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My astronomy project:
Making of a heating band or dew heater


Content:

  1. Introduction, attach a heater to the dew shield
  2. Heater band for 5" refractor, field test outdoors
  3. Making a USB powered dew heater
  4. Lens USB dew heater
  5. Dew USB heater narrow band model with regulator

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!


5: Dew USB heater narrow band model with regulator

The lens dew heater I bought earlier doesn't fit my short focal lenses very well. I need a more narrow heater band. As an example my project where I build a 300 mm lens astrophotography system.


Dew USB heater narrow band model with regulator

The two lenses on my 300 mm system. To the left my own built dew heater with three power settings. To the right the lens dew heater I bought earlier.


Dew USB heater narrow band model with regulator

At top the new dew heater I bought, much more narrow and will fit my lenses better and not waste with the power as much as the earlier at bottom do.


Dew USB heater narrow band model with regulator

The lens heater was delivered with a power regulator. It turns on and off the power in a slow pace. A couples of seconds between each cycle, but this is a slow thermal system to heat so it works. It has three power level settings: 1/1, 1/2 and 1/4 correspond to about 2, 4 and 8 Watt.


Dew USB heater narrow band model with regulator

Dew heaters mounted on the lenses, what a different ! All the cables I must get rid of later, my plan is, if my test show that the 1/4 power setting is enough, I cut the cables and solder the two heaters in series of each other. That will reduce the power to 1/4 of each without a power regulator.


From my measurements I have done a power table to see the difference between the old and the new dew heaters. Powered from 13.7 Volts:

Device Ampere Watt Note
The old dew heaters
Homebuilt dew heater 1 0.06 0.82 *
Homebuilt dew heater 2 0.13 1.78  
Homebuilt dew heater 3 0.20 2.74  
Wide heater 0.35 4.79 *
The new dew heaters (single)
Narrow heater direct 0.55 7.53  
Narrow heater 1/1 0,52 7.12  
Narrow heater 1/2 0.26 3.56  
Narrow heater 1/4 0.13 1.78 *

From this I can see that my old heaters in normal (*) mode takes 5.6 Watts. The new heaters used in 1/4 power mode will take 3.6 Watts, there are two of them. The power out from the heating bands are lower because of losses in the cables and in the 12 to 5 Volt regulator. I will save 150 mAmp or 3.5 Watts on the 12 Volt side. Everything to get the battery to last longer is good.


Later after some test out in the cold:

Dew USB heater narrow band model with regulator

After one night with -8 Celsius degrees I found that the dew heater worked perfect even at the lowest power mode, 1.8 Watt on each dew heater. But I don't like all these cables. Including the regulators it must be almost 5 meters of cables and I need less than 0.5 meter.


Dew USB heater narrow band model with regulator

Away with the regulators, but still the long cables on the dew heaters.


My new dew heater's cables cut into pieces !

Dew USB heater narrow band model with regulator

Cut the cables to 0.45 meter and saved one 0.15 meter of cable with the USB A connector. My plan is to connect the two dew heaters in serial of each other, then it reduce the power. It would be something like 1.8 Watt per dew heater.


Dew USB heater narrow band model with regulator

To the left the cable of the two dew heaters and to the right the short cable with the USB A connector. Now I have to solder them together.


Dew USB heater narrow band model with regulator

To do work like this I have to call in my assistant, the Handyman !


Dew USB heater narrow band model with regulator

First I solder the two wire that make them to be serial connected.


Dew USB heater narrow band model with regulator

Handyman hold them together and I solder them. I put the clamp over the shrink tube to not get it too hot when I solder, protect it to shrink already now.


Dew USB heater narrow band model with regulator

Put one big shrink tube over all cables, before I solder them together !


Dew USB heater narrow band model with regulator

After soldering and added shrink tubes.


Dew USB heater narrow band model with regulator

So much cleaner look now with the new short cables.


Dew USB heater narrow band model with regulator

Install the dew heaters on the lenses and turned the power on. I get 0.29 Ampere at 13.7 Volt. That give 3.98 Watt or 1.99 Watt on each dew heater. That is more power than earlier, why ? Because the shorter cables means lower resistance and lower power loss in the cables, more power to the dew heaters. If this will be too much I can connect the regulator again, only need one now. To my shortest lenses, the 50 mm f/1.8 and the 16 mm fisheye 1 Watt is enough.

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To page VI, to be continued

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