Note to my friends, I was entering the latest log entires at the bottom but have decided to reverse that so the most recent entry is at the top.
The solar powered power system is complete and operational. I am now using each month, each new moon. The next phase of the project is to build the actual observatory building. This consists of three components, the base, the floor and the frame structure. The base is a heavy concrete pedestal which the telescope mount is placed. The floor can be concrete or wood just like the floor of your house, it has be isolated from the base so that any vibration is not transmitted to the base. The frame structure is similar to any small shed with 2" x 4" wood framing with sixteen inch centers. The only real difference (between the observatory and a typical shed) is that the roof will roll back. I am basing my design on the designs presented in John Hicks book on building a roll off roof observatory (https://www.amazon.com/gp/product/1493930109/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1)
Three Stones Observatory sits adjacent to the local power lines (you can see the line in the background image of this page). I could arrange to have a power meter brought onto my site (and will most likely do that at some point in the future), but were is the fun in doing that? I want to power my observatory using a set of solar panels I inherited. The goal of this project is to build a solar powered battery charger system. The system will charge a 100AH deep cycle battery during the day and provide up to eight hours of power during the night.
Follow up notes..1/28/2018
The battery charger is a Epever Tracer A series MPPT Solar charge controler. It rated for -25C to +45C operation. That should cover it.
The battery is a Renogy Deep Cycle AGM Battery 12 Volt 100Ah Battery Solar Energy Storage battery. It can be operated (discharged at -15 C to +50C) and charged at 0 to 40C.
Three Panels of 150 Watts each
The design consists of a three panels of solar collectors which feed to a solar battery charger. The battery charger uses an algorithm called MPPT (maximum power point tracking) to obtain the most efficient charging conditions to the battery. The battery will hopefully accumulate a complete charge and be available for use on clear nights.
I built a stand to hold the solar panels. I wont be tracking the sun, the mount will be positioned facing south. The panel mount holds the panels at a 42 degree angle (the latitude of Chicago) so that they will be perpendicular to the suns rays. The photo of the solar panel mount shows that its ground mounted. I plan to place some paving stones at six points, each corner and the mid points. I am somewhat worried about the wind pushing the panel over so I may anchor the corners.
The battery will be housed in an box to keep it protected from the weather and cold. The battery box has two layers of R10 insulating foam.The image below shows the outer shell of the housing and the support structure for holding the battery in place.
Battery box controller
The battery box is designed to keep the battery above 32 degrees (F) no matter what the external outside weather. It does this by utilizing a small microelectronic board that has a temperature sensor, heater element and a blue tooth module. The temperature sensor samples the internal temperature and averages the temperature value. If (after thirty minutes of sampling) the temperature value is below the threshold of 32 it turns on the heater element. The heater remains on for the next thirty minute sampling period. This cycle repeats until the temperature in the box is at or above 32. I tested the controller and the foam shell during a period when it was -10 F. The Bluetooth module allowed me to extract the samples and other statistics over a week long period. I set box outside my house and monitored its behavior of the period when the outside temperature was in that fridge zone (below zero). The unit would turn on about once a night and stay on for one 30 minute period and then turn off. The controller worked very well. The images below show a test foam shell, the second image is the shell closed off and power being delivered to the controller via the wires seen poking thru on the side.
The battery heater consisted of a Nichrome wire loop that is powered by 12V (roughly since the battery is actually never at 12V) . The wire is a about 2 Ohms per foot so I needed just over 2 feet to get the right current flow for 30 Watts. The wire is sheathed with shrink wrap tubing ( the wire gets warm but not hot enough to ignite the tubing or the paper wrapping). The battery box controller turns on the voltage to the heater element when the average temperature gets below my 32 threshold.
The images below show the Nicrhome wire looped and held in place by the double sided adhesive paper. The second image is the heater element bonded to the side of the battery.
battery box completion
The battery box is nearly completed. I have enclosed the battery and wired up all the wiring needed to connect the battery to the solar charge controller and the solar cells. It was extremely cold in my garage but over the last couple weeks I have been able to get out there to finish the work. I have a few more tasks. The last image shows the access door up, the small window in the top needs to be set with a piece of Plexiglas. The image second to the right shows the wire which will connect to the solar panels. The two photos to the left show the internals of the battery insulation and the battery being placed in side.
1/27/2018 Finishing Stuff
I mounted the solar panels on the mount frame. I used some zinc coated angle brackets I had left over from a previous project. I broke the brackets into two pieces and drilled a hole in the center. I used these to hold the interior edges of the panels in place. The brackets are screwed down using some 4 1/2 lag bolts. I also put a piece of VHB tape on the side of the bracket next to the panel so as to keep from scratching the aluminum.
1/27/2018 Finishing stuff II
I finished up wiring the system and made a plexiglass cover for the front. The wiring consists of connecting the battery to the charger, connecting the wiring going to the solar panels to the charger and connecting a power harness (for the telescope and mount) to the charger.
I have completed the housing and have move the unit to my back yard for testing.
We 've had cloudy and over cast skies the last week or so. The battery has been charging and is nearly full capacity. The real test will when I can run the telescope and mount from the battery and then have it re charge over the following couple of days. Of course snow is not conducive to battery charging or astronomy