I have a "multi LED-lights" lamp that I'd like to install permanently on the
boat. The little LEDs need 3 volts. I'm not electrician but would like to
try : is there an easy way to convert 12V to 3V ? I don't want to go through
a lighter plug adapter, and all the connections and wires going with. Is
there an "easy something" I can weld on the + wire to reduce the output  ?

Thanks a lot

Bryan

Bryan:

Something easy that you can weld on the + terminal and make it work?

Since your led device draws a constant current, then you can splice a single
resistor in the + wire to make your led light think is is getting 3 volts on
a 12v supply.

If you have a multimeter it is fairly easy to figure out the proper size
resistor.

Using two AA, C or D cells as your 3 volt power source, measure the current
that the leds are drawing. Let's assume it is 100 ma (ma is milliamps, one
thousandth of an amp) or 0.1 amps.

Then you want your resistor to be sized for a voltage drop 9 volts with a
current of 0.1 amp, leaving 3 volts for your leds. Using Ohms law, E=IR,
9=0.1 * R. Solving for R you get R = 9/0.1 or 90 ohms.

Your leds are probably fine with anything near 3 volts, so a resistor
anywhere near 100 ohms would work. But it has to be a so called power
resistor, not the typical 1/4 watt resistors. Since wattage = volts x amps,
the resistor is dissapating 9*.1= .9 watts. So, you need at least a 1 watt
rated resistor.

You probably can find the resistor you need at any Radio Shack.

The above is the easiest way. A slightly more complicated way is a three
terminal voltage regulator. They are also available at Radio Shack and take
a little but not much more wiring to make it work.

David