Old 02-22-2015, 06:31 PM #1
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Default how to set up TEC cooling?

Hey guys.

For any of you guys out here who aren't just interested in laser pointers or handheld lasers, what kind of advanced cooling system do you guys use?
Heatsink with fan seems to work for several mW lasers which aren't meant to run for a "long" time.

I want to make one of those knife edge array builds with DTR's 3.5W 450nm NDB7A75 diodes and see how bright I can get.
Each diode costs about $195 (this hobby hates my wallet) so I definitely wouldn't want to take any risks and provide them with the proper cooling they need.

Though I have had few laser projectors and maintained them and replaced broken parts over the years, I'm still not very experienced with electronics (or thermodynamics).

I know commercial laser modules and some custom builds use TEC coolers.
How do you use and control the TEC coolers?

Here's what I currently have in mind for a home-use diode array TEC cooling:
TEC cooler/heatsink/fan sandwich, TEC controlled with thermistor and a PID controller.
Is this a decent annd economical way to do it?
How would you set it up yourself?



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Old 02-22-2015, 10:46 PM #2
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Default Re: how to set up TEC cooling?

A sufficiently large aluminium base plate will provide adequate heat sinking. TECs are only used to control wavelength (some red diodes or IR pump diodes) and that's not something you need.
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Old 02-22-2015, 10:56 PM #3
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Default Re: how to set up TEC cooling?

Sorry for asking this, but are you sure about that?
I've read in few places here that you'll need a TEC cooler if you want longer duty cycles and once that that is the reason laser pointers can't be on for a long time like laser modules in laser projectors.
And yes, I know some laser's (DPSS?) wavelength depends on the temperature a lot. But doesn't mean it is the only reason for advanced cooling.
I mean I'd be glad if I have just misread that, will just make my life easier.
Thanks.

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Old 02-23-2015, 12:02 AM #4
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Default Re: how to set up TEC cooling?

Yes I'm sure.

Obviously, letting your diode overheat will shorted its life. But your system does not need a TEC to stay cool enough. Some of the self-appointed thermal engineers around here think that unless the heat sink is cold to the touch, the diode is in danger. This isn't true at all. Ironically, what DOES put the diode in danger is running the current to within 10% of diode death, which how the vast majority of people like to run their pointers, unfortunately. If you're concerned about the longevity of your system, run it within its ratings.

Learn some more about projectors, and you'll see that very few of them use TECs unless there is DPSS involved.
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Old 02-23-2015, 12:32 AM #5
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Default Re: how to set up TEC cooling?

I guess I misread some stuff and/or people building such stuff are wrong too
http://laserpointerforums.com/f65/11...sia-86149.html
Quote:
Continuous operation time: 15 min. Pause: 10 min.
Okay then.
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Old 02-23-2015, 01:04 AM #6
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Default Re: how to set up TEC cooling?

Quote:
Continuous operation time: 15 min. Pause: 10 min.
I'd question how he arrived at those numbers. If they're correct, simple math shows a modest 40% increase in heat sinking ability allows continuous operation.
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Old 02-23-2015, 01:09 AM #7
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Default Re: how to set up TEC cooling?

All of that true, adding a fan without a TEC reduces the size of the heat sink needed for a given duty cycle, but with a TEC and fan combination even more so, at the expense of cost and complexity as well as more which can go wrong with the system. I've used bigggggg TEC's, 50mm wide squares and they suck a lot of current at 12 VDC, not so sure I should have put them in now, but back then I was using the system outside at 100+ degree F. temperatures and I sure felt better about my lasers staying cool, necessary or not. If not then a waste of money I suppose but I intended on adding more devices later which may have required it. I sure overbuilt it, what a heavy mass of metal, you can see it by following the link at the bottom of my signature for my projects page.
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Old 02-23-2015, 08:46 AM #8
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Default Re: how to set up TEC cooling?

Quote:
Originally Posted by Cyparagon View Post
I'd question how he arrived at those numbers. If they're correct, simple math shows a modest 40% increase in heat sinking ability allows continuous operation.
How do you calculate what volume heatsink you need btw?
It seems I won't need a fan and/or TEC cooler if the heatsink is large enough. How can I know that except tests posing the diode at risk?
I understand the answer might not be a simple or short one. Maybe there's also some simplified and less accurate way to find this out, or some rule of thumb? Any info will help.

Quote:
Originally Posted by Alaskan View Post
All of that true, adding a fan without a TEC reduces the size of the heat sink needed for a given duty cycle, but with a TEC and fan combination even more so, at the expense of cost and complexity as well as more which can go wrong with the system. I've used bigggggg TEC's, 50mm wide squares and they suck a lot of current at 12 VDC, not so sure I should have put them in now, but back then I was using the system outside at 100+ degree F. temperatures and I sure felt better about my lasers staying cool, necessary or not. If not then a waste of money I suppose but I intended on adding more devices later which may have required it. I sure overbuilt it, what a heavy mass of metal, you can see it by following the link at the bottom of my signature for my projects page.
How did you control the TEC coolers though? What do you think about using thermistor and PID controller?

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Old 02-26-2015, 05:26 PM #9
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Default Re: how to set up TEC cooling?

Jetlasers 532nm TEC (Not for sale) :



As you can see the extended 3 layers you won't see from normal jetlasers handheld, it's for military use very stable @800mw.

Sadly it takes 2x18650/2x26650 to run this thing!

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Old 02-27-2015, 02:09 AM #10
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Default Re: how to set up TEC cooling?

The method of driving the TEC can vary depending on what you want to do.

PID control isn't really necessary unless you really need to regulate the temperature of something to a precise value. Usually only needed for DPSS crystals and controlling pump diode wavelength.

For a plain ol diode laser, driving the TEC at a specific voltage that produces adequate cooling can be done for applications where ambient temperature doesn't change much.

Basic temperature control can be accomplished with a thermistor, comparator and a power mosfet; but you can go fancier with a tiny microcontroller to do fancier things.


TECs mostly behave like a resistive load, so driving them doesn't require anything special.
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Old 02-27-2015, 10:33 AM #11
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Default Re: how to set up TEC cooling?

Not to mention u would need to isolate the heat dump from the heatsink/host and that could be somewhat of a challenge. Your going to have to worry about condensation and the lot. I would suggest a adjustable driver to play around with the current on the Peltier to achieve a duty cycle that keeps the sink room temperature.

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