I also have joined the LED revolution and started with the mirror turn signal lights. These had two small lamps that were not very bright, I replace the internal assembly with a hand built 12 LED assembly so that 6 LED are pointed to the rear and 6 LED are pointed to the front. Big difference.

Original lamps

LED lamps

LED assy:


All pictures of the LED mirror project can be seen here:
Mirror LED conversion
More later on clearance lights and tail, front LED conversion.

Nice addition. I have turn signals mounted on the side of the Barth near the mirrors that I am thinking of putting in an LED bulb later on.
Jim

quote:

Originally posted by MWrench:
I also have joined the LED revolution and started with the mirror turn signal lights.

A very nice job. Do you have part numbers, prices and where you purchased them from? That board that you have the led's mounted to, is that just a regular wafer board? I know the led's have a larger range for voltage and that the same light could be used on a 12v or 24v system. I've seen the same led used in construction equipment and over the road trucks. Are all of these run in a parallel circuit?

Bill N.Y.

Thanks!

I bought them from a electronics surplus shop here locally, they were about $0.30 each, I will get you the parts numbers later today. I have red and clear LEDs as well.

The board is a perf board that I have used for years to build a lot of electronic stuff on, it has holes on 0.1" grid and is of epoxy construction, easily cut to form most any flat shape. Should be available in any surplus electronics store.

The circuit is a series/parallel with 3 parallel groups of 4 LEDs in series. The dropping (current limiting) resistors are 160 ohm for each of the three groups. I used 2, 82 ohm 1/8 watt resistors in series becuase I didn't have 1/4 watt 150 ohm laying around.

Schematic and calc:

I have been told if you put 4 LEDs in series you don't need a resistor.

Does anyone have any thoughts on this?

Timothy

You must have a current limiting resister because once the diodes have been forward biased, they will draw infinite current, read meltdown!

Each diode will start drawing current (amber diodes) at about 1.6-1.8VDC, the diode is fully saturated at about 2.0VDC, then it will continue to draw increasing current as the voltage applied to it increases, but it will maintain roughly 2.0VDC across it until it fails.

Red diodes have about a 3.4VDC forward bias, etc.

On the little LED single light flashlights, they use a very small watch battery which the battery will have fairly high resistance so no resistor is needed there, but for auto applications or AAA cell batteries and up all require some form of current limiting.

Some of the better tail light assemblies have a solid state current regulator and can be varied so that tail light current is lower then stop light current, this varies the light output correspondingly.

I use three or four LED in series depending on the application and what "drop out voltage" I want the light to operate to. With red LEDs because their normal Vf (voltage across the diode when biased on) is 3.4VDC, that way the light will light down to about 10VDC but will get dim about 10.5VDC.

HTH

quote:

Originally posted by timnlana:
I have been told if you put 4 LEDs in series you don't need a resistor.

Does anyone have any thoughts on this?

Timothy

Oh, Oh, here we go..........I have even put three in series with good result. Four in series is not as bright. A resistor is not really needed, but I like a resistor in series to act as a current limiter if something fails. However, an LM317T used as a current regulator is my fave. LEDs operate best at a specific current. A current regulator keeps the LED at its design optimum while voltage varies. A current regulator also allows the circuit designer to choose between max brightness and service life or somewhere in between. However, this is more of a consideration on interior lights that are used with voltage that can vary from 12.0 to 14.2 volts. An exterior light operates at a voltage range of approx 13.2 to 14.2, depending on the alternator temp and regulator design, so regulation is not quite as important..

HMMMM, how can I say this without sounding, well you know!

You MUST have some form of current limit if the input voltage to a LED string is greater then its total voltage drop!! LEDs work best around 0.030A to 0.060A and they do have a MaxIf (forward current rating)which is less then 1 amp! Exceeding this and you WILL burn up the LED. Once any diode is forward biased, it want to conduct any and all current thru it with little change in its voltage drop, LEDs are no different!

If in the case of the amber LEDs, have 4 in series, the combined forward voltage drop across the entire string is about 8 VDC, LEDs have a soft knee so it will vary a slight amount but will be close to 2VDC per LED. NOW when you apply 12VDC-14VDC across this string, without a current limiting resistor, you are exceeding the voltage drop of 8VDC by 4-6VDC, As the voltage across the LED string does not go up by any significant amount, whatever current that is available thru the wires will be applied to the string of LEDs, that can be many, many amps! There is NO mechanism internally in the LED to limit the current once it has been forward biased!! Tiny wires (around 0.001") connect the lead frame to the LED chip, these will blow in short order!

Examine any LED lamp assenmbly for automotive use and you WILL find current limiting resistors or a regulator of some sort.

It is NOT a correct statement that if you use 3-4 LED in series for a 12VDC-14VDC application, no resister is needed, you will burn up the LEDs

Try it and measure the current thru the string you will see the current goes thru the roof after the LED forward voltage is exceeded if no resistor is in place.

I have no idea of what or how you have tried in the past BUT every LED needs some form of current limiting to work correctly, have a long life, and not blow out in an instant.

Hey Ed...

Looks-like there is definitly an interest here in what you have manufactured for yourself.

Maybe the question should be:

"What would you charge to put a bunch of them-there devices together and sell them to Barthmobile Members???"

...you would be taking my order today, if you were interested in such a venture.

Looks GREAT! ...and probably can't be "found" anywhere else for that particulair "light".

Don't want to put you on the spot if it is too much effort ...just curious if you might be interested.

Thanks Robin!

If enough people were interested, I would do up a PCB, hand wiring is just to laborious. It would be easy to make up a set and mounting inside the existing piece would be a simple matter of removing the mirror and taking two bolts out of the lamp to remove the existing bulb assembly and then bolting the new one in place.

I don't think it would cost much, could even do a "kit" form for those that like to DIY.

I am thinking about the rear tail lights as well because I haven't found any that I like, I would also like to use the stock lense assembly and make something fit inside.

Back to Tim's question, four 3.6 volt LEDs in series can operate very well on 12 volts. Many people do this without a series resistor, as Tim mentioned. All is well if there are no failures. When there is the wrong kind of failure, you lose the whole string. I have also done it with three 3.6 volt LEDs on 12 volts. Pretty bright, but beyond the nominal design limitations. I suspect the loose Chinese production tolerances could explain this. The board was built with sockets to allow for replacement of weaklings. The first week of dry camping culled the herd pretty well, and only the strong survived. And continued to survive.
The experiment was interesting, but I reverted to better design practices and used a series resistor for each string.

Some of my fellow experimenters at work did even worse things. Some with surprising success.

I don't do any of that any more, though. Current regulation is my thing now.

I'm definitely interested..not sure what a PCB is tho..a kit would work for me..thanks

PCB=Printed Circuit Board