Essential Question: Which Peltier is the most Efficient for reaching coolest temperature, and is the 6V 2A peltier inefficient?

I was looking into more efficient Peltiers for my project and tried to test the amperages of certain Peltiers on a 5V power supply.

Here are the results I have up with:

Using a 5V power supply,

  • TEC-12704 (12V 4A standard draw) drew 5V 1.4A.
  • Peltier TEC-12705 (12V 5A standard draw) drew 5V 1.36A.

I don't understand how a Peltier rated higher than the previously mentioned runs at a lower power, and furthermore, when converting 12V -> 5V current output using ratios, (12V/5A = 5V/XA, where a 12V 5A Peltier should draw 5V 2.083 Amps? Why is this happening!

  • Lastly, I tested a 6V 2A Peltier which ran at 5V 2.2 Amps, more amperage at a lower voltage? - so does that mean this is inefficient compared to the last 2 Peltiers?

Currently I am using the 6V 2A Peltier, trying to find a more efficient Peltier and need to figure out: are these weird numbers due to one Peltier being more efficient than the other (critical to my project) or something else?

  • \$\begingroup\$ There is a back emf due to seebeck of junctions between Peltier plates, resulting in less current for same Vin \$\endgroup\$ – sstobbe Jan 20 '18 at 4:17
  • \$\begingroup\$ @sstobbe hi, could you explain this a little bit more: I am a super beginner. Also, if you could explain this in terms of efficiency that would be great \$\endgroup\$ – Omar Sumadi Jan 20 '18 at 4:18
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    \$\begingroup\$ Hi, if you disconnect your 5V supply after some time and measure the terminals of the peltier you will find its generating a voltage proportional to the temperature differential across it \$\endgroup\$ – sstobbe Jan 20 '18 at 4:22
  • \$\begingroup\$ @sstobbe interesting: well, based on these reading, is the 6V2A peltier inefficient, because I need to tell the efficiencies of the peltiers to see what I should buy out of the 3, or should I go for a higher powered one? \$\endgroup\$ – Omar Sumadi Jan 20 '18 at 5:02
  • \$\begingroup\$ meerstetter.ch/compendium/… \$\endgroup\$ – Tony Stewart EE75 Jan 20 '18 at 6:18