Introduction
Below are the instructions for a low sun angle solar panel capable of generating ~8.6v @ ~ 90mA. This is the design that was launched from Neumayer Station III in Antartica on November 24, 2022.
Objectives of this design include:
- Power the instrument package at very low sun angles – starting near the horizon
- Power the instrument package regardless of the solar array orientation to the sun – 360° access to sunlight
- Withstand the Antarctic environment – temperatures and potential high winds at launch
- Durable enough to survive transportation across 4 continents before launch
The Antarctic balloon has transmitted its first data packet when the sun is only 1.8° above the horizon. This would indicate the actual power up of the electronics can take place with the sun at or slightly below the horizon.
Launching the balloon was only part of the challenge. It had to make it to Neumayer Station. The solar panels and electronics were built in Illinois, USA. Then shipped Tennessee USA for final assembly. Next it took a short trip to Alabama, USA where it met Todd, KN4TPG, the graduate student who would launch the balloon as part of his research project. Todd flew on a commercial airline from Alabama to Germany, where he met the research team. The team took a charter flight to stopping in South Africa before ending at Neumayer Station.
Bill of Materials
Parts required to build the solar array are below. Prices are in US dollars as of November 2022.
* Fishing line is used for the harness to connect the solar array to the balloon. Depending on your method of attaching the two, this length will vary.
** Filament is used to print templates to build the array. No 3D printed parts are included in the final array. Any size or type of filament can be used.
Tools
Recommended tools include:
- Solder gun or station (40w)
- Medium, flat tip (~3 – 4mm)
- Tip cleaner
- 3D Printer or print service
- Heat resistant work surface
- 2 – Needle nose plyers
- 2 ~2″ F or C style clamps
- Wire cutters
- Wire stripper
- Hobby (X-ACTO) knife with new blade
- T-Pin (or large sewing needle)
- Metal ruler (6” minimum; 12” recommended)
- 6 – Small or Medium paper binding clips
- Clear tape
- Scissors
- 3 ~2″ x 4″ pieces of cardboard (to wrap harness lines around)
- Pencil or fine tip marker
- Optional – Magnifier light
- Optional – Soldering helping hands
- Optional – 1mm drill bit (use by hand)
Templates and Files
Four 3D printed parts are needed as templates and build supports. One template is provided to assist in aligning the diodes to the panels.
Four 3D print files are in the ZIP file. The files are used to build the array and are not part of the final assembly. Any 3D filament is acceptable. Printer settings are not critical.
- Infill – 10%
- Layer height – .15mm
- Support – None
- Adhesion – None
Overview
Here are reference pictures and assembly diagrams. Refer to these graphics as you proceed through the assembly process.
Use the template to shape the wire frames.
See how much the wire overlaps inside the frame. Use the 3D printed holders and small clamps to hold the wire in place. NOTE the wire end on the left is near the gap and the wire end on the right extents farther past the gap. Ensure the wire lines up the same way. This is very important when sizing the wire frame for the panels.
Strip the insulation from 8 inches of 30ga wire and tightly wrap it in the space. The opening corresponds to the spacing between the panels. Two layers of wire should be sufficient. DO NOT solder the wire yet. Make two sets of wire frames.
Carefully remove the plastic coating on three solar panels. Pay careful attention to which side is positive (conductor connects into the blue panel area) and which is negative (conductor does not connect to anything in the blue panel area). The panel’s negative side at the bottom with the three circles indicating where to remove the coating.
On the positive side remove the coating in the center of the above the blue seam.
Use a wide soldering iron tip and gently move the plastic from the center to the side of the connection area. Do not apply too much heat or the metal connector will separate from the panel (be careful with the two negative contacts near the edge of the panel).
Diodes located on the inside of the array will connect to the panels via small holes placed in the positive bus. The yellow box highlights the area where the plastic coating was removed. Use the T-pin or small (~1mm) drill bit. Carefully drill from the top, through the panel. Be sure to support the panel from the back while making the hole.
Verify connectivity with a voltmeter. You should see voltage between the three negative contacts and the positive side.
Repeat this process for all three panels.
The wire frames must be sized to the exact shape of the panels. This is done using the 3D printed templates to hold the panels in place while adjusting the wire frame to match.
