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johnobuttons · 10-23-2009, 12:47 PM

I've been spending entirely too much time and money building and testing a variety of LED bulbs for interior lights!

Hopefully my experiments will give some of you a better idea of how some of the different LED's perform.

I should say that a major goal of ours was to make the lights as bright or brighter than the original bulbs.

I intend to post each bulb as a separate message in order to make the project managable.

The first bulb I'll document was constructed by combining 4 "Array LED G4 bulbs"

Array Lighting | Array LED G4

The results are shown in the following pictures. I'm including exposure information for the photographs because it will allow us to compare different bulbs.

The first picture shows the combination of 4 array lights mounted on
perforated circuit board from radio shack. The red wires are only standoffs which hold the bulbs away from the diffuser. The 1156 bulb base can be purchased from:
High Powered LEDs

The second picture was taken at:
exposure 1/1500 sec.
aperture F8
"film speed" ISO 80 on my camera.

To the eye, the light is extremely bright and has a nice warm white color.
The camera settings tone it down considerably to allow direct comparisons between bulbs.

The third picture was taken at:
exposure 1/160 sec.
aperture F8
ISO 80

Here the diffuser from Airstream light fixture has been placed over bulb.

The bulb is running at 12V 0.33A or 4W
It replaces the standard 1156 bulb which uses 21W.

In my next message I'll show pictures for the original bulb.

johnobuttons · 10-23-2009, 01:30 PM

Here are pictures of a standard 1156 bulb taken at the same exposure.
The 1156 bulb is at 12.8V, 1.33A or 17W

HowieE · 10-23-2009, 02:27 PM

Your 4 G4 boards. How are they wired series or parallel to the plug? In other words how many boards could you put on one plug if you wanted more or less light from a given fixture?

What is the cost of the boards

DaveFL · 10-23-2009, 03:54 PM

Quote:

Originally Posted by johnobuttons

Here are pictures of a standard 1156 bulb taken at the same exposure.
The 1156 bulb is at 12.8V, 1.33A or 17W

From here it appears to be only one led board needed as it is brighter than the bulb, looks like they need to be pushed back to the reflector to get nice difused light without wire shadows. How do you get the 12v, with prices of led's getting cheap and life so long why not wire direct. Should be able to wire in series with a resistor to get the right voltage.
Thanks,
Dave

vinstream · 10-23-2009, 04:53 PM

Great Post.... Excited to see what else you come up with!

johnobuttons · 10-23-2009, 05:20 PM

Hi Guys I'll answer some of the questions first.

Howie wants to know the price of the G4 array boards. They are about $10 apiece.
They are wired in parallel and direct to the socket, so each board sees 12.8 volts or so. These boards seem to have some active regulation (not just resistors). As the voltage goes up, the current rises to a certain point and then remains constant.

johnobuttons · 10-23-2009, 05:41 PM

This next bulb is probably the most cost effective.
It consists of 76 white leds. The leds come from China and cost about 10 cents each. They emit light over a narrow angle of about 15 degrees.
DealExtreme: $10.51 14000mcd 100Packs White 5Mm Led

The leds are wired with 19 parallel strings of 4 LEDS. In order to play it safe and avoid any possible burning out LEDs I included a simple voltage regulator on the board. I will describe the voltage regulator on next post.

The first picture shows the board.
The second picture shows the board using 1/1500 sec, f8, ISO 80. Because the board is not aimed precisely at the camera the LEC's appear dim.
The third picture is identical to the second picture except the board is aimed more at the camera and more of the LED's appear bright. (remember these LEDs have a narrow 15 degree beams).
The fourth picture shows the board with a diffuser over it. 1/160 sec, f8,
ISO 80.

This makes a really nice reading light over our couch. The only drawback is the cool white color.

HowieE · 10-23-2009, 06:13 PM

Any chance you will post the diagram?

johnobuttons · 10-23-2009, 06:18 PM

One of the challenges of using LED's in an RV is the range of voltages which range from 12V for a nearly discharged battery, to well over 13V for a battery being charged. Overvoltage is a real enemy of LED's because current increases very rapidly with voltage and with heating. The puppies run away with the current going up, making them hot, and so forth.

For some of these LED bulbs I added a voltage or current regulator.
The simplest is a voltage regulator. For efficiency, the LM2941T is the best IC. Here's a link to the datasheet.

http://www.national.com/ds/LM/LM2941.pdf

Initially, I used R1 = 1000 ohms
R2 = 8200 ohms

This works out to an output of 11.5 Volts

Later, I increased R2 to 9200 ohms giving a nominal output of 12.9 Volts.
This voltage is not seen under most conditions, but it does insure that LEDs will never be exposed to more than 12 .9 Volts.

johnobuttons · 10-23-2009, 06:27 PM

It's been bothering me that the picture of the 1156 bulb is SO dim.
There's a reason why my picture isn't quite fair.
In an RV, the 1156 is placed with a white reflector above it.

In my pictures I didn't use a reflector, so the picture of the 1156 is too dim.

bibbs · 10-23-2009, 07:12 PM

I am realy glad you are posting this LED info.
I have wanted to make some of thoes.This will help A lot. Reflectors will help spread the light a little more

johnobuttons · 10-23-2009, 07:18 PM

This light was constructed from a LED "tape" purchased from Deal Extreme in China. A single 2 inch piece of tape contains 3LED's and a resistor.

