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HEATERS FOR NEWTONIAN OPTICS
 PRIMARY MIRROR HEATERS  
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.

Kendrick Primary Mirror Heater Elements

  

 SECONDARY MIRROR HEATERS  
There are many types of holders for Newtonian secondary mirrors on the market and we have attempted to address many of these and their various sizes.


Standard Elipticle heater		   
Split heater		   
DewGuard heaters
(Temperature Sensing)		   
Wrap-around heater

Our Standard Eliptical heaters and the DewGuard heaters fit behind the secondary mirror and work best in Newtonian telescopes that have the removable type of secondary mirror housing pictured here. Please note that the DewGuard heaters have electronic parts that will prevent them from working inside ProtoStar mirror holders.

The Split heater is also meant to be attached to the back of a secondary mirror but is to be used with larger secondary mirrors that are attached to mirror stalks. As the heater is flexible, it can easily be placed around the mirror stalk and then the heater is glued to the back of the mirror.

The Wrap-around heaters can be used with secondary mirrors that are attached to stalks* or can be wrapped around the outside of a mirror holder**.
*Some stalks connect to the secondary mirror using double sided foam tape. This tape will insulate the stalk from the mirror, making it difficult for the heater to do its' job.
**Using a Wrap-arpound heater on a typical secondary mirror holder will increase the size of the secondary mirror obstruction but it will be very effective. If your secondary mirror is larger than 1.83" in width, we recommend using the Standard Eliptical heaters.

More information on these various heaters can be found below.

 STANDARD ELIPTICAL SECONDARY MIRROR HEATER  

These heaters are very effective at preventing and/or removing dew and frost from your secondary mirror. Using your Kendrick controller, you may turn the power up high to quickly clear the optics of moisture if they are dewed or frosted over or you may use a very low power setting to keep the optic barely above air temperature and prevent the formation of dew or frost.

These heaters work best in Newtonian telescopes that have the removable type of secondary mirror housing pictured here. They can also be used with secondary mirrors that are attached to stalks. To use them in this situation, the mirror will need to be removed from the stalk, the heater glued to the back of the mirror and the mirror (with the heater) glued back onto the stalk. If you do this, be careful that the mirror is firmly attached to the stalk again as you will not want it falling off onto your primary mirror!

FITTING DIMENSIONS
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

Installation Sheet Instructions for S2, S3, S4 Heaters
Adobe PDF Format Installation_Instructions.pdf 452 KB

S2, S3, S4 Secondary Mirror Heater Elements

 SPLIT HEATER  

The Split heater is designed to be used with larger secondary mirrors that are attached to mirror stalks. As the heater is flexible, it can easily be placed around the mirror stalk and then the heater is glued to the back of the mirror.

This heater can be used with secondary mirrors that are 75 mm (3.00") or greater. To be effective at its full potential, it will need to be covered with foam or some kind of insulating material so that the heat is directed into the glass and not the atmosphere.

SPECIFICATIONS:
Wire length: 380 mm (15")
Connector: RCA plug
Wattage:2 watts
Center hole dimensions: 50 mm x 74 mm

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 WRAP-AROUND SECONDARY MIRROR HEATER  
The Wrap-around Secondary Mirror Heater is the newest addition to our Newtonian heater line.
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.

NOTE: Some of these mirrors are attached to the stalk using a double sided foam tape. The foam tape does act as a mild insulator from heat transfer and larger mirrors may still have dewing problems due to this.

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.

2028 Installation Sheet
Adobe PDF Format 2028_installation_sheet.pdf 1.85MB

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 DEWGUARD TEMPERATURE SENSING SECONDARY MIRROR HEATER  

The Dew-Guard Temperature Sensing heaters (DG1, DG2 and DG3) are designed to accommodate secondary mirrors from a minor axis (the narrow dimension) of 1.83" to 5". See "FITTING DIMENSIONS" below.

These heaters are installed behind the mirror in the secondary holder and are held in place by the polyester batting or foam 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, The S2, S3 and S4 heaters come with a thin, narrow copper tape. This allows the heater wires coming out of the secondary holder to be soldered to the copper tape, which is run along the length of one of the spider vanes. 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.


Click here for larger image

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 Dew-Guard heaters have temperature sensors built in and are self regulating.

FITTING DIMENSIONS
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 Dew-Guard HEATERS

The Dew-Guard heaters are a 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.

INSTALLATION OF DEW-GUARD HEATERS
The Dew-Guard 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 Dew-Guard 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 Dew-Guard 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 Dew-Guard 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 Dew-Guard. 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 Dew-Guard. If you plan to leave a battery permanently attached to a Dew-Guard heater, it is advisable to put a switch and a fuse in line with the heater. The Dew-Guard 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 Dew-Guard. The LED will not light when power is applied if the secondary mirror is above the air temperature.

The Dew-Guard 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 Dew-Guard 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.
Dew-Guard 1 (Small) - turn potentiometer counter clockwise to increase heat
Dew-Guard 2 (Medium) - turn potentiometer counter clockwise to increase heat
Dew-Guard 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)

  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"

Dew-Guard Temperature Sensing, Secondary Mirror Heaters.
 

 



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