DIY Thermal LPM for under $50

[LazyBeam]

I like those $2 radioshack breadboards. SUPER easy to solder and finish up real nice looking

 

[Xplorer877]

I like those $2 radioshack breadboards. SUPER easy to solder and finish up real nice looking

Yeah I agree for a circuit that is this simple I just use the prototype boards. I like the big one.
Grid-Style PC Board with 2200 Holes - RadioShack.com

Make the circuit as small as you can and then cut it out with a ban saw. It's harder to solder but etching is time consuming and kinda expensive.

-Tony

 

[laser_freak]

Yeah I agree for a circuit that is this simple I just use the prototype boards. I like the big one.
Grid-Style PC Board with 2200 Holes - RadioShack.com

Make the circuit as small as you can and then cut it out with a ban saw. It's harder to solder but etching is time consuming and kinda expensive.

-Tony

I use every excuse I get to play with acid I'll probably etch a board this weekend for this LPM.

 

[kiyoukan]

i once made my own boards out of some plastic and tin foil.
I glued the foil to the plastic then milled it out with my dremel.
oh and spray some heat resistant paint on top of the foil to keep it lasting

 

[lazeerer]

How is it coming along guys. Any Updates?

I'm Still Waiting on my parts. nothing came in yet. Cant wait to get this project done.

 

[TTerbo]

well its definatly will work....and if it doesnt you have yourself an Ipod speaker amplifier

 

[lazeerer]

Hey all , So I went to Home Depot today to pick up a can of this high Temp. Spray paint.
Link:
Amazon.com: Rust-Oleum 241169 High Heat Ultra Enamel Spray, Black, 12-Ounce: Home Improvement

So Before applying it to the TEC i put it on a couple of test surfaces and i applied to a ceramic tile on both sides. The front of the ceramic tile was a little glossy, it was a bath room standard white tile and the back was just ceramic with no finish/glossiness to it. So i applied it and let it dry for 3 hours.

So i then went to test and see how this paint holds up and it justs starts smoking/burning as soon as i focus my 1amp. 445 on it or my 350mA red on it etc it starts burning with all my laser i tried it with."I tested both sides same results and i also tested with the dot unfocused slightly and still burns/smokes but just takes a little longer"

This Paint is Rated for 1000 DegreeF.I dont understand!!!:banghead:

Am i doing something wrong?

:thanks: Guys you all have been very helpful in this Thread.

Edit: This Paint is acutely ratted up to 1200 DegreeF

 

[LazyBeam]

The most absorptive "easy" material to obtain and use is carbon black. Don't breath it.
I would reccomend a light coat of black high temp paint and dusting it with carbon black.
Powdered printer toner would be a good substitute for carbon black as well.

Also, why focus your laser? If your TEC is 15mm x 15mm (or whatever) just focus your laser to the size of your TEC. This will distribute heat more evenly over the TEC and decrease extreme temperature differentials on the hot side of the TEC. Your laser laser will not burn and this should lead to a more accurate and consistent TEC reading.

Make sure the paint is FULLY cured. "handling" and "dry" times printed on the back of the can are not necessarily the times needed for the paint to shed all of the VOCs that are in it and reach 100% cure. Elevated cure temperatures will help drive off VOCs faster.

 

[MarioMaster]

You have to watch, some paints require you to bake the painted item in an oven to make the paint actually handle what it says on the can. This would be bad for a TEC since the junctions usually melt much above 100c

 

[Xplorer877]

I thought this might be a problem. What about black charcoal dust? Charcoal ignites at like 2000 degrees F doesn't it? And that stiff is BLACK as can be. I'll do a bit of testing whit what I've got and see.

Better yet rather than sprinkling the dust over wet paint, what about sprinkling it over some Arctic silver alumina adhesive? Spread out a VERY thin layer of the stuff and then generously dust it with carbon black.

