Kaleidoscopic Solar Oven Temperature vs Time

by Curlydock
Nov. 13, 2007

In my previous post, on September 27, 2007, I went into detail describing the “Kaleidoscopic” type of solar oven that I have been using to bake bread.

image 93

Now I post the time versus temperature for an actual bread baking episode. The episode occurred in Jefferson County, Kentucky, USA, on a day in October, 2007. There had been a recent rain and the cloudless sky was unusually clear and free of haze. Starting at 10:55 AM EST, the bread baked to completion in about an hour. The maximum temperature recorded, between the black lid and top glass bowl, was 320 F (160 C). Just as I removed the bread, I saw the temperature was 325 F and probably still climbing. The ambient temperature was 64 F at the beginning and 70 F at the end.

The results are tabulated and graphed in the next image:

solar_oven_time_temp.jpg

__Time____Ambient______Oven________Note___________

10:55 AM ___ 64 F ___ not recorded ___ start baking

11:05 AM ___ 64 F ___ 240 F (116 C)

11:15 AM ___ 64 F ___ 275 F

11:20 AM ___ 66 F ___ 280 F (138 C)

11:30 AM ___ 68 F ___ 290 F

11:34 AM ___ 68 F ___ 300 F (140 C)

11:44 AM ___ 69 F ___ 308 F

11:56 AM ___ 70 F ___ 320 F (160 C) ___ condensation seen

12:06 AM ___ 70 F ___ 320 F ___ good odor, end baking

The optimum design for this type of oven is a fascinating problem. I wonder if 60 degrees is the best angle for the vertical axis and what the best sizes and proportions are for the reflecting panels. I am pretty sure it would be pointless to have the width of the vertically hinged panels be either more or less than three times the diameter of the oven cavity, for example. But I would like to have some way to test these personal prejudices.

To that end, I have given in to the temptation to do a detailed theoretical analysis. My way of doing this is to write a computer program that uses something like “ray tracing” to simulate the oven, allowing me to more easily see how different configurations affect the solar flux concentration. That program is pretty much finished and I hope to post some of the results in the near future.

Insectary Plants and Beneficial Insects by Curlydock

My recent surge of interest in insectary plants and beneficial insects found me in the garden with my camera. I spent about an hour taking pictures of any insect I saw and noting the plant each insect was seemingly associated with.

I did this on September 8, 2007, in my small experimental urban organic garden located in Jefferson County, Kentucky, USA. These are a few of the pictures.

I am not expert at insect identification. If you think my guesses or any other data I give are not correct, please feel free to leave a comment with your own opinion.

To avoid the use of chemical poisons, I hope to eventually have enough of the right kind of insectary plants. The theory is that the right plants will attract the kinds of good insects that predate on the bad insects. Bad insects do bad things like chewing big holes in my broccoli leaves, for example.

I understand that one should not attempt to wipe out the bad bugs altogether. Enough of the bad bugs should exist to feed the good bugs so the good bugs will stay in the garden and not have to leave in search of a meal. While this is not mechanically efficient, an argument could be made that mechanical efficiency is not a sustainable way to relate to the environment.

One should seek the productive balance innate in stabilized diversity and then not sully that balance with pollution, poisons, and the exhaustion that comes from expectations of competitively efficient exponential growth. The correct balance can be productive enough to sustain the lives of farmers and those who depend on farmers for meals, were the world not obsessed with greed.

Since the good bugs burn a lot of energy in their hunt, they need the nectar and pollen of flowers to help sustain that energy. To that end, some plants are better than others at attracting good bugs. The shape of the blossom might help or hinder the access of a particular insect to the pollen and nectar the plant offers. Also, some plants can attract aphids or insects that are specific to that plant and will not harm garden plants but will provide meals for the good bugs. Not all plants bloom at the same time, so in a diversity at least one plant will always be supplying the good bugs with what they need. It is also possible that the wrong plant would attract bugs bad for the garden or host diseases also bad for the garden.

So, it can get complicated. I need to study hard to find the right combination of insectary plants to grow in or near my garden. On the bright side, the complexity of the study is deep enough to keep one interested for a whole lifetime. One need not study rocket science to keep from getting bored. How nature grows diversity will suffice.

bumblebee

Image 417 is perhaps a bumblebee. Some think it is, instead, a carpenter bee. They look a lot alike but I understand the abdomen of the carpenter bee is slick instead of hairy. This insect is beneficial because it pollinates flowers. The bee rests on the flower head of Garlic Chives (Allium tuberosum). The bee was so still I thought it might be dead or asleep. Or drunk? When I finally nudged it, it moved sluggishly but it never flew or even buzzed all the time I was there.

image 498

Image 498 shows what seems to be a different type and much smaller bee. This one is on a marigold blossom.

image 398

Image 398 shows what I believe is a soldier beetle called Pennsylvania Leatherwing (Chauliognathus pennsylvanicus). Many say it is beneficial but at least one said this insect’s value may be exaggerated. Even if it does not eat bad insects, at least it seems to be a good pollinator of Garlic Chives, for there were a lot of these soldier beetles there.

image 490

Image 490 may be a Green Bottle Fly, I am not sure. Green Blow Flies are supposedly associated with decaying flesh, but there were a lot of these really interested in the Garlic Chives. Nothing smelled dead.

image 437

Image 437 may be what is called a “Question Mark” butterfly, but I am not sure. It rested close to corn and beans.

image 460

Image 460 shows a wasp that repeatedly returned for a drink of water from the little watering hole. Many wasps are beneficial because they predate on bad bugs.

