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Thread: The big TEC driver thread!

  1. #31
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    Quote Originally Posted by dar303 View Post
    Nice to see some action here!
    Maybe the optical feedback project should get its own thread?
    Well... there's no reason my optical feedback controller shouldn't control the TEC as well. That way you could find out what temperature was best for the maximum light output.

  2. #32
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    That's only useful if you're building your own DPSS laser (or modifying an existing). I wouldn't want to use it with a direct injection laser.

    If you do, you must consider that the wavelength changes with temperature. Also that longer wavelengths have a higher photon flux at a given radiant power, but at the same time Rayleigh scattering will be more efficient at shorter wavelengths. Looking at the relevant equations I get that the wavelength dependence of the photodiode current is (λ[1]/λ[2])^3.

    That is of course assuming there are no particles in the air. If there is, Mie scattering will dominate and the equation becomes nearly impossible to solve.

    For a DPSS laser it is of course completely different, but what you are talking about here is close to building a whole driver circuit. Even so, I don't think you should use 'spill' light; the error will simply be too big unless that photodiode is inside of the laser module, which must be hermetically sealed and dust free. I am of the opinion that the sensor must be in the beam.

  3. #33
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    Quote Originally Posted by tocket View Post
    (nice stuff)
    Let's take this to another thread like the nice man suggested :-)

  4. #34
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    On another note... Damn those H-bridges are expensive! It's probably better to not use the TEC in reverse mode and just drive it off a single MOSFET. I didn't know MOSFETs were that expensive either, might almost be worth to start salvage them from old electronics.

  5. #35

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    Quote Originally Posted by dar303 View Post
    Nice to see some action here!
    Maybe the optical feedback project should get its own thread?
    Or rename this one the big PID control thread? After all, that's so useful a theme, and TEC control almost always goes right to that level. As you can see in just a few posts..
    Does anyone have good sources for small TEC's they want to share?
    The ones on ebay are usually big ones, 40x40 mm or so.
    eBay. I can't remember who the seller was I bought from in 2006, but he's good. I got 75 of them for a good price. They're small, about 8 mm by 11 mm with bare wire termination and solder on each side. Not many people seem to want them because they're not big fat and powerful, but they are ideal for cooling a single diode, the small TEC's have a higher density than larger ones, the ones I have pump at least 2W of heat, maybe 4 at Qmax, but playing safe with 2 or 3 is best, and they run nicely on a 3.3V supply. I deduced their power from other examples and looking at their geometry and by trial and error, as you can afford to risk one if you have tens of them. The seller seemed to regularly have boxes of them, so it's worth hunting.
    Quote Originally Posted by tocket View Post
    I don't think you should use 'spill' light; the error will simply be too big unless that photodiode is inside of the laser module, which must be hermetically sealed and dust free. I am of the opinion that the sensor must be in the beam.
    I've been thinking that too. Though as a photodiode can be sensitive, and shrouded easily if a neat beam is to enter, it might be best to use a bit of microscope slide glass at a Brewster angle to part off just enough light for the sensor while leaving most intact.
    Last edited by The_Doctor; 01-15-2009 at 04:03.

  6. #36
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    I would just use the light that passes through my dichro. That's a waste beam anyway, so it's not doing any good.

  7. #37
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    Quote Originally Posted by tocket View Post
    I would just use the light that passes through my dichro. That's a waste beam anyway, so it's not doing any good.
    Let's take this over to http://www.photonlexicon.com/forums/...ead.php?t=6458 so we don't derail the TEC thread any more than I already have. (sorry folks )

  8. #38

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    Quote Originally Posted by tocket View Post
    I would just use the light that passes through my dichro. That's a waste beam anyway, so it's not doing any good.
    Good enough.
    Quote Originally Posted by heroic View Post
    Let's take this over to http://www.photonlexicon.com/forums/...ead.php?t=6458 so we don't derail the TEC thread any more than I already have. (sorry folks )
    Good enough.

  9. #39
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    As this year I decided to put more time into my new laser projects I came around TEC cooling as many here.
    As I'm not fluent in PCB design I decided to choose the easy way of blocks-building.
    Here's the setup I assembled today for consideration. It's electrically effecient (excluding the general TEC physics , requires no PCB, has PID with autotune ability, has digital readouts, has presettable, configurable alarms, requires only single supply, etc. The down side - it's not bidirectional- has no ability of heating, but should work for laser diodes, using them as heaters.

    Below are some general pictures.

    The main parts are:

    - Power line cable
    - high current line votage rectifier
    - rectified AC power line filter cap (if big cap used - soft start resistor required!)
    - Vicor DC generation 2 module 300V DC in - some V req'd out
    - 2.7V Zener diode, for Vicor safety
    - 1000uF cap
    - 47 Ohm resistor
    - optocoupler, here MOC8112 used
    - OMRON temp controller with SSR output, here E5CJ-Q2MT used
    - a thermocouple
    - something peltier-equipped to be cooled

    Optocoupler inverts signal from OMRON, so it must be configured for HEATING, while it will be cooling. Set OMRON to use shortest Control Period - here lowest is 1 second, E5CN series has 0.5 second minimum.

    1000uF cap + 47 Ohm resistor slows down Vicor voltage trimming speed (oscilloscope shows voltage out with 0.5sec/div, 1V/div).

    Thanks to optocoupled control several Vicors can be used in series in order to get more voltage to Peltiers. I'm planning to use this configuration for 4pcs. of 15V/7A Peltiers ran from two 24V/250W Vicors trimmed down to 15V. Why use generation 2 Vicors (black ones) ? They can be trimmed down to 10% voltage, while gen.1 (the grey ones) go down only to 50% voltage.

    Piotr.K
    Attached Images Attached Images
    Last edited by LesioQ; 01-28-2009 at 14:25.

  10. #40
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    Thats a nice large-scale setup! What laser have you tried it with?

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