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post #1 of 2 (permalink) Old 02-08-2007, 01:44 PM Thread Starter
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Location: Austin/St. Paul
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LED how-to

This is a cut and paste from a Motorcycle site I belong to.
But other than the MC specific stuff all the information can be used for cars.
(Voltages etc..)

Below are some tips and formulas needed to
create LED conversions.

Related web sites:
(cheap LEDs, unknown quality, outragous shipping!)

(good prices, good shipping, good service)
Super Bright

For calculations
(thanks Jax..)

First decision, after color, will be power.
1000 MDC (unit of LED "brightness") = 1 Candle power.
Most lamps used on motorcycles vary from 2 to 10 CP..
However you will need to "play" with the number of LEDs
needed to fit your application. The turn signals I made,
though I was replacing a 3 CP (3000MDC) bulb were
made with 6 10KMDC LEDs. (60 CP)
This was partly due to the "angle" of the LEDs and
partly due to the subjective nature of comparison.
(side by side) I also wanted to spread the LEDs out
so that I avoided the single bulb in the middle effect.
See my results at the end...

Next will be the viewable angle.
For applications where you need "bulb" like performance
go with a wide angle:
40 degree

For applications where you want a spot (plate lights)
or are useing several all viewed from a narrow angle
(or are using a colored lens like turn signals)
you can choose narrow:
15 degree:

Once you have these you can find the specs from the
supplier. Ex:

A load resistor is needed. An LED has such low resistance that some load needs to be added to the circuit to prevent effecting a short. This resistor allows the LED to run in its optimum rated level so it lasts as long and provides the power it is rated for. Always use the actual max voltage of your application!

Use this formula in selecting the load resistor.

Plug in your numbers:

Order up your LEDs..
And buy you resistors.
I suggest at least 1/2 watt resistors for constant use lights.
Running lights and such.
1/4 watt will be fine for LEDs seeing intermittant use.
Brakes, turnsignals. However this is a "weak link"
Always over build if you can..

After they arrive test them out.
Wire a resistor to your 12v+
Then touch one lead to the resistor and the other to the 12v-
If the LED does not light switch leads.
One LED lead will be longer than the other.
For the life of me I can never remember which one is what..
Once you have it figured out make a note of it :lol:
For sanity leave the LED on for an hour or so.
Keep an eye on the tempurature of the resistor.
If it apears to be getting hot you will need a higher wattage unit.

To create a replacement part for my LP turn signals I
first removed the bulb holder:

I then traced the lens to a piece of cardboard.
I trimmed it to where it fitinto the housing and
then figured out LED placement.

Crappy photo I know....
The two holes at the far end hold the Lexan in place using the housing screws

Once the templet was complete I laid the template over
a sheet of Lexan, traced the outline and transfered the LED locations.
(I used a center punch to go through the card into the lexan.)
Lexan is available in the glass section of home improvment stores for use
in replacing window panes, it is sold be the inch so for a project like this
is very cheap.

I drilled the holes for the LEDs very close to the actual LED size so that
they needed to be "pressed" in. This allows me to skip the gluing portion
Next press in the LEDs so that the + leads are facing the same way.

To speed things up I twisted each resistor around a drill bit
about the same size as the LED lead.

Solder up the resistors.
One for each LED soldered to the + tail.
Cover with some shrink tubing..
I then carefully folded the leads so that I could solder them up
together. (sorry no pictures of that)
Solder the resistor wires (free ends) together and this is your
plus "wire". Solder all the ends of the LEDs together (use some
extra wire if needed) and this is your ground.
Attach two wires (or solder in the "salvaged" stock wires.)
Use a meter to verify the polarity of the incoming voltage and try
them out!

Add some RTV to keep out the rain..
Put the parts together and go..

My result was this:

Turn signal, nice brightness and fuller light distribution.

I did the same for the rear light.
I traced a shape that would fit inside the shell.
I mounted it using 1/4 -20 screws :lol:
But they fit into two existing holes in the shell and
to make it reversable I didn't want to change the shell.

Running light:

The next generation will spread them out a bit..

Stop light:

Stop light.

In my design I used single resistors for each LED.
This way any one resistor burning out means that only a single
LED goes out not the whole sheebang.. Resistors are pennies a piece.
And don't add much work..

Rapid flashing.
The flasher, or relay that controls the on/off cycle of your turn
signal is controlled by current. Current flowing through the
flasher to the turn signals heats it, once heated enough it turns off the
turn signal, it cools, turning it on etc, etc.
With LEDs the current is so low the flasher goes into "fault"
mode. It flashes twice as fast. This is designed to tell you that a
bulb is out.. (who walks around the car every day to check?)
Nifty for a car annoying (maybe) if you switch to LEDs..
So you need to increase the load:
this gadget does it..

The resistor simulates the light bulbs.

But you can wire one yourself (if you want) with a large 5-6 ohm resistor
and a few diodes.. The big resistors (really big!) can be purchased through
car stereo suppliers (example:Webber Speakers ) at a very nice price..
However $15 ain't bad. Buying the wrong size resistor could result in a fire.
There are also special relays that do not have "fault" mode or are adjustable.
These are more expensive and I have not researched Motorcycle applications.

Note: HS2020 says that for a few $ you can pick up a 2 prong flasher relay form AutoZone. This will work with low resistance applications.
Her is the How to for that:
Some stick with the rapid flashing.. Like pulsing headlights and stop lights they grab attention (maybe) better than standard...

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post #2 of 2 (permalink) Old 02-08-2007, 02:18 PM
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Thanks Peter, Great Post!

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