The watering hole is made of an overturned garbage can lid. I keep it replenished with water from the rain barrel. I change the water at most after every couple of days to keep mosquitoes from breeding in it and to keep it from stagnating. I had hoped the watering hole and an adjacent shelter hole would attract a toad, but I have not seen a toad yet. I did see a blue-tailed lizard not too far from the water, but that was much earlier in the year.

image 378

Image 378 shows, I believe, the eggs of a Leaf Footed Bug or Stink Bug. The eggs were attached underneath a leaf of broccoli. I did not see any adults this day, but I have seen them before. They have hind legs that are flattened like a spatula or leaf. Some of them may be beneficial, sucking on caterpillars of bad bugs. But I suspect the ones around here are only interested in sucking juice from the broccoli.

image 379

Image 379 shows a moth caterpillar that might be an “Inch Worm”. It has been feasting on the broccoli and a bad type. I hope someday I see a beneficial insect feasting on it.

image 383

Image 383 is a young, I think, type of Harlequin Bug. They also eat the broccoli.

image 433

Image 433 is a Garden Spider, (perhaps Argiope aurantia). I understand that these spiders need a source of water. This one was about 4 feet from the watering hole and very near the corn and beans. I believe spiders are, on balance, beneficial.

In conclusion, many insects could be seen in one hour in my organic garden. Some were beneficial and some were not. Many pollinators were seen. Many destructive insects were seen. I would like to see a lot more beneficial predators. I recently transplanted some Golden Rod to my garden. I found it on a farm in an adjacent county. I have heard that Golden Rod is a good insectary plant. That it aggravates hay fever and allergies is a bad rap and is not true, from what I have read. I plan to introduce more selected flowers in the future. When I planted the Garlic Chives (Allium tuberosum) I did it for food. I did not know it was an excellent insectary too, until I saw it in action.

Simplest Radios

by Curlydock

The simplest radio

receivers require no batteries, gasoline, coal, oil, nuclear, wind, geothermal, tidal, or solar power.

And, they are indeed simple. Using them and building them out of parts found in the junkbox or scavanged from yard-sales will not hurt the planet and will not make Greedy Gates even richer.

I built this one for a recent experiment. It has only five electrical components. The only power it requires exists in the signal it receives. In our metro area (Louisville, Ky) in one afternoon I received eleven stations loud and clear. These transmitters were all local and within about a twelve mile radius. Their powers ranged between 500 watts and 50 Kilo-watts. The 500 watt station is roughly 5 miles away.

These radios are variously called crystal sets, crystal radios, or foxhole radios. In the “foxhole” variety, the home-made simplicity includes the signal detector, which is a razor blade and piece of pencil lead!

The All-Powerful Antenna

For this type of radio to work well, every consideration must be made to conserve the precious power that arrives in the signal. This typically requires a very long and high outdoor antenna and a good ground connection. This antenna is a wire between 30 and several hundred feet long. The ground connection can be a cold water pipe (but only if it is metal into the earth) or a metal rod or pipe driven 4 to eight feet or so into the earth. Good performance depends on a good ground connection and such connections are sometimes hard to come by. For safety, one should also install some kind of lightning arrestor and disconnect the radio during bad weather. Also, one should install the antenna well clear of power lines. All this may be difficult to impossible in a metro environment.

Until this experiment,
I believed crystal radios could not be made portable or operate effectively with an indoor antenna. Now I know otherwise. You still can’t stick it in a pocket, but you can easily carry the radio and antenna around while you listen to a station.

Given the appearance of the antenna, you would attract a lot of attention outside. Whether attracting attention is good or bad depends on you and your needs and the particular setting, I guess.

Anyway, here is a picture of the crystal set and antenna I built and used in this experiment:

crystal set used in experiment

It sits in the comfortable chair, for scale, next to the special loop antenna. The loop antenna has a 32-inch outside diameter. This installment is really about the antenna, because that is what made the radio able to receive as well as it does.

The antenna is not as heavy as it looks because the bulky part is cut from thick sheets of styrofoam insulation, which is mostly gas and therefore light. The rings are glued like a sandwich over the sector fingers, which were made of scrap pieces of a wall covering that resembles pressed fiber board (like some clip boards are made of). The antenna can easily be lifted from the pvc pipe support and carried around slung across your shoulder, all the while supplying signal to the radio.

