The lightweight Digital Dew Heater control unit measures 5" x 2.5" x 1". It comes with a permanently attached 12' (3.65m) power cord. The control unit is not a transformer and must be supplied with 12V DC power. The power cord terminates in a cigarette lighter plug for connecting to your car's cigarette lighter output or an optional rechargeable battery in the field, or to an optional AC to DC inverter in the backyard or observatory. A 12 amp hour capacity rechargeable battery is the minimum recommended. The control unit is fully protected against power surges or reverse polarity by a fuse in its cigarette lighter plug and diode protection in its microprocessor circuit.
It has four independently controlled 12V DC RCA jack heater outputs, to power four different Thousand Oaks heater strips. Other heater strip brands using RCA connectors are fully compatible with this control unit. With the addition of an RCA splitter cord, 5 to 6 heaters can be attached. A red LED indicator for each channel shows when a heater strip is connected and drawing power from that channel. A separate green LED shows when the control unit is receiving power. The green LED also serves as a low power warning in the "battery saver" mode.
The battery saver function provides peace of mind when using your car battery, as it assures that you will always have plenty of battery charge left to start your car engine. The control unit automatically turns off if the voltage drops below 11.1. At 11.25V, the green LED starts to flash to show that the control unit will turn off in approximately 30-60 minutes. The factory default is ON for car battery use, but the battery saver function can be turned off when using a dedicated battery.
The advanced energy-saving pulse width modulation microprocessor is very energy efficient. It controls the 12V DC power to the heater strips by pulsing it on and off many times each minute and varying the width of each pulse rather than the voltage. Variable settings on the controller allow maximum conservation of battery power. Most users will be able to get in a complete observing session without needing to start their car engine to recharge the battery. Each heater output has a full range of adjustment from 0-100%, not merely from 40% to 100% as with some competitive models. This helps prevent tube currents or seeing degradation. It also eliminates the problem of overheating or not reaching the desired temperature, regardless of heater strip size and/or the number of heaters. The microprocessor provides a stable power output for precise temperature control. Without this control, output voltage can "wander" due to moisture, temperature changes, and/or age as seen with competitive models. The system is capable of keeping every optical surface you are using during an observing or astrophotography session free of moisture all night long.
In addition to the four variable outputs, there is an extra RCA outlet with a constant 12V output for any accessory device requiring 12V DC. The control unit is supplied with Velcro tabs that allow you to attach it to any convenient location on your tube assembly, mount, or tripod.
Put your heater strips on your telescope at the beginning of an observing session, with the control unit at a low setting. This should be good enough for most observing sessions and will give you maximum battery life. The higher settings are only recommended for removing moisture already collected on your objectives or for cold winter nights. If moisture has formed on your optics, put the control unit on high and wait 15 to 30 minutes for the optics to warm up. The thin corrector plates of Schmidt-Cassegrains should clear by then. The thicker objectives of Maksutov-Cassegrains or refractors can have any excess moisture removed with a tissue. You can then reset the control unit to a lower setting for the balance of the observing session.
The control unit has a maximum power rating of 10 amps. Add the maximum amperage draw of all the heater strips to be used (listed in the description of each heater strip). The total should not exceed the 10 amp capacity of the control unit. Do not attempt to boost the capacity of the control unit by increasing the fuse size.
