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DiscoverCircuits.com
-- Hobby Corner
"Hobby Circuits for
your Hobby Projects"
Last Updated on:
08/29/2008 02:09:11 PM
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CANDLE POWER
designed by David Johnson, P.E. |
| I was challenged by a Discover Circuits visitor a while back. He wanted to know how to generate some electricity from the heat
produced by a common candle. He further added that he didn’t want the heat to electricity converter to use any moving parts. That meant a steam or Stirling engine would be ruled
out. I put my thinking cap on and came up with two different methods to produce a very modest amount of electrical power. I first purchased a common “millivolt” thermopile voltage
generator from an eBay auction. These are often used to monitor the pilot light of a gas fireplace. The typical unit generates about 0.8v open circuit. As the illustration shows
below, with the thermopile placed in a good hot candle flame, I measured an open circuit voltage of about 0.8v and a short circuit current of 200ma. The DC resistance of the device
measured 4 ohms. With a quality DC motor attached to the device, the voltage dropped from 0.8v to 0.4v but the motor spun nicely. With a 4 ohm series resistance, the peak power for
this device would therefore occur when the load resistance equaled the source resistance or about 4 ohms. Under these conditions the thermopile would pump about 100ma into a 4 ohm load
or about 40mw of power. If an 85% efficient DC to DC converter were used to boost the voltage to a higher level, this would be enough to light a 2 volt red led at a current level of
16ma. Such a current would be enough to produce a nice output from the LED. If the candle power circuit were used to charge a 1 amp-hour lithium ion cell phone battery, it might
take about 5 days to charge it up. Although this device works, it clearly would not be practical for anything but a way to power a pilot light indictor lamp or some other low power load.
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| The second method I experimented with used an array of solar cells, positioned around the outside of a candle. As shown in the
illustration, an array of eight 2.0cm X 2.5cm solar cells could generate about 20 milliwatts of power from the light produced by a single candle flame. This is only half that produced by
the thermopile method but does produce a much higher voltage. Someone suggested that some calcium oxide (lime) held in the candle flame might increase the amount of light produced and
thus improve the energy conversion. This method had been used back in the 1800s to boost the light from gas powered lamps. The term “lime light” came from this technique. |
| For a short movie showing a candle powered motor, double click here. (download of movie is slow,
please be patient) Some time later, I will post a circuit which could take the low voltage from the thermopile and boost it to a more useful voltage. |
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