510nm pointer for $19 legit?

[Benm]

A polarity indication by sticker or other marking is obviously a good idea.

As for the spring being the negative contact: That is indeed very often the case, for the whole flat negative / nipple positive thing on -commonly used- batteries.

But as always there are exceptions and problems with this: You do get those 18650 (and probably other) lithium batteries that have a flat top, probably intended to be used in battery packs where the contact is spot welded.

To have those replaceable an make reliable a contact, a spring on both sides is sometimes used, and in that case you could easily put it in the wrong way around AND make electrical contact.

Polarity marking and/or reverse polarity protection would be very good ideas in such designs. In that case the only motivation not do to it is financial: even putting on a sticker costs a few cents that come from a very small profit margin. Actual electrical protection using a mosfet would probably cost a dime or two, and a few mm3 of envelope space.

 

[RedCowboy]

My 515-520nm direct pen uses 2 x AAA batteries and they go in positive towards the spring, negative towards the tail end, it is a 2 piece that screws together at the middle, but the polarity is opposite of all my 532nm pens.


---edit---

My point is that they are not all the same so pay attention. :beer:

 

[paul1598419]

It would be as the 808nm diodes used for pumping are often case positive.

 

[Benm]

Indeed, virtually all 808 nm diodes are case-positive, i guess this has to do with the process they are built in and optimal thermal coupling. Also, they used to have feedback diodes in the can that required the 3 pin can design.

Nowadays the 3 pin can design remains quite popular, but the laser diode is often electrically isolated from the can, and you don't need to do anything with the pin that's connected to the host (you may want to connect it to the driving circuitry via a high value resistor to reduce static electricity problems if you're host is not complelety metal/conductive).

 

[lazylazer]

The comment about polarity is correct.
Turns out this laser pointer is case negative; opposite of my previous DPSS laser pointers.
I incorrectly thought the pointer was DOA but it in fact works.

I should have tried reverse polarity but was afraid it would damage the pointer.

Apology to laserland.

 

[diachi]

The comment about polarity is correct.
Turns out this laser pointer is case negative; opposite of my previous DPSS laser pointers.
I incorrectly thought the pointer was DOA but it in fact works.

I should have tried reverse polarity but was afraid it would damage the pointer.

Apology to laserland.

Most, if not all DPSS pointers use 808nm pump diodes which are case positive, thus the pointer is generally case positive.

Direct diodes can be either or, the diode's are often case neutral. Best to check the packaging/ask the seller if you are unsure about the polarity.

 

[Benm]

Checking is always wise, especially since switchmode drivers can be very easily modified to reverse polarity if desired for any reason.

Your typical 532 nm pointer running off 2 AAA alkalines will not have this issue, but higher end models could.

Higher end circuits will often have protection against reverse polarity though. This could be the nice mosfet solution, or on older designs even the 'crowbar' approach where you simply put a diode over the input and a fuse inline, such that you blow the fuse when you reverse polarity.

But things that are built to the lowest possible cost will have neither mechanism installed, and could be damaged by inserting the batteries the wrong way around.

 

[paul1598419]

This laser is 510nm, right? That is not a DPSS laser, but a direct diode laser.

 

[cornweda]

I have this laser pointer pen from Laserland and their larger 520nm laserland pointer which I pot modded. These are not illegal as they are set to 5mw (not all Chinese lasers are illegal imports). I use the smaller pen style laser on my telescope and it works well in the cold (you might have to switch to lithium batteries if you go really cold), where the 532nm DPSS laser pointers don't work.
This is a great laser pointer at a fantastic price and good build quality for such a low price. The cheaper lasers don't usually have reverse polarity protection. Even some of my high quality expensive lasers can be damaged that way.

Paul it is a direct diode and not 532nm DPSS laser. it is stated as 510nm, but didn't compare colour with my other 510nm laser to see if it is really 510nm diode laser (compared it with my other 532 DPSS lasers and it is forest green colour and not 532nm). Also, it has good beam quality for a cheap diode laser and the dot is visible on a building a mile away at night. The beam is wider than the standard DPSS laser pens.

Update:
I watched a video where the guy in the video banged this pen against a metal plate over and over again and it was undamaged. He also took it apart using a vice and it was well constructed and difficult to take apart. It had a plastic lens, but a nice heat sink. It can be pot modded, but I did not take mine apart and try. For $19 it is a real bargain.