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Will this Damage my Sanwu Pocket Laser?

beamjunkie7

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Hey Everyone -- I was wondering if anyone who knows more about the diodes and drivers used in the Sanwu Pocket lasers (specifically the 200mw 405nm model) could tell me whether or not I would damage the diode by running the laser on a 1.5V AAA instead of the prescribed 3.7V 10440 battery. The idea is to limit the output as much as possible (as he really does not want or need 200mw) and increase the convenience factor (no need to worry about charging).

I would like to purchase this laser for my dad, as he loves lasers and he often carries one in his pocket but most 405nm lasers are too large for that. I have the 455nm and 488nm Pocket lasers, and feel they are ideal for this use case. His favorite color is purple, and I have given him cheap-o purple lasers before but they are not nearly as well-built or portable.

When I swap the 10440 for a AAA in my 455nm model the output drops significantly, but I am not versed enough to know whether this is hurting the laser or not (so I only did it for a second).
Does anyone know if this is an awful idea, or if under-driving the diode would be alright?

Thank you for your advice!
 



Encap

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Common sense would be to ask Sanwu about it.

Hope you realize that 405nm is not very visible and difficult for most eyes to focus on as well---405nm is 10X less visible than 455nm so.. a 20mW 455nm is about the same brightness visually as a 200mW 405nm you can run the comparisons here: https://slickscreen.github.io/laser-tools/brightness/
 

beamjunkie7

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Thank you for the reply, Encap. I did send an email to Sanwu customer service asking the same question, but I respect the knowledge on this forum and figured I'd ask here as well to see if anyone had any opinions.

I do know that 405nm is much less visible, and I have several 405nm Ebay lasers (both pen format and larger hosts) that all have visible dots and are likely around 50mw (based on their ability to pop black balloons and light matches with black Sharpie on them, when focused).

These are fine with me -- as long as the dot is visible, that is all I need this laser to do.

The only reason I am buying the Sanwu Pocket model is because of its excellent build quality and small form factor. If they made a 50mw version, that's what I would get, but alas they do not.
 

Cyparagon

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Undervoltage doesn't damage any drivers I've ever heard of. Efficiency may suffer greatly, and the diode may not lase, but I don't see any mechanism where it would be harmful.
 

Unown (WILD)

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I'm surprised the driver doesn't have under voltage protection for the battery. 1.5v would kill any liion battery
 

Benjamax

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I'm surprised the driver doesn't have under voltage protection for the battery. 1.5v would kill any liion battery
It may still have protection because a Li-Ion battery that has dropped to 1.5V is really dead and would give almost no current. So it may recognize ~1.5V+current as Alkaline or NI-MH.


edit
To answer the OP from my own scope of knowledge (which is not a lot but better than nothing), I am unaware of diodes that die from too little power. I guess in theory it's possible for a driver to pull that trick if the design is criminally stupid.
 

beamjunkie7

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Thanks to everyone who replied! Sanwu replied to my email and offered to reduce the output of the laser as a custom order, which I had heard they might do -- pretty cool of them. They also said it should not cause any harm to the diode to run under-voltage with a AAA.

To clarify, my fear with running too low of a voltage was that the current would increase, and therefore heat would increase. P=V*I
-- If the driver is set to demand a certain amount of power, then current would have to be higher than expected to make up for the lower voltage of the AAA and that is inefficient and sometimes harmful.
-- However, if the driver is set to demand a certain amount of current, then the AAA just has to supply that amount of current and the voltage is an afterthought which will just cause the total power to be lower, and should be alright.

I figured the second option was more likely, as my very limited knowledge told me that drivers are often set to a certain current, but I was definitely not sure of that. If any of this is wrong, feel free to correct me -- I am doing my best!

The point about the low-voltage cutoff detection on the driver (or lack thereof) is a good one, I didn't consider that. Maybe the driver just isn't that intelligent? Or, maybe Benjamax is right and it is just seeing the battery as a more standard chemistry.
Or, it doesn't consider chemistry at all, and it is just asking for a particular current regardless of voltage?
 

Unown (WILD)

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One way of knowing for certain is seeing what the specs say on input voltage. If it says 1.5 to 3.7 or something that would let you know.
 

Cyparagon

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Well, I have a litany of bench power supplies and a sanwu pocket. It's the 489nm version, but I ran some tests for you anyway, since the limitations appear to be driver IC related, given the the rather sudden cutoff.

The driver stays in regulation anywhere between 1.9V and 5V. I didn't go higher than 5V. The current draw is highest at 1.9V, about 1.1A for my model, then drops drastically below that voltage. At 1.5V, current draw is down to 200mA. At 1.47V, current is down to 125mA. This is lasing threshold - below this point, there is no real laser light being emitted. At 1.45V, there is no current draw. Less than 1mA anyway.

So it would appear alkaline cells are not ideal, since you only use <5% of the capacity before the driver stops drawing current. It would be better to use one of the energizer lithiums at 1.7V, or perhaps a NiZn AAA at 1.65V, but the latter is comparatively expensive and requires a special charger and has lower energy density anyway. In any case, the brightness changes a lot depending on the cell's charge level at these low voltages.

This also means protected lithium cells are preferable to non-protected. 1.9V Usually isn't low enough to damage lithium cells from my experience (it's the 0V or reverse charge from others that may be in series that ruins things), but nevertheless it is lower than advised by the manufacturers, so best to avoid it if you can.
 

beamjunkie7

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Thanks to everyone for the suggestions and great information.
Cyparagon, that is exactly what I needed to know, so I really appreciate you taking the time to test your laser!

I ended up ordering my dad the 50mw 505nm Sanwu Pocket laser.

After reading more about the 405nm wavelength, and reminding myself how dangerous lasers are to your eyes (especially short wavelengths like 405nm), and remembering my dad already suffers from some macular degeneration, and knowing he probably won't wear goggles using his laser...I made the executive decision to buy the weakest Sanwu Pocket model they offer.

The 505nm wavelength is still cool and unique, and the lower power level makes more sense for what my dad will use his laser for. For fun, it should still pop a black balloon when focused (and with goggles ON), and it will have an epic beam at night. He mostly uses it as an EDC laser.

Can't wait to see how it looks, and finally give my dad a high-quality laser of his own! Fingers crossed that it will arrive before the holidays...I ordered it November 25th, so I know it will be a close call. Thanks again for the help!
 




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