-Tony

 

[lazeerer]

Also, why focus your laser? If your TEC is 15mm x 15mm (or whatever) just focus your laser to the size of your TEC. This will distribute heat more evenly over the TEC and decrease extreme temperature differentials on the hot side of the TEC. Your laser laser will not burn and this should lead to a more accurate and consistent TEC reading.
.

For some reason i thought you had to focus it. Thanks for letting me know that it will be better to unfocus it.

EDIT:
So i unfocused it a little larger then i did in my original test and no more burning/smoking.:wave:

 

[LazyBeam]

Just make sure that when you calibrate your laser & meter that you use the same focus setting on the calibrated meter as the DIY meter when setting the DIY meter's gain.

 

[laser_freak]

Just make sure that when you calibrate your laser & meter that you use the same focus setting on the calibrated meter as the DIY meter when setting the DIY meter's gain.

The amount you focus the laser should not affect anything.

 

[TTerbo]

Just make sure that when you calibrate your laser & meter that you use the same focus setting on the calibrated meter as the DIY meter when setting the DIY meter's gain.

it wont matter.......that would mean unfocusing the laser gives out a different power :thinking: which it shouldnt

 

[HIMNL9]

it wont matter.......that would mean unfocusing the laser gives out a different power :thinking: which it shouldnt

The amount you focus the laser should not affect anything.

Ehm ..... not totally right, sorry .....

First consideration to do: the reading surface of a thermal sensor is NOT resistant to anything, to infinite abuses ..... one thing is using a 200W thermal head with ceramic plate, another is using a 2W reading head with special ultra-thin plate ..... using an 1W FOCUSED to a burning point on one of the sensitive (and delicate) low-power high-resolution plates, can easily end in damaging the surface of it, that, considering the usual cost of thermopiles, is not exactly a funny thing .....

The same thing is more valid for TEC sensors, that have a coating made with paint, usually ..... regardless the quality of the paint, and the presence of the ceramic substrate for draw the heat, it can be damaged also more easily from a focused beam with burning ability (i made the same with one of my tests, too, thinking the paint was good ..... it was "high temperature paint for exhaust tubes" for motorcycles, and they reach a high temperature, so i thoughd it was resistant to burning lasers too, but i burned it on the TEC surface with only 200mW of 405nm, focused for burn, so, just imagine) .....

The first "good" rule, then, is: always try to defocus the beam a bit, when you read a laser ..... if you have a small reading surface thermopile, like the ophir ones sold with some LPM also here, or a small TEC sensor, like the lasersbee one, is always a good thing to defocus the beam to AT LEAST half the diameter of the sensor, also more, if the laser is hold with a stand ..... this prevent unwanted plate / coating damages

Second consideration to do: there is a phisical difference from a thermopile and a TEC cell, that gives you different results in heat distribution and heat draining from the measuring area, so the point where you target the reading area IS important for a correct reading, other than the reading time .....

In more clear words: the TEC cell have the plates made in ceramic (ok, ok, a special ceramic, but i suppose you don't need the formula ), that is more thick and highly thermally conductive, much more than the thermopile reading plate ..... also, the cells are distributed on all the back surface of the plate ..... from the counterpart, the structure of a TEC cell, also if not used for cooling, is much, much more heat transfering than a thermopile reading plate ..... this made it relatively insensitive about the exact point where you shine your laser, cause all the heat transfered to the plate from the laser, is spreaded really quickly on all the surface, and influence in almost equal mode all the cells (except than shining it on a corner, but also this is someway compensated) ..... so, almost regardless than the fact that you shine the laser exactly on the center or not, the reading is practically the same (some minimal differences are always presents, but are so small that does not influence the reading in a really effective way) ..... at the same point, anyway, the more quick transfer of heat from the reading plate to the "cold" plate, due to the big mass of the junctions, tends to "equalize" slowly the temperatures, falsing the reading in long-cycles readings ..... anyway, this does not have a big influence reading low-powered lasers, only reading high-powered ones, indicatively from over 500mW and up ..... this can be, anyway, minimized using a big or very efficent heatsink on the "cold" plate (a thermal compensation can be helpful, too, for long readings, but is not indispensable at hobby level)

