Question for all you DIY LPMers

[SCOTTIEMANN21]

so Im in the process of making a LPM but there is something I dont understand...

The type of LPM Im making uses a tec module on a heatsink but everyone seems to be using either a black heatsink or painting their heatsink black. Now I understand that the reason to paint the tec black is to absorb the light energy from the laser but correct me if Im wrong the heatsink is connected to the "cool side" of the tec.

In that case why would we want the heatsink absorbing light energy from the laser. I know the laser is focused on the tec but their is usually some type of light divergence outside of the beam.

Wouldnt we get a quicker and/or more accurate reading if the heatsink only absorbs the energy from the tec? And in that case why wouldnt we just polish the face of the heatsink in order for it to reflect excess light energy outside the collumated beam?

Has anyone experimented with this or can anyone give me insight on this subject before I either polish my silver heatsink or etch it and anodize it black?

-Scott

 

[Fretwrecker94]

Maybe through the explanation of my DIY LPM's heatsink you'll find an answer.

I used a 12mmx12mm TEC Peltier that I painted with rustoleum. I thermally adhered it to my heatsink. It doesn't matter which "side" goes on the heatsink. That's because the Peltier really has no designated hot or cold side. Just reverse the polarity and the sides switch. It's just a matter of the color of the wires that drives people to connect it in a certain way. But as long as one side is adhered to the heatsink you'll be fine. Make sure its well attached. If it's connection shifts after its all set up you will need to re-calibrate it.

In my experience, the heatsink's color really doesn't matter. You'll be fine leaving it alone. But who knows, maybe you just like the look of a polished sensor!

*Edit* Maybe some pictures of you parts will help... and I kinda wanna see you set-up thus far

 

[SCOTTIEMANN21]

yea I understand the tec doesnt have a cool side or hot side it just depends on how you hook it up.

Im just curious as to whether or not people have tried a polished heatsink that will reflect divergent light as to make the heatsink more efficient. I would actually like to see back to back results using the same calibrated LPM and various lasers of different powers just swapping out Identical heatsinks with Identical Tecs. one heatsink polished silver and one anodized matte black and without changing any of the electrical settings see if it reads different numbers for each laser. and maybe at the same time video it with timing and see if they reach the same numbers at the same amount of time.

I know this might have less of an effect at lower power levels but it would be interesting to see...

ok so after typing all that I just realized I just recruited myself to do this experiment (unless someone else has already tried)

by the way Ill take some pictures of what I have later tonight but its still just in parts Im just working on hacking up the case so everything fits in nicely.

 

[lasersbee]

so Im in the process of making a LPM but there is something I dont understand...

The type of LPM Im making uses a tec module on a heatsink but everyone seems to be using either a black heatsink or painting their heatsink black. Now I understand that the reason to paint the tec black is to absorb the light energy from the laser but correct me if Im wrong the heatsink is connected to the "cool side" of the tec.

In that case why would we want the heatsink absorbing light energy from the laser. I know the laser is focused on the tec but their is usually some type of light divergence outside of the beam.

Wouldnt we get a quicker and/or more accurate reading if the heatsink only absorbs the energy from the tec? And in that case why wouldnt we just polish the face of the heatsink in order for it to reflect excess light energy outside the collumated beam?

Has anyone experimented with this or can anyone give me insight on this subject before I either polish my silver heatsink or etch it and anodize it black?

-Scott

A Black heatsink will heat up faster than a White heatsink...
just like a Black heatsink will cool down faster than a White heatsink.
A heatsink will always try to find equilibrium with the surround air
temperature.

The answer is there....


Jerry

 

[SCOTTIEMANN21]

A Black heatsink will heat up faster than a White heatsink...
just like a Black heatsink will cool down faster than a White heatsink.
A heatsink will always try to find equilibrium with the surround air
temperature.

The answer is there....


Jerry[/QUOTE]

but say the whole heatsink is black to cool off faster but just the surface the tec is mounted to that will see divergent light is polished to reflect excess light, therefore the most or almost all of the heat that the heatsink is absorbing is strictly from the tec and not from any divergent laser light...

I dont know maybe Im beating a dead horse I was just curious...

maybe Ill try that experiment I stated above and see if anything changes

-Scott

 

[lasersbee]

Here's another hint.... Heat differential....

