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

[Jim Wooddell]

Jay,

With all due respect, there are hundreds of sky cams out there that use
110vac line voltage to power a heater circuit.  There are millions upon
millions of 110vac products out there in outdoor service.  They are safe.
Additionally, you seem to assume everyone has 12v available at their camera
capable of powering a Walmart heater/defogger.
So, I think you are talking out your arse.

Regards,

Jim Wooddell


On Thu, Nov 20, 2014 at 9:46 PM, HEADLIGHTS Studio <
studio at studioofbluelight.com> wrote:

> 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 <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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-- 
Jim Wooddell
jimwooddell at gmail.com
928-247-2675
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