diy dew heater
Posted 25 September 2010 - 02:22 PM
I'm considering making my own dew heater and controller.
here's they idea i'm working on:
for the dew heater elements i would use regular resistors in heat shrink tubing. each heater would have 3 series of resistors.
The controller would consist of just three swithes controlling a singe serie in each element. it would be a binary coded system. like 1-2-4 ging me 8 levels of power.
Now i just wonder how much power each element should have.. so what would be the power required for a telrad, for a 60mm finder?
and would self adhesive velcro be a good material to put the isolated resistors in?
I appreciate your thoughts,
Posted 25 September 2010 - 05:51 PM
Posted 25 September 2010 - 07:58 PM
Posted 27 September 2010 - 05:51 PM
I've found that 3W, or 48 Ohms works well for 2" eyepieces, and 2W (72 Ohms) for 1.25" eyepieces and 50-80mm finder objectives. (More heat is needed for eyepieces because of the close proximity of the warm, moist eye.) Your 4" refractor should stay dry with no more than 3W. (I've fitted out 8-10" SCT's with no more than 4W, by placing the heaters on the inner surface of the corrector cell. Compare this to some commercial heaters which can squander near to 30W--albeit on a timed duty cycle.)
Posted 28 September 2010 - 09:36 AM
very helpful information..
Posted 28 September 2010 - 06:03 PM
The controller is modeled after a single phase electrical panel, using two terminal strips as "bus" bars, one for ground or common, the other for the hot or line side of the circuit. I made the connections to the strips using crimp on lugs and a crimp tool, both of which you should be able to find in an electronic supply store. I installed a fuse between the positive or line side terminal strip and the battery to prevent a short circuit from damaging my equipment or even causing the battery to explode. Never build a device like this without a fuse, it's there to protect your equipment. I control the amount of heat using variable resistors in between the switches and the RCA jacks the heater plugs into. On the load side of the switch, I connected a red LED which then goes to the ground terminal strip so I can tell in the dark if the heater is on or not. A couple of jacks do not have a variable resistor in line with them so I can power my digital setting circles with 12-volt power.
For some instructions on how to make dew heaters, go to www.dewbuster.com, which is where I got the information to make my own.