| WRAP-AROUND SECONDARY MIRROR HEATER |
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The Wrap-around Secondary Mirror Heater is the newest addition to our Newtonian heater line.
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These heaters are an elegant solution to the problem of the dewing over of the exposed secondary mirror on Celestron, Meade, Orion, Sky Watcher and other dobsonian telescopes that have exposed secondary mirrors that are glued to a stalk.They will effectively control and prevent dew on the exposed secondary mirror.
This heater is a formed, flexible heater that wraps around the stalk of the secondary mirror stalk. As there is no way to put a heater behind these types of secondary mirrors, this heater must be wrapped around the stalk. The heater then heats the stalk, which in turn heats the secondary mirror.
The heater wires can be taped down against one of the spider vanes (we recommend black electrical tape for this) and the heater wires terminate in a male RCA connector.
As the heater needs to be secured against the stalk in order to keep it in place you will need elastic bands or electrical tape to do this (not included). Or, if you wish to glue it in place, this can be done with the use of silicone glue, which is readily available at any hardware store.
The 2028 Wrap-around heater has a wattage rating of 10 watts (.8 amps) and the 2028-S has a wattage rating of 4 watts (.33 amps). This is fairly high for a heater of this type but this is necessary because the heater is exposed. Wrapping the heater with an insulating material will substantially reduce the power requirements of the heater. Depending on which Kendrick controller you are using you can reduce the amp hour draw of these heaters to almost nothing. Your observing environment will determine what setting you must use.
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| PRIMARY MIRROR HEATERS |
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We have heaters for 8" to 18" mirrors. They are very effective in the prevention of dew on Newtonian telescope optics, particularly for those who have Dobsonian telescopes with open truss tube designs.
These are installed behind the mirror in between the mirror and the mirror cell and are held in place by putting a thin skim of RTV silicone onto the heater and allowing the heater to dry to the back of the mirror. We do not recommend using heaters that would wrap around the outside of the optic as the thickness of Newtonian primary mirrors make this ineffective due to their mass. It is much better and much more effective to heat a primary mirror from behind.
P8 will fit 8" mirrors, P10 is for 10" primary mirrors, P12 is for 12" to 14" primary mirrors, P16 is for 15" to 18" primary mirrors.
These heaters can be used with a temperature sensor with our Premier Digital Dew Controller (#2002) or our DigiFire-10 Controller (#2001-10) for accurate optic temperature control or with any of our controllers in duty cycle mode.
| SECONDARY MIRROR HEATERS |
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Pictured are our heaters for secondary mirrors in Newtonian telescopes. We have two types of heaters for secondary mirrors. We have the passive resistance flex heaters (S2, S3 and S4) and the DewGuard Temperature Sensing heaters (DG1, DG2 and DG3). The S2, S3, S4 and the DewGuard heaters are designed to accommodate secondary mirrors from a minor axis (the narrow dimension) of 1.83" to 5".
These S2, S3 and S4 heaters are installed behind the mirror in the secondary holder and are held in place by the polyester batting that is supplied with these holders. The wires are then run across the spider vane and can be taped in place. For those who prefer as thin an electrical connection as possible, a thin, narrow copper tape is supplied with each heater (Please see drawing below). This allows the heater leads coming out of the secondary holder to be soldered to the copper tape, which is run along the length of the vane. The RCA jack is then soldered to the other end of the tape. It is highly recommended that the solder points be epoxied into place as the soldering process ruins the glue holding the copper strip in place at these points.
A 6' patch cord is supplied with each heater so that power may be supplied from the controller if the controller is mounted farther down your scope.
The S2, S3, S4 heaters can be used with a temperature sensor with our Premier Digital Dew Controller (#2002) or our DigiFire-10 Controller (#2001-10) for accurate optic temperature control or with any of our controllers in duty cycle mode.
The DewGuard heaters are self regulating.
