12v shed led light?

[strideredc]

I am trying to work out what I need for this project, I have a couple of luxeon stars from a old Q3 and want to run them in my shed from a 12v lead acid battery (2.8ah I think, its from a burglar alarm) powered buy solar panel.

What step down converters would I need?

Is this the sort of thing I need? http://www.taskled.com/nflex.html ?

Any help would be great!

Thanks


ps. sorry if its not in the right section, i wasnt sure

 

[RonM]

I'd like to do the same thing, but hope to find a cheaper solution than the one you linked to. I have a 12V car battery, solar panel, and two 12V incandecent "landscape or deck" type fixtures. It works fine, but hey...it's not LED.

 

[Illum]

for the records, I've been working on this project for awhile also

3 luxeon I's [RX1H] two CPU grade heatsinks, and a 6.8 ohm resistor capacle of at least 1 watt



version 7.10, with three switches 1 for fan, one for LED, one for auxillary [any expansion that may take place, but will need to bump the fuse block to a higher value]

for the connectors, 22 gauge wire and ATA power cords salvaged from old computers

My plan was to have adequate lighting in specific rooms of the house than runs on the 12V 19AH in my jumpstarter

dont ask me the technical questions...please, im not that advanced:candle:

 

[Skibane]

For the price of a step-down converter, you could buy another LED*, put all 3 of them in series, and drop the remaining excess voltage with a small-value resistor - would be just about as efficient as running 3 LEDs in parallel off a step-down converter, and a lot simpler, too.


*(Actually, for the price of a converter, you could probably buy an entire new set of 3 Cree or SSC stars! )

 

[adnj]

I second that. Run the LEDs in series and your Vin worries are gone. Just remember that the average 12V battery is about 13.5 volts. For dropping the ressitance, try a potentiometer. You can get one from an old radio's volume control (read FREE).

 

[WhiteFox]

I second that. Run the LEDs in series and your Vin worries are gone. Just remember that the average 12V battery is about 13.5 volts. For dropping the ressitance, try a potentiometer. You can get one from an old radio's volume control (read FREE).

Are you sure? In a car with the engine running it would read 13.5-14v because it's charging off the alternator. I think car batteries are around 12.5v the most with nothing on them.

 

[RonM]

Temperature: 67 degrees Fahrenheit

Percent Unloaded
charge voltage
100 - 12.61
75 - 12.28
50 - 11.98
25 - 11.74
0 - 11.62

Of course charging voltage in a car will probably be over 14V, but that shouldn't matter here because the battery is being run off of a solar panel not a charger. Unless the panel is large, I doubt it can provide too much voltage on an open circuit.

 

[txmatt]

I've been wanting to do a similar system. I was actually thinking of drilling holes in my 4x4 privacy fence posts (angled down a bit for watter shedding) and puttng Nichia CS's in the holes and routing the wire out the back of the post to provide dim security lightng in the alley.

Panels have open circuit voltage in the 15-17 volt range so you definitely want to see what your panel will pull your battery voltage up to when the panel is lit.

With small panels you can run them straight to the battery. For any panel larger than a few watts, you're better off buying an inexpensive solar controller, most of which use PWM to provide multi-stage charging for the battery. Some of the nicer ones have built-in circuits that provide dusk to dawn timers which can be used to run 12VDC loads which I hope to use to cycle my LED's.

 

[adnj]

Nominal voltage is about 12.5 volts. The solar panel should provide about 13.5 volts at load to charge the cell. Design the circuit for 13.5 volts because of residual excess charge. It is not uncommon to see a dV of 0.5 to 1.0 volt after the battery comes off any charger and drop very quickly. As the battery charges, internal resistance will increase and drop the charge rate. For the best possible cell life, regulate the trickle charge voltage at 13.2v.

Are you sure? In a car with the engine running it would read 13.5-14v because it's charging off the alternator. I think car batteries are around 12.5v the most with nothing on them.

 

[Illum]

I think car batteries are around 12.5v the most with nothing on them.

it varies....
12V is the nominal voltage...but a satisfactorily charged cell will have anything from 11.5-13.5V. so when choosing a current limiting resistor...find the nearest largest just incase your cell has more voltage wont overdrive the LEDs to the point of

I've hit 14.5V before, I know I overcharged it

 

[Skibane]

For dropping the ressitance, try a potentiometer. You can get one from an old radio's volume control (read FREE).

Most radios use a potentiometer in the 1K-100K ohm range - probably much higher resistance than would be usable in this application.

If it was me, I'd just take a handful of small-value resistors (in the 1 to 10 ohm range) and start tack-soldering various combinations of them in series with the 3 LEDs, until I came up with a combination that produced the desired current (i.e., around 0.5 to 0.75 amps for a 3 watt Luxeon).

 

[WhiteFox]

strideredc, how bright would these LEDs be? I'd love to do a solar charged lighting system in my room that would be bright than the dual Circline Fluorescents, and cost nothing to run at night time since a solar panel in my window would charge a medical grade battery I have during the day.

 

[txmatt]

Interesting article in the April/May 2007 issue of Mother Earth News (I don't see it on their web site yet) about a small solar lighting setup for a cabin or shed. It consists of a 50 watt Kyocera PV panel, charge controller, 12v, 50AH gel cell battery, three 15-watt 12VDC compact fluorescents, and one 3-watt 12VDC LED light, plus fuses, breaker box, etc. There's a $700 kit available with all of the major components. You could certainly do it cheaper but a cool project to tinker with solar. It should be up on their site...

http://motherearthnews.com/

in the not too distant future.

 

[[email protected]]

I'm working on a similar situation for a chicken coop. I was going cheap and tried to use what I have. I have an old 12v car battery that I used Epsom salt and 2 weeks of charging to restore and a 750 watt inverter. The battery should give me about 45 amp/hours and I plan to use a 5 - 23 watt incandescent light bulb. At 23 watts that's (23/110)x10 = 2.09 amp/hours. 45 amp/hours will give me about 21 hours of light if my math is right.