/diy/ - Do It Yourself

>>171949
Airflow is essential, but unlike what >>171955
states about it, you do not need any sort of fan inside for a solar dehydrator. Natural convection will draw in cooler dryer air constantly, unless your design is so faulty as to not have proper convection. Thus make your dehydrator to have good ventilation. It is very easy to make a solar dehydrator that is far too hot, if the ventilation is not enough. Make your dehydrator so that you can readily adjust the airflow. Simple sliding doors in the top and bottom will work.

You also do not need any sort of desiccant. Proper air flow and sunshine will be more than sufficient.

All you need to make a solar dehydrator is cardboard and metal screens. Though you can make a more permanent one if you wish. Don't be tempted to use reflector panels. You'll end up cooking your food or whatever you are drying. Blacken the inside where the sun will strike so the ambient air temps rise very fast. Do not put foil inside because it will only reflect the light onto the items you are drying and cook them without giving you good air temps. don't make the unit too tall. If it is too tall then the items at the top will end up cooking, the items at the middle drying properly, and the items at the bottom not getting warm enough. If you need to, make more than one dehydrator.

Use an oven thermometer. As a rule of thumb, heat the interior by closing the vents until the ambient temperature reaches 160F top 165F then immediately open the air vents until the temps drop to 130F to 140F range and maintain that temp range from then on. For things like jerky you'll need to use a meat thermometer to ensure it reaches the 160-165F range internally prior to reducing the heat. For other special foods, consult several sources on google.

>>145833
>You will have such a small area that you will get hot/cold spots and end up with a mess.

On a small scale you are correct. This is why you'd need to build one with a focal point of about 3 inches max. using around 400 3 to 4 inch mirrors. I don't have the proper calculations on that, but that is an educated approximation. It also depends on the mass you are melting.

>>145827
Yes, you can do that. You'll need to make sure the tabs are black, so paint them if needed. A Fresnel lens would be easier to use, but not very /diy/, even though you can salvage a massive one from an old Rear Projection TV and build a special frame doth hold and align it. A parabolic mirror chip array would be cool.

Check out penny melting solar furnaces on youtube. Most use Fresnel lenses.

>>138931
Well, the larger your reflectors (mirrors) the further away you can get from the focal point. As distance extends the spot of light they cast as the reflection get fuzzier. This unfocused area scatters the amount of solar power. You want a focal point as tight as possible.

Keep that in mind for focal point distance and even the shape of the reflectors if you are using the multi-mirror array. Round mirrors will reflect a better focal point than square ones (the sun isn't square for instance) and allow you to better align all the mirrors to a single spot.

>>138894
>Each "test" I've seen people doing this, used incorrect mirrors.

Oh, except for the one in the 1960-1970s that used metal polished mirror to completely destroy a mock up ship in seconds. I don't' recall the correct year.

>>138867
Archimedes was Greek (287BC to 212BC). At that time he would probably had metal polished mirrors instead of the glass-metal backed mirrors we are accustomed to now. On Mythbusters they did succeed in charring and small flames. Each "test" I've seen people doing this, used incorrect mirrors.

The mirrors used by Archimedes were most likely slightly parabolic metal-polished mirrors. the amount of parabola those type of mirrors would need would be extremely slight, just enough to counter the edge glow of the focal point. This means each mirror's reflected light would have a tighter focal point than the ones used by Mythbusters, that group of school children, or anyone else. Not only that, but polished metal mirrors have less light loss than glass-backed mirrors because the light does not pass through glass twice where it can be lessened in power by as much as 10%. Because of these things, the focal point of all the mirrors will be smaller and far hotter. The ships back then had pitch and tar on them. This is ideal for an SDR to ignite the ships almost instantly, because of its dark color and ignition properties, if the mirrors were large enough of course. It would be like a laser passing right over the ships as they sailed through the focal point and anyone on board caught in the focal point would most likely die of 4th degree burns.

The technology to do this was available at that time, though I highly doubt they simply used shields and instead use purpose-built mirrors because you'd need very large mirrors in order to help reduce the size of the reflection blur at that far distance of focal point.

