I want to put together a string of 5mm LEDs that will be powered by by a 5V, 50ma solar panel I bought from Radio Shack.
Just playing around, I connected up to 11 white LEDs ( 7000mcd, 3.3V, 25ma each ) in parallel to the solar panel. Using my multimeter at peak lighting, voltage was about 2.7V and the current was 30ma. The lights have worked consistently and remained nice and bright without getting even remotely hot or even warm for over a week so far.
My questions to you are these:
(1) What would be the maximum number of these LEDs I could power with the 2.7V reading I’m actually getting from my solar panel and 25ma max? And how do you calculate this? This way, I can know how to adjust for different voltages, LEDs, and amperage.
(2) Would I even need a resistor(s) here? If so, how many and where would they be connected? I’m not sure if 1 resistor in series between the solar panel and the 1st LED would suffice. Or if I need individual resistors in series between each LED in the string and perhaps the solar panel.
FYI, to connect everything, I just used some old speaker wire I had leftover. It’s the kind that has 2 copper wires individually wrapped in plastic. Just split it down the middle so I would have individual wire strands. And sized the wires, then stripped off the ends to wrap around the LED leads. The final version will be more professional. This is only my “playing around” version right now.
Thanks everyone for your help!
Thanks everybody for all your help! I had a feeling I didn’t need any resistors because I’m dealing with very low voltage and current.
FYI, I did measure the voltage across each LED and it was pretty constant at 2.65-2.7V.
My ultimate goal is to make a solar string light that I can use for some small area lighting. So it’ll either be a thin ribbon type or I may put it inside a small plastic tube. Not sure yet.
And I’ll connect it to 2-4 rechargeable AA batteries, 2500ma Ni-MA ones. It depends upon which solar panel I’ll use. But the two I have, the Radio Shack and one from a garden solar light, are relatively low amperage and voltage. So I’m not concerned with overcharging.
I also have a voltage regulator I could add if need be. And will definitely be including a rectifier (blocking) diode so current won’t flow back into the solar panel. Plus, I have the photoresistor from the garden light to incorporate into the mix. And some 100 ohm resistors I could add if needed.
- Solar Panel: How Can I Set-up My Small Solar Panel To Charge AA Solar-rechargeable Btteries? (5/22/2011)
- Solar Lights: How Can I Power LED Light Strings With A Solar Panel? (6/24/2011)
- Solar Lights: Any Craft Or Hobby People Out There? (6/27/2011)
- Solar Products: In Terms Of Light Out-put,how Do Solar Landscape Lights Compare To Low Voltage Lights? (7/26/2011)
- Solar Panel: Can You Charge A Phone With A Small Solar Panel? (5/11/2011)