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DIY Thermal LPM for under $50

Bionic-Badger

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For PCB fabbing, you might want to look at BatchPCB as well. $2.50/sq inch. About twice the shipping time though.
 



HIMNL9

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You need to search for old types 200mV DC modules, like this one or similars, if you want to be sure that they use resistor dividers ..... other models and "new types" can be made only for the given voltage, or have all the components in SMD, and be difficult to modify onboard .....

Anyway, if the module is 200mV, they have usually around 10 MOhm input resistance, so it's easy to place a 10-to-1 divider resistor network (like, 1MOhm parallel / 8,18MOhm serie) on the input, and turn it to 2V .....
 

gillza

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PCB Only ... (no way I could do that ... each 3214 pot is $3.22!)
Jib77,

Forgot to let you know, I got the boards last week. Waiting for my paycheck to start ordering components to try and build that circuit. If i succeed (never done SMD) i will post it here :)
 

lasersbee

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I finally got the LPM PCB's from China, after a 2 month wait (MakePCB.com, really good quality and price but takes forever and you do not get any updates). On the same day I got another order I placed 2 weeks ago from a domestic source.
Just out of curiosity... Why did you go SMD rather than
easier to mount Through hole components....:thinking:

BTW... nice PCBs...


Jerry

You can contact us at any time on our Website: J.BAUER Electronics
 
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lasersbee

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Because he was planning on heat-sinking the board?
What board.... :thinking:
There is absolutely no current high enough to heat up
that PCB using that Op Amp circuit that would require
heatsinking...


Jerry

You can contact us at any time on our Website: J.BAUER Electronics
 
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jib77

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Just out of curiosity... Why did you go SMD rather than
easier to mount Through hole components....:thinking:

BTW... nice PCBs...


Jerry
Mostly for size ... I wanted to make it small enough to mount it on the TO220 heatsink opposite the TEC.
 

lasersbee

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Mostly for size ... I wanted to make it small enough to mount it on the TO220 heatsink opposite the TEC.
Nice clean idea in theory.... but..

Sorry to say....Not a good Idea...IMO

The fiberglass PCB will act as an insulator and slow the
heat dissipation speed of the Heat Sink.
I wouldn't recommend it if you want your LPM to be as
accurate as possible..
Just like we do not recommend installing Thermopiles into
enclosures... the heat generated by the Laser Beam has
nowhere to go and can throw off readings...
Even more so with the 445nm beasts that are being built...

BTW... if you are not too worried about accuracy... I'm sure
that will be fine...

Just my $0.02....


Jerry

You can contact us at any time on our Website: J.BAUER Electronics
 
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goninanbl00d

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Nice clean idea in theory.... but..

Sorry to say....Not a good Idea...IMO

The fiberglass PCB will act as an insulator and slow the
heat dissipation speed of the Heat Sink.
I wouldn't recommend it if you want your LPM to be as
accurate as possible..
Just like we do not recommend installing Thermopiles into
enclosures... the heat generated by the Laser Beam has
nowhere to go and can throw off readings...
Even more so with the 445nm beasts that are being built...

BTW... if you are not too worried about accuracy... I'm sure
that will be fine...

Just my $0.02....


Jerry
The majority of the heat should be dissipated into the fins, as opposed to the back of the heatsink.

If the heat is being dissipated out the back of the heatsink, then the heatsink isn't doing it's job correctly.

The heatsink is meant to remove heat from an object, and allow the heat to dissipate into the ambient air, either by forced ventilation or by natural convection.

If it's simply leaking out the back then it's not working correctly. The heat should be taking the easiest path out, which should be out the fins.

Invariably there will be some heat leaking out the back instead of going into the fins, but the majority of it should be going into the fins.

The only case in which I can see readings being affected is if the board is actively generating heat. The amp should be calibrated to offset that, if that is indeed the case.

Also, care to explain this?



As far as I can see, the back of the thermopile is enclosed, and hermetically sealed.The heat will be dissipated into the air inside the compartment, and will stay there. There's no way air can circulate in that cavity.

Air is a very poor conductor of heat, and that plug cavity makes a much better insulator than the fibreglass board does.

With the fibreglass board, there's a small gap (mounting standoff), and as a result, there'll be (small, but nonetheless existant) convection currents moving between the board and the heatsink.

And before youask, I don't have any hidden agendas. I just find it odd that you suggest the opposite to what you do. Perhaps it was my mistake not to know who Nospin was.
 

HIMNL9

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^ Uhm, but keep in mind that, for LPM purpose, the main thing that the heatsink have to do is NOT to dissipate heat (this can be the point if the TEC was used as cooler, NOT as sensor) ..... when you use a TEC (or a thermopile, for this) as power sensor, the main purpose of the heatsink is to KEEP the temperature of the "reference" plate as more stable as possible (once all the assembly have reached ambient temperature, before to start the measure, ofcourse) .....

For this purpose, a lot of fins only helps in reaching a stability point at ambient temperature more quickly, but then for KEEP IT STABLE, the more important thing is THE MASS of the heatsink (or, being more precise the THERMAL MASS) ..... can say that, once the assembly is at ambient temperature, a solid block of aluminium or copper is better, for this, than a lot of fins ..... so, in this special case, the fact that the back of the heatsink is enclosed, or don't have air circulation, is almost ininfluent.

I made some LPMs in this way, and a pair of them have the sensor totally enclosed in the box, with the rest ..... once you left them stabilize at ambient temperature, there's no difference in the readings, from them and the "open sensors" ones (ofcourse, you NEED to left them reach stability with ambient temperature, if you carry them from one place to another with different temp, but this is valid also for open types).