On the other side, a thermopile have a totally different structure, especially the sensitive ones that are able to read very few milliwatts ..... builders had to become to a compromise from sensitivity and dimensions, and this means that the reading plate is, sometimes, extremely thin and delicate, made from special materials for maximize the heat transfer speed and at the same time kept small enough for become influenced from very low powers ..... but, you know, infinites does not exists ..... regardlass from what material you use, there's no materials that have an infinite heat transfer speed ..... and also, for the constructive principle of those sensors, the reading elements are a lot of bimetal thermopiles made with very thin metal plates, connected in serie for increase the reading, and placed all around the circumference of the plate .....

This cause a difference in the reading for different zones of the reading surface ..... cause the heat transfer from one place to the whole plate is not infinite, the thermal resistance of the plate itself, causes a higher reading when you shine the beam on the borders of the plate, where the bimetal junctions are directly posed, and a minor (but more correct) reading, when the beam is shined exactly on the center of the plate, cause in this way the reading is the effective power reading of all the heat, equally transferred to all the bimetal junctions (yes, is not that your laser is more powerful if you shine it on the borders, you are simply doing the reading in the wrong way, doing this )

So, for a correct use of a thermopile, is required, usually, that the beam is defocused at least on half of the reading surface, and that it will be directed and kept more centrally possible on the reading plate.

And as final consideration, regardless if you are using a thermopile or a TEC or a piezothermic element, all these elements, more or less, are sensitives also to thermal radiating power (purely heat) generated from the measured devices ..... so, for a real power reading, is not enough to correctly "zero set" the meter and shine the laser on it ..... the better and more precise reading is obtained following some simples, but indispensables, rules:

1) no air currents around the sensor (it can draw heat from the hot or the cold face, falsing the reading).

2) never keep the sensor with the hands (the heat added from the hands, slowly change the difference of the temperatures from the two faces, making the reading imprecise and incostant).

3) no big lamps or heating elements around the sensor (not too good making a reading, having a 100W halogen lamp half meter from the sensor, or similar )

4) NEVER keep the lasers close or touching the reading assembly (the heat from the laser body can false your readings, also 40 / 50% sometimes ..... i always laughed seeing sellers that shows on their sites 400 or 500 mW green lasers, and "proof" the output power showing a pic where the power is read keeping the laser in contact with the reading head ..... i can bet whatever you want that, in these cases, at least 40%, if not more, than the readed power, is infrareds AND heat from the laser body ) ..... a decently precise reading can be obtained keeping the laser AT LEAST 20cm away from the reading head ..... also the double, if possible, is also better

5) ofcourse, frequently check the zero set of the meter ..... thermal derive, thermal transfers from the sides, changes in temperature of the ambient, also just the radiant heat added to the items from the body of the reader, in extreme cases, always changes the thermal model scheme of the ambient and reading setup ..... if you have the patience, and really want that your measure is the more correct possible, check the zero set after each measure, and if the time is not a problem, do at least 3 measures for each laser you're measuring, and made a medium value from the 3 measures (i know, this is almost a lab procedure, but, it's the more correct possible, for hobby level ..... we don't have NIST labs in the pocket or in a desk tire, after all, so we must do that what we can, with that what we have ..... )

(sorry for the long post )

 

[TTerbo]

wow nice post.....
i dont see how my post isnt true..
someone said "make sure the lasers are at the same focus when you calibrate it" well that shouldnt matter...if it did that would mean a "dot" focused to 1mm would have different output to the same laser with "dot" of 1cm.....thus meaning if yuo unfocus the laser to 2cm and measured the mW it would give a false reading.....
this wouldnt happen.....i hope someone understands what im talking about..i found it hard to explain. the brain is a marvelouse thing, but sometimes doesnt want to share its secrets