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EB-42T Prototype
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First EB‑42T Prototype

Our first prototype EB cooker was an EB‑42T.  The goal was to build a relatively large cooker that was capable of cooking faster than many other panel cookers.  The 42 inch diameter EB‑42T was chosen because it is the largest EB cooker that can be cut from a single piece of 48 inch wide material.  Figure 1 shows the first almost completed prototype.  The reflector portion of theEB­42T looks a bit like a parabola, but is safer than a parabola because it does not have a point focus.  It is a triple angle cone consisting of three cone sections and a circular disk.

 

 Figure 2 is a drawing of the triple cone reflector with the target (pot) represented as a sphere.  Figure 3 is a drawing of the reflector viewed from the rear.  Figure 4 shows a cross section view of right half of the cooker, with the spherical target appearing as a circle.  Note that the dashed blue lines that are tangent to the circle represent the reflections of vertical (on axis) suns rays that are reflected from the edges of each cone section.  This shows that the cone sections are designed to insure that when the cone is pointed directly at the sun all of the reflected energy will hit the target sphere.  In practice, the cooking pot will replace the target sphere. The orientation of the pot relative to the reflector cone will vary, as the cooker is oriented for different sun elevation angles.  However, if the smallest dimension of the pot is equal to the diameter of the sphere all of the reflected energy will hit the pot for all sun elevation angles.  We recommend using a pot with smallest dimension larger than the sphere diameter to insure that all of the reflected energy will hit the pot even when the cooker is pointed a few degrees from the sun.

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Figure 1

First Almost Finished EB‑42T Prototype

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Figure 2 

View of Triple Cone

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Figure 3 

Rear View of Triple Cone

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Figure 4 

Cross Section of EB‑42T Cooker with Spherical Target

 

Figure 5 shows how the three cone sections laid out and ready to be cut from a single piece of 48 inch wide material.  We have experimented with different ways of drawing the large circles.  Unless you have a very large compass, you may need to be a little creative when drawing the circles.  One method that works is to use a small strip of wood or metal that is a little longer than the radius of the largest circle (A yard stick or a meter stick will work).  Put a small nail in one end for the center point, and then drill a small hole at the radius of the circle.  Then use the stick as a guide for drawing the circle.  First, drive the nail through the stick into the material where you want the center of the circle.  Then insert a pencil through the hole in the stick and rotate the stick about the center point to draw the circle.

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Figure 5                       

Layout of Cone Sections

 

In addition to the three cone sections shown on Figure 5, you will also need to cut a 6 inch diameter disc from the material used for the cone sections.

Joining the cone sections

The three cone sections and the center disk are assembled to construct the triple cone cooker.  We have used two ways to join the ends of segments as well as different cone segments.  The first, which works well for thicker materials, uses bendable straps with fasteners.  Figure 6 shows how straps are used to join cone sections.  Holes are drilled through the ends of the straps and at selected locations on the cone sections. Then fasteners are placed through the holes and tightened. Often cone segment materials require that a reflective coating be applied.  Sometimes the cone material is itself reflective on one surface. The second method, which works well for thin cone section material are the tabs made by leaving a section of material at selected sites on the cone segment. Often the smaller radius edge of the cone segment is selected so when two cone segments are joined the tab is on the outside of the lower cone segment. Holes are drilled so fasteners can be inserted with the flattest surface of the fastener on the reflective side of the cone surface. Each method has its advantages with the straps method providing butt joints between cone segment edges.

Stand for EB42T

The EB42T cooker requires a stand to support the cooker.  We have built two different frames for this cooker.

Sawhorse Type Stand

The first Stand we built was an A Frame sawhorse style structure.  This frame is shown in Figure 6.  It also can be seen in Figure 1, which also shows the pot and pot holder. This frame consists of the two A Frame ends with reinforcing strips between the legs.  The pot holder is made from 3/8 inch diameter re-bar and bent to extend through the mid point section of the upper cone segment. The ends of the pot holder attach to the solar cooker frame through bearing blocks.

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Figure 6

Cooker on Sawhorse Stand and Straps Joining Cone Sections

 

New Portable Stand

The Sawhorse type frame was very strong and stable even on windy days.  However it proved to be cumbersome to move from place to place.  Therefore we replaced it with a lightweight portable frame similar to the one that had been used with the EB800.  For a more detailed description see the section on the EB800D.  This frame is not as stable as the sawhorse stand in windy conditions.  However, we have used it on windy days buy placed a toolbox or other weight on the base.  Figure 6a shows the new frame before the reflector and potholder were added.  Figure 6b shows the EB42T on the new stand.

 

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Figure 6a

Portable Stand

 

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Figure 6b

EB42T on Portable Stand

Scaling the EB-42T to make different size cookers

In the following table can be found dimensions for building a selection of triple cone EB style cookers.  There are many options and currently EB suggests for  all except the smallest sized cookers the  triple cone segment is better.

Dimensions of Cone Sections for EB Triple Cone Cookers
EB-24T EB-30T EB-36T EB-42T EB-48T EB-54T Cutout
Cooker Diameter (inch) 24 30 36 42 48 54 Angle
    (cm) 61.0 76.2 91.4 106.7 121.9 137.2 (deg)
Outer Cone Sect Outside Radius (inch) 16.97 21.21 25.45 29.69 33.93 38.17 105.4
(cm) 43.1 53.9 64.6 75.4 86.2 97.0
Inside Radius (inch) 12.11 15.14 18.17 21.20 24.23 27.26
(cm) 30.8 38.5 46.2 53.8 61.5 69.2
Middle Cone Sect Outside Radius (inch) 10.29 12.86 15.43 18.00 20.57 23.14 60.4
(cm) 26.1 32.7 39.2 45.7 52.3 58.8
Inside Radius (inch) 6.17 7.71 9.26 10.80 12.34 13.89
(cm) 15.7 19.6 23.5 27.4 31.4 35.3
Inner Cone Sect Outside Radius (inch) 5.42 6.78 8.13 9.49 10.85 12.20 18.4
(cm) 13.8 17.2 20.7 24.1 27.5 31.0
Inside Radius (inch) 1.82 2.27 2.73 3.18 3.63 4.09
(cm) 4.6 5.8 6.9 8.1 9.2 10.4
Center Disk Radius (inch) 1.71 2.14 2.57 3.00 3.43 3.86
(Target Radius) (cm) 4.4 5.4 6.5 7.6 8.7 9.8
Minimum  Length of Material* (inch) 33.93 42.41 50.90 59.38 67.86 76.35
(cm) 86.2 107.7 129.3 150.8 172.4 193.9
Minimum Width of Material* (inch) 27.25 34.06 40.87 47.68 54.49 61.30
(cm) 69.2 86.5 103.8 121.1 138.4 155.7
Target Sphere Diameter (inch) 3.43 4.29 5.14 6.00 6.86 7.71
(cm) 8.7 10.9 13.1 15.2 17.4 19.6
* If cooker cone is cut from a single sheet of material with no splices.

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Figure 7 Bill and Alan with Completed Cooker