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Bert

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Reply with quote  #21 
Still trying to decide on the reflectors support material. Here is something cheap but I'm not familiar with Aspen wood.

https://www.menards.com/main/building-materials/panel-products/construction-panels/sheathing/plywood-sheathing/2-x-2-acx-handi-panel/p-1444425372065-c-13337.htm?tid=-7042128005311410870&ipos=29

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Bert K.
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dbc

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Reply with quote  #22 
Bert,  If I can amplify on Doug's comments about shiny vs. black, I was surprised by something when I first used a reflector-type cooker: The reflector surface was no warmer than ambient, except where it was real close to the cooking pot, yet the cooking pot got really hot.  The 'greenhouse' enclosure was just 2 large pyrex mixing bowls, with the black pot resting inside.  Nothing there to absorb any solar radiation except the pot itself.

If you want to test a shiny interior, you could make some temporary inserts out of cardboard with regular aluminum foil glued on (foil is pretty shiny if you put it on smooth and avoid scuffing it up).  You could fit them around the inside, and hold them from flopping around with some little wooden shims.  Cheap and quick.  If you use white glue (Elmer's Glue-All or School Glue), you can wipe off any that gets on the shiny front side with a damp cloth after it dries.

My box cookers are 'low-end', mostly made out of cardboard and foil, with just a single reflector at the back.  Yours will have higher gain with 3 or 4 reflectors and more sophisticated positioning, and so will surely reach higher temperatures.  You might need tempered glass.  I probably should have used tempered, but I just used common window glass.  Don't remember if I thought about it much at the time.  I haven't had any problems though.

About the Aspen wood, if it's actually from an Aspen tree, the wood is light but not especially strong, maybe OK for this application.

Good idea about the back door if you can still do it.  I agree it would be easier if you design it in from the beginning.  Some builders have made sort of a 'bottle cork' door that just fits in by friction.  If it's too late for the door, you could consider attaching the reflector assembly to the main box with hinges.  The biggest advantage to a back door is you lose less heat if you have to check the food to see if it's done.
Bert

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Reply with quote  #23 
Don,

My oven's inside is already shiny so it will be easy to test that.

I understand the theory about heating only the pot. The one thing that has me puzzled is that if the solar oven is pointed squarely at the sun then the bottom would reflect almost everything back out. Except for were the pot blocks it of course.

Maybe if the bottom was black and the rest was shiny?

I really hope that both you and Doug are right though. It will make things easier since it's that way now. Also I don't want to paint the inside.

I have a feeling that I will be improving on it after I have it working. The first one is the hardest to figure out.
Maybe a back door.

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Bert K.
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gbwillson

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Reply with quote  #24 
How will you be measuring the output? Instead of simply a thermometer inside the oven you could check the temp of water inside the pot. That way you can see not only how long it takes the contents of the pot to heat up, you won't have the temperature swings you do when measuring air.

Greg in MN

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Bert

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Reply with quote  #25 
Greg,

I was planning on using this one.

https://www.amazon.com/gp/product/B0778CTRZ2/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

It can show the temp of both the oven and the food at the same time. 

I could keep an eye on it when inside the house also.

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Bert K.
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dbc

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Reply with quote  #26 
Bert,  I don't really claim to know which finish is best; there have been successful designs both ways.  Some of the 'shiny inside' models (including mine) have a black absorber plate raised a bit off the bottom that the pot sits on.  I have seen aluminum, cookie sheets, even cardboard with foil painted black (I used aluminum deck-plate turned upside down and sheet metal with a bent lip at the edge.)  Since you have a suspended tray for the pot, you could make the bottom black, either permanently or with a slip-in test panel.  As you say, this might stop solar rays reflecting straight back out.  Sun that hits the sides bounces around and hits the pot anyway.

Also, it seems to me the more outside reflector area you have vs. the inside of the box, the less is matters what finish you use inside the box.
Bert

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Reply with quote  #27 
Don

Good points. The oven won't always be pointed exactly right anyways.
It probably will work fine either way. Might be fun to experiment with it a bit though.

Our electric stove is an energy hog. I'm hoping the solar oven will help with that.

I have the box's lazy susan installed and the tilt working pretty decent. Just need to make the inside pivot rack for the pot, the reflectors and then touch up the painting.




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Bert K.
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stmbtwle

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Reply with quote  #28 
Are you going to put a tracker on it? That would be nifty!

I've been piddling with building a tracking "table" but I'm not sure what I'd do with it. Maybe I should build an oven?


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Willie, Tampa Bay
Bert

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Reply with quote  #29 
A tracker would be cool. Maybe I will get one on there eventually. 
Yes, build an oven. We need to get more people making them so we can brainstorm. [smile]

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Bert K.
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Gordy

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Reply with quote  #30 
dbc,

Quote:
Some of the 'shiny inside' models (including mine) have a black absorber plate raised a bit off the bottom that the pot sits on.  I have seen aluminum, cookie sheets, even cardboard with foil painted black (I used aluminum deck-plate turned upside down and sheet metal with a bent lip at the edge.)  Since you have a suspended tray for the pot, you could make the bottom black,


So if I understand, this would be the size of the bottom of the oven and act like the fins in a hot water collector, but to bring heat to the pot.

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Gordy,
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