Hi, I am a neuroscientist developing a study on pain responses. For this purpose I wish to use a Peltier element to produce a controlled level of heat. I have purchased a 3x3cm elements rated between 5v - 16v max with 3.3 amp max current. I wish to be able to control heat output. In the lab we have a variable DC current source. What I need to know is whether any additional control elements will need to be introduced into the circuit to produce the desired effect? This is a methodology that has been used previously in psychology studies so I know it must work but have been unable to find any constructional details in the published literature. I would be most grateful for any assistance anyone can provide. Many thanks.
Colin's response: "Place a 1 ohm 5watt wire-wound resistor in series with the element and increase the voltage until you get the desired heat/cooling effect.
Note: the current must not be greater than 3 amp. "
IS there some reason I am unaware of for adding a series resistor here? All you will be doing is dropping the voltage across the resistor and wasting power.
Peltiers are load devices which draw their own current. As long as the supplied voltage doesn't exceed what the rating indicates it won't exceed more than 3 amps and all will be well.
My advice to the OP would be to build a feedback temperature controller or purchase one. If building such a circuit is more than you have time or expertise to do, I suggest purchasing one from a lab supplier like Watlow, Omega, Fisher Scientific, etc. That is if the project is funded.
If your power supply is variable then you should be able to manually control the temperature easily enough by adjusting the voltage within the specified range.
You said something about a "variable current source". So that we don't confuse terminology, is this a variable DC power supply or an actual regulated current source? If you are actually manipulating the current instead of the voltage, by nature of Ohm's Law the proper voltage would be attained when the current indication is less than 3 amps, you can prove this with a DC voltmeter across the load. At 3 amps you should be no more than 15 to 16 volts.
But again, the most optimal set-up would be either an "on/off" thermostatic or analog PID controller with a sensing element providing feedback to maintain automated temperature.
And if you choose to go a manual route, the resistor is uneccessary. You have variable control with your power supply. If anything I would add a series 2.5 to 3 amp fuse instead of a resistor to ensure the rated current is never exceeded by an accidental "overvoltage".
With manual control, you could easily monitor the surface temperature of the test specimen with an inexpensive digital thermometer purchased at a hardware store, electrical supply store, or even perhaps a department store. A cheap thermometer designed for checking food in the oven could be hacked and extra lead length added to the sensing element (thermistor, rtd, ic chip)
This would be a very easy thing to do.