TEC/peltier question?

[mixedgas]

oh ok.. ill get one from him...
i get all my stuff from him anyway..
should have guessed..

One of the points I guess I did not correctly articulate in a previous post is that peltiers driven full slam to their max rating some times fold back along their response curve into heaters. Also it is not good to condense ice onto your diode.
Steve

[uk-laser]

Yes, just to clarify - you can't run a peltier off a laser diode driver and just turn up the current. You need a TEC driver which will take feedback from a thermistor mounted on (or preferably just under) the object you are trying to cool.

[andy_con]

so robin wheres best to put the thermistor, on the yellow blob on the side of the alum block? or actually on the tec cool side?

[thesk8nmidget]

Yes, just to clarify - you can't run a peltier off a laser diode driver and just turn up the current. You need a TEC driver which will take feedback from a thermistor mounted on (or preferably just under) the object you are trying to cool.

it may not be the correct way (im not all that smart in the peltier field) but there are a few people using some drivers to run their plates and they also havent had problems.


as it may not be the right way people have gotten away with it working fine.

does anyone have a link to a proper peltier driver?

[uk-laser]

so robin wheres best to put the thermistor, on the yellow blob on the side of the alum block? or actually on the tec cool side?

Ideal place would be to drill a small hole where the yellow dot is and glue the thermistor into the hole.

it may not be the correct way (im not all that smart in the peltier field) but there are a few people using some drivers to run their plates and they also havent had problems.


as it may not be the right way people have gotten away with it working fine.

does anyone have a link to a proper peltier driver?

A bit like driving a car with a brick on the accelerator.
As long as the road is flat your speed (temperature) will be constant.
I prefer the closed loop approach myself.

http://www.die4laser.com/D4Chill/D4Chill_Sch.pdf
http://www.die4laser.com/D4Chill/D4Chill.jpg
http://www.die4laser.com/D4Chill/D4Chill.txt

By the way - adding TECs recklessly can cause more problems than they solve.
As Rob pointed out cool below the dew point and you have water on your optics.
Provide inadequate cooling to the hot side of the TEC and you have thermal runaway and lose everything.

[tocket]

In my opinion the temperature sensor should be as close to the target of your cooling as possible. Since its the laser diode that we want temperature regulated in this case that is where you should try to put your sensor.

Now, considering the small heat flux from the diode in that large aluminum block I don't think the diode package and block surface temperature will differ much, so you can just place it on the surface of the block as long as you insulate the exposed side of the sensor (Ideally the whole block should be insulated).

[uk-laser]

Ah, the position depends on the type of controller.
If it is proportional control only you want the sensor as close to the TEC as possible whilst still being thermally linked to the mass of the block.
If you have PID then you place the thermistor as close to the diode as possible.

[andy_con]

[img]Ideal place would be to drill a small hole where the yellow dot is and glue the thermistor into the hole.[/img]

i can do that, cheers robin

[uk-laser]

As others have mentioned - insulating the block afterwards will reduce the power you need to pump. Since the hot side requires the removal of several times the pumped power a little insulation can give big power reductions.

[mixedgas]

As others have mentioned - insulating the block afterwards will reduce the power you need to pump. Since the hot side requires the removal of several times the pumped power a little insulation can give big power reductions.

You just need a simple on/off (proportional) not pid controller to get started.

http://www.mcshaneinc.com/html/5C7-350.html

overkill at 55$ but it was the first search I found. Note, if your TEing a expensive 635 diode, you should use TEC in moderation as TECing drives the current density up in the device. Older diodes did not like that. ie back off on the diode current and monitor its power as you adjust the tec downwards

then there is this, settable from 0-100C and 15$ US, they will have a UK distributer
http://www.velleman.be/be/en/product/view/?id=347925

you can also go back to my first post on this topic and build woodward's little circuit.
Knowing the legendary stephen woodward's skill set, it would work like a charm.

or velleman kit http://store.qkits.com/moreinfo.cfm/FK934

Steve