>>138786
It's far easier to use. Making any other kind requires more work, but is fun to do. If you make another kind I recommend doing it with a single light in a room. This way you can use that single light's reflected rays to angle the focal point of each mirror without blinding yourself of causing fires.

>>138708
> WEAR WELDING GOGGLES if you value your eyesight.

A 1000 times this. Even my small 15"x15" Fresnel lens is enough to cause temporary blindness if you look at the objects you are burning with it.

Also, if you want to burn things faster, paint them black where the sun hits them . Things of light color reflect too much sun off in order to heat of quickly..

>>138480
I made one some time ago. you can make one from the Fresnel lens from a discarded Read Projection TV. Those lenses can be 4' wide! I've done the mirror chip method; flat surface with mirrors aligned to make a focal point. Google, "Fresnel lens melting pennies" or something similar. There are youtube video of that.

The best thing I can recommend is making sure that whatever parabola/reflector method you use that you make the focal point further down and out of the sun's rays, from the sun to the reflector(s), this way you can play with the focal point without putting a shadow over the reflector(s). There's a guy who took a large 1980s satellite dish and covered it all in aluminum foil to make an SDR. It was pretty cool and there should still be links for it somewhere online.

Remember, that focal point can be excessively hot and ignite things on fire instantly. Even a bird flying through it can die if you have a big enough reflector array. There was some art thing in a European (I think European) country that happened to include a parabola and it was killing flying birds at certain times of the day when the sun was bright on it. Don't even pass your hand through the focal point because it can instantly burn you.

If you do get burned, use yellow mustard on the burn ASAP. Leave it on for 15 minutes. This will cool the burn and more importantly will help prevent tissue damage and pain (I've been using it for years).

A SDR is a great way to heat a Stirling Engine, fyi.

Now I basically make solar box ovens. I've been wanting to tray an SDR with a fiber optic array at the focal point to see if you can make a wood burner out of the fiber optic cable. It's probably a pipe dream though.

>>138509
lol Those guys are idiots when it comes to science.

>>130863
Hot glue, epoxy, or a balloon like in this pic.

I try to stay out of /diy/ homebrewing threads because of this, >>130850 explanation, but this is a /diy/ answer to a /diy/ question. lol

>>128390
Glad to have helped.

The best advice is more reflector area the faster your food will cook.

You can also pre-heat an oven by lining it with brick or stone then heating it up for a while before putting your food in. The thermal mass will keep temps even when clouds pass by. When the sun goes away completely you can wrap the unit up and hold all that heat in for longer so it is still cooking your food. Paint the stones/bricks black with oven safe paint.

A black interior oven will raise the ambient air temps inside while a reflective interior oven will reflect some back out and a lot on the food or container you are cooking. Both had advantages. I prefer the black interior so no heat it lost.

Check out this style of box cooker and how you adjust the reflector panels. This is a modified kyoto solar cooker. It normally only has 1 reflector in the back. I edited 3 more in which is a design I plan on making next.

Plans I made for a solar funnel cooker. I never made plans for the cooking jar or the hangers though. There's a few plans online though.

Also, for your panels of any cooker, using aluminum means it will corrode over time. Making the panels so they can be easily removed, stored, and replaced cheaply.

>>128343

>>128342

>>128340

Here's plans for a panel cooker like the Cookits.

>>128095
OP, this is a 2-second sketch I did some years ago. It was to be a pizza oven that I never got around to making. This uses a non-tinted glass sliding patio door as the glazing (taken out of the frame and put into a less weighty wooden frame). Pitty I never fleshed out the design. I'm only posting it because your description reminded me of it.

The collapsible cooker cooking terrible pizza for a terrible but tasty American dinner.

This is a solar funnel cooker. I used coat hanger wire to make the jar hanger and for making a cage so that the plastic shopping bag didn't touch the jar sides. It would have instantly melted if it had. The bag acts as a wind break and slight insulation. This works fairly well but is cumbersome to use because of its shape. I put scotch tape over a section of the jar then painted it and removed the tape so there would be a small viewing port to check if food it baking or boiling. The mason canning jar also acts to pressure cook the food. Don't make any kind of pasta in this as it will pressure cook it to oblivion and be HORRID. This is good for beans if you leave room for the foam.

