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

[James Beauchamp]

I found that mine is a little between the two extremes.  The waste heat isn't enough to keep the condensation off during wet times, but the stock 36 watt heater configuration was too much.  Bringing it down to 18 watts was about perfect for oklahoma.

During the drought year I unplugged the heat completely and it was fine.  This fall found the 18 watts as just fine to keep it clear.


Sent from my iPad

> On Nov 22, 2014, at 1:55 PM, Ed Majden <epmajden at shaw.ca> wrote:
> 
> Chris:
>    Maybe where you live but on the WET Coast of Vancouver Island more heat 
> is required.  Even the Sandia All-sky can dew up here.
> Ed
> 
> ----- Original Message ----- 
> From: "Chris Peterson" <clp at alumni.caltech.edu>
> To: <meteorobs at meteorobs.org>
> Sent: Saturday, November 22, 2014 10:01 AM
> Subject: Re: (meteorobs) Heat required to prevent dew in a box for allsky 
> camera
> 
> 
>> The Sandia design isn't the best. In fact, for a video system (as
>> opposed to the DSLR case that started this discussion) there is no need
>> for heaters at all. The electronics in the enclosure generates enough
>> waste heat to keep the dome dew and frost free under the worst of
>> conditions. All that is required is a simple internal circulation system.
>> 
>> Chris
>> 
>> *******************************
>> Chris L Peterson
>> Cloudbait Observatory
>> http://www.cloudbait.com
>> 
>>> On 11/22/2014 10:54 AM, James Beauchamp wrote:
>>> Ok guys, engineer here...
>>> 
>>> Jim is correct on the sandia all sky system.  The heaters are simple and 
>>> work very well.
>>> 
>>> You don't want to use low voltage for heating.   It is a waste of energy 
>>> for conversion and transport, in addition to adding more stuff that can 
>>> break.  With standard insulation techniques and standard wire, it will be 
>>> safe.
>>> 
>>> The sandia NMSU design uses a simple DIN mount thermal controller with a 
>>> settable turn-off temperature, feeding two metal cased power resistors 
>>> that deliver about 36 watts of heat.  They are mounted on a small metal 
>>> plate.  Together with the little 2 inch fan to circulate the air, they do 
>>> pretty well.
>>> 
>>> With that said, I found the heat output on mine to be too high.  When it 
>>> was on, it cooked the surrounding plastics with enough heat to fog the 
>>> dome with what looked to be a fine oily silt. Probably the plasticizer 
>>> from the wires, mount, and PVC.
>>> 
>>> Tired of constantly cleaning the lenses, I reconnected the two resistors 
>>> in series, which reduced the heat down to 16 watts and it worked fine. 
>>> I've had no issues with fogging, condensation, or ice since then.  I 
>>> eventually fed the unit with a COTS light sensor (modular unit for 
>>> Christmas lights) that turns the heat on after dark.  Since the software 
>>> is disabled in the day, there was no reason to cook the unit needlessly.
>>> 
>>> Jim, one thing on these, don't forget the .636 factor when using AC. 
>>> They are published as 50 watts, but that's the DC value.
>> 
>> _______________________________________________
>> meteorobs mailing list
>> meteorobs at meteorobs.org
>> http://lists.meteorobs.org/mailman/listinfo/meteorobs
> 
> _______________________________________________
> meteorobs mailing list
> meteorobs at meteorobs.org
> http://lists.meteorobs.org/mailman/listinfo/meteorobs