Cooling with TEC...

Hi, just wondering: If I cool with a thermoelectric pump (TEC) my diode housing (Aixiz), what's the best way? Should I put it directly over the cooling surface, or mount the housing in a heatsink, then the heatsink over the cooling surface?

Will the cold temperature reached by the peltier damage my diode if it is directly above it?


Thanks.

razeman said:

Hi, just wondering: If I cool with a thermoelectric bomb (TEC) my diode housing (Aixiz), what's the best way? Should I put it directly over the cooling surface, or mount the housing in a heatsink, then the heatsink over the cooling surface?

Will the cold temperature reached by the peltier damage my diode if it is directly above it?


Thanks.

Click to expand...

It's a thermoelectric cooler, not a weapon of mass destruction..

and you want to mount to a heatsink, and then mount the heatsink to the TEC. You can control the amout of cooling by controlling the amount of current through the TEC. LM317 drivers work quite well for powering TECs..

Cold wouldn't kill a diode like heat will. Just watch out for condensation. Depends on the host, is it a box style or portable?

ElektroFreak said:

It's a thermoelectric cooler, not a weapon of mass destruction..

and you want to mount to a heatsink, and then mount the heatsink to the TEC. You can control the amout of cooling by controlling the amount of current through the TEC. LM317 drivers work quite well for powering TECs..

Click to expand...

I meant pump, not bomb, my English is a little rusty.

Be very careful as you get the diode cold. You may run into problems with thermal runaway due to the increased efficiency at lower temperatures. Another good benefit though is the lower wavelength which results from the shortening of the laser cavity on the diode due to thermal expansion.

If you use a TEC, remember, it only moves heat, it doesn't get rid of it, if you just attach a TEC to your module and don't heatsink the other side, it won't work well.

What you mean with "thermal runaway due to the increased efficiency at lower temperatures"?

Also what else to be aware when lowering the temperature of the diode? Let's say to...-15 Celsius? -> 3 Farenheit

Also: lower wavelength which results from the shortening of the laser cavity on the diode due to thermal expansion.

You meant thermal contraction?

Regards

Thermal runaway I believe can be explained by the slope of the graph of the efficiency of a diode. When you graph a diode's power output in mW over its current input in mA, you get a slope which generally increases along the graph, provided current is increasing. A diode of lower efficiency will have a graph with a slope that is generally < 1. A more efficient diode will have a slope generally > 1.

Now, by cooling the diode you will get an increase in efficiency. Since you are removing heat, you are also decreasing the resistance across the diode, which in turn lets more current through the diode, and will increase the voltage across the diode. Since Voltage * current = power, when you increase both the voltage and current across and through the diode at the same time, then power of the diode will increase exponentially. The exponential curve happens to be concave up, in shape. So instead of having a nice faultless line to work with, you have an exponential curve to work with. So if you try to apply the measurements taken from linear results, you could easily end up getting a result (or a Y value) that is much higher than anticipated, which would of course, endanger your diode if you were pushing its limits in the first place. You might end up over- powering your diode.

WAIT! Don't stop reading! This is something that I simply inferred all on my own. This is not based on fact, but from what I could guess might happen (electrically) if you cooled a diode too much. I COULD be completely wrong! Just my 2 cents.

You are pretty close!

Just make sure you are on a constant current source for the diode and make sure the hot side of the TEC is very well heatsunk. Additionally, you need to be careful to avoid condensation on the cold side, especially when running at that low of temperature.

Definitely must cool the hot side of the peltier...

A fan with a finned heatsink is best. Well, I am not really all that knowledgeable on the subject, but I did build a couple of basic TEC box style 'Ice Box' builds that work very well.

As was mentioned, you can control the cooling with the amount of current you feed the peltier. (as long as you dissipate heat from the hot side)

Take a look at this build for some ideas:
http://laserpointerforums.com/laser_pointer_forums_3/forum/showthread.php?t=37239
Jay

Yeah I've collected a bunch of heatsinked-fan coolers from core 2 duo pcs that we'll be enough =D.

But my initial question hasn't been exactly answered, what is more advisable, putting the housing directly over the peltier, or... mounting it inside a small heatsink; then laying the heatsink over the peltier.

Thanks.

I think that it's not good to cool LD below ambient temperature. In most cases TEC is used to STABILIZE temperature, not to improove cooling. Unless you have a temerature sensor on the LD and a circuit that uses this sensor and TEC to stabilize the teperature you can simply put the LD on a larger heatsink without using a TEC, this is my opinion.

razeman said:

Yeah I've collected a bunch of heatsinked-fan coolers from core 2 duo pcs that we'll be enough =D.

But my initial question hasn't been exactly answered, what is more advisable, putting the housing directly over the peltier, or... mounting it inside a small heatsink; then laying the heatsink over the peltier.

Thanks.

Click to expand...

You must have missed it...

ElektroFreak did answer this question. Use a heatsink for the module, mount the heatsink to the peltier.
Jay

But unless you plan on having a really long run time and/or plan on using a very powerful diode (I mean at LEAST 200mW, up to several Watts), then I think TEC is a little overkill.

It's about 400mW, think might be necessary

hi

Dont know if this will help but i have a tec cooling a laser diode and here is a picture of the set up the axzi housing is inside the heatsink connected to the tec then the hot side of the tec is connected to a larger heat sink and a temp monitor is used too keep the temp stable you dint have to have a temp monitor ,

^That diagram is exactly right.