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Testing solar panels, wiring, and setup

One of the most difficult parts of the game The City (see previous post) is the electricity production and distribution.  The more houses you distribute power to, the more favor you curry with the residents, the more likely you are to win.  There are a variety of issues which make implementing this seemingly easy concept difficult:

1) Designing the circuit to be hard/impossible to break, burn out LEDs, solar panels, etc.

2) Connecting LEDs together in an easy, effective, and problem free way for the game player.  The LEDs represent "power delivered" to each house.

3) Determining the light conditions which will produce sufficient voltage to run the LEDs, and having the LEDs be clearly off or on (any half-lit LEDs is going to confuse gameplay - is the house electrified or not??)

So we'll start by looking at each of the major components (LEDs, solar cells, connectors, and the board itsel) to how we can achieve our goals.

LEDs

Light Emitting Diodes work under a variety of voltage ranges, depending on the wavelength of light emitted: red LEDs are typically 1.8 - 2.5V, while violet or ultraviolet LEDs are 3.6 - 4V.  If you hook a red LED (range 1.8 - 2.5V) up to a 3V battery, it will quickly burn out!  So for any given LED, you need to make sure it sees voltage that is always within it's acceptable range.  If you hook up the same LED at 2V but push too many amps through it (for 3 or 5mm LED that's usually greater than .050 amps or 50 milliamps), it will also burn out.  See the graphs below to understand the normal working conditions for a typical red LED (NOTE: mA is milliamps - 1000milliamps = 1amp).


So, for the game we need a circuit which maintains a pretty constant voltage (1.8 - 2.5V) and which can ensure amperage doesn't go too high.  IN ADDITION, we need to make sure that the LEDs are either on or off (not somewhere in between), so the amps going to each LED should not fall below a baseline brightness.  This is tricky as we'll see!

Broken cells aligned in series

random broken cells

Solar Cell

Solar cells seemed like a good power choice for this game because 1) solar is the future and displaying that technology in the game would be really really fun, 2) the power output of solar cells varies depending on the lighting conditions, which could make an interesting element of gameplay, 3) solar cells produce a relatively constant voltage over a wide range of lighting conditions which is important so that we don't blow out our LEDs.  First, I had to learn some about how solar cells work.  This was more difficult than I originally imagined, partly because what I'm doing is a bit different than the standard use case, which is big solar panels on your house which convert the DC current generated by the panel to AC current for your house.   For the long and detailed explanation, you can go to http://science.howstuffworks.com/environmental/energy/solar-cell.htm.  However, that doesn't help us much - what we want to know is how can we create a system using solar cells which maintains a relatively constant voltage (so our LEDs work and don't blow out) in a DC circuit.  Normal batteries, like AAA for example, produce a constant voltage (there's some caveats here like the battery's charge level, the number of times it's been recharged, the battery technology, etc.).  That means, pretty much, whenever you hook up a 2V battery to any circuit it's going to output 2V.  When you hook up a solar panel, however, the voltage produced is dependent on the amount of light AND the resistance in the circuit itself.  That makes the task of keeping a constant or very tight voltage range (like 1.8 - 2.5V for our red LEDs) pretty tough because we plan on having varying light levels AND circuit conditions!  My first solar cell testing occurred with these usable but broken solar cell pieces.  They are from http://www.siliconsolar.com/solar-cells-by-the-watt-p-502129.html and are really cheap - about $0.50 per cell.   The voltage across each piece varied from 0.3V to 0.6V when they are placed in front of a bright shop light.  When they are placed face up in a well lit room at table level, they read around 0.06V!  That's a big difference.  You can put each cell in series by lining them up as shown here - this causes the voltages of the cells to add together.  So using a few cells in series under bright light, we can achieve 1.8 volts.

The voltage (measured on the multi-meter) increases as you test through more cells in series (from 0.337 to 1.07V)

When placed in parallel, the voltage remains the same but the available amps increases.  For the purposes of the game, a setup in parallel at about 2V would be ideal.

 

This whole concept of using solar cells is fairly complex, so I'll probably do an entire post on the power generation system (solar cells, batteries, and other options).  I've also got an additional 6 or so types of solar cells, from 0.5 - 4V and am testing in a standardized setup to correlate solar irradiance with voltage produced (thus the big light).

 

 

Board Pieces and Cards

And then there is the board itself which will have the following components:

0 Land development tiles (masonite)

0 Telephone poles and wires (masonite, 26 - 30 gauge wire with wire ferrules, 3mm red LEDs)

0 Resource, Progress, Character, and Special Cards

I'm working on finding an illustrator and graphic designer to take care of the cards and design, which will be a critical component of the game.  More on that later once we have pretty pictures to show off.

Telephone Pole, Wires and Land Development Tiles

Telephone poles in land development tiles

Telephone pole w/ integrated LED and wire ferrule based connector

Other side of LED integrated telephone pole

Telephone poles are what connects power from the power supply (solar panels) to each tile.  How they plug into the land development tiles, and how power lines plug into them, are critical for avoiding LED blowouts on the part of players - we don't want players wiring LEDs backwards!  As a result, the telephone pole itself can be placed in only one spot on each tile, and connecting telephone wires are just long enough (and no longer!) to reach between these poles.  This makes miswiring the system very difficult (not impossible, but difficult).  Initially, I wanted to put the LED on the land development tile, but it eventually became clear that that was too difficult for a variety of reasons (wiring from the ground, to a pole, back to the ground with even semi-rigid wire is difficult and ultimately just looks funny, plus finding an easy, cheap, effective connector was also not possible though I tried many options).  As a result, the LED is integrated into the telephone pole.
Finding (or in our case, creating) an easy connector between the wires and the telephone pole took some fooling around.  Ultimately, the laser cutter was used to do a deep raster (engraving) cut in the telephone pole (which is made from a piece of 1/8'' masonite).  This engraved portion was sized so that the LED leads set in it with just enough space between them for the wire ferrule to fit (see picture on the right).  Small holes were lasered into the masonite so the wire ferrules could slide between the folded LED leads, and viola! connection!  Now, is this a sustainable connection which will last the test of time (as Sid Meier used to say), and are our machining tools and purchased materials have the tolerance to produce a repeatable product?  Don't know, but it it's a good start and we'll keep testing.

All of this material is boring and brown, but once we have illustrations we'll overlay a top down, "Where's Waldo" like view on the land development tiles to make the world come alive!

For more on the alternate forms of energy that you can use for your benefit visit the following link - utilitysavingexpert.com.

Next Time

Next post - more about how solar cells work (if you're lucky you'll get some nice graphs based on collected data), updated designs for telephone poles and hopefully some pictures of a more completely looking prototypes.  Sometime in the near future, we'll get some illustrations too!

Oh, and why is there a picture of a storm trooper you ask?  I went to Confusion (my first sci fi convention) a few weekends ago, and this guy showed up from the 501st squadron (501st.com).  All I could think of was how hard it would be to make his suit using a laser cutter... I think I need to expand my manufacturing base a little.

One Response to “Testing solar panels, wiring, and setup” Leave a reply ›

  • I strung over 1000 of these tetgoher in basically the same fashion for our college's entry into SunRayce '99. We had a form, like you mention, to line up the cells and space them about 1.5mm apart. For large numbers, we found it most efficient to tab the tops first, then string them in the form, soldering the tabs to the bottom. I think we used solder-bearing paste instead of flux pen and solder separately. Keep in mind, when you build your own panel, the worst cell limits the entire string.

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