(meteorobs) Heat required to prevent dew in a box for allsky camera

[HEADLIGHTS Studio]

OK, it is just plain dangerous, fraught with the possibility of disaster, to
have live Line Voltage inside a small outdoor enclosure in a wet
environment. Exposed NiChrome Wire is better known under another name,
"Death Wire". While it may have been prudent in 1994 to use line voltage for
de-fogging a limited number of pedestal units, it is 2014; much more
attractive, safer, and inexpensive alternatives are available off the shelf
at Wal Mart. 

 

My Meteor Observatory just went through driving rain, 29 degree freezing all
night, heavy fog, and has been exposed this way for years, without requiring
attention or maintenance; providing uninterrupted observation.

 

I drew a quick and dirty schematic.

http://www.salsburg.com/NAVSPASUR/CameraPedestal.jpg

 

 

Good Luck.

 

Jay

 

From: meteorobs-bounces at meteorobs.org
[mailto:meteorobs-bounces at meteorobs.org] On Behalf Of Howard
Sent: Wednesday, November 19, 2014 10:19 AM
To: Meteor science and meteor observing
Subject: Re: (meteorobs) Heat required to prevent dew in a box for allsky
camera

 

Its very common to use resistors as heating elements for dew heaters in
astronomy applications. Or nichrome wire if you want to work with that (its
sometimes a bitch to solder). Its fairly simple to size the resistor network
to get the desired wattage.  Google it, there are plenty of examples on the
web.  You only want enough heat to raise the window temperature a degree or
two above the air temp. 

Typically I use 33 ohm 1/2w resistors in parallel to achieve whatever
wattage I think or determine is needed. Running off a 12v DC source it works
fine but of course runs down a battery eventually. You switch the voltage on
and off using either some kind of relay or use a pulse width circuit. The
later is the exact principle used by Kendrick type dew heater controllers.

Easy stuff, not rocket science. I've built a boat load of these over the
years: highly effective.




Using Line Voltage and Resistors like those in the Sandia rig is expensive
and dangerous, it is not advisable; besides the resistors are difficult to
obtain. Relate to the fact that those Sandia rigs were designed in the 1990s
by highly experienced Engineers with large budgets. Running Line voltage to
something on your roof or outside your observatory is fraught with problems
and dangers (Lightning, Sunlight, Animals).Inside my pedestal, I use a 12VDC
Windshield Heater (has a fan) from Wal-Mart, switched by a Car Horn Relay
from an auto parts store, and a cheap electronic thermostat from Lowes.
Total cost, about $35. I run it on 2, 5 Volt USB Chargers connected with
Malibu Lighting Wire (Lowes) which is Sunlight resistant. The problem with
internal Moisture is caused by an inadequately sealed Pedestal. It is
advisable to use a large number of desiccant bags inside the Pedestal.
Moisture will eventually destroy the Lens and Camera. I use 6 inch PVC Sewer
Stand Pipe and Joiners with modified screw-on end caps; on the bottom for
connections and mounting and on the top, the dome. This makes it large and
heavy, but is very durable, inexpensive, easy to service and maintain.
 
-----Original Message-----
From: meteorobs-bounces at meteorobs.org
[mailto:meteorobs-bounces at meteorobs.org] On Behalf Of Jim Wooddell
Sent: Friday, November 07, 2014 7:38 AM
To: meteorobs at meteorobs.org
Subject: Re: (meteorobs) Heat required to prevent dew in a box for allsky
camera
 
 
 
Hi Mark,
 
The Sandia Allsky cams use two resistors on a metal plate, a thermostat and
a fan to keep everything toasty in the winter.  Works fine.
 
Jim Wooddell
 
 
 
On 11/6/2014 11:59 PM, Mark Bowling wrote:
  

What do you guys do in the summer?  I get a lot of moisture build up 
inside. I've been using desiccants, but that gets to be a pain.
 
Mark Bowling
Vail, AZ
    

 
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