A different case happens if you need to make long-times readings of a high power laser beam ..... in this case, the capacity to dissipate the heat transferred from the reading face to the reference face start to become important, too, but in these cases, i usually use big-mass heatsinks with forced air circulation (fan), with the reading face insulated from the airflow ..... the more important thing, for a sensor with that limited thermal mass, is not the presence of the enclosure on the back, is that you don't keep it with your fingers or that you don't place it on a surface with a high thermal conductivity and different temperature than ambient air, like metal plates, for avoid that these things changes the thermal equilibre .....
 

goninanbl00d

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^ Uhm, but keep in mind that, for LPM purpose, the main thing that the heatsink have to do is NOT to dissipate heat (this can be the point if the TEC was used as cooler, NOT as sensor) ..... when you use a TEC (or a thermopile, for this) as power sensor, the main purpose of the heatsink is to KEEP the temperature of the "reference" plate as more stable as possible (once all the assembly have reached ambient temperature, before to start the measure, ofcourse) .....

For this purpose, a lot of fins only helps in reaching a stability point at ambient temperature more quickly, but then for KEEP IT STABLE, the more important thing is THE MASS of the heatsink (or, being more precise the THERMAL MASS) ..... can say that, once the assembly is at ambient temperature, a solid block of aluminium or copper is better, for this, than a lot of fins ..... so, in this special case, the fact that the back of the heatsink is enclosed, or don't have air circulation, is almost ininfluent.

I made some LPMs in this way, and a pair of them have the sensor totally enclosed in the box, with the rest ..... once you left them stabilize at ambient temperature, there's no difference in the readings, from them and the "open sensors" ones (ofcourse, you NEED to left them reach stability with ambient temperature, if you carry them from one place to another with different temp, but this is valid also for open types).

A different case happens if you need to make long-times readings of a high power laser beam ..... in this case, the capacity to dissipate the heat transferred from the reading face to the reference face start to become important, too, but in these cases, i usually use big-mass heatsinks with forced air circulation (fan), with the reading face insulated from the airflow ..... the more important thing, for a sensor with that limited thermal mass, is not the presence of the enclosure on the back, is that you don't keep it with your fingers or that you don't place it on a surface with a high thermal conductivity and different temperature than ambient air, like metal plates, for avoid that these things changes the thermal equilibre .....
If that is indeed the case than a <2mm thick piece of metal may not be the best way to go about it. In the end, the change in temperature would be rather readily felt.

If the back was open, any change in temperature would be readily felt.

If the back was closed, there's no way for air to circulate, hence any temperature difference would be intensified.
 

HIMNL9

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If that is indeed the case than a <2mm thick piece of metal may not be the best way to go about it. In the end, the change in temperature would be rather readily felt.

If the back was open, any change in temperature would be readily felt.

If the back was closed, there's no way for air to circulate, hence any temperature difference would be intensified.
Yes, but usually that type of sensor is not specifically designed for long-time readings with high power lasers, right ? ..... i mean, is difficult that a home / hobby user needs to do a 5 or 10 minutes sampling on an 1W laser, is more usual to use it for check for instant powers, and this requires usually 15 seconds, or few moew .....
 

goninanbl00d

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It will only do for a short reading.

I can forsee issues even for 60-second readings- aluminum is a good conductor of heat, and the heat will travel across the thermopile and into the aluminium much faster, and while this helps to maintain a consistant temperature, it does mean the aluminium gets warmer much faster.

Either way, the heatsink to which the thermopile is mounted should be much bigger, with much more mass directly behind the thermopile. Even a few extra millimeters helps.
 

lasersbee

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The majority of the heat should be dissipated into the fins, as opposed to the back of the heatsink.

If the heat is being dissipated out the back of the heatsink, then the heatsink isn't doing it's job correctly.

The heatsink is meant to remove heat from an object, and allow the heat to dissipate into the ambient air, either by forced ventilation or by natural convection.

If it's simply leaking out the back then it's not working correctly. The heat should be taking the easiest path out, which should be out the fins.

Invariably there will be some heat leaking out the back instead of going into the fins, but the majority of it should be going into the fins.

The only case in which I can see readings being affected is if the board is actively generating heat. The amp should be calibrated to offset that, if that is indeed the case.

Also, care to explain this?



As far as I can see, the back of the thermopile is enclosed, and hermetically sealed.The heat will be dissipated into the air inside the compartment, and will stay there. There's no way air can circulate in that cavity.

Air is a very poor conductor of heat, and that plug cavity makes a much better insulator than the fibreglass board does.

With the fibreglass board, there's a small gap (mounting standoff), and as a result, there'll be (small, but nonetheless existant) convection currents moving between the board and the heatsink.

And before youask, I don't have any hidden agendas. I just find it odd that you suggest the opposite to what you do. Perhaps it was my mistake not to know who Nospin was.
:wtf:Whoa... backup it Nelly....
I didn't expect that from helping a member...:eek:

My post was to help you... not offend you...
It is obvious that I did offend you.... It was not intentional...
I apologize if I hurt your feelings.....................

No need to get so defensive....

I thought I would share the information we had gathered
designing the LaserBee...

To answer your snotty questions as you posed them I'll
go through them as indicated by color above...

1) The heat is being dissipated by ALL the Heat Sink's surfaces and
held stabilized by its Thermal Mass....

2) There is a difference in a BOX and a SOLID aluminum BLOCK
3) What does Nospin have to do with what I posted....:thinking:

Do what you want....
I must be wrong and you must be right... what do I know...
Sorry to have tried to help you......:cryyy:

BTW... I see you did like our choice of Heat Sink design choice..


Jerry

You can contact us at any time on our Website: J.BAUER Electronics
 
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