Cheap source for 0603 PRE WIRED Warm White LED's

[Lemosteam]

Hello all, I found these at a local Walmart store in the Christmas lighting section (ignore the online price- they are actually $4.96): http://www.walmart.com/ip/Seasons-4-Commercial-18-ct.-Warm-White-Invisalite-3-AA-LED-with-Green-Wire-and-4-in.-Spacing-Case-of-24/17632816.  The set runs on 3 AAA (4.5v) with a small switch pack. 

Walmart photo of the warm white version below, I think there was a multicolor version too:


Only other source I could find for something similar was on Ebay for $4 For a single wired LED EACH, but I'm sure others know of different sources at various prices.

There are 18 equally spaced warm white 0603's on two 0.013" diameter magnet wires about 4" apart, and they are "bulbed" with some form of clear polymer.  I thought I could melt it off at first but it would not budge (it looks like clear hot glue).  So I ground it off just shy of the LED with my dremel.  Here is a before and after shot together, er, OK after and before  :

 

Would make a great indoor lighting set for a factory, or once cut individually, 18 headlights or backup lights.  I was hoping they were 0402's but it was wishful thinking.  Got to pick up more before they are gone for the season!

[peteski]

Nice find John!  Thanks for sharing.

The "hot glue" is most likely epoxy resin (pretty much impossible to dissolve).

[Ian MacMillan]

The retail pic of them lit up looks more "white" than "warm white" to me. Can you post a photo of yours lit?

[Lemosteam]

You are welcoome peteski.

Ian, I will try to take a pic tonight.  I need to buy another set as I fried the remaining 14 while trying to test their voltage, as peteski knows, I am electronically challenged. 

The remaining four are being used as a light source for a tube I am using to look for light leaks in my daughter's clarinet, the original reason I bought them.  I can take a picture of that, but they are encased in a clear vinyl tube and that may affect their color.  Maybe I'll try to put one in a GHQ headlight housing.

[mmagliaro]

You are welcoome peteski.

Ian, I will try to take a pic tonight.  I need to buy another set as I fried the remaining 14 while trying to test their voltage, as peteski knows, I am electronically challenged. 

The remaining four are being used as a light source for a tube I am using to look for light leaks in my daughter's clarinet, the original reason I bought them.  I can take a picture of that, but they are encased in a clear vinyl tube and that may affect their color.  Maybe I'll try to put one in a GHQ headlight housing.

This may be from "Capt. Obvious", but you are testing these with some sort of resistor in series, right?  It's almost impossible
to not blow them up, even if you keep the voltage very low, without a resistor to limit the current.  Start with a 2k ohm if you
have no idea what these are, and work your way down from there.   And stay below 5v no matter what.  Assuming the
cathode/anode are not marked in any way, you'll have to try them with polarity in each direction.

[Lemosteam]

Max, nah, I just ran them with throttle leads right from my Tech II.  Duh.     I'm not sure if I even have an assortment of resistors that I could use.

Captain Obvious has much more brains than I WRT electronics.     I just can't seem to get the concept.    

When wired in series would a single resistor act for all of the LEDs in the strand?  Would I need a resistor between each LED?  If I open up the battery pack for the set, would the resisitor be easily identifiable, if there is one there?  I suppose I could test the output from the battery pack in terms of ohm?  I'm clueless where to set my multimeter except when measuring voltage.

I can test the next set easily enough if I know what to do.

[Packer]

Neat. Are the wires actually soldered or just gloobed on? If they are soldered I have an idea to take off the epoxy resin, Don't know if it'll damage anything else though.

Aren't most LEDs 3 volts? When I get LEDs with unknown values, I test them with resistors that will work for 1.5v bulbs off of 12 volts.

When wired in series would a single resistor act for all of the LEDs in the strand?  Would I need a resistor between each LED?  If I open up the battery pack for the set, would the resisitor be easily identifiable, if there is one there?  I suppose I could test the output from the battery pack in terms of ohm?  I'm clueless where to set my multimeter except when measuring voltage.

I'm not all that great with electronics either, but given the thing (seriously, what is it supposed to be?) has 18 SMDs, I doubt they are in series (4.5/18=.25 volts, is kinda low for an LED IMO). They are probably in parallel, assuming the SMD are held up by wires of some sort.

