Achieving consistent power from cheap 5mW green

I recently bought this: odicforce
and (though completely new to lasers) the observed brightness seems to match online videos and descriptions. There's minimal warmup time, and I basically find his "binning" type approach credible.

I got Pana Eneloop precharged AAAs because brightness on alkalines, though initially great, declines quickly so it gets through batteries too fast. Turns out the drop from 1.5V to 1.2V simply kills brightness from the outset, unfortunately.

To achieve consistent (or at least economically repeatable) new-alkaline-level output, I see two potential options:
- A single (reputable brand, not unprotected) lithium ion 10440 + dummy 'spacer' AAA. Some say the voltage increase to 3.6V or so could fry the laser, but most say cheap ('eBay type') pens can cope with one alone. An increase in brightness is often reported, and I can believe that given the reverse effect of lowering voltage. The pen is cheap so it's a risk I'm prepared to take. Not so keen on expensive chargers or missing fingers, though.

- It's listed as including an "ACC driver". Can I just 'adjust' this upward to increase brightness counter to the decreased NiMH voltage? Is that the same as 'pot-modding', in which case the earlier post (linked) said binning rendered mine unsuitable?
No! So maybe this is my solution?

Apologies for my noobiness. I've read around and got this far, just need someone knowledgeable to fit it together and help me decide

I would say go with the 10440 and spacer. The driver will produce a little more heat, but it shouldn't be enough to hurt it, if you stick to a decent run time.

As for your second option, that is pot modding, as the only adjustable part of the driver is the pot. Although the driver may not have a pot, as these cheap green modules tend to have a resister in place of the pot.

Also, in the end, it may still fluctuate in brightness, as these lasers are inherently unstable and sensitive to temperature.

Many of the greens I have tested have worked fine down to 2.1V input. I hope you're not just guessing at power from looking at it. Have you at least verified the battery current is lower on NiMH?

I am indeed just guessing, but the visible brightness is clearly diminished with the eneloops. With brand-new alkalines I can see the actual beam at night / dim indoor lighting. With the eneloops it just looks like a <1mW dot - no beam in the aforementioned conditions, and barely visible at all in bright sunlight.

My cheap multimeter estimates the following for each pair of batteries used:

Panasonic Eneloop Ni-MH 750mAh
3.8A & 4.05A
1268mV & 1275mV

Energizer alkaline disposable
2.9A & 3.05A
1438mV & 1523mV

...so the current is actually higher for the eneloops, but voltage is lower which further implies voltage is the culprit. Forgive my lack of electrical knowledge, but doesn't the 'CC' in 'ACC driver' mean current drawn is independent of the battery anyway (ie. determined by the pot)?

In which case by my math, increased power output is possible by increasing voltage or current (ie. decreasing pot resistance).

Thanks again for your help

If the laser is drawing over 400mA,
something is wrong.

benxyzzy said:

I am indeed just guessing, but the visible brightness is clearly diminished with the eneloops. With brand-new alkalines I can see the actual beam at night / dim indoor lighting. With the eneloops it just looks like a <1mW dot - no beam in the aforementioned conditions, and barely visible at all in bright sunlight.

My cheap multimeter estimates the following for each pair of batteries used:

Panasonic Eneloop Ni-MH 750mAh
3.8A & 4.05A
1268mV & 1275mV

Energizer alkaline disposable
2.9A & 3.05A
1438mV & 1523mV


...so the current is actually higher for the eneloops, but voltage is lower which further implies voltage is the culprit. Forgive my lack of electrical knowledge, but doesn't the 'CC' in 'ACC driver' mean current drawn is independent of the battery anyway (ie. determined by the pot)?

In which case by my math, increased power output is possible by increasing voltage or current (ie. decreasing pot resistance).

Thanks again for your help

Click to expand...

How did you measure current in your reading? did you put your DMM in current mode and connect batterys directly to DMM or something?

benxyzzy said:

3.8A & 4.05A
1268mV & 1275mV

Energizer alkaline disposable
2.9A & 3.05A
1438mV & 1523mV

Click to expand...

Please do not measure the current of just the cell with a multimeter. The ammeter function is an electrical short, and is exceedingly bad for the cells, and might damage your meter as well.

Put your ammeter in place of the tail cap. This will show you how much current the laser is drawing when you press the button. Google the correct way to measure current if you are not sure.

