Tired of fiddling with the heater strip every time you change eyepieces?
Wish your Star Diagonal (or Paracorr) had a built-in heater? Well
here's a solution, just follow the instructions below to add a nichrome
wire heater to your Star Diagonal that is compatible with the
DewBuster™ Controller and other 12-Volt dew-heater controllers.
Your Star Diagonal will not be modified and the heater takes up
very little space. Dob owners can use these same instructions for
their Paracorr since the principle is the same.
Tools and Materials:
Ohmmeter - Used to measure resistance of
Nichrome Wire - may be obtained from an
old hair dryer. Should measure about 17 Ohms resistance from
end to end. NOTE: If purchasing new nichrome wire divide 17
by the wire's Ohms per foot to determine how many feet
of wire are needed.
Copper wire - for heater cord, Use 2-conductor
#24 AWG or larger wire long enough to reach from the Star Diagonal
to the DewBuster™ Controller.
Insulation - For wrapping around
the heater to reduce heat loss. A neoprene drink can insulator
RCA Plug - for connecting to DewBuster™
17PP058 works well.
2 Crimp Terminals - Ring Terminal or Butt
Splice connectors to fit #18 wire (example
Mouser 644-BS18-M). The ring size does not matter as it
will be cut off. These are commonly used to make electrical
1/16" Heat Shrink Tubing - used to
keep nichrome wire from shorting against itself as it is wrapped
around the eyepiece holder (example
Measure nichrome wire from end to end with Ohmmeter to ensure
it measures at least 17 Ohms. If much less it will not work
because the nichrome wire will get too hot.
Twist end of nichrome wire to one of the copper wires of
heater cord, then insert into terminal and crimp. For increased
reliability, solder the joint after crimping, but solder does
not stick to nichrome wire so you must crimp first.
Connect Ohmmeter to the crimped end of the nichrome wire
and touch the other lead to the opposite end of the nichrome
Move test lead along the nichrome wire until you find the
spot where it measures 17 Ohms and cut nichrome wire about a
Cut a piece of Heat Shrink Tubing about an inch longer than
the nichrome wire, slip it over the nichrome wire, then use
heat gun to shrink the tubing.
Wrap two turns of electrical tape around the eyepiece end
of the Star Diagonal (as shown above) to insulate the wiring
from the metal Star Diagonal.
Wrap the heat shrink covered nichrome wire tightly around
the star diagonal as shown above (the wraps can touch each other
as long as the heat shrink keeps them from making electrical
Cut back enough heat shrink to expose 1/4" of nichrome
wire and twist it to the other copper wire of the heater cord
(see above). Insert into Butt Splice or Ring Terminal and crimp.
For increased reliability, solder the joint after crimping.
Wrap remaining portion of the nichrome wire around the Star
Diagonal so that the entire length of nichrome wire is in contact
with it (see above). Wrap electrical tape around the nichrome
wire to insure it does not slip out of position.
Using an Ohmmeter, recheck the heater resistance to insure
it is about 17 Ohms. If it reads much lower then you have a
Wrap the heater with insulation to reduce heat loss to the
Wrap the outside of the insulation tightly with black electrical
Install an RCA plug onto the heater cord (polarity does
Recheck the heater resistance to insure it is still 17 Ohms
and you are finished. NOTE: To allow the diagonal to be neatly
stored in your eyepiece case, simply wrap the heater cord around
the diagonal when storing.
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Copyright 2015 by Ronald & Teresa Keating. All Rights Reserved.