HarveyH42

When I say 'satelite dish', I mean the old style, 10-12 foot models. I'm the proud owner of two (one 10 and one 12 foot, both are mesh and aluminum frame).

First problem, how to calculate the focus. Heavy math was many years ago for me, had trouble with a recent concrete pyramid project... I'm sure if given an equation, I can still solve it.

Second problem is the mesh. The 10 foot dish has the mesh intact, though about getting reflective paint and seeing how that turns out. Hope to get enough heat to boil water. Melting lead alloys would be much better, but a little optimistic. The mesh on the 12 foot dish was held on by cable ties, between weathering and my cat, most eventually broke, so its just a frame now.

I saved some (about 500 square feet) of mylar/bubble wrap type shipping insulation. They throw this stuff away almost daily at work, seemed like useful stuff...

Haven't messed with it in a while, but got the itch again. My first experiments weren't exactly ideal. I didn't have a decent temperature probe, and it was slightly overcast and windy. I simply taped the mylar wrap to the 10 foot dish and layed out in the yard, basically pointing toward the sun. Definately focused the sun, big difference in temperature standing near it. I measured around 170 degrees near where the reciever/detector was mounted (guessing focus). Wind kept pulling the wrap off the dish, haven't figured a more perment way to anchor it yet.

Anyway, a little constructive feedback. I'd like to boil water at the very least. Useful for coffee, distillation, steam power...
Higher temperatures 460-470 dgrees F would be good for melting pewter (unreleated hobby)...

justDIY

i think you're right assuming the feedhorn is at the focal point of the dish ... I seem to remember, the wavelength of the radiation does not affect focalpoint, as long as the material making the reflector can reflect said radiation... so focusing microwaves or visible light, as long as the dish can reflect it, it should focus on the same spot

google should have some how-to pages for you

the hard part as I understand it, is a good heat exchanger ... the focal point is going to be small, and once you get it working well, will be very hot... one design I saw used a water block made from some sort of ceramic... another was a coil of copper tubing

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Oznog

Tough part is making it smoothly reflective. I mean if you just cover it with mylar, it's going to scatter in a million slightly different directions. It can't focus on a small collector area, and as you increase the collector area it will block the light to the dish. Now if you paint both sides the of the collector then it's still converting the blocked sunlight into heat, but you're lowering your ability to concentrate that heat in a small area that allows you to boil water or whatever.

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HarveyH42

I already know that this material is less than idea, beyond free and plentiful... When I first brought it home, I had about a dozen 4 ft X 20 ft sheets rolled up. They were a little wet from condensation, so I had to unroll them all so they could dry (didn't want mold or mildew). The outside temp was mid 80's, but my backyard (almost completely covered) was much hotter, had stop every few sheets and cool off in the house, wipe off the sweat, before going out and rolling up some more. Wish I had thought to measure it, but likely close to 100 degrees. I would like to see some numbers from a 12 ft dish perfectly mirrored, just to get some idea how hot this thing might get.

spuffock

I don't know about the temperature, but with a 12 foot dish perfectly mirrored you should grab 3 kilowatts on a good day.

Aphromann

I have recently stumbled across a technology that is still new to me; a paint that has the propeties of a solar pannel. http://news.nationalgeographic.com/n...arplastic.html
It seems simple in theory and should give you a greater power supply with the increased surface area, and reduction of space. Its going to cost a few organs and a diamond finger, but should solve any problems you were experiencing. As for the focal point, it is already there on satelite dishes. Like my father always said, "Dont go trying to re-invent the wheel when it worked the first time." I'm not sure why it would be mirrored, sense the refraction and defration should not be sending light to the center, but back out in front of the focal point, hence the focal point. Any reciever that extrudes in front of the dish should be the focal point, meaning that the current surface does not direct it inward, but out to the focal point from any point. You would generate about the same energy if the entire surface was covered with such paint.

As a simple reminder, never-ever stand between a satelite and any reciever, as the radiation emmitted could be potentially lethal.

justDIY

are you being serious, or is that intended as a joke!?

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Aphromann

It was not meant as any joke. I have five years experience in telecommunication and am aware of the transmissions sent from a satelite to a reciever. Much like a bad cell-phone that sauses incredible amounts of EMS, a reciever is similar. Motorolla and Sprint both claim to acknoledge that they offer cellphones that emmit dangerous levels of EMS, I know that Sprint has one, because I called and complained about it. In theory, if a cell phone can interfere with grounded utilities such as televisions and speakers, a reciever that is streaming any amount of large information would have a much greater affect. Its not that the wavelengths may cause harm, its that the energy being transmitted may caus harm, if not cancer. This argument got me a brand new Razor free of charge

Nigel Goodwin

Did you steal the razor?

I don't see how such an incorrect argument could have won you anything?, the signals at the receiver dish are miniscule - so tiny you need a dish to collect and concentrate them, and even the concentrated amount focused on the LNB is incredibly small.

A cellphone puts out a number of watts, the energy focused on the LNB is probably in the micro-watts, if not less? - more than a million times LESS than a cellphone.

Sorry, but your worry is completely ridiculous!.

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HarveyH42

It sounds like a few people are getting a little off track. This isn't for power generation, only heat concentration. I'm not transmitting satelite signals either.


The 12 foot dish is stripped down to just the parabollic aluminum frame, had to lighten it up some and better balance so I could move it around the yard a few times over the past 10-12 years (yeah, I tend hang on to neat stuff...). I could estimate within a foot where the LNB was mounted. Figured if there was a simple equation I could mount the collector more accurately. Pretty sure I have the parts that the LNB was mounted to some place...

The 10 foot dish is mostly intact, so the focus won't be a problem. Thought to use a couple cans of that shiny chrome spray paint on the mesh. I know this will only be a 50% coverage at best. But considering the wind we get, a little breathing room is a good idea.

Nigel Goodwin

The whole thing with a dish is the precision of it, the dish needs to be an accurate parabola, and the focus is at an exact point. Assuming you're going to accurately and smoothly fit a reflective surface to the dish you can easily find the focus point because you can SEE the visible light, where you can't the microwaves - just hold a piece of card up and move it backwards and forwards to find the focus, bear in mind it 'might' burst into flames!

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HarveyH42

When I first got the mylar stuff last summer, I pointed the 10 foot dish in the general direction of the sun, draped/duct taped some sheet to it. Got out my meter and temperature probe. It only has a 36" lead so had to stand pretty close, barely do-able. I got around 170 degrees near the focus. Don't think the paper would burst into flames (toilet paper maybe), but I'd most likely get a little singed, great tan though...

I'm on vacation first week of Sept., might rig something up and play with it then if the weather stays clear. This is suppose to be huricane season, fortunately none so far. But with all this heat, we can expect some bad ones this year.

hjl4

This has been done before, and is feasible.
I've seen a web site, that describes exactly what you want to do, and they used aluminum foil, for there tests.
The presicion, of the surface of dish , does not have to be so smooth.
They concentrated the suns rays on a 12x12 peice of aluminum with pipes running through it, and had tremendous results. They actually, could heat a room in there house with such a system.
Same with the solar barbecue, it is not concentrated on such a small surface that accuracy, is critical.
BTW, I was going to do the same thing as you, but my dish was too weak to have the mesh covered by aluminum foil, as the wind would of taken it away.

mramos1

Maybe they are thinking microwaves? I have stood in front of mine many times.

mramos1

HarveyH42. I am in Boynton, need some help. I can bring my 3x4 fresnel lens over. hehehe.. I have a couple 1x1 as well.

EDIT: They are in feet not inches.