

That saves having to take it on/off, but does add more cables/batteries to the mix.

[sheeny]

Kitchen science! Love it! Well done!:thumbsup:

I agree with rogerg - make a laser heater!:D

Al.

[bojan]

Guys, current green lasers work in temperature range between 10-30C only.
This is because of their design (on wikipedia you can find why it is like that, and it was discussed in another thread last month, I think).
We will have to wait for new lasing materials to be developed before we will be able to use them in wider temperature range .. and for affordable price of course:-). The story is similar to the development of LED's - first there were red LEDs, then amber.. and only couple of years back we have commercialy available Blue (and White, which is actually blue LED radiating into fluorescent medium which absorbs and re-radiates energy in green-red bandwidth, which then appears white to our eyes).

[sculptor]

I feel kinda more foolish than usual now you've explained that, bojan. The SPECIAL WARNING on the laser when I bought it was written in white ink in zero point font, for my reading pleasure. However it does say something vague about "warm-up time: 5 mins". They must mean 5 mins in the thermos with the coffee, rather than 5 mins of use.

The heated laser sounds sensible and fun, but in the mean-time, I've made a simple socket, permanently mounted on the scope, for the laser to slip into (and out of) easily and precisely. Socket made as follows: Took a 4" length of aluminium tube that just barely clears the (cylindrical to 0.05 mm) body of the laser. A transverse slot about 8 mm long and about 5 mm back from the "caudal" end holds an O-ring which projects a tiny bit into the lumen of the tube, thus taking up any free play and holding the laser in place. At the "cephalic" end, a tight longitudinal slot accepts the "go" button, thus preventing axial rotation. The wall thickness is such that the "go" button, when pressed, is just flush with the surface. A piece of springy PVC sleeve sits over the slot. The entire assembly clamps permanently into a six-screw finderscope mount. When you push the laser into its socket, the PVC sleeve (a) pushes the button on, and (b) further takes up slack. Did not even need to fire up the lathe.

Now the laser can stay warmy toasty in my ski-jacket, be produced to educate unsuspecting guests, or be slipped into the socket on the scope for the couple minutes it takes to do the first three alignment stars. Some foam tube round the business end may also help delay cooling during those few minutes.