Re: TECH: Need an Ohm's law refresher

Dang! Well it just goes to show what a helpless pup I am when it comes to
LED electronics.

Here are the LED's I ordered: http://www.coolerguys.com/840556011262.html
3.0 - 3.3 volts, no other info given.

They suggest a 470 ohm resistor with a 12 volt power supply, but I figured
since I'd run 'em in series I wouldn't need a resistor.

So, how do I figure out the resistor value, and whether or not I can run
them in series or if I need to go parallel with one resistor per LED?

Randy

"Mark Clayton" <spamuser1603@xxxxxxx> wrote in message
news:nrEWf.2$nA3.0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
FYI:

You can't do it without a resistor or other current-limiting
mechanism. Without current limiting, you'll get either
excessive current (if the voltage drop is below the supply
voltage) or no current (if the voltage drop is above the supply voltage.

-Mark
--
http://pinballpal.com/


"Randy P." <pinball@xxxxxxxxxxxxxxxxxx> wrote in message
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"kirb" <kirbseepe@xxxxxxxxx> wrote in message
news:1143671031.543182.124140@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Randy P. wrote:
There is a 12 volt power source (or at least they're 12 volt lamps.)
3mm
LEDs draw 28ma (.028 amp) and require between 2.25 and 2.6 volts -- I'd
opt
for about 2.5 to get them nice and bright.

12V / 2.5V would be 5 LEDs in series with no resistor.

Wow that actually seems like a really simple way to look at this ;-) The
original setup was two ropes, each with 12 lamps -- running in a
sequence where every third lamp was lit at a time. So you'd have 4 lamps
on a side at a time, then the next pair of 4 lamps, then the final pair
of 4 lamps (3 wires with a common return.)

They were wired in parallel, but series LEDs sounds like a great idea. I
just found some white 3mm LEDs that run at 3.0 volts -- so four of them
would be ideal.

Thanks guys!

Randy





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