Instructables
loading
loading
Picture of Solar Death Ray (TV Fresnel Lens)
Solar penny melting photo.jpg
DSC_7432.jpg
DSC_7428.jpg
DSC_7431.jpg
DSC_7427.jpg
DSC_7434.jpg
DSC_7433.jpg
DSC_7595.jpg
DSC_7584.jpg
DSC_7585.jpg
DSC_7586.jpg
DSC_7587.jpg
DSC_7588.jpg
DSC_7589.jpg
DSC_7592.jpg
DSC_7594.jpg
DSC_7597.jpg
For all of you would-be eco-friendly mad-scientists, I present to you a way to dominate the world! But only on sunny days - THE SOLAR DEATH RAY!

This is simply a free projection lens from the front of an old television, mounted in a wood frame. It's any easy project anyone can build with only simple wood-working skills.

I got this lens from our local electronics recycling center. The public can drop off old televisions, computers, or other electronics for free recycling. I simply used my swiss-army knife to remove the few screws that hold on the bezel, and then slid the lens out. There must have been at least 5 junk projection TVs there when I did this.

The lens is roughly three feet by four feet, with a diagonal of just over 60 inches. 

To make the frame, I ran 2x4's through a table saw with the blade depth set to about half an inch. The plastic lens is about 1/8 of an inch, the same thickness as the width of the saw blade.

The 2x4's are then placed around the lens, with a pair of wood screws in each corner to hold the frame together. The wood was left long to act as handles, and make the Death Ray easier to hold and aim.

At this point, I haven't built a stand for the lens, but may in the future. As it is, the Death Ray works well being held by one or two people, and not having a stand discourages leaving the lens in the sun unattended.

This past weekend, we had a children's birthday party, and it was a sunny fall day, so we broke out the Death Ray and melted pennies. Some of my friends are science teachers, and children LOVE to see things like this. (So do the Adults!) Needless to say, there was plenty of adult supervision.

Modern American pennies are mostly Zinc, which has a melting point of about 800 degrees F. They are coated with copper, which has a melting point near 2000 F. We were able to liquify the pennies. An auto-darkening welding helmet worked well to allow me to look directly at the target object and adjust the focus.

The Solar Death Ray is loads of fun! I highly encourage you to make one. Just make sure not to leave it unattended, or where children could use it unsupervised, as it focuses a serious amount of solar energy. I keep this covered with heavy dark cloth if it is outdoors. I store it in my dark garage.

Be safe, and have fun with the SOLAR DEATH RAY!

For more of my recycled backyard fun, please visit http://ecoprojecteer.net
I was interested till I read about the pennies. Then I was impressed.
moonchylde3 months ago
Just pulled one of these screens out of a dumpster yesterday. Now I know what to do with it. I plan to take it camping... " Who wants to bet I can't start a campfire in three seconds without matches?" LOL.
parora51 year ago
where can we buy Fresnel lenses ,just like urs
ChrisC9 parora54 months ago

smaller versions in the old type of overhead projectors used in schools. Located just under the top glass. much more manageable and probably not so much "death ray".

bennelson (author)  ChrisC94 months ago
If you want to BUY a large lens like this, they do sometimes show up at Surplus or Scientific stores. Here's a link to one of the types of places you can find them.
http://www.sciplus.com/
ChrisC94 months ago

Another fresnel screen option is to find some the "old-school" overhead projector machines. Under the flat-glass top is a 14 X 14" fresnel screen with the infamous circular flexible screen pattern. It does about the same thing only not so big and not so flimsy. Much more manageable! And schools are disposing of these machines like crazy. I got 4 screens for free!

ChrisC9 ChrisC94 months ago

and yes, DARK sunglasses are probably needed.

parora51 year ago
where can we buy Fresnel lenses ,just like urs
ChrisC9 parora54 months ago

see my reply above about finding smaller versions of the fresnel screen inside the old-type overhead projectors. Get a bunch for free I should think.

