diodespeltier
I have a Peltier (TEC) module, with diodes in series with each lead. (see image below)
I'm not quite sure what the specs are for the diode, but it says 130 on one line and SB560 on another, so I did a google search and found this.
How can I figure out how what the actual voltage on the Peltier element will be?
The original circuit is a "low-side" current sense. The first variant is a voltage source with a high-side current sense. The second variant is the same but is now adjustable (tweak trip current). The third variant replaces the two diodes with a transistor to make it a little more precise. All these circuits are not going to be very precise as the Vbe junction of any transistor is sloppy and changes a lot of temperature. The low side vs high side just depends on your application (maybe you don't have access to the high-side).
The three transistor version is going to be the most precise and give you adjustments to trim some error and tune the current trip level.
You could use a Polyimide etched-foil thin-film heater such as those made by Minco.
As far as refrigeration goes, if this was a serious high-volume application I'd be looking at something other than Peltier modules, probably completely out of the EE realm. Peltiers are just too inefficient and have too much thermal mass.
Best Answer
If I wanted to know the voltage across the Peltier, I would measure it directly with a multimeter.
The Peltier datasheet you linked a says it's rated for a maximum current of 3 A DC. If you push 3A DC through it, then the graph at the bottom of that one-page datasheet seems to indicate that the voltage across the Peltier should be about 0.8 V. That's the voltage directly across the Peltier at 3 A DC no matter what other stuff you have in series with it -- diodes, resistors, inductors, whatever.
From the description, it sounds like one Fairchild SB560 Schottky diodes b is in-line in each of the two wires that come out of this Peltier cooler. (I'm a little mystified what they are for, but I've already speculated on a few possibilities).
Like all diodes, it has a datasheet c. On the first page of the datasheet, it says each SP560 has a forward voltage drop ("VF") of 0.67 V at 5 A. But at the 3 A you're probably trying to use, the graph on page 2 of the datasheet shows it has a forward voltage somewhat less than 0.6 V -- maybe 0.56 V?
So I expect the total voltage across the entire series chain when 3 A is going through the chain -- two diodes at 0.56 V each and a Peltier at 0.8 V -- to be roughly 1.92 V.
Honestly, that's an unusual power supply voltage. The Peltiers I'm using this week are 12 V 5 A (similar to d e ); and 12 VDC power is more convenient than 1.92 V or 0.8 V.