Cheap source for 0603 PRE WIRED Warm White LED's

[peteski]

Yes on everything DKS said!

[DKS]

There's a good explanation of what an unregulated power supply is and why it behaves the way it does (which is why it's bad for LEDs) here.

Also... this thread may be a good candidate for the DCC/electronics forum.

[GaryHinshaw]

Wow, ok gents!  I know the power pack is variable, but isn't that the point of the resistor?  Or am I still confusing things.  Or are you worried about frying the resistor?  I may not have been clear but my point was to hook up the powerpack leads where the 9v is connected and still run through the resistors.

By the way, one of the LEDs from the set burned very brightly on the 100 ohm resistor, but you are saying that it would have eventually fried?

Not complaining here and I appreciate your patience while my brain catches up.

The teacher in me can't resist adding another explanation to this thread.... sorry if it's overly pedantic.  To a good approximation, all the LED cares about is how much current is going through it (and different LEDs have different current needs).  The question is how to supply that current.  This is where you need to know Ohm's law, which relates current to voltage in simple ("linear") circuits.  If you have a voltage source with voltage V hooked up to a load (resistor, motor, etc.) with resistance R, the current in the circuit will be I = V/R, where I is in amps, V in volts, R in ohms.  If you have two loads in series, with resistances R1 and R2, the resistances add, and the current will be I=V/(R1+R2).  A diode has essentially zero resistance, so when you hook it up in series with a normal resistor, the current is just I=V/R.  So all you really care about for powering your diode is V/R.   

The uncertainties discussed above are 1) what current does your diode want?  2) what fluctuations does your voltage source have? (Note: a 50% change in V produces a 50% change in I, which could be bad.)

-Gary

P.S. Even before I read DKS's comment, I took Ian to task off line for not moving this thread already!   

[peteski]

I was also surprised that it took this long for the thread to be moved. 

[Ian MacMillan]

I am very sick and on medication...I can't be moving threads all day. 

[peteski]

I am very sick and on medication...I can't be moving threads all day. 

Sorry to hear that Ian. I hope you get well soon. My post was more in jest than being a whine. 

[Ian MacMillan]

Sorry to hear that Ian. I hope you get well soon. My post was more in jest than being a whine. 

All I hear is whine!


Found these at the Rochester WalMart! Oh wait...they were red! Off to HD.

Still have use for red though.

[nkalanaga]

I looked at several WalMarts in the western WV/NE Kentucky region today.  None carry these, and one said they aren't available from the warehouse if the stores WANTED to carry them.  Apparently WM doesn't sell the same things everywhere, as there were several times that items mentioned on the Atlas forum weren't sold in this area.

[Lemosteam]

Hi Guys,  I guess that's my fault.  I assumed because it's Wlamart that each store could sell the same product.  Let me know Nick and I'll pick some up for ya.  I did see the same sets branded as Moth-Ra Stewart at Home Depot as DKS mentioned.

[DKS]

Apparently WM doesn't sell the same things everywhere, as there were several times that items mentioned on the Atlas forum weren't sold in this area.

Walmart's stock is definitely regional. They look at buyer preferences, and analyze every sale from every store to decide how much of what to stock where. (They have their own satellite, and beam sales records to the Mother Ship every night.)

[Philip H]

Interestingly they also have a fully built out store at the Mother Ship whose sole purpose is to test product placement in stores to see the relationship between where and how much you buy.  Those end caps always have you are looking for for a reason!

Now back to our regular programming.

[krokodil]

If your are interested in LEDs for lighting up the lower deck on a layout, LED strips are a good option, they come in lengths of three and 16 feet, but can be cut every two inches if needed. they come in 32 or 64 LEDs per foot and are available from warm to daylight. They have flexible backing and are backed with duble stick tape for easy mounting (surface needs to be smooth and non-fibrous). On the internet they are available for $15 - 25 for a 16 foot roll. With close to 1000 LEDs the high density strip uses about 48W  (or 4amps at 12 Volts), I use wall plug in transformers (about $10 each).