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| The Weather Shelter Idea |
| The Davis Vantage Pro2 works great! It's been trouble free and dependable. However, there was a noticeable spike in the high temperature readings in direct sunlight. (the readings are normal on cloudy days). According to Davis, this is due to "effects of daytime radiation". After a month of this effect, I decided to buy the optional daytime fan aspirated kit to fix this problem. OK, it worked, somewhat, even though the description of the kit says "nearly 75% as effective in reducing the effects" as the 24 hour aspirated model. Again, it did help some, but I wasn't impressed with the outcome and besides, the fan ran about three hours a day. ??? That's about five hours a day that it doesn't run. "That can be improved" My idea was to totally eliminate the radiation effect without hampering air flow and to maximize the fan "on time". |
 The red line in the chart represents the temperature during a typical "partly cloudy" day with the standard radiation shield. Shortly after 2pm, the clouds begin to break and the direct sunlight warms up the shield. Clouds passing over then cools off the shield creating the unstable readings. |
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| Solar Panels |
| After installing the optional fan aspirated radiation shield, a dual solar panel replaces the original single panel and is no longer used. This solar panel is way too valuable to discard or collect dust so it's kept to power the fan in tandem with the new dual-cell solar panel. When the solar panel is mounted on the rain collector facing south, it generates a current for three hours or so operating the fan and the transmitter. When angled several degrees higher, the length of time it produces current is substantially extended. Being angled up higher, the rain and snow doesn't want to drain off and it dries up over the lens leaving a dirty film that eventually reduces the current output.
To get the optimum current output for the fan, the single solar panel is on the rain collector facing west that catches the sun after 4pm till sunset. The mounting for the dual solar panel is angled higher under a plexiglass cover to shield it from the elements and birds. One of those panels provides power to the transmitter and the other panel powers the fan. These catch the sun about 90 minutes after sunrise till late afternoon. The panel on the transmitter is wired in parallel with the panel under the cover to provide current to the fan for most of the daylight hours. |
| Shelter Construction |
A 1/4" aluminum plate is used as the base plate and two heavy duty "L" brackets are bolted on for the main mounting brackets. The sensors/shield is removed from the rain collector by removing the three nuts under the funnel and bolted on the bottom of the mounting plate. A pair of 14" wide plastic window shutters purchased at a home improvement store were cut with a "box knife" to use on all four sides. The top of the front and back panels attach to the bottom of the base plate. The sides are attached on the inside of the front and back panels. All brass hardware is used to bolt everything together. |
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A bolt and nut (in the shadow) shows the lip on the rear panel attached to the base plate. The bottom is kept open for maximum air flow.
This solar panel was on the ISS. It is now located on top of the shelter under Plexiglas to protect it from the elements. The top cell powers the ISS and the lower cell powers the fan. These are pointed to the south and angled up higher than on the ISS.
The panel on the ISS is facing west and is wired in parallel with the lower panel on the shelter (facing south) to power the fan at least two time longer.
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| Summary |
| Your probably thinking "I'm not ripping apart my Davis like this idiot did ". Relax... Every component of the Davis weather station is in its original condition. No wires have been clipped, no holes drilled and the hardware hasn't been changed nor has any of it been discarded. The unit can be easily re-assembled back to its original condition.
This article lists the end results that has worked for me but may not work for you if you consider making one of these yourself. Basically, "Your mileage may vary" but is worth the time and effort if you have direct radiation issues. Here are the benefits of the shelter. Stable temperature and humidity readings. The shelter is light weight, provides plenty of free air flow, and keeps the sun off of the Davis radiation shield. An additional hour of "sun time" is the result of the dual solar panels angled up higher than the factory ISS mounting. Combining the south panel with the west panel provides about 250% more on time for the fan during sunny days. Dirty rain water isn't dumped over the Davis shield. No dirt or algae build up. |
With a cover blocking the direct sunlight on the radiation shield, the temperature reading is stabilized throughout the day providing greater accuracy.