DealExtreme: $18.55 12V Flexible Cuttable LED Tape (1M 60-LED White)

The tape was cut into 4 inch pieces containing 6 LED's.
These pieces of tape were attached to a piece of flexible plastic about 4" x 4".

The pieces were wired in parallel.
The whole thing takes 4A at 12.8V.

The pictures are as before:
First, finished light "bulb"
Second operating "bulb" 1/1500 sec. F8 ISO 80
Third diffuser 1/160 sec. F8 ISO 80

johnobuttons · 10-23-2009, 09:36 PM

Here's one of the newest HIGH power LED's.
It's called an Endor Star and it's a heavy hitter.

EndorStar - Luxeon Rebel - LED Supply.com

I used the 300 lumen neutral white star (Price about $17)

These things get HOT and need a heat sink and a current regulator.
I'll put the details for the regulator in the next post.
It controls the current limiting it to 400mA in this case.

Here are the pictures:
The first shows the endor star mounted on a 2"x2"x0.5" heatsink.
The second shows the endor star running at 400mA. 1/1500 sec, F8, ISO 80.
The third shows the endor star with diffuser. 1/160 sec, F8, ISO 80.

These things can actually operate up to 1A = 1000mA. However a bigger heat sink would almost certainly be required.

johnobuttons · 10-24-2009, 12:09 AM

Current regulators are the holy grail for LED's. No matter what happens to the temperature or voltage, the current stays the same. There are lots of ways to make a current regulator.

One way is to use the LM2941 chip again.
The circuit is shown in the attachment.
I used a value of 3.3 ohms for R1.

The current produced will be 1275/R1 (milliamps).
So for this resister choice the current is 386 milliamps.

All of the current flowing through the LEDs will flow through R1.
So the power dissipated by R1 is the square of the current x R1 or
about half a watt. I used a 1 watt resistor for R1.

If this is too technical I'll be happy to do the calculation for a different current should you want to soup it up. Remember if you increase the currrent you will probably need a bigger heat sink. This was about the biggest heat sink I could fit in my smaller light fixtures.

toastie · 10-24-2009, 05:33 AM

I'm going with these LED Puck from Vintage Trailer Supplies

johnobuttons · 10-24-2009, 10:27 AM

Here's a commercially made bulb called a Sensibulb (about $40)

Manufacturer of Innovative Marine Electronics | Technologies LLC

It fits beautifully in standard fixtures.
It includes a first-rate current controller driver.
BUT it's not very bright for the money.

The first picture shows bulb off (Zoom is set so whole diffuser will fit in picture)

Second shows 1/1600 sec. F8 ISO80 of lite bulb
Third shows 1/150 sec. F8 ISO 80 of lite bulb with diffuser.
Fourth is a close up of bulb.

johnobuttons · 10-24-2009, 10:36 AM

Here's a bad choice which shows up if you search for LEDs
It has 36 LEDs arranged in a 6x6 square array.
There is no voltage regulator only resistors.

I used these things wired in parallel.
They were my first trial of LED lighting.

As you can see, some of the LEDs in this double unit have already burned out. If you want to use these you will need a voltage regular!!

johnobuttons · 10-24-2009, 12:11 PM

The last thing I wanted to mention was the "Cadillac" of current regulators.
These supplies can take a very wide range of DC voltages and transform them into precisely the right voltage and current for high-power leds.

LED Drivers - Constant Current Drivers - LuxDrive - LED Supply.com

I used the buck puck
3021-D-I-700 BuckPuck - LED Supply.com

along with an external potentiometer allowing a range of currents from 0 to 700 mA.

I hope all this information is useful. Contact me if you need more details.

JohnOButtons

richinny · 10-24-2009, 04:38 PM

john, this is a great thread!

i know a little about these things so i'm dangerous, lol.

i noticed you're using an 1156 lamp, i think the fixtures are in my unit are rated for 1141 lamps. i actually had some Dorcy brand 1141's melt some holes in diffusers. they now add more light from the fixture under the microwave and now they're vented too!

were the 1156 stock in your fixtures?

can you put bypass switches on the resistors to give a low/med/high output?

johnobuttons · 10-25-2009, 10:44 PM

Ricky,
I'm glad you enjoyed the thread. Does a little more knowledge make you a little more dangerous :-) ?

I bought my 1995 Sovereign in 1998 and never considered the possibility that the 1156 bulbs in all the lights might not be stock. The main difference that pops up for the 1141 vs. the 1156 is that the 1141 uses1.44A where the 1156 uses 2.1A. So the 1156 should be brighter and hotter.

It's easy to get low/med/high out of LEDs. My recommendation would be to use either the voltage regulator or the current regulator circuit shown above rather than just resistors. The current regulator works well for a 12V battery and 3 LED's in series. The voltage regulator will work for a 12V battery and 3 or maybe 4 LED's in series. The LM2941T IC costs less than a dollar. It doesn't take much room and will protect the LEDs from high charging voltages. If you use just resistors, your LEDs will vary quite a bit in brightness, being either too bright (and maybe burning out) during charging) or unnecessarily dimmer when the battery is low.