Phlatlight PT-54 TEC driver

[DTR]

I got a question from a buyer and I am not sure exactly what to recommend as I have not used the TEC before in a project. Here is what he asked.

"I don't mean to cast any doubts on the description of the modules, but I wonder if the TECs really can operate at 12 V. I am running them at 5 Volts (about 2 amps) and the thermistor reads around 0 degrees C. I am a bit nervous about running the TECs at 12V not wanting to burn them up. How much current do they draw at 12V?"

Now this is how I answered.

I am no expert on the TEC's but from what I have understand they require current limiting drivers like laser diodes do. As they heat up their internal resistance drops and they will draw more and more current. I don't think you can just feed them a specific voltage with no current regulation. But I will ask around.

Anyone have any suggestions on how to correctly drive these TEC's?

 

[AnthoT]

I got a question from a buyer and I am not sure exactly what to recommend as I have not used the TEC before in a project. Here is what he asked.

"I don't mean to cast any doubts on the description of the modules, but I wonder if the TECs really can operate at 12 V. I am running them at 5 Volts (about 2 amps) and the thermistor reads around 0 degrees C. I am a bit nervous about running the TECs at 12V not wanting to burn them up. How much current do they draw at 12V?"

Now this is how I answered.

I am no expert on the TEC's but from what I have understand they require current limiting drivers like laser diodes do. As they heat up their internal resistance drops and they will draw more and more current. I don't think you can just feed them a specific voltage with no current regulation. But I will ask around.

Anyone have any suggestions on how to correctly drive these TEC's?

Well maybe just simple current limiting ic's an LM317 driver may work even, just using the current limiting like in laser diodes, but an LM1084 would work better because of its higher output current :beer: it should work the same as a 317 type driver
I beleive the hot side is also suppose to be heatsinked :beer:
EDIT: found this for you, show your customer this http://laserpointerforums.com/f67/lm1085-diy-driver-62227.html he can drive it at 1.8Amps which should suffice

 

[Tech_Junkie]

Type in "TEC driver" in the google search box at the bottom of the page. There are tons of threads.

And you do need a driver.

 

[DTR]

Type in "TEC driver" in the google search box at the bottom of the page. There are tons of threads.

And you do need a driver.

I did find several threads most informative being this one.
http://laserpointerforums.com/f42/tec-basics-do-they-need-driven-61275.html

But I was hoping for some more specific info for this exact TEC. I have not seen any posts with people using them. But they are pretty common around now and thought some would have some experience with them.

 

[Tech_Junkie]

Some can handle more abuse than others, but they basically all work the same. I've never read about any testing of the projector ones, nor builds using them.

The answer to your clients question is in that thread. Just point it to him, or quote a post, case closed. Why make it more complicated than it is?

 

[Cyparagon]

You only need a driver if you want precise temperature control. Virtually all the mini-fridges just feed it a straight 12V.

 

[Meatball]

Perhaps a current limiting resistor in series at the very least can leave the current through the TEC a little less depending on its instantaneous junction temperature difference.

So... 12V if you must, but if you want to limit the current to say 1A, just put a 12 ohm resistor in series and the current should never pass 1A.

 

[DTR]

You only need a driver if you want precise temperature control. Virtually all the mini-fridges just feed it a straight 12V.

I am guessing if you run it unregulated it requires that the heatsink can disperse all the heat being made by the TEC?

Perhaps a current limiting resistor in series at the very least can leave the current through the TEC a little less depending on its instantaneous junction temperature difference.

So... 12V if you must, but if you want to limit the current to say 1A, just put a 12 ohm resistor in series and the current should never pass 1A.

Good suggestion. I assume the resistor would be producing a lot of heat it self.:evil:

 

[DTR]

Ran a little test tonight. Look like it draws about 1.6A @ 5V and about 2.4A @ 12V.

 

[raysoptics]

I am the potential buyer. TECs come in a lot of flavors and I have some experience using them. I simply don't know the specification for the TEC in the Phlatlight module and while I was experimenting it seemed that the module was pretty cool running it at between 5 and 8 volts (2 to 4 amps). I would rather run the TEC from a 12 Volt regulated supply since I could just use a computer supply. The eBay auction page said that the TEC could be run at 12V but I thought it might be overkill. I just needed some re-assurance that I would not blow up a bunch of the modules over time. Thanks

 

[raysoptics]

Thanks for running the experiment. Since TEC cooling is a function of their operating current I will use a voltage that results in about 2.7 amps.

 

[bobhaha]

As far as I understand it, the TEC doesn't produce heat DTR. It only transfers it between its two surfaces. Its maximum range of differential on the two sides is 70 degrees C (typically). To keep this differential the TEC will require a higher current. Limiting the current of the TEC will only limit the max transfer rate of heat between the two sides.

Pushing 12V through it will actually increase the differential range in comparison to pushing 5V through it. Thus the TEC will need a larger current to keep the two sides at that differential.

Does that make sense? Correct me if I'm wrong please.

 

[raysoptics]

My understanding about TECs is that they will transfer heat from the cold side to the hot side as a function of current. However, the TEC will self heat like any other device by V*I where V is the voltge across the TEC and I is the current flowing through it. The TEC transferrs heat to the cold side from the hot side proportional to its thermal resistance between the two sides. The net cooling is the the amount of heat pumped by the TEC from the hot side to the cold side minus the heat that flows from the hot side to the cold side. If the hot side can be kept from warming (fans, water cooling etc.) The heat pumped will be proportional to the current through the TEC. If the hot side temperature rises, the pumping efficiency drops so more power is required to achieve the same temperature drop. The ratio of the heat pumped from the cold side to the total power consumed is called the C.O.P (coefficient of performance). If the power dissipated by the TEC is not important to you, the current can be increased and the method used to remove heat from the hot side can be more aggressive. If power dissipation is important to you, then the current (and voltage) through the TEC should be reduced to just pump enough heat to maintain the cold side temperature at the desired temperature. The Phlatlights draw 8 amps at about 2.5 volts or 20 Watts. The TECs in these modules should pump slightly more than 20 Watts to keep the LED temperature from rising. Any more TEC operating power will do little more than consume unnecessary energy without providing much benefit.

I hope this helps clarify how TECs work and explains why the sweat spot can be important.

 

[Bionic-Badger]

I reverse-engineered the circuit that the projector was using and it was just using a 12V DC-DC converter for power delivery. I can't remember the details because I wrote it on something that I lost (like the back of an envelope). That would probably be the most energy efficient and controllable (with feedback) method of driving the TEC, as they like PWM rather than an "analog" level of voltage or current.