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July 31, 2014

Happy Birthday!

Lake Mendota

Lake Mendota

   Twelve years ago today the domain was registered and has been Andrew Que's corner of the net ever since.  While our website has existed in some form since early 2001, it did not acquire a permanent domain name until this day 12 years ago.  Since then our site has hosted dozens of sub-domains (most of which still exist) and several domains.  The photoblog is now more than 9 years old.  It has been a good run, and I hope it will continue for many more years to come.
   Our bike ride today was a trip I had been planning for a couple years and now have finally attempted.  I wanted to bike around each of the lakes in the Madison, and had already done Lake Wingra and Lake Monona.  Today I added the largest of the lakes, Mendota.  I tried to plan a route that kept me off the busier roads which are hardest to keep away from on the northeast side of the lake.  The loop totaled 23.3 miles with two 10 minute breaks.  The first was in Warner Park, and the second was along the lake shore path by the UW campus.  My biggest problem with riding is soreness in the shoulders and hands, but the breaks help.  I've been meaning to do this ride for a couple of years.  Now that it is done, it is time to set some more goals and I have a few in mind.
   Operation Lux logged a rather low-light day.  Despite not being cloudy, the peak luminosity was just over 75,000 lx.  I noticed during my bike ride things seemed a bit hazy, and the light experiment confirms this was the case.  However, even though the peak light was lower than usual, there where very few cloud interrupts.  Even with this lower peak, the total amount of light energy for the day was around 3,500 Wh/m2.  Yesterday, although the peak luminosity was close to 95,000 lx, the total light energy was just under 3,700 Wh/m2 mostly because the cloud cover kept interrupting.  Interesting.
   Our bike ride today took us just under 14 miles, and mostly northeast.  One of my objectives was to see how the traffic was on county road Q, and find a path through the North Lake subdivision into Orchid Heights Park.  This would allow me an alternative to traveling along county road M for my much larger planned trip—a complete circle around Lake Mendota.  The other goal was to see if I was sufficiently recovered from whatever bug I contracted a few days ago.  If I get sick, it's usually never bad.  However I found I just didn't have the stamina I should while riding.  So the last couple days have just been shorter rides.  Today I felt pretty good during the ride and I think I am sufficiently recovered to get back to longer rides.
   Pictured are some cattle along county road Q.

July 29, 2014

Battery Selection Begins

   Started working on a spreadsheet to take the daylight data, and combine it with a solar panel and battery.  The idea is to plot the charge of the battery/batteries in relation to the daylight.  When the sun is out the bright the batteries will be taking charge.  When the sun is low the solar panel might be generating just enough power to supply the computer.  In the evening the batteries are discharging.  I wanted to see how various solar panels and battery capacities would work.  Moreover, I wanted to see how much discharge could be expected from a typical day, and a cloudy day.  With two cloudy days in the records I have pretty good data to work with.  Using the assumption that I could expect 75% of the energy put into a battery to come back out, and the Pi's load of 3.5 watts, I found that a 30 W solar panel with a 15 Ah 12 volt battery would not normally drop below 70% charge on sunny days, and could deal with the two cloudy days by dropping down to 20%.  However, I have been eying a more powerful SBC which has a 10 watt draw.  Here I found that a 30 Ah battery with a 100 watt panel would stay above 60% most days, but barely survive the two cloudy days dropping below 10%.
   What isn't factored in is the maximum charging current of the batteries.  A 30 watt panel would produce a 2.5 amp charge current at 12 volts, which is probably ok for most batteries.  However, a 100 watt panel could produce an 8.3 amp charge and this might be getting close to the limit for some batteries.  I haven't even looked at charge controllers yet.

July 28, 2014

More Power Data

   Added some more fetches to Operation Lux for calculating power usage.  First, the power generation is now given in both watt hours and amp hours (a typical rating for batteries).  The power draw can also be entered and a time period given, and the surplus energy will be calculated.  This allow one to see if a given solar panel will produce enough power to run a device of a given wattage.  The default of 3.5 watts is given for a 24 hour period, which represents a Raspberry Pi running for a day.  This setup does not factor in losses from cables and batteries, but will give a basic estimate of solar panel requirements.
   Did a 24 mile bike ride today to visit the town of Waunakee.  Encountered a strong headwind during the entire northward portion of the ride.  After stopping for lunch went west and ended up back by Epic System's Galactic Wind.  From the valley I stopped in at the side of the road I could clearly hear the low "woosh" of the turbine as the blades went by.  I also heard a higher pitch whine and the sound of metal on metal from time to time.  After observing the turbine for a bit I believe this sound to be the yaw motor used to turn the nacelle into the wind.  On my return trip I again went through the town of Ashton and used trails by Quisling Park, Middleton Firefighters Memorial Park, and the Pheasant Branch Trail to get home.  About two blocks from home it started to sprinkle and after I was home it began to rain.  So I was just in time.

