Hello Richard,
I have modified my Canon 1100D using a copper cold finger, a 45W TEC and a squared ring-shaped NiCr wire, about 35 ohms.
https://sites.google.com/site/beppel...al-dew-control
I filled with small granules of silica gel the tiny groove inside the plastic frame, empted after the lpf#2 filter removal.
This has resulted in the reduction of the relative humidity inside the sealed chamber I made between the filter and the sensor surface.
A NiCr resistive wire (384 ohm/m) was stacked on the frame, at a small distance from the filter edge. All is 12V powered in series with a resistor of 120 ohms.
Therefore, the wire dissipates about 1/5W (2.7V x 78 mA).
The developed power heats the lpf#1 filter only (I left it in its place), while no significant calor is transmitted to the air inside the chamber.
I noticed through various tests that the power dissipated by the NiCr wire should not be too high. In this case, in fact, the temperature inside the chamber will increase too much, causing the formation of some (few) filaments of frost on the sensor.
With a power of about 0.20-0.25W, I have
completely solved the condensation issue, even at a sensor temperature of more than -10 ° C.
Note that in this manner the sensor surface is not directly heated, therefore
the sensor total cooling is not diminished by an excessive power of the dew heater.
The current flowing inside the TEC is efficiently controlled by my homebuild PWM & low pass filtered controller. This is not a standard thermostat that turns on and off the cell, but it's exactly a power supply that varies the voltage just in
continuous, being driven - in real time with very small hysteresis - by the variation of the NTC resistance.
Giuseppe
Como, Italy