Norfolk Astronomical Society

Telescope Dew Heating Calculator #2

2002 Glendon L. Howell

Input Loop Parameters

Source Voltage  volts
Resistor Size  ohms
Number of Resistors  

Computed Results (See Notes Below)

Volts Per Resistor  volts
Resistor Power  watts
Loop Amperage  amps
Total Loop Power  watts


Source Voltage - chosen to be 12 VDC due to safety and remote availability.

Resistor Size - standard sizes readily available are 10, 15, 22, 33, 47, 68, 82, 100, 150, 180, 220, 270, 330,390, 470 ohms, etc.

Number of Resistors - 4 to 6 is a good number to work with around 1.25-inch barrel eyepieces. The necessary number will vary with your application.

Volts Per Resistor - in a series circuit, with each resistance the same, equal voltage is dropped across each resistance.

Resistor Power - should not exceed the wattage rating of the individual resistor. Typical ratings are 1/4, 1/2, 3/4, 1 watt, etc.

Loop Amperage - in a series circuit, the same current must flow through all component resistances in the circuit.

Total Loop Power - this is the total heating power of the loop. For best performance this value should fall at 2-3 watts, which should be sufficient to keep optics clear.