Run-time observations for a 1xAAA green pointer

[comradmax]

Bought a 40mW LPM verified 532nm pointer from this thread. It is powered by a single AAA battery, and came with a AAA primary from the seller. The laser has an impressive visible beam, the dot is TEM00, little to no splash. Typical run-time is ~5m, see the rest of this post for more info.

I have done some tests with rechargeable Soshine NiMH 900mAh AAA cells. This battery is able to provide more current than a regular primary cell, the output is also more stable with the NiMH.

Typical output
The behavior with primaries vs NiMH is different, probably due to the battery's ability to supply current. Primaries: power at full from the start or takes less than 5s to "warm-up", after 30s power starts to drop, beam not visible at 1m mark. NiMH: beam goes to full power from the start if batteries are fresh, otherwise about 30s to "warm-up", high is strong for 1m from this point, then dies off to a dim beam.

Dimming
With both types of batteries the laser would get warm to touch by the time its output droped. I confirmed that the drop was not due to the battery: I would quickly try a fresh one, and it would turn on with the same dim output. I would let it sit and cool down for some number of minutes longer than 5.

Subjective testing methodology: only care about the run-time while beam is visible. Sure, the dot is still very bright even when the beam is invisible, so this can still be used as a pointer. My main concern was with run-time at full power, so this is what I tested. Here are my steps:

1) turn the laser on
2) let it "warm-up" to full power
3) when the beam becomes dim, turn it off
4) measure voltage from the battery

Here is a plot of the several runs I did. All the slopes look close enough to say that the rate of discharge was the same. Once the battery drops to ~1.3V the laser would not be able to boost up to full power again. The top line is from a cell that just came off the charger. The other lines are fully charged too, but sat for some time, so their voltage settled to a lower value. As you can see the longest run-time was with the super-fresh batt and lasted for a total of 400s.

 

[00Giorge]

Pics?

 

[RA_pierce]

Are you aware that DPSS lasers have optimal operating temperatures?
As the laser warms up, it will climb in power. Once the optimum temperature is reached, it will peak, settle, and then drop in power from there until it is allowed a cool-down cycle.

Are you sure that the batteries are drained after only 400s of use?
The NiMH batteries I use will work well down to 1.27V per cell in most of my lasers.
I don't use them in the 1xAAA 5mW greenie I have because the voltage is too low.
A good, new primary will start off at 1.6V, so Alkalines may be your best bet for this laser.

While the low battery capacity may contribute to your dimming issue, you need to keep in mind that a small laser with minimal heat-sinking mass will require a short duty cycle.
DPSS lasers behave differently. Some prefer warm, some prefer cold, and others like to be in-between. Even if the batteries are still capable of supplying sufficient power, excess heat will change the performance of the laser.

 

[comradmax]

Pics?

Pics of what, sir? It may be hard to see, but there is a link in my 1st sentence to the thread where I bought this laser. Other than that I didn't do anything cool to take pics off.

Are you aware that DPSS lasers have optimal operating temperatures?

Are you sure that the batteries are drained after only 400s of use?

you need to keep in mind that a small laser with minimal heat-sinking mass will require a short duty cycle.

Yes, I think I understand the operation of DPSS lasers. What you described is exactly how the laser behaves: warms up to operating temp, then gets too hot and output starts to dim.

I have let my batteries rest for long periods of time. Sometimes they rebound in voltage enough to lase again. I did, however, notice that when under 1.3V they all consistently are not able to boost up enough voltage to lase at full power. One of my primaries was depleted down to 1.28V, but I have not done much testing with those yet.

Your point about short duty cycles is fully taken. I think this is the trade-off when using a little AAA cell for power. This is a tiny keychain green laser with 40mW output after all.