bennelson (author)  parora51 year ago
I wouldn't buy one. This is a project in recycling. The lens is part of a common older style television that gets thrown away now. You can find them at junk-yards, recycling centers, or by asking in classified ads.
If you really want to buy one, I sometimes see them in Scientific and Surplus stores.
preppamom1 year ago
We made one a couple of months ago...very cool. Got the tv from someone who was advertising it for free, was just going to throw it out. Definitely have to do!!!
Very fun Instructable! I will hit up our local recycling center for a lens and perhaps try blacksmithing with it. However, I see you have a wonderful white smoke coming from the pennies. Please don't sniff those fumes. Burning zinc and copper emits fumes that cause Metal Fume Fever. It is nothing you want to deal with. I lost a friend to it. The American Welding Society (AWS) has a nice little article about Metal Fume Fever at: http://www.aws.org/technical/facts/FACT-25.pdf. Other than that, you've got a wonderful project there! Thanks for posting.
Kayak Kid1 year ago
King of Random made something like this before.
Engineers in London did a similar thing. Mostly by accident.

http://www.gizmodo.co.uk/2013/09/its-not-just-cars-londons-walkie-scorchies-setting-fire-too/
I like the lab coat you must be a reel science person just like on the picture box at aunt Mabel's over head projectors use them also and you get a couple of glass lenses too
I hope the local ant colony's are paying tribute
mickyra1 year ago
Could this help make a solar oven function better?
holly-g1 year ago
Why?
EmcySquare1 year ago
PLEASE NOTE:
Not ALL projection TV screens use fresnel lens, so not all TV will work
Quester551 year ago
Got Mine Years Ago from an Electronics Out-let & Surplus Store, Except mine was Thicker than those used In those Old Projection T.V.s. I also got hold of some 1Inch thick Lenses, Talk about your Death Ray, Use a Projecting Lens & you'll Make Those Ant Mounds & Gofers Beg for Mercy, as their Ground Melts & turns to glass.
Drat! Cloudy Days, my one weakness! I'll get you CBS weather report! Mark my words!!
Gamer Guy1 year ago
I've seen this project before, was this your own, original idea? It uses rather similar steps.
bennelson (author)  Gamer Guy1 year ago
I guess I would consider this more or less a "public domain project". Lots of people have built magnifying solar concentrators from projection television screens. There's nothing particularly new or novel here.
Mostly, I'm just showing how I happened to do it and sharing my fun and excitement.
Cool! I was just curious, saw a vid, thought you might of uploaded it, and you never know, some people do steal, but most others, like you just show how cool these projects are, and what you've done. Thanks, and great job!
Thanks for the "new" memories. I had a large plastic Fresnel lens more than 50 years ago when I was about 12. Glass would explode when heated. Insects would just about disappear. Yes it was dangerous, but exciting. One caveat for all users. Prolonged viewing of the hot spot may cause damage to your eyes. I was seeing black spots for hours after each session. Thanks the instructable. Maybe there are some practical applications beyond melting pennies!
bennelson (author)  Digital Docent1 year ago
Yes, do NOT make a habit of starting at the hot spot! I was wearing a welding helmet for viewing. Dark glasses (such as for gas welding) would work well too.
rdwygail1 year ago
Rdwysam
You can set this up as a solar cooker. Just place a pan under the hot spot, add grease and cook your meat, make a stew, boil water whatever you would normally do on a stove. It's easier if you make a frame so you can aim it and maintain the same position.
tioga0011 year ago
What kind of TV are you talking about? I am confused.
You need o find a rear projection screen TV.
It was pretty much the first affordable big screen TV's before Plasma, LCD and LED TV's took it's place.
makermike1 year ago
Interesting that this should pop up. I was playing around with the fresnel lens from an overhead projector yesterday (much smaller than yours, only about 1 sq. ft.) It set paper smoldering in about two seconds. I'll have to build a stand and play around with it some more.

Eye protection is key here, though! That spot is bright!
Pinkly1 year ago
Ha! I have a cousin who would have LOVED this when we were kids. He was the "pull the wings off flies and burn ants with a magnifying glass" type of kid. Have you tried to, say, cook an egg with this thing? I'd find that more impressive (and practical) than melting pennies (though that's still impressive)
Pinkly Pinkly1 year ago
Or boil water. Should be a piece of cake.
Ev1 year ago
I have one! Use a spray bottle of water to find the focus with the mist. A partially inserted perpendicular nail or screw in the frame helps aim the panel directly at the sun.
HAHA where was this when I found that anthill right outside my house.
bennelson (author)  ILoveLights1 year ago
You must have pretty big ants!
They are the military kind.....G I ants......
kurshiukas1 year ago
now, with a bit of sun direction regulation electronics and copper coil and a water barrel - we have a pretty eco-water heater