The Astrozap dual channel dew heater controller is simple, easy to use, compact, and lightweight (only 7 ounces). Its heavy duty plastic case measures 3.5" square by 1.5" deep (2" counting the two control knobs). It is supplied with a 2" Velcro strip for easy attachment to your telescope. There is a green LED indicator to show when the controller is getting power.
The controller has a fused male cigarette lighter plug on a 6' long cord. This allows you to connect it to a car's cigarette lighter plug or (preferably) a rechargeable 12V DC battery (to avoid accidentally draining your car battery and leaving you stuck at your dark sky site after a night of observing). The fuse has a 5 amp rating, the maximum amperage capacity of the controller.
There are four RCA output jacks on the controller into which you can plug your heater strips. All heater strip brands will work, in addition to Astrozap heaters. There are two control knobs, one for each channel. Each knob controls the power going to two of the four 12V outputs. For example, this allows you to use the two outputs of one channel to power the heaters for the main objective of a small scope and a laptop computer's LCD screen, while the second channel can be used at a different power setting to control the heaters for a Telrad and an eyepiece. With the addition of an RCA splitter cord, even more heaters can be attached, as long as you don't exceed the maximum output capacity of the controller.
The controller uses Pulse Width Modulation technology to control the power going to your dew heater strips by turning the power on and off many times each minute. When the control knobs are set on medium, for example, the heaters draw the same amount of current whenever they are on, but they are on only 50% of the time. The power output from the Astrozap controller can be varied over a 5% to 95% duty cycle range. When the controller knobs are set at their lowest settings, the controller is effectively off. Two amber LEDs indicate the power level of each channel. The brighter each glows, the higher the duty cycle for that channel's two outputs. Low to medium is the recommended setting for most observing conditions. The controller is RFI (radio frequency interference) free, an absolute necessity if you are going to be doing digital imaging.
Owners of 12" and larger SCTs may need two controllers - one for the main objective heater and a second for any other heaters you wish to operate. The heater strips for the objectives of these size scopes can nearly max out the power output capacity of the controller by themselves.
