Question for all you DIY LPMers

[SCOTTIEMANN21]

yes I did read that thread Ive been reading and working off of jufrans mariomasters and your LPMs to make mine but I will have to solder my generic board until I get my cnc machine and can make a slightly more professional board

 

[SCOTTIEMANN21]

where in maine do you live by the way? I know MarioMaster lives in Williamsport according to his info and I used to go to Pennsylvania College of technology in his hometown..

Im just gonna need someone somewhat local to help me either calibrate this or tell me what my lasers read to calibrate it myself... I would prefer someone local for shipping purposes or if they are local enough to actually meet them.

 

[Sputnik77]

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:

Yes, thats what I was saying!! However, its not due to relatively low power lasers, its due to the nature of a TEC being used in this manner.

However, I was also implying , even with 2 identical heatsinks, you will not be able to measure the difference with that meter, and I doubt a multi thousand dollar professional meter would. Any difference that shows up will be from some other variable.

Also, do you have a link to the schematic you are using? I have not came across it yet and want to have a look at it and compare it to my own design LPM.

 

[cilegray]

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

I didn't have the chance to read through the whole thread, limited time at work... so don't know if this has been rectified, or specified... but

Black will heat up faster than white; true only if absorbing heat from light. Aluminium is aluminium, and has the same heat transfer properties regardless of color. AFAIK any type of anodizing or painting will slow down heat transfer with ambient air by creating a layer of less conductive material between the two... acting as an insulator.

I would be inclined to say that a bare aluminium heatsink would be the most efficient, given it's clean and oxide free.

 

[Sputnik77]

I didn't have the chance to read through the whole thread, limited time at work... so don't know if this has been rectified, or specified... but

Black will heat up faster than white; true only if absorbing heat from light. Aluminium is aluminium, and has the same heat transfer properties regardless of color. AFAIK any type of anodizing or painting will slow down heat transfer with ambient air by creating a layer of less conductive material between the two... acting as an insulator.

I would be inclined to say that a bare aluminium heatsink would be the most efficient, given it's clean and oxide free.

Yes, that is correct as well. However, bare aluminum will not be oxide free, quite the contrary. Aluminum oxidizes VERY fast. Even if its undetectable by the eye, it is there. However true that a heavier layer will affect thermal transfer greater.

This is simply a non issue though. If you want something to do, just to keep boredom at bay, by all means do it.

 

[SCOTTIEMANN21]

Boredom?... tell that to my wife... aha

I have about 4 to 6 projects going on at any given time including a project car a project sportbike and various other projects

Im just curious about heat/energy transfer of light in this specific application... if the heatsink's job in this application is to give us enough temperature differential to create a voltge signal then why are we hindering it in helping it to absorb light heat/energy from divergent light? wont having a black heatsink allow it to absorb more divergent energy and thus decreasing the temperature differential from the ambient temperature we are working with?

 

[Fretwrecker94]

I'm in the Greater Portland area. But I don't think I'd be the best person to calibrate your LPM if that's what you were getting at. I'd suggest, when it's built, sending it to a reputable member who can calibrate it against a reputable and credible LPM.

 

[Sputnik77]

if the heatsink's job in this application is to give us enough temperature differential to create a voltge signal then why are we hindering it in helping it to absorb light heat/energy from divergent light?

Because the detecting face of the TEC is in the same ambient light/temp conditions it will be the same temp, so it doesnt matter as long as this condition is true while at zero, regardless of ambient light amount or temp.

The heat sink it there to provide enough differential only when a laser light is on the detecting face, heating it up, and as the laser is removed, it pulls the heat from the detecting side, eliminating the differential so it zeros back out. Even though the temperature of the whole assembly has risen from ambient due to the energy the laser put in to it.

If the assembly was in a sealed box, and the laser left on long enough, the heat sink would eventually rise to the same temp as the detecting face and no output would be observed. However, in practice, a very small differential may still be present.

While you are in theory absolutely correct, it is extremely impractical to try to measure these differences and I think you would be chasing an offset from caused by another variable.

 

[SCOTTIEMANN21]

portland area ehh... my sister lives up that way but she is moving home in the next couple weeks.. if you every go to the restaurant ler garage it is owned by my dads cousin and very close relative of mine, she is wonderful and the food is great...

sputnik... you seem to be very smart in this field.. what other variables do you think I could/should be looking for to make my DIY LPM as accurate as I can? and from what I understand from what your saying is that I wouldnt even be able to register a difference on my LPM from the different color/surface variations in my heatsink on my LPM? and if I could would that be linear or exponential?... as I assumed earlier it would be more evident with higher power lasers.

 

[lasersbee]

Can you find the shiny Thermopile head in these pics....:thinking:

Another clue.... Why are Car Radiators painted black and
not chromed or polished....:thinking:


Jerry

 

[cilegray]

Afaik some rads are bare aluminium but given the conditions they face with rain + temp change and a thin wall = good reason to prevent corrosion over a small percentage increase in cooling

edit : As for the thermopiles... if I were to commercially market a product specifically designed to point lasers at a rather small aperture... I wouldn't surround it with a large mirror either. You know... liability

 

[lasersbee]

Hmmm... wonder why they don't paint car radiators to match
the color of the car... that would also prevent corrosion and
be color coordinated...:thinking:

I wonder why most of the Thermopile Heads I've seen in the
past from companies like Coherent... OPHIR.... Newport.... etc
are black....:thinking:

But then again what do I know about Thermopile heads...

Jerry

 

[cilegray]

We could argue about that all day but that's beside the point, but just to give my opinion ;

Car rads eat alot of debris and small rocks, you wouldnt want to see the dings and chips, and it's not an aesthetically pleasing component, so they're black.

For thermopiles, again, I would want the smallest possibility of catching someone in the eye with a reflection off the sink, so black is the logical choice. Why don't they paint high-end CPU heatsinks black ? Or what's up with the blue and red anodizing on VGA card heatsinks...

Regardless... painting aluminium the color of your choice does not improve its thermal properties.

 

[piferal]

We could argue about that all day but that's beside the point, but just to give my opinion ;

Car rads eat alot of debris and small rocks, you wouldnt want to see the dings and chips, and it's not an aesthetically pleasing component, so they're black.

For thermopiles, again, I would want the smallest possibility of catching someone in the eye with a reflection off the sink, so black is the logical choice. Why don't they paint high-end CPU heatsinks black ? Or what's up with the blue and red anodizing on VGA card heatsinks...

Regardless... painting aluminium the color of your choice does not improve its thermal properties.

You're wrong and Jerry is right, is scientifically proven that black color (black matte, better) is the most efficient color for heat radiation.

 

[cilegray]

You're wrong and Jerry is right, is scientifically proven that black color (black matte, better) is the most efficient color for heat radiation.

Actually after reading up on this subject of blackbodies... it appears we are both right, in a case where you have convection or forced air, black anything is bad vs bare aluminium. In cases like a LPM, which dissipates heat purely by radiation, black IS better... never dealt with heatsinks without air movement before... learned something new

 

[SCOTTIEMANN21]

ok guys calm down:crackup:

I see I struck up a nice heated debate :gun:

anyways I think I have enough info that for this specific aplication matte black is the way to go... atleast when it comes to less professionally made LPMs.

In any case I have to wait til my garage warms up to actually anodize my heatsink but I can work on completing the rest of the LPM until then...

wish me luck and :thanks: for all of the technical responses and knowledge

and by the way lasersbee you are correct, I have been working in the automotive industry for many years and all of the radiators I see are either bare aluminum or black, the only polished or chrome ones I have seen are for show cars where fassion preceeds function.