TEC/peltier question?

[uk-laser]

Looking at the $55 TEC controller and the $15 Velleman kit they are both temperature controlled switches. ($55 solid state, $15 relay!)
This is not going to help you if you are trying to drive a 3.7V 5A peltier.
(unless you have an extra 3V PSU sitting around)

Also driving peltiers from a voltage source you never get their rated pumping power.
You have to voltage derate up front to avoid over-currenting them.
A typical 12V peltier datasheet:
http://www.hebeiltd.com.cn/peltier.d...TEC1-12705.pdf
To get maximum pumping power you need a supply of approx 16V with a 50C Hot side temperature and 30C gradient. Conversely with a 25C hot side temperature and zero gradient the maximum voltage is approx. 14V.
Now you can run this relay switched from a 12V supply but when you have a 30C gradient and a 50C hot side temperature you only have 3.5A flowing through the TEC.
This gives a pumping power of 23W rather than the 32W you would have got by putting a 5A constant current through the device.

Driving from a voltage source is much easier to do (hence cheaper) and most people can live with the small performance trade off. In consumer goods *nobody* runs peltiers in current mode. (see PC coolers, 12V cold boxes etc…) For industrial use practically everybody runs a current through the peltier (see Maxim MAX1978/1979, Hytec HY5640, Newport 300 series temperature controllers etc….)

The main problem is voltage rating of the micro peltiers. Most are just a few volts.
If anyone knows of some 12V micro peltiers (15mm x 15mm or smaller) I’ll be the first in on a group buy.

Robin

[mixedgas]

The main problem is voltage rating of the micro peltiers. Most are just a few volts.
If anyone knows of some 12V micro peltiers (15mm x 15mm or smaller) I’ll be the first in on a group buy.

Robin[/QUOTE]


Robin, no argument here, However, from my point of view, having built 150 watt cooling systems, he is far better off with even a simple bang/bang controller then a constant on system with overvoltage where he will rapidly see foldback. 26 watts may just get him where he needs to be. Ideally he would have bipolar PID, but unless he can talk maxim out of a sample board, he may be SOL with the surface mount package. So much depends on the thermal inertia of his setup, ideally we would measure all the parameters of his setup So we to know the dimensions of his mount and start design interations.

Keep in mind but he asked for a simple low cost controller.

If he leaves the peltier on full blast, he will load down his psu, risk generating condensation , and get severe foldback. Far better to have less load, less foldback, and no condensate. So ideally he gets at least a current source and a simple controller, now he's looking at what, 75$ and he's not even there yet.


do we need to start the cost benefit analysis? Besides, why not use the larger device, more common, and less cost. Under the educational use clause of the copyright act I have attached Woodwards circuit for small peltiers from EDN magazine. It needs scaled to match his device.

Fair enough?

Steve