ADJUSTING VOLTAGE FOR LED'S

[bobhenry]

Help Help Help !

My solar panels for the caboose have a tap for 3 6 9 and 12 volts.

I have chosen LED lighting that requires 4 1/2 volts will they take 6 volts ?

If not what do I need to do to make these items compatible?

[WesGrimes]

You can use an LM7805 chip from Radio Shack to make a voltage regulator.
Here is a tutorial: http://www.afreeland.com/node/16

[zipz71]

The lm7805 is a good choice. The input voltage should be at least 2 volts higher than the output to work properly, so 7 volts minimum. They can take up to 35 volts input. You still need resistors at the LED's. You can figure out the value using this calculator.
http://led.linear1.org/led.wiz
Other than what you posted you will need to know the forward current of the LED.

[WesGrimes]

Jeff is correct, if you are using LEDs by them self, then you deffinetly need resistors or the will pop.

If it is a prepackaged LED assembly, it probably already has resistors built in.

[Bogo]

You can use an LM7805 chip from Radio Shack to make a voltage regulator.
Here is a tutorial: http://www.afreeland.com/node/16

Industry has pretty much ditched the old linear regulators. You need to clamp one of them to a heat sink or you will burn it up. I'm much in favor of going to the newer three pin switching regulator replacements. Often they don't need a heatsink. The V7805W-500R (http://www.digikey.com/product-detail/en/V7805W-500R/102-2449-ND/2757924) is one example from CUI. For high voltages or in situation where it may see voltage spikes it requests a 47uF 100V capacitor on the input. You'd need one on the linear regulator too. The nice thing about this switching regulator is it doesn't waste power. It's at least 87% efficient and in some cases over 95% efficient. With a linear regulator, lots more energy is wasted. For 12VDC input, and 5VDC output, the regulator is at best 41.6% efficient.

Depending on what LED you have, you may wish to get a purpose built LED driver circuit. They will directly power the LED with X mA of current. you need to select one with the right mA output for the LEDs that can be powered by your supply. Here are a number of different ones: http://ledsupply.com/led-drivers.php It would also be possible to build from the chips, but that is more work. I don't know the specifications for the LED you have so I don't know how to narrow down which would be best. Notice on some of the LED drivers that they are made to power strings of LEDs. When they talk buck, they mean the supply voltage is above the LED string voltage, and when they use boost they mean the LED string voltage is above the supply voltage.

[WesGrimes]

What he said
Not as cheap or easy, but better. You only need a heat sink if you are drawing a bunch of current.

[kludge]

Got a data sheet or a link to the LEDs you'll be using?

Some use resistors, some use a controller. The 4.5V rating sounds like they were made for flashlights.

If they just use resistors you can put three modules in series and hook them straight up to your 12V system. They'll be a bit dim, but they'll work. If you're on shore power running off the converter it'll be about perfect.

[bobhenry]

Got a data sheet or a link to the LEDs you'll be using?

Some use resistors, some use a controller. The 4.5V rating sounds like they were made for flashlights.If they just use resistors you can put three modules in series and hook them straight up to your 12V system. They'll be a bit dim, but they'll work. If you're on shore power running off the converter it'll be about perfect.

They were and are flashlights. HF had their 6.99 flashlights on a door buster special for 99 cents each and I got 14 of them. So if I can pair them up in series and run off of the 9 volt tap I will be able to power them direct with full power ???

[H.A.]

..

[kludge]

I'm not familiar with solar panels, or what the taps might be, but I'm inclined to agree with HA.

[Shadow Catcher]

OK Bob I just gotta ask why on earth go to the trouble of cobbling together a set of lights which are not particularly bright, and not just buying some LED 12V arrays that will fit into a fixture that are warm white and bright enough to do some good... On Ebay two DC 12V 0.9W Car/Motor Marine truck/boat Cabinet 24 SMD LED G4 Lamp Light Bulb for 5.99 including shipping. These are what I have in CR. This is just an example, and there are lesser arrays for less money. Unless this is purely recreational

[Bogo]

Some people like to tinker and learn something new along the way. I guess I got my tinkering and learning about LEDs done 30 to 40 years ago. I just get a refresher every so often. I'd toying with doing some LED sculptures this winter. Should be interesting to see what happens.