Here's a tiny one I made to toast a cheap off-brand pop-tart. I didn't use the glue though, only the tape. The foil is from the tart wrappers, glazing is the plastic bag, box is the tart box, and the black thing is black-painted foil. The towel acts as insulation as does the one in >>128323

I think this took about 30 minutes to cook though it may have been done sooner than that. With 4 reflectors the plastic glazing was starting to melt.

I'll post a few pics of the different solar cookers I've made.

This one is a collapsible solar box oven. I used it for years. I kept it behind the seat of my truck. It was great for heating up road food and for camping and hiking trips.

A dog destroyed it while it was cooking. The dog actually dug under a 6 feet tall fence to get to it. lol It was only a prototype anyway.

Pic is of my bread riser and my main cooker. Most solar box ovens are low enough temp that you can rise your bread and bake it in same cooker. Mine gets too hot even without the panels attached.

>>128108
A solar furnace is very specific when it comes to alignment. You will also need a massive Fresnel lens. Like one from an old dead Rear-projection TV. Those can be 4 feet wide. This type of solar cooker relies on clear skies at all times and has very high heat loss.

>>128113
Google, "Cookit solar cooker". These are easy to make, light, portable, easy to learn and use, and work very well. There's a massive world wide program to hand these out to peoples such as you listed. They are literally rape prevention (in Africa, no joking) and respiratory disease prevention devices.

>>128138
Smoke is not good inside your lungs.

>>128283
The use of multiple glazings over the main box os common. Normally no more than 2 glazings are use. 3 causes too much blockage and reflection. 1 causes heat loss when wind hits it and causes condensation inside on the glass which also affects heat absorption of the cooking chamber.

>>128303
As the sun moves across the sky it is best to rotate your cooker to directly face it. Panel cookers and especially box ovens need to be realigned far less than a parabolic cooker for instance.

>>128095
>so much metal

This will weigh a ton, as others have already stated. If you wish, you can us thin sheet metal for the inner cooking chamber of a solar box cooker. The rest of the cooker can literally be all cardboard, even the reflectors. For the reflectors, it is best that they are not a mirror polish. A mirror polish creates a smaller focal point. You need a focal point that hits the entire window of the cooking chamber, not one smaller area of it. This is why simple aluminum foil works best.

There's no real reason to make a metal one unless you are making it to withstand an outside environment 24/7. In which case go for an all metal oven. If it needs to be portable, use a dolly for something that heavy, if it is going to be big unit.

>>128101
This is why I should read ahead when starting to answer questions. lol

>might put wheels on 2 legs like a grill

Great idea. Make sure you put lots of insulation in it and that it can't get wet in rain. A handy tarp and bungie cords is a must. Build a compartment under the cooker to house these things. Then if it rains while the panels are up they won't pool water of you put a tarp over it.

Materials,

-If your solar box oven is to attain high temperature you should use clear thermally toughened safety glass for the inner glazing. You can usually get by with plate glass for the outer glazing and for low temp cookers.

-Portable units for traveling that may be taking hits, bumps, and jarring (ones for camping for instance) should use safety glass for the glazing(s).

-If you make a solar box oven, I recommend making the reflector panels in the style used by the Heaven's Flame solar cooker. They are easy to make, and can fold up for storage. They also capture a lot of sun at just the right angle.

-For winter use, the sun is low, a gimbled tray inside the cooker will come in very handy. You can also make a unit that is angled to the sun more than it normally would be.

-Tightly packed cardboard is a very good start with insulation. You can use it as the inner insulation shell. Other less heat-tolerant insulations can be used further away from the center of the cooking chamber. For instance, an inch of cardboard, an inch of Celetex(black fiberboard, and two pieces of blueboard foam are what I use on my main box cooker. The foam would melt quickly if it wasn't properly insulated away from the cooking box heat. The sides of that cooker are usually cool while inside temps are 400F+.