LED Garden Light circuit

[bryan1]

Hi I found this circuit on the net and built a prototype up but running it with a solar cell from an existing garden light and a 1.2 volt nicad battery, the thing wouldn't work. However when I used a lithium ion battery from an old laptop battery which measured 3.75 volts even after sitting in a box for 2 years not only did the drive part of the circuit work but I used 5 10,000mcd high brightness white LED's and found it nearly lit up my workshop. As I couldn't get the solar part working I deleted the solar cell, diode. Q1 and R1, then I made the circuit up on a 7X8 bit of veroboard. I've used a 26 ohm resistor for R3 providing around 125 milliamps to the LED's ( Is is the right amount of current ). Also I would like to incorporate a light dependant resistor to turn the circuit off in the day and I need to know if I just connect say a 1 watt 6 volt solar panel to the circuit will that charge the lithium ion battery or would more complex circuitry be needed.

Cheers Bryan1

 

[jrz126]

sounds like an awful lot of current, but I havent used any white leds yet. How many leds are you running and how do you have them wired?

(BTW, I have 62 6000MCD blue leds mounted in the headliner of my car, imagine that one :shock: )

 

[bryan1]

Hi Jrz,
the LED's are wired in series so I'm assuming that each LED would get 25 milliamps of current.

:shock: 62 6000mcd LED :shock:

 

[John Sorensen]

the LED's are wired in series so I'm assuming that each LED would get 25 milliamps of current

If they're wired in series, then each of them sees the same amount of current (125mA?!). The current that flows out of one flows into the next.

Do you mean they're in parallel? Then the current will split up but only if you have individual resistors for each LED. This is because manufacturing differences from one LED to the next makes them very poor sharers of current when just strapped in parallel.

It's an interesting little circuit, though.

j.

 

[bryan1]

Hi John,
Yep silly me they are wired in parallel , I just put them in a breadboard.

Cheers Bryan1

 

[jrz126]

you will want a resistor for each LED. they wont last that long without it.

and you'll probably want 20 ma per led too.