Jerry

 

[Sputnik77]

Actually, you are correct in thinking that light hitting the black heat sink could potentially hinder accuracy. HOWEVER, that would really only be the case if the heat sink mass was the same as the detecting face of the TEC. Since its a much larger mass, the accuracy hit is practically immeasurable by any equipment available to us as hobbyists. In light of that, ANY added mass, no matter how big, would be larger than the detecting face, as the non-detecting face with no added mass, is already the same.

I think the easiest way to explain this is that a TEC in this case works on temperature differential.

The heat sink in this particular usage is to maintain a large enough differential to produce a useable voltage signal. With no heat sink, heat from the detecting side would transfer into the non-detecting side making your voltage output much less than needed, and eventually, as the TEC stabilized at the higher temp, would output no voltage at all.

Just paint or anodize it black. A polished surface would be dangerous, and would provide no real world difference in accuracy.

 

[SCOTTIEMANN21]

Lasersbee... thats an answer I was looking for. It made me realize that the experiment I stated before was only half complete. In order to figure out exact figures I would need 3 Identical heatsinks: one silver with a polished face, one anodized black with a polished face and one anodized matte black. and to see the true effects of the different conditions I would need a thermal camera to see the temperature differential throughout the heatsink..

and Sputnik, so what your saying is that in theory my hypothesis is correct. However the relatively low power lasers we usually deal with I wouldnt see any measurable difference in accuracy. am I reading what you wrote correctly or am I off...

anyways I think I should look into getting a few identical heatsinks to test this theory out with....:thinking:

 

[rhd]

Has anyone experimented with this or can anyone give me insight on this subject before I either polish my silver heatsink or etch it and anodize it black?

On a more practical note, since this assembly is something that you're intentionally pointing lasers in the direction of, I would much rather it be as possible.

You should always wear safety glasses when operating lasers, but even with safety glasses on, I'm not sure how crazy I would be about having a highly polished silver surface right next to the TEC that I'd be aiming 2W of laser light at....

 

[SCOTTIEMANN21]

fretwrecker... like i said all i have right now is parts because im working on hacking up the box to fit everything in...

everything should be in these pictures as well as the heatsink i will be using.

the only things missing are the two 9volt batteries, the box which is in the garage and the tec which is in the mail, for the tec I chose a 15X15mm with 31 pairs.

 

[SCOTTIEMANN21]

rhd... I completely agree and to be honest I would be spending more money then its worth to actually do this experiment and I dont have that kind of money right now. but im just mulling around theories and ideas for another project.

if I did I would be using a labby with a known output and all variables would have to be ruled out including having the labby pointing at the tec at the same distance and the same spot which is easily reproducible without even having to look at the beam or the spot it hits.

 

[Fretwrecker94]

Just wanted to see photos I very much enjoy seeing the starting material then seeing the great products! Out of curiosity are you following someone's schematic or is it a total DIY?

 

[SCOTTIEMANN21]

im following jufrans schematic with mario masters part list but the case and heatsink are going to be attached to eachother and they will look a bit different but youll have to wait for the finished preduct to see how it looks

btw keep an eye out on the red lasers page I will be posting about my red handheld I recently made with my half a$$ heatsink.. I just have to up the mA a little bit but I didnt install a pot so I have to swap out the resistors :shhh:

On another note I recently bought 2 greenies off amazon cheap... I did search a lil for them and the company selling them said they put out atleast 4.99mW and from what it looks like they deffinitely do :evil: one Im keeping stock because its nice and thy other Im hacking up and attempting the dreadfull diode replacement and making my own driver to see if I can squeeze a little more power out of the crystal set...

anyways hears a sneak peak of the handheld :beer:

 

[Fretwrecker94]

I attest to that schematics authenticity. It works like a charm! That's a nice sneak peak!

 

[SCOTTIEMANN21]

that heatsink is lopsided I made it using an old handlebar end from my sportbike using a drill in one hand and a dremel in the other... the only good thing is that drilled hole is straight so the beam is straight

and you made an LPM based off of jufrans schematic right?

 

[Fretwrecker94]

that heatsink is lopsided I made it using an old handlebar end from my sportbike using a drill in one hand and a dremel in the other... the only good thing is that drilled hole is straight so the beam is straight

and you made an LPM based off of jufrans schematic right?

http://laserpointerforums.com/f70/pic-heavy-my-diy-lpm-71361.html#post1027783

Sure did! But mine used a manufactured PCB according to his schematic.