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is there

giving

If you really want to power something, you're better off getting a solar cell (available at Radio Shack?) or even a reasonably large photodiode. LED's have a very small area, hence the amount of solar power collected (proportional to this area) is small. LED's just were not designed to be used as a power source.

In any case, you may want to measure an i-v curve (current vs. voltage), either for the LED or a solar cell. To do that, you'll need to connect different resistance values across the output terminals, and measure the voltage. Then calculate the current for each reading from

current = voltage / resistance

What you have done so far is to measure one point on the i-v curve for your LED, using a very large resistance, the resistance of your meter (perhaps 10 M-ohm?) This reading is the open-circuit voltage.

Make sure that each point is measured in full sunlight, preferably with the device oriented toward the sun for a maximum reading (you can just hold the device in your hand, and orient it until the meter reading is maximized). At any rate, the device should be kept in a fixed orientation for all readings. If some clouds cover the sun during the measurements, wait until they have passed by before continuing.

I would guess that using resistances between a few ohms and 100k to 1M would provide a sufficiently complete plot.

You are correct that changing the amount of light hitting the device (LED or solar cel) will affect the amount of current produced. Hence the need to do a series of measurements all with the same amount of solar power.

Reply to
redbelly98
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You have more than an LED. It is an LED and a silicon flasher and current control integrated circuit. So any readings you get out of it are going to be difficult to understand.

Any plain LED will generate some voltage (open circuit) and drive some current when shorted. There will be some value of output voltage between zero and open circuit voltage that allows it to provide maximum power (voltage times current). I expect that bluer LEDs will produce more open circuit voltage because those shorter wavelength photons have more energy, each. The current depends on the die size and how efficiently the lens reflector the die is mounted on focus light on the die.

--
John Popelish
Reply to
John Popelish

LED's were not designed to work as a solar cell. But, because of the way that they are structured, they will give off some voltage at a few uA (microamps), when the sun is shining directly on them. You can do some tests to see how much current and voltage they put out, and then make an array of them in a parallel and series combination to give you a useable voltage and current output.

It would be much more feasable and practical to get the proper solar cells, and make a solar panel. This would involved mounting them on a panel of some type, and properly wiring them up.

You can purchase a solar panel ready made that is voltage regulated, and having a fuse protection wired in. It can be used to run some devices for you. This would be most feasable in the end in comparison to something you would put together yourself. I have seen these solar panels sold at places that sell utilities for mobile homes, boats, and some large hardware centers. They are standardly built to put out 12 Volts at several Amps for running various small utility devices, or for charging auto and boat batteries.

--

Jerry G.
=====


"Zman"  wrote in message news:41c5673a@duster.adelaide.on.net...
> Hey there
>
> when placed in the sun, a small led gives off a reading on my voltmeter,
> goes up and down. The only thing is, how do i know what reverse
> current/voltage im going to get just by looking at the information? is
there
> a formula to use and does mCd make a diff in voltage or current when
giving
> power out?
>
> the specs are
>
> 15VDC 5mm LED
> (all typical values)
> luminous intensity 120
> Peak emission wavelength 573
> spectral half width 15
> flash rate (freq) 2.4
> operating voltage 5
> forward voltage 5
> reverse voltage .04
>
>
> thank you
>
>
Reply to
News.ca.inter.net

Hey there

when placed in the sun, a small led gives off a reading on my voltmeter, goes up and down. The only thing is, how do i know what reverse current/voltage im going to get just by looking at the information? is there a formula to use and does mCd make a diff in voltage or current when giving power out?

the specs are

15VDC 5mm LED (all typical values) luminous intensity 120 Peak emission wavelength 573 spectral half width 15 flash rate (freq) 2.4 operating voltage 5 forward voltage 5 reverse voltage .04

thank you

Reply to
Zman

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