A Fresnel Lens cooker that Heats from Below

by Bruce Joseph
(Tucson, AZ (USA))

Fresnel cooker from the side

Fresnel cooker from the side

Fresnel cooker from the side
Focal line on bottom of cast iron pan.
Small cast iron pan on cooking surface.
Cooked lamb burger in pan.

I recently modified my Fresnel lens "grill" to heat from below. This allows more conventional cooking than the old version, and is more practical to use.

Instead of the lens being mounted on straight arms that pivot at the focal line, this new version uses arms with a 90 degree elbow, and a mirror placed at a 45 degree angle at the elbow. The arms still pivot at the focal line.

Because of some losses added by the mirror, this cooker is slightly less efficient than the original. The first thing I cooked, was a 1/3 pound lamb burger. It took about 8 minutes (as opposed to 6 on the "grill.") It will also ignite a 2"X4" in under 10 seconds, where the old grill can do it in about 5.

Still, this grill should allow me to steam veggies, and cook in pots and pans, and possibly even be the heat source for a solar oven, which the old version simply could not do.


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Greetings again Bruce,

Thank you for sharing this with our site visitors, this is great...you really did some nice and practical revisions of your Fresnel lens cooker.

We look forward to hearing more from you when you wish.

Nathan
Admin.

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Feb 01, 2012
Re: Mirror
by: Anonymous

Hi Jim,

Cracking the mirror is one of my concerns. I started off using a polished piece of steel, but it wasn't as mirror-like as the glass mirror, and lost too much energy.

So far, the glass mirror gets warm, but not really hot. (It's a reasonable distance from the focal line.)

I'd would like to try an acrylic mirror too.

Wow, a 5'x9'parabolic must generate some real power! I'd like to hear more about it.

Feb 01, 2012
Be careful with your mirror
by: Jim La Joie

Great design.
I did something similar with a 5' by 9' parabolic reflecting onto a mirror under a BBQ grill. The mirror shattered due to the heat. If you have not already done so, soften the focus to reduce the heat or use a polished metal mirror.

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