Attach the three panels between the ring templates using the notches on the inside. It may be easier to place both rings vertically about 3 inches apart, attach one panel with the templates near the center of the panel, then roll the template rings forward to attach the next panel. Keep the ring templates near the center until all the panels are in place.
Attach the inner ring template by matching the spaces with the notches between the panels. Use paper binding clips to secure both template rings in place. Slowly move the templates to edges of the panels covering the positive and negative power buses.
Place the wire frame over one end of the panels with the wire wrap fitting in the gap between the panels. The frame should be slightly too small. Using two needle nose plyers very gently pull the wire out 1 – 2mm at a time. It may be helpful to use the plyers to straighten the wires in wrap. This takes tension off the wrapping and makes it easier to adjust.
The wire frame is the correct size when it fits over the panels with no gaps between the panel and the frame. The wire should not bend the panels inward.
After sizing is completed, use flux and solder the wire wrapping. Be careful not to extend the solder beyond the wrapping.
Repeat the process for the second wire frame.
The bottom wire frame is attached first. This is the ground connection from the panels. It connects to the ground bus on each panel in three places and provides stability and electrical connections to the panels.
Use the 3D printed ring templates for the next steps. VERIFY YOU HAVE ALL THE PANELS FACING THE SAME DIRECTION WITH THE GROUND CLOSEST TO YOU.
Place a wire frame between the ring templates. Follow the process above to attach the templates to the panels.
At this point you should have one ring near the top and bottom of the panels with one wire frame between them.
Move the wire wrapping on the frame to a gap between the panels. Slowly move the ring templates to the edges of the panels. The bottom ring should be flush with the bottom of the panels with the wire frame sitting on top of it. The top ring should be near the positive bus, about 10mm from the edge.
Aline the panels so the bottom of all panels touches the surface and the spacing between the panels is uniform.
Optional – cut 15mm of 30ga wire. Wrap the wire along the wire frame between the panels. Start with the wire between the panel and frame. Wrap it around the frame and between the frame and adjoining panel.
VERIFY YOU HAVE ALL THE PANELS FACING THE SAME DIRECTION WITH THE GROUND SIDE AT THE BOTTOM, NEXT TO THE WIRE FRAME.
Solder the ground connections between the wire frame and panels. Use flux on all connections. Be careful when soldering the end connectors, too much heat will cause the bus tape to separate from the panel. There are three solder connections per panel – at the two edges and the middle.
Remove the bottom template. The ground wire frame now provides support for the bottom half of the panels.
Connect the negative lead to the wire frame using ~10 inches of black 22ga or 30ga wire. Wrap the lead in any gap between the panels, facing the top. It may be helpful to coil the wire and tape it to the inside of one of the panels to keep it out of the way.
The positive leads from the panels are diode protected to prevent current from the panels in the sunlight draining into the panel away from the sun. The diode connection provides the power connection. The wire frame at the top is only for support and MUST BE INSULATED from the positive power connections.
To assemble the top support and power connections, start by sliding the 3D printed template about 5mm below the positive power bus. Place the remaining wire frame on top of the template with the wire wrap in a gap between the solar panels. Slide the wire fame next to the template. There should be a small gap between the wire frame and the areas where you removed the plastic coating on the positive power bus.
Diodes are polarized and must be connected in the proper orientation. The cathode side (with the white stripe) must face toward the center of the array and the anode (black side) facing toward the panels. The cathode side will soldered to the 3mm washer.
Use needle nose plyers to make a 3mm hook on the white strip side of the diodes.
The diodes will not be long enough to reach the panels. Strip three lengths of 22ga wire approximately 3 inches long. Solder the wire to the anode side of the diode.
Print out the 120° template. Firmly crimp each diode connection around the 3mm washer and place on the template. Tape the diodes in place over the template. This aligns the diodes with the holes in the positive side of the panels. (Note: the template has been updated to include mark and cut references, not shown in the pictures.)
Add 10 inches of 22ga or 30ga wire to the washer. This will be the positive power lead to the electronics.
Use flux and solder the connections to the washer.
