DewBuster™ Controller Technical Bulletin
14" SCT Dewing Up.
First and foremost, be sure to place the heater strip around the aluminum tube just behind the corrector plate casting and be sure to use a dew shield. You may wonder why a dew shield is needed when you have heaters. The answer is because heaters are intended to replace the heat energy being lost to the night sky through radiation cooling. Not using a dew shield is like trying to heat your home with the doors wide open, you lose more energy than you can put in. Adding a dew shield is like closing the doors so the house can warm up and the thermostat (DewBuster) can start cycling the heat to maintain the proper temperature. I suggest making a dew shield with Reflectix insulation and making it overlap the heater strip and tube as much as possible to help prevent heat loss and get more of the heat into your telescope where you need it. See my directions for making a dew shield for more information.
Second, make sure you have a robust battery or power supply because 14" SCT's are big scopes and need all the heat they can get. Voltage plays a huge factor and as shown in the graph below, a fully charged battery or 13.8V power supply will generate 30% more heat than a 12V power source. If the power source can't supply enough current the voltage will drop each time the big heater turns on and that means it is not producing full heat. If you plan to use a power supply I would suggest a 10 amp 13.8V power supply like the Pyramid PS15. If you plan to use a battery I would suggest a deep cycle marine battery of at least 75 Amp-Hours.
Third, insure you have low resistance connections and heavy gauge wiring. I recommend the heavy duty power cord on 14" and larger SCT's because it eliminates the cigarette plug and glass fuse and provides heavy duty connections, 16 gauge power cord, and a low resistance solid state fuse. The end result is that almost full battery voltage reaches the heater. In contrast the cigarette plug power cord will lose about a volt which translates into 20% less heat.
If after following the above recommendations you still experience dew, then check to see if the DewBuster™ Controller's LED remains on for the Temperature Controlled output driving the 14" heaters. If so, this means the heater is not warming the telescope up to the desired temperature. Try wrapping around the outside of the heater with insulating material to reduce heat loss. In some cases a second heater strip may be needed and this can be plugged into the second Temperature Controlled (you do not need another temperature sensor since the first heater has a sensor). Since the DewBuster™ Controller monitors temperature, it will automatically compensate so that the pair of heaters uses no more power than a single heater, yet it will have the ability to produce extra heat when needed.
