batteries - Trouble with Peltiers TEC and USB Output Current

here is the website I will be referencing: http://www.instructables.com/id/5-Mini-USB-Fridge!/

So I was reading from Inscrutables on powering a small Peltier TEC to cool your hand while reading, and so I bought a 5v 19.4 Watt Peltier.

The instruction website got me under the impression that a peltier will run at the 5 Volt and whatever current it receives. So, I set up the peltier element using my USB cable plugged into a USB battery pack and nothing happened. The item and fan turned on for one second, then shut right back off.

I got a current reading of 5v, 3.9 Amps when I plugged the Peltier USB into a USB wall wart which confused me since the maximum output of the USB cable and charger is stated to be 5V 2.4 Amps. So logically, I need to find some way to power the Peltier off of a rechargeable battery 5v 2.4 Amps.

• According to the instruction website I should have been totally fine powering the peltier from a USB battery pack as the instructional sheet was using a 12v 60 Watt peltier element powered by a USB cable.

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Potential Solution and Question

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I believe the problem lies in that the USB battery pack is shutting off to save itself from outputting a current of 3.9 Amps when it can only reasonably allow a draw of 2.4 Amps.

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  How can I stop this, how can I make it so that the peltier runs off the USB battery pack at its maximum capacity of 2.4 Amps, 5 Volts?

  
  
  


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  And why is the peltier pulling 3.9 Amps and not defaulting to the 2.4 Amps I am giving it through the rechargeable battery pack, as did the peltier powered by the USB cable in the Instructables website?

  
  

Answer

You bought an element rated for 5 V 20 W. This means that it will draw ~4 A when connected to 5 V stable supply. Period. It won't draw more. It won't draw less. There is nothing you can do about this, it is practically a ~1.2 Ohms resistor. The Peltier is not "defaulting" to anything because it has no idea that someone has some limit.

To get your Peltier battery to run at 2.4 A from 5 V, you need to get an element rated for 5 V 12 W. Or get the element as suggested in the video, 12V-60W, which comes down to resistance of 2.4 Ohm.

And yes, the charger likely shuts down at 3.9 A.