# Replace 12V DC lighting with LED

Discussion in 'Electronic Basics' started by [email protected], Oct 5, 2008.

1. ### Guest

We have a older boat with 12V DC lighting. I would like to rewire the
existing fixtures with current LED components. Can anyone advise me
on the specifics of this project? I know I can get components from
theledlight.com. I need advice on specific components, resistors
etc.

2. ### JamieGuest

You need to know which LED's you plan on using.

Also, LED's are polarized which means they'll only work
in one direction..
Any ways.

Assuming you have some common LED which could be around
1.7 volt of a drop, lets say 25 ma's of drain on the power source.

Taking your 12 volts into consideration, you would need a resistor
to drop the current to the diode.

R = (SourceVoltage-LEDVoltage)/LEDcurrent =
(12-1.7) / 0.025 = 412 Ohms.

Wattage needed for this.
W = (12-1.7) * 0.025 = 0.2575

I think a generic 1/4 R should work for this.
-----
You can place these diodes in series.
assume you use 4 in series 6*1.7 = 10.2 volts required..

You need to keep the required voltage below what your
supply voltage is because the diodes need current flowing
through them..
Now with this, you can use a different value R in series.

R := (12-10.2)/0.025 = 72 ohms..

A note that you should know, the closer you get to the
source voltage using mulitple LEDS in series and lowing
the R value, the more shoft of brightness you're going to
see when the battery voltage starts to drop.

So you may want to use a lower series count of LEDS into
an array cluster.

http://webpages.charter.net/jamie_5"

3. ### whit3rdGuest

It's likely that an RV or boat dealer can get you a variety of LED
or other (fluorescent) fixtures and lamps. Buying is the easy
route here. I've seen auto lamps that are bayonet-mount
dropin replacements for incandescent bulbs.

If you must build, be aware that low-power lighting (like, 1W or
less) can be done with an LED flashlight lamp, available in the
\$5-or-under range, and high power (like, 10W) requires an array
of devices, and probably requires a bit of 'ballast' design
work. Switching power supplies and linear regulators and simple
power-wasting resistors all have their place, you'll need to
study all the alternatives, if only to eliminate them.

The '12V' power is NOT clean and reliable, you will want
all your work to survive brief 50V spikes and various kinds of
brownout and overvoltage.

4. ### Phil AllisonGuest

** So why not just buy them ??

** Most 12 volt LED lighting products come ready to use on 12 volt AC or
DC.

What are you crapping on about ?

...... Phil

5. ### JeffMGuest

It would be smarter to just buy finished goods that fit what exists.
....and you can get finished goods from about a billion other places