Capital Driving Club Discussion Forum

I've go a decorative/accent floor lamp that originally came with ten little halogen bulbs. The controller burned out and I wasn't a big fan of the halogen bulbs anyway--So much heat. Anyway... I've decided to try to rewire it with LED's and right now you can get strings of Christmas lights for cheap. The only problem I can see is that the strings typically come with 50-60 bulbs each. So I'm reaching out to you electrical engineers out there for some tips to make this thing work. Any ideas?

http://www.parts-express.com/pe/showdet ... er=073-072

Cut to length, plus you can add a controller and change to any color you want!

jake

I need to use the existing wiring in the lamp and I am too lazy to want to understand electronics well enough to design this myself. This lamp is wired to handle 10 separate 12 volt halogen lights in 10 separate globes. I need to buy or build a new power supply and need advice on what type/voltage/etc led's to use. Thanks for the link Jake--it looks like that company has the parts I need and at a reasonable price.

okay... if I have all 10 lights wired in parallel with a 9 volt dc power supply-- do I need a resistor for each light or just one for the whole lamp? These are white LEDs that apparently are rated at 3.6 volts. And what resistor do I need?? Help!!

Uhhhh... I dunno if this is right or not. You should get Jared or Scherpf to check it as they both probably are smarter/paid better attention in school than me. Or you could try it and see if it catches on fire.

Find the current of your power supply. 5.4 divided by that number is the value resistor you need (maybe). Stick it in front of everything like I show it in the first representation.

OR. If you want to do one resister for each LED, multiply the resistor value previously found by 10 (maybe).

I can't really read schematics and haven't played with algebra since the mid seventies but if I understand... I should put the resistor on the positive side of the circuit. And since my power supply is a 200ma cell phone charger I need a 27 ohm ? Resistor?? The resistors I am seeing are all in the hundreds or thousands of ohms. But I am learning something today! Just wish I knew exactly what. Thanks Eric. Hope to see you at the Awards Lunch.

Just Googled 27 ohm resistor and they are readily available for under a dollar. Guess I should try it and see.

Resistors are rated by ohms and max wattage. Watts = V * i = 5.4 * .2 = 1.08

So I would get a 27 ohm 2W resistor? Radio shack has a 27 ohm 5w for $1 which you might be able to find local and would probably work. It needs to be in between the power source and the first light.

That's the kind of info I need!!
Thx Eric

Did it work?

ericw wrote:Uhhhh... I dunno if this is right or not. You should get Jared or Scherpf to check it as they both probably are smarter/paid better attention in school than me. Or you could try it and see if it catches on fire.

Find the current of your power supply. 5.4 divided by that number is the value resistor you need (maybe). Stick it in front of everything like I show it in the first representation.

OR. If you want to do one resister for each LED, multiply the resistor value previously found by 10 (maybe).

Kinda late and may not matter (since it may turn out to be close enough to the actual value) but you shouldnt use the current rating of your power supply. That simply indicates the maximum current the supply can provide. Actual current will depend on total resistance.

and if you dont want to deal with resistors and/or math, these circuits are small enough to just use a voltage regulator. $3 at your local RS gets you a 3.6V 1A VR.