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Solar radiation aspirated shield project
I have recently upgraded the solar radiation screen which has the temperature and humidity sensor mounted inside. The Outer Plastic Container was from a toilet brush holder, you need the type that is white opaque and the plastic as thick as possible also tapered, the top is wider than the bottom. I cut out a hole in the bottom to fit the inner pipe which is a piece of white plastic downspout, this forms the inner wall which was filled with liquid foam insulation. A large plastic ring was made to sit inside on top of the insulation foam. The Plastic used to make the top ring/fan plate holder and the cover outer rim ring were cut from a type of plastic which has a smooth top and bottom is sandwiched in between a very fine plastic foam; this material is commonly used for making outdoor signs (foam X) it is very easy to cut and has amazing insulation properties. The top housing has several layers of foam X and air gaps in between to form a substantial  solar shield. The plastic on the outside has also been sprayed with a rubber paint to protect the outside plastic against the  elements. Sensors are mounted through the side and a fan in the top draws the air through from the bottom over the sensors, it's important that the airflow does not alter the air temperature and humidity as you want them to be the same as the air in a shaded area,  the fan is not very powerful  just enough to draw the air through the tube. Near the bottom of the tube is a nylon mesh to keep any little bugs out, the temperature and humidity sensors are now at optimum performance when it starts to rain the humidity responds straightaway, no lag time due to the efficiency of the screen and airflow.




The  transformer voltage is set to 7.5 V DC instead of the 12 V supply. This has lowered the speed of the fan just enough to allow a sample of air to move through the chamber over temperature and humidity sensor modules.This gives us the maximum performance and accuracy of the air temperature/humidity sensors.


- Power: DC 12V
- Triangle Screw Distance: approx.
26mm between each two
- Mounting Hole Dia: approx. 2mm
- Dimensions(mm): approx. 45 mm(Diameter)
- Cable Length: about 100 mm
Max. Air Flow Volume:    22.8 cfm
Max. Fan Speed:    2800RPM
0.80 maps


I wanted the fan on the aspirated shield to have a way to indicate a fan failure-fan lock.
The simplest method was to use a reed switch with a small magnet attached to 1 of the fan blades .
As the fan moved over the reed switch it would cause an open and closed circuit making the LED flash on and off. When the fan became stationary the LED would not flash indicating a fan failure this did work reasonably well . I decided I wanted to put some protection within the fan circuit so I decided to use a  MAX6684 this ia a integrated fan-failure detector. The circuit I have experimented with works extremely well as soon as the fan stops a LED will be on indicating fan failure or fan lock. The circuit also as a fuse on the 12 V input and one on the 5 V line.  The  circuit board measures 62 mm x 52 mm .Please see video clip of the testing of the circuit with the a  MAX6684 integrated fan-failure detector

 

Please click the link to download  the testing of the fan failure protection circuit