[mmagliaro]

Max, nah, I just ran them with throttle leads right from my Tech II.  Duh.     I'm not sure if I even have an assortment of resistors that I could use.

Captain Obvious has much more brains than I WRT electronics.     I just can't seem to get the concept.    

When wired in series would a single resistor act for all of the LEDs in the strand?  Would I need a resistor between each LED?  If I open up the battery pack for the set, would the resisitor be easily identifiable, if there is one there?  I suppose I could test the output from the battery pack in terms of ohm?  I'm clueless where to set my multimeter except when measuring voltage.

I can test the next set easily enough if I know what to do.

Well, then, I'm glad I spoke up!  LOL!
Seriously, I have no idea how those Christmas LED sets are wired.    I would guess there is some limiting resistor in
the battery pack, but that would be of no use, because you want to light up one at a time.
If they are all wired in series, or in parallel, either way, some kind of current limiting has to be in there, but its value
will mean nothing to what you need to light up a single LED.

Do this.  Go get yourself an assortment of resistors at Radio Shack in values from, say, 100 ohm up to 3300 ohm.  (You could also
buy a 1/4 watt assortment bulk pack they sell that has a lot of useful values in it.  That's probably cheaper).

My guess is that with a little 0603, the current will be very low, so start on the high side with the resistor.  I would start at 2.2k.
You put it in series with the LED, hook it up to, say, 3v, try it in both polarities.  If you get nothing, try a 1500 ohm, and so on.

If it works, but it gets really bright as you turn up the voltage, and you're not even close to 12v yet, then you need a HIGHER
resistance, so go to 2.7k.

Work your way up or down in resistance.   Again, I have no idea what the current rating is on those things, but  I have plenty of little warm whites that I've been using in my engines that work well with a 1.8k ohm dropping resistor.  And those aren't surface mount,
so yours will probably need a HIGHER resistance to protect them at a full 12v.

Since they are unmarked, of course, you'll have to experiment a little and probably fry a couple before you find an ideal value
that gives you plenty of brightness and doesn't burn them out after extended periods at 12v.

[Dave Schneider]

I am not an EE, but I did take electronics in shop class (30 years ago). 
How about buying a variable resistor (potentiometer?), setting it at the high side and then dialing it down an observing the "brightness". Find the value that works well and then measure the selected resistance. The plus side is that you don't have to read the color code on the resistors, which I have a hard time seeing at my age!

Best wishes, Dave

[Lemosteam]

All, sorry for the crude representation but they are wired like this.  One side of the equals sign is positive and the other negative.   The strands of magnet wire are parallel and the SMD LED is soldered on at 4" intervals:

O=========O==========O==========O===========BATTERY PACK>> 3 AA bats.   

This would mean they are parallel?

There is switch off the circuit board inside that has ON/BLINK/VARIABLE

[victor miranda]

18 leds

4.5v implies they are in parallel.

small sizes like those are often quite bright at 5 ma
and can survive at 20ma.

18 times 5 ma is 90 ma....
18 times 20 ma is 360 ma ...

I read some where that alkaline AA (bigger than AAA)
can only source about one amp I can imagine that a AAA
battery can only do about a half amp

so the string is safe without a resistor...
I truly can't imagine the maker
would not add a reverse blocking diode.
A small resistor is very likely, just to limit the current a bit

why not mark one side with a dot of white paint
and then cut them off the string.
scratch the paint off and use a multimeter to get polarity.

18 little lamps is nice.

[victor miranda]

All, sorry for the crude representation but they are wired like this.  One side of the equals sign is positive and the other negative.   The strands of magnet wire are parallel and the SMD LED is soldered on at 4" intervals:

O=========O==========O==========O===========BATTERY PACK>> 3 AA bats.   

This would mean they are parallel?

There is switch off the circuit board inside that has ON/BLINK/VARIABLE

yes parallel.

[Lemosteam]

Just stopped  by walmart for a second set and what to my wondering eyes should appear, but a larger set with 36 LEDs for $6.96.  Sorry no rhyme.