Cyparagon said:

Please do not measure the current of just the cell with a multimeter. The ammeter function is an electrical short, and is exceedingly bad for the cells, and might damage your meter as well.

Put your ammeter in place of the tail cap. This will show you how much current the laser is drawing when you press the button. Google the correct way to measure current if you are not sure.

Click to expand...

I Was just waiting for him to reply then i was going to say what you said Cyparagon,
Lucky hes not using Li-Ion batterys, otherwise he may be asking why the wires got hot or the Battery exploded and possibly DMM fuse blows

How did you measure current in your reading? did you put your DMM in current mode and connect batterys directly to DMM or something?

Click to expand...

This is exactly what I did.
You are all right in that I don't know what I'm doing. It's all cheap, freshly bought kit with which I am prepared to learn and experiment. I wondered why the batteries were warm afterward

Put your ammeter in place of the tail cap. This will show you how much current the laser is drawing when you press the button. Google the correct way to measure current if you are not sure.

Click to expand...

with eneloops
2.48V
105mA (roughly)

with alkalines
2.8V
146mA

I should mention the visible difference in brightness has lessened as the Energizers lose charge. But it's still obvious, as per the above readings.

I may attempt to quantify the brightness with a webcam or something...

EDIT:
The guy at odicforce replied to my email from last night (I'm in UK) answering everything
- ACC based on LM358 chip
- OK with input voltage up to 5V and output 'should not vary much' between 3-5V
- They have a pot which can be increased 'a bit'; 5mW lasers have small crystals but can often convert more than 5mW; heating may misalign the crystals and infrared conversion could be an issue.

I remember reading the crystal / IR stuff before, but am mainly concerned with boosting up to a consistent 5mW rather than going higher.

Getting a consistent 5mW could be very
difficult without temperature control. If
you do decide to pot mod, don't turn the
pot while the laser is running. Also, the
pot is likely reversed. That is, turning
it counter clockwise increases output. Be
careful not to allow the current to go
above 500mA.

Thanks for all your advice. This has become an entry-point to (very) basic electronics for me.

So I drilled a few holes in the pen looking for the pot, which took a couple of guesses as turns out it's on the underside, bottom-left corner of the board (not above the button like many photos & vids online).

It was already 80-90% toward the max though (CCW increases output), and turning all the way didn't seem lead to much/any improvement. I think my hope of 'compensating' for low voltage using the pot (decreased resistance = increased current = increased power) was misguided

So short of some voltage-boosting component, li-ion may be the only way. In which case I'll cut down the pen tube rather than use a spacer ( remove all the drilled holes and reduce form-factor )

You may want to consider nickel-zinc (NiZn) cells. The energy density is not as good as NiMH, but they are rechargeable, and operate at 1.6V nominal.

I actually saw some of those in Maplin a couple of days ago, but didn't know what they were at the time (plus they'd sold out of the requisite chargers).

Increasing the pot did actually increase current by 15-20mA - maybe more with fresh batteries, given these Energizers have now seen some use. It's just not enough to really make a difference, given the voltage is still below recommended 3V minimum.

I bought some protected Trustfires, charger and AAA spacers from DX, but they'll take awhile to get here. I'm still kind of interested in boosting the voltage from more typical / easy to find / safe batteries if possible. Form factor is somewhat flexible now I've drilled into the original casing

Well there is no question they can put out
enough short circuit current, just not when
the load is dropping 2V. Some joule thief
type setup might work, but it would have to
be done very carefully so as not to fry the
fragile laser diode.

I've cut down many a pen laser to make a shorty running on a single 10440 Just take something like a paint brush that will contact a decent amount of the bottom cap, hold the host and smack the brush end down so the end cap pops off. Watch where it goes though. I use a small hacksaw with the host pulled tight against something to make a nice clean cut. Be careful you don't cut too short!
You can see some of them I believe in my link showing the pen tutorial stuff. Think you'll get a kick out of that thread.

-Pete

Never heard of NiZn cells. Will have to look that one up.

Thanks Pman, that is useful! My 10440s finally came today and it's the brightest yet, so I'll probably follow those threads when I chop it down.

They came precharged to 3.72V; I'm guessing stick them in the charger when it drops to about 3V?