Before removing the diodes from the template, use a fine tip marker to mark the 73mm point on each diode and cut the wire at the 78mm mark. Then cut each wire at the 78mm cut reference (Note: The pictures were taken with an older template that does not have the reference marks.)
The diodes are mounted through the holes in the center top of each panel. The positive lead from the washer should face down, toward the center of the array. When looking down from the top, the washer should be in the center. The marks on each wire should intersect the panels. At the 73mm mark, bend the wire horizontally (along the direction of the power bus), over the cleared part of the bus. Examine the location of the washer and repeat for the next two wires, adjust their lengths as needed.
After you are satisfied with the location of the washer and positive lead examine each connection to verify the bent lead is over the cleared part of the bus. This is where you removed the plastic coating.
Ensure the wire frame is not touching the diode leads. Move the template are wire frame down, if necessary.
Use flux and carefully solder the connections in place. Be careful not to use too much heat or the power bus may separate from the panel. SOLDER ON THE OUTSIDE OF THE PANEL. DO NOT LET SOLDER WICK INSIDE.
Remove the 3D printed template and slide the wire frame down about 1 inch from the top.
Apply two layers to Kapton tape over the diode connections. Cut the first layer slightly longer than the area cleared of plastic. Cut the second layer about 10mm longer than the first.
Slide the wire frame up, next to solder connections. Apply Kapton tape on the two sides of each panel, but do not cover the gap between the panels.
Verify you get a voltage reading between the power leads before proceeding.
The harness assembly is designed to distribute the stress from the balloon to both wire frames and provide an attachment point for the electronics.
Cut three 10-foot pieces of 20lb. fish line. The length is dependent on your balloon design and may vary. It may be helpful to wrap the line around small pieces of cardboard.
The lines are attached in the gaps between the panels. Tie a knot around one of the ground leads. Loop the line several times around the wire frame next at the top. Keep the line taught, but it should not flex the panels.
Keep the knots centered in the gap, then apply a small amount of super glue to each knot. Repeat for the other two harness lines.
Make the harness for the electronics by cutting three pieces of fishline about 12 inches in length. Tie one end of all three together and apply super glue.
Use the 120° template to mark 73mm on each line.
Cut 1 inch of fiberglass tape. Use a T-pin to make a hole in the center. With the sticky side of the tape facing away from the center knot, pull the line through the tape. Repeat for the other two lines.
Using a ruler, mark the middle of each harness line attached to the array.
Slide the fiberglass tape between the 73mm mark and the center knot. Loosely tie one line at the 73mm mark to the harness line at the middle mark.
Repeat with a second line. Look from the bottom of the array to keep the knot centered. Use the 3mm washer as a reference.
Tie the third line and adjust as needed to keep the knot centered. The lines can have some slack in them and should not be pulling the harness lines between the panels toward the center.
When satisfied with the placement, glue the knots. Gently apply the fiberglass tape to the knot and inside of the panels. This provides reinforcement for the electronics harness.
After the harness is assembled, apply the Kapton tape. Cut a piece of tape 125mm in length (10mm longer than the panel is high). Center the tape over a gap with equal amounts to tape overlapping each panel. Try to keep the harness line in the middle of the gap.
Gently press the tape in place using pressure from both sides along the panels. Fold the extra tape around the bottom. Make a small cut in the tape at the top to accommodate the harness line.
Cut two pieces of tape to fit on the inside. The lengths will depend on where you attached the electronics harness lines.
Repeat the process for the other two gaps. For the gap with the negative power wire, place the outside tape as usual. Before placing the inside tape, lay the wire next to the harness line then out toward the center of the array, next to the electronics harness. Apply the inside tape as usual. Optionally apply an additional 2″ piece of tape perpendicular to the gap to hold the wire in place.
Next Steps
This completes the assembly. Depending on the specifications of your electronics package, a voltage regulator may be required.
The electronics and power connections are protected in the center of the array and can be attached using the harness. Optionally components can be taped to the inside of the panels.
Antenna wire can be attached to the balloon harness. Optionally an additional line can be added to the bottom wire frame to support the second half of the dipole antenna. It is recommended to attach the driven element up toward the balloon.
Feel free to modify the array and the build process. If you come up with some good alternatives, let us know in the comments.
Northern Illinois Bottlecap Balloon Brigade 