Other materials can be used. In other versions, I used bamboo chopsticks taped in pairs on either side of wood popsicle sticks, creating the slot that the cable is woven through. I have also cut the whole ring and set of sectors and slots from large sheets of cardboard. To strengthen large diameters, you might want to use white glue or flour paste to build up several layers of cardboard. Use styrofoam, plastic, wood, cardboard, pvc pipe or plexiglass but keep the use of metal in the antenna to a bare minimum. Even the non-metal structure should be kept to the minimum needed for support of the wire. For example, if you use large sheets of cardboard, cut out the middle so that it is a ring instead of a disc. Discarding anything that is not needed in the viscintiy of the antenna will improve it’s quality. Ideally, if you can figure out a way to support the wire on nothing but air, more power to you (and to your radio)!

The weave of the cable is important. Here is a close up showing how this weave was accomplished on this antenna:The weave in the sector slots

This neat alternation is possible only with an odd number of sectors. Use 5, 9, or 11 sectors, but not 6, 10 or 12, etc. No, it is not numerology. I am not superstitious. Try it and see!

The reason for this weave is that it keeps the individual turns of wire separated from each other. The separation is needed because if the wires lay close together, as in a close-wound coil, something called capacitance will build up with each added turn to such a degree that it spoils the quality of the coil. I know it sounds like I am just pulling this out of my…, but, believe me, it’s true!

The wire

I used in the antenna was about 90 or 100 feet of cable from a spool labeled: “100-Ft. (30.4m) Telephone-Station Wire 8-con.(4 twisted pair) 24-Ga. Solid Color-coded.”

It was copper wire.

I first wound the whole antenna and then went back and cut each turn.

That can be done neatly if you cut all the cable on each side of one particular support slot but on only one side of the plane of the disk. That sounds complicated, but however you end up with a coil of eleven turns with one tap per turn and an extra tap for the odd end is ok with me.

The eight individual wires in these cuts were then cleaned of insulation and soldered together. The ends were then re-joined as they were before they were cut, along with a wire from this joint that terminated at a tap made of a tiny brass nail embedded in a piece of plexiglass. Each end of the original cable was treated the same way. Since the antenna has eleven turns, there are 12 taps.

Here is a close up of the taps:

eleven turns and twelve taps

The reason for all those taps is that it offers the most flexibility in choosing the way the antenna is connected to the other components.

The reason for connecting the eight individual wires in the cable in parallel for each turn is that the cable becomes a rough approximation of a special kind of wire called “litz” wire that is ideally used for this sort of purpose but is expensive and hard to come by. At the very least, wiring our telephone cable this way reduces resistive power losses by increasing the copper conductor cross section.

You could also use coaxial cable of the type for connecting between TV or FM antennas and their equipment. It doesn’t matter exactly what kind of coaxial cable as long as it has a large diameter and a good shield. Then, ignore the center conductor and use only the shield when you make your taps. The copper cross section in the shield is much more than that of the center conductor. You could connect the center conductor to the shield at each opportunity but it will probably not matter much. The signal will all want to flow in the shield anyway, due to something called the “skin effect”. No, I am not making this up.

Now is a good time to introduce

The schematic:
schematic for crystal radio
See the taps? There are two sub-circuits to connect, each having two alligator clips.

Where the variable capacitor is connected determines the tuning range. Select taps enclosing more turns to lower the minimum tuning frequency. Connect the capacitor across fewer turns to tune to higher frequencies. I have found the whole AM broadcast band is covered with two taps.

Where the germanium diode circuit is connected affects the selectivity, or the ability to tune one station at a time. It also affects signal loudness because the different taps affect what is called “impedance matching”. In addition, there is a transformer action, but the actual transformed output voltage will depend on the “Q” or bandwidth. The theory is complicated but fortunately the best tap points are easily found by trial and error (as long as you don’t have to keep cutting and soldering over and over again. That is the beauty of having each turn with a permanent tap.)

Generally, the radio works best when the detector circuit taps between a number of turns equal to about a third of the number of turns the capacitor is tapped between. But the best position can change if you change the type of detector or earphone.

Speaking of earphones,

the kind you get with just about any electronic equipment these days will not work. The earphone has to be a high-impedance type. A few places still sell them. If you can’t find one, look for an older telephone. Sometimes the receivers on them work passably well, indeed very well if you can find a matching transformer. Details about how to fix these sorts of problems can be found elsewhere on the Internet. Just do a search on “crystal set” or “crystal radio”. It is a remarkably popular topic.

Here are a couple of shots of the box housing the variable capacitor, resistor, germanium diode and various binding posts. I took a bit of artistic licence with one of them.

crystal radio

close up of crystal radio

If you build one of these I would like to know your results. Just post a comment here to that effect. I am particuarly interested in knowing how this design functions outside of the city. How many stations will it receive in a non-metro environment?

Also, if you have any questions about the design feel welcome to post them here.

Frankly, I am looking forward to spring so I can put away my winter projects and get back to gardening.

About curlydock

I have four years vocational experience as analog electronics design engineer and many more years avocational experience in the same. I am a former member of the Society of Amateur Radio Astronomers. Now I am interested in sustainable survival practice on both personal and planetary scales. I program with C in the Linux environment. I am presently living off my savings in Louisville Ky.

I have a gallery where I sell art and photographs. My gallery is at

http://eulif.imagekind.com/bucolic