Notes from Windward: #69

Heating Things Up Prematurly

bringing the spun dish on-line

     Since Windward is an intentional community, one of the standards by which we judge how we're coming along is the gap between what we intend to happen and what actually happens. Expectations are founded on past experience. When working with dynamic components in new ways it's not uncommon for things to do the unexpected.

     A good example would be the ultra-strong, rare-earth magnets that go into making an axial flux generator. You've probably seen cartoons where someone is carrying a magnet so strong that it causes knives to leap off the table and fly at them--that's an exageration, but not by much. It is genuinely surprising when it happens to you in real life, and a lot less funny. And when a finger gets caught between two of these high-power magnets, it's not at all funny.

     Yesterday, we had a similar thing happen with the spun satellite dish that we're planning on using to generate steam. Last summer, a neighbor donated the parabolic reflector in support of our solar research work, and this spring Camille did a great job of removing the paint and polishing the dish's surface. The next step will involve modifying the dish's mount so that a control computers can provide the two axis control needed in order to track the sun throughout the day.

     With the crew gathered at the landing for the morning walk, it was a simple matter to pick up the dish and mount it back onto the pole. We made no attempt to line it up; just put it on the steel pole and cinched down the bolts so that it wouldn't move when the wind blew.

the crew gathers in front of the newly polished dish

     Satellite dishes are built to track the geosynchronous belt that lies some 22,000 miles above the equator; they're not set up to track the sun. That's what makes it possible for a home satellite receiver to track from one satellite to another using only one motor arm. Tracking the sun is more complicated in that not only does it move from east to west during the day, it also moves north in summer and back south in winter.

     As chance would have it, the dish was pointing close enough to the sun's track that as the sun crossed the dish at just the right angle, the heat toasted the old electronic package and it's plastic weather cover. Here are some pics that give an idea of how hot the dish's target area got. Good thing that the old electronics weren't usable.

the fried amplifier at the dish's focal point

the melted cover

melted plastic splattered on the dish

     It's one thing to know intellectually that the dish is able to concentrate five kilowatts of energy on a small area--it's something else to see the results, and smell the tang of vaporized plastic. Naturally, we unbolted the dish and swung it around to point northward. That should prevent a repeat of this unintentional firing of the solar boiler until we have the controlling electronics in place and operational.

     All in all, it was an exciting glimpse of what's to come.

Notes From Windward - Index - Vol. 69