July 27, 2014

Dead Power Supply

   Sometime after 4:30 pm, ππ shutdown.  I reset it around 7:15 pm but it was out again 9:00 pm and wouldn't come back.  After I retrieved the device from the roof I found the 5 VDC power supply was dead.  These supplies are basically cellphone chargers so I replaced it with an other one I had laying around.  It looks like the power supply got wet and rusted the lead off a resister.  There is also some corrosion on one of the electrolytic capacitors.  The new supply I put in a separate plastic container and hopefully that should keep it dry.
   Today was a very sunny day after two rather cloudy days.  Yesterday brought in 1,731 Wh/m2·day and the day before that 1,038 Wh/m2·day.  Both would require a solar panel rated about 25 times more than the wattage desired.  A typical sunny day (this month at least) generates at least 3,000 Wh/m2·day which means a solar panel rated about 10 times the desired wattage should be sufficient.  The best days can be over 4,000 Wh/m2·day.  I might have to consider a battery bank that sustain the server for several days for cloudy times and letting that capacity charge back up on the bright days.  Even the cloudy day two days ago wasn't as dark as I expect it could get on a fully overcast day, and I would like to know that number.  More data!
   Pictured is the sunset was observed during our 13 mile bike ride today.  The town of Ashton makes a pretty good north-west pivot point.  This trip only took an hour and 18 minutes which included several stops for pictures and 4 hill climbs.
   Did a 15 mile bike ride today into downtown Madison where I spent about an hour doing some long exposure photography.  On several of these I ran some High Dynamic Range (HDR) filtering and came out with a few shots I was pleased with.  The ride itself was the first night ride I've done in awhile.  Having not ridden downtown from this direction before I had a little trouble figuring out where the bike path was going.  A couple of times had a turn back because it was clear I was no longer following the path.  I am not sure doing this ride during the day would have helped.  I also gave my head light a good workout.  It ran for nearly 2 hours without issue.  There are four color settings for power level: green, blue, yellow and red.  This is the first time I have seen yellow, but no change to light output occurred.

July 25, 2014

Applied Geometry

So while working on the galvanometer project I ran into a tricky math question. I wanted to scale the needle length and degrees of sweep based on the dimensions of the image. Here are some examples:

In both examples, the needle in the galvanometer is a different length; longer in the top and shorter on the bottom. The sweep is also different, less on the top, and greater on the bottom. The divisions are the same for both. This was the kind of auto-scaling I wanted to achieve. But the math was being tricky. I spent a day playing with the math from an algorithms standpoint, but didn't get anywhere. So I decided to play with it geometrically.  I needed an arc to pass through 3 points: the bottom left corner, the top center, and the bottom right corner. Since I was using a perfect circle, as long as I passed through one of the bottom points to the top center I could be assured the arc would do the same on the other side.

Initially I approached this as an equation with two known (one bottom corner, and the top center), and two unknowns (radius and angle). I failed to find any system of equations that did what I needed.

In the past I have used a geometric approach to solve these kind of problems, looking for way I could draw a solution rather than calculate it. So I played around for awhile in Sketchup before I discovered the following.

In the above drawing I have half the galvanometer (width is really ½ width). Point A is the top center, and B is the bottom right. What is known is the width and height, and the unknowns are the needle length (line AC), and angle c (∠ACD). I found that by drawing a line from A to B, dividing this line in half (point D) and making a line perpendicular to AB at point D, this would intersect line AC at exactly the correct location. That is if line AC were rotated at point C, point A would end up perfectly touching point B and making the desired arc. So the length of line AC is the needle length. The sweep angle can also be derived from this drawing. Angle c is half of what it would need to be to rotate AC to touch point B. And since this drawing is half the total sweep, angle c is ¼ the total sweep for the galvanometer.

This did not take long to implement, and had the desired results. One added benefit was the fact the math worked just fine for ratios that had more than 180 degrees of sweep. However, there are a couple of scenarios now possible with the galvanometer I needed to address. If the sweep is greater than π radians (180 degrees), the needle's start is no longer off the screen. Here is an example:

I no longer have a galvanometer, but a more general analogue gauge. So I added a correction to make the needle center when it was not off the screen. The last issue was when the ratio was such that the needle length was greater than half with image width. This caused some of the chart to be drawn off screen. When this happened, I simply limited the needle length to half the width. The results are exactly what I desired.

The library needs some cleanup and I need see if anymore functionality is required. Afterward I plan to add this to my open source libraries.

July 23, 2014

Power Calculation Script

   Now that Operation Lux has a decent amount of data I want to stop using spreadsheets to do energy calculations.  At the bottom of the page I added some Javascript that will allow energy production to be calculated for a given solar panel.  A list of solar panels of various sizes allows the characteristics to be filled in automatically.  Then the amount of light over a given period can be entered, and the amount of energy produced is returned.
   I did a 17 mile bike ride today to visit the town of Cross Plains.  There is a long 250 foot climb to the top of a hill on the way out, followed by a fairly rapid drop at the top of the hill.  Pictured is a few from a park in Cross Plains I stopped for a break before the return trip.
   Today's bike ride destination was the small wind farm just north-west of Middleton.  It is called Epic System's Galactic Wind and consists of 6 turbines generating up to 9.9 MW.  They are fairly visible and being a fan of wind power I thought this might be a good destination for a bike trip.  The winds on this trip were fairly high, and the way to the turbines I had a good tailwind.  They turned out to be much further away than I had initially though, and getting to them required a little zip-zaging on back roads. I couldn't pre-plan the trip because the turbines don't yet appear on the satellite image maps, but they are visible from at least 10 miles away so I didn't figure I would have a problem.  This was the first time I actually heard a wind turbine from a distance.  In the past the only time I could hear a turbine was when I was under it.  From my observation point about 300 yards from one of the turbines I could discern a low swoosh as the blades rotated parallel to the tower.  It was quite subtle and reminded me of a muffled ocean wave. 
   The wind speed for the afternoon (as logged by the Dane County Airport) were between 13 and 18 MPH which according to the Vestas V-82 (the turbines that make the wind farm) datasheet means each turbine was generating between 200 to 1200 kw of electricity.  On my 2 hour and 18 minute ride, I estimate each turbine generated about 3.9 kWh of power—enough electricity to run our house for 3 months.  Such number dwarf my little solar project.  But then it costs about $2 million to put up a turbine like those at this wind farm.
   My trip finished up at 19 and 2/3 miles.  The day was already getting warm and I had consumed close to 2 liters of water (most of which I think went into soaking my clothing with sweat).  However, I think it a good trip.