Just before the set of 14 fried, I think I was at about 40% throttle.

Edit: Also confirmed that there is a multi color set, but the clear blobs are now orange, red and green.  Not sure if there are white LEDs inside the blobs or respective color ones.  There is a red set with clear blobs though...

[peteski]

John,
LEDs aren't all that complicated or difficult to understand but one has to change their way of thinking in how to power them up compared to incandescent bulbs.

A light bulb can be considered a pretty much linear device when it comes to voltage and current.  If a bulb rated at 3V is powered with a voltage 10% above its rated voltage (or 3.3V), it will consume roughly 10% more current (because it is a linear device), it will glow a bit brighter and its life will be reduced (but it will still last many hours before burning out).  Because they are linear, they are rated by their voltage and since they can withstand slight voltage fluctuations, then can be hooked up directly to a voltage source (power supply).

LEDs are non-linear semiconductor devices (diodes).  They are rated by current, not voltage.  Well, the Forward Voltage specifications are also provided but that is mainly used in calculating proper power supply for them which will supply them with the appropriate current.  Their Forward Voltage will also be different depending on the chemistry of the LED (which also controls the color of emitted light).


If you have a white LED which is rated for 10mA of current (and a maximum of 20mA) and the typical Forward Voltage at that current is specified as 3V. If you have an accurate power supply that can produce exactly 3V then you can hook the LED directly to it and the LED will glow at 10 mA and will last for thousands of hours.

But unlike a light bulb, if you were to increase the power supply's voltage by 10% to 3.3V, the current passing through the LED could increase by much more than 10%  That is the non-linear operation which makes it different from the light bulb. At 3.3V the LED might be conducting 50 or even a 100mA (which means it far exceeded its rated current ind the smoke will come out very quickly)!

In the ideal situation, each LED (or a string of series-connected LEDs) should be powered by a constant-current power supply adjusted to supply the current needed for the LEDs to glow at their rated (or below the rated) current.  That would guarantee that the LED will not be exposed to over-current.

But in real world examples (especially in the hobby world), constant current power supplies aren't used.  But adding a simple resistor in series with the LED creates kind of a buffer which limits the current going to the LED evne when the power supply voltage fluctuates. But this also means that the supply voltage needs to be at least few volts above the forward voltage of the LED.  That is usually not a problem since models operate at voltages more than 3 Volts.

Again, the best practice is to have a separate series-connected resistor for each LED (or each circuit of series-connected LEDs).  But that also doesn't always happen.

Sometimes (as is the case with these holiday lights), there are bunch of LEDs in parallel.  I suspect that the battery box does have some sort of current limiting device in it (could be a simple resistor or maybe a basic transistorized constant current supply).  IN theory, if all the LEDs are identical, the total current suppled to the string of LEDs will be equally divided among them. But in the real world, some LEDs will consume a bit more current than others.  That is because there are slight variations in the LED manufacturing process. But this is a four dollar string of lights. It is a throwaway item, not designed to last for decades.

There are also LEDs which have resistors or other current limiting devices built-in inside their housing. Who knows, these LEDs might have such type of device inside them. If that is the case then the string will have a voltage higher than 3V (which is a typical forward voltage for white LEDs).  If that is the case, then the LEDs properly powered up and should last a long time.

This is a very basic explanation of how LEDs work - I hope that I shed some light onto your understanding of LEDs. 

As far as removing epoxy goes, if there is a chemical which removes epoxy, it will most likely also remove the LED lens (as that is usually epoxy too).

[peteski]

John,
another warning: using a throttle (especially an older one) is not recommended. The output voltage is very poorly regulated and it usually depends on a load placed on the output (like a locomotive's motor). WIthotu the load, even at low throttle settings, the output voltage will be 12V or more. That is an instant death for most LEDs!

I have a very simple LED tester I've been using for dacades. I took a dead 9V battery apart and removed its top (with the contacts). I stuck that on a new 9V battery. Then I soldered a 1000 ohm resistor 1/4W to one terminal then attached wire leads to the other terminal and to the other end of the resistor. This creates a nifty tester for all LEDs which has a 1000 ohms in series with the 9V battery.  You will never burn out any LEDs using it.