S2 fits minor axis of 1.83" to 2.14"
S3 fits minor axis of 2.60" to 3.50"
S4 fits minor axis of 4.00" and up
DG1 fits minor axis of 1.5" to 2.5"
DG2 fits minor axis of 2.6" to 3.1"
DG3 fits minor axis of 3.5" to 6.5"
FURTHER INFORMATION ON THE DEWGUARD HEATERS
The DewGuard is the first temperature controlled heating system designed to help prevent dew formation on a telescope's secondary mirror. The uniform distribution and controlled heating avoids air currents and optical distortion. Newtonian telescopes in the 6" to 36" range can experience condensation on their secondary mirrors. This may be due to the open structure of their upper tube assemblies or severe condensation conditions. The DewGuard will keep it dry.
INSTALLATION OF DEWGUARD HEATERS
The DewGuard is attached to the back of the secondary mirror using silicone adhesive (RTV). Apply a small amount (about 1/32" thick) on the surface of each small square heater. Center the DewGuard on the back of the diagonal, wire end of the circuit board higher, or toward the open tube end of the diagonal, and allow it to cure overnight. You will need to supply the DewGuard with 12 volts DC (9-12V DC is suitable). The preferred place for high capacity (usually heavy) batteries is by the primary mirror or rocker box to have the smallest effect on balance. We recommend gel-cell batteries for capacity, charging characteristics and low temperature performance. A thin wire can be attached along the edge of the spider with super glue producing the smallest effect on diffraction. The spider itself can be grounded to the DewGuard and act as the ground wire, eliminating one wire. Red is positive. Attach the pigtail sensor and LED away from the secondary in a convenient location with free air circulation. Do not stuff the sensor into the packing that is supplied with most secondary holders. It is however, OK to stuff the polyfill wadding into the holder and against the DewGuard. The unit is supplied with a 9 volt battery snap connector. A 9 volt battery will work for 3-12 hours, depending on the particular environment. Twelve volt operation is best, therefore cutting off the snap connector or using another snap connector (watch polarity) will be necessary to rewire the DewGuard. It is advisable to put a switch and a fuse in line with the DewGuard. The DewGuard consumes about 0.02 watt at while connected to a power source to operate the temperature sensor.
OPERATION
Note: The indicator LED will only light when the temperature conditions activate the DewGuard. The LED will not light when power is applied if the secondary mirror is above the air temperature.
The DewGuard senses both the ambient temperature and the glass temperature using two sensors: one on the circuit board and one on the pigtail. It compares these and applies power to the heaters when the glass to air-difference is less than or equal to the preset value. A small LED indicates power consumption and is at "half" brightness when there is a 2 degree or smaller difference between the air and glass. The adjustable potentiometer is preset at the factory with heat being applied when the secondary mirror is still 1-3 degrees C above air temperature. A small screwdriver can be used if adjustment is necessary.
Using a small temperature difference preset will cause the unit to turn on sooner and may be used for the most severe conditions. A large temperature difference preset will allow the mirror to nearly reach air temperature before turning on, the preferred setting for typical dew or frost conditions. This will give the longest battery life and have a negligible effect on the optical figure of the secondary mirror while avoiding tube currents. The unit will remain off until the secondary mirror reaches the preset air/glass setting, then cycles on and off as the secondary mirror is gently heated.
ADJUSTMENT
We have found that the factory setting of 1-3 degrees C above air temperature has been sufficient for virtually all applications to date. We suggest that you first try the DewGuard at the factory setting before adjustments are made. If adjustment is necessary, the potentiometer is a 3/4 turn, so small changes are all that is needed.
| DewGuard 1 |
(Small) - turn potentiometer counter clockwise to increase heat |
| DewGuard 2 |
(Medium) - turn potentiometer counter clockwise to increase heat |
| DewGuard 3 |
(Large) - turn potentiometer clockwise to increase heat. |
SPECIFICATIONS
| Temperature control Operating range Reverse polarity protected |
+ or - 15 degrees C 12 volts DC nominal, (6-18 volts will work) |
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DG-1 |
DG-2 |
DG-3 |
| Elliptical size range |
1.5"-2.5" |
2.6"-3.1" |
3.5"-6.5" |
| Heating power |
Max. 2 watts |
Max. 3 watts |
Max. 4 watts |
| Current (@12 v) |
Max. 0.2 amp |
Max. 0.3 amp |
Max. 0.4 amp |
| Heating elements |
(4) 1/2 watt |
(6) 1/2 watt |
(8) 1/2 watt |
| Actual size (minor axis) |
1.25" |
2.25" |
3.2" |