pgardn-question

[dr. fager]

Hey, I know it's a stretch but you're our resident scientist. I'm trying to find the guts of one of those garden solar LED's that come on when there's no light on the solar panel. Unfortunately, the only thing I can find are the lights themselves...they come in 4-6 packs, I could buy one and gut it but I'd rather not. I can find the solar panels...and AA chargers which is all they are but not sure how to make it only come on at night.

Spent way too much time on google...moderate electronics knowledge...

anyway thought it was worth a shot.

Originally Posted by dr.fager

Hey, I know it's a stretch but you're our resident scientist. I'm trying to find the guts of one of those garden solar LED's that come on when there's no light on the solar panel. Unfortunately, the only thing I can find are the lights themselves...they come in 4-6 packs, I could buy one and gut it but I'd rather not. I can find the solar panels...and AA chargers which is all they are but not sure how to make it only come on at night.

Spent way too much time on google...moderate electronics knowledge...

anyway thought it was worth a shot.

It probably works the same way that street lights do. They come on at night because the have a Cadmium-sulfide photo resistor. What this resistor does is resist the flow of current. So when the battery in your yard light is fully charged, like during the end of the day, no current from the battery will be allowed to flow to the light because the resistance of the photoresistor is very high as long as light shines on it. Now interestingly enough, when night comes, this resistors resistance changes drastically. It becomes a very good conductor so current can flow right thru this resistor to the light.

The next question of course would be how exactly does the Cadmium sulfide combination lose practically all its resistance when it is dark. For this I have a guess. Post back if you want my guess. It based on the electron configuration that is probably present in the Cadmium Sulfide combination.

Anyways do this experiment. Take your solar yard light during the day and put your finger over different components in the circuitry. If the diode(light) comes on, you have found your photo resistor. Oh yes. Do this late afternoon so you know the solar panel has already fully charged the battery.

I will try and find a picture of what one should look like. I have found them in my broken solar yard lights. My daughter and I have broken the stems on some of them so they just lay around so we decided to open them up.

An LED is a light emitting diode. I just wrote diode above. But the bottom line is that they require a very small current and put out a lot of light, that is why they are so wonderful.

Wo ho Dr. Fager I have hit the mother load. I was about to go out and take a closeup picture of one of my busted up lights but as I have stated before on the board, there is a great site called how things work...

and guess what... THey have a flippin picture!!!! What a great site I tell ya.

http://home.howstuffworks.com/solar-light1.htm

God I love this site. It should be in everyone's toolbox.
Now this does not look exactly like my lights, but the basic guts are the same. You can also read more about these lights as it has some pages before, and some pages after.

Oh yes. Sorry I got to this so late. I have been at school all day and just got back from a volleyball game.

Ok I am a bit confused. It seems to me as light hits CdS (cadmium sulfide) that the resistance should decrease, not increase. The light should, by my reasoning, make for a looser electron configuration making current flow easier...

So the circuitry must involve a setup where if you cover the CdS photoresistor, the resistivity increases, so the current takes another pathway that allows current to flow from the battery to the LED. It must be that way. I could probably draw it out in a simple way.

[dr. fager]

Thanks so much, basically I'm trying to put one in something I'm building for my parents. This should get me well on my way, I find it very frustrating what I've forgotten since college entered as a Physics major...had a semester of electronics, all gone..

Website is a gem, I have it bookmarked now.

Thanks again!

Originally Posted by dr.fager

Thanks so much, basically I'm trying to put one in something I'm building for my parents. This should get me well on my way, I find it very frustrating what I've forgotten since college entered as a Physics major...had a semester of electronics, all gone..

Website is a gem, I have it bookmarked now.

Thanks again!

Hey F = ma about says it all. Good luck. Just dont send current thru your heart like I have attempted on occassion. Dont think you will have to worry if you are building something that is not plugged into the wall or a car battery.