How I can power correctly my LEDs?

[Pegasus]

Hi People!
I need some help to finish the installation of my solar panel.I have it in my garden to light during the nigth.It has 10 watts output and charge an accumulator.I'havent the inverter so I connected directly to the battery,a couple of homemade 12V led lamps.
These leds are very sensitive to the voltage fall and there is the problem that when the battery is not fully charged,the light of the leds is weak,or worse,it makes no light.Is there a electronic solution for my problem?.I need something that mantains constant the battery output to light the leds, also when the voltage of the battery is not enough.
Let me know.Thank you.
Regards,
Cyrano

[gyulasun]

Hi Cyrano,

Basically the circuit you need is called a DC/DC converter,  or switch mode power supply of a kind. It would receive for instance in your case a DC input voltage range between 10V to 15V and would give out a stabilised 12V output voltage for your LEDs.  There are lots of such products, a random search on dc dc converters by google yielded this:
http://www.martekpower.com/powersupplies/dc_select.html
and picking a low cost 10 Watt series 1000HN, its data sheet: http://www.martekpower.com/pdfs/1000_hn.pdf   
or the 15 Watt series 1500HN, data sheet here: http://www.martekpower.com/pdfs/1500_hn.pdf

So these are ready made, usually off the shelf products, with moderate or slightly higher prices.  There are circuit schematics on the web or in textbooks on switch mode power supplies if you are inclined building such for yourself.

rgds,  Gyula

[Freezer]

Might want to take a look on this forum, as they have some useful information on led stuff as well as other lights.

http://www.candlepowerforums.com/vb/showthread.php?t=188227