LED's from 300-LED reel don't work - -

I did a set of four cars, the Vista Dome took more time that the other three cars in total.   So yes, it will take a little more time.

Hopefully a few simple questions on this circuit

I am working on ordering the items for tis circuit

the .1uf 50V cap I can order in 1% 2% or 10% what should I order

What are others using for the Resistor R1

what are the specs for the Bridge rectifier Radio shack equlivant?

This is to be used for LED light strips for TMCC opperations and DCC (HO scale) passanger cars using the LED Strips

I am no electronics expert but can put together a circut with components that I am told to purcahse and use

the .1uf 50V cap I can order in 1% 2% or 10% what should I order

Dont matter

What are others using for the Resistor R1

depends on how much current you want out and how many LEDs are being powered. You could use an adjustable pot maybe 500 ohm with a minimum fixed resistor also in series to protect the LEDs from over current

what are the specs for the Bridge rectifier Radio shack equlivant?

Most any bridge rectifier will work,RadioShack is expensive.Here is one example

www.radioshack.com/product/ind...p?productId=12673823

WWW.allelectronics.com has them cheaper

www.allelectronics.com/make-a-...DGE-RECTIFIER/1.html

This is to be used for LED light strips for TMCC opperations and DCC (HO scale) passanger cars using the LED Strips

In that case I see no reason to use the regulator,though it will work. A simple bridge rectifier and resistor will protect the LED strips. They are wired in series of 3 so a 300 ohm resistor or more per 3 would protect the LEDs on an 18 volt feed. For further dimming a larger resistor could be used. You could also series wire the strips without a resistor,they would still be bright enough.

I use individual LEDs described in the caboose lighting post here

www.jcstudiosinc.com/BlogCategoryMain?catId=426

Dale H

The cheapest capacitor is the right choice, the precision doesn't matter at all.  I'd use a 1/2 watt resistor for R1, and the value will obviously be 100 ohms or less for lighting a string of these LED's.  I'm guessing the current desired would be in the 20-40 milliamp range for proper brightness, depending on the number of LED's in the car.

Let's select standard values to make them easy to find.

For 20MA, 62 ohms is proper for R1.

For 38MA, 33 ohms is proper for R1.

Using the formula above in the diagram, you can calculate other values.  Truthfully, I just pick a likely resistor in that range and do a trial to see how bright they look.  I then adjust the current based on the results of my empirical test.

For strictly command operation, you might consider using a simple diode in place of the bridge rectifier.  The reasoning here is you don't need the voltage headroom provided by the bridge, and it'll lower the power dissipation of the regulator.  Also, for currents much above about 30ma, I'd consider the LM317T which is the regulator in the TO220 package for higher power handling capability.

Mike...

I just did 11 cars with the drawing and part numbers here.

Parts from digikey and LED's from Amazon. Could not be happier.

Fun project. Don't second guess it. Just do it.

The cost and time are minimal...

Now I'll step down from my soap box....

have LED strips now (4 rolls) other items ordered today

John

 2 questions on the above circuit, a clever use for the regulator. I use LM350 for such uses.

Could you put also a 1000uf condenser across the + and - to eliminate flicker from dirty track?

How about a minimum resistor for R1 for 20 ,40 or 60 ma as needed,then put maybe a 1k pot also in series to dial down brightness as needed? 

Dale H

Dale,

You certainly could put a pot in to vary the current.  For the pot, it would really want to be a much smaller value, say 100 ohms.  Remember, by the time you get out to 100 ohms, you're already at 12.5ma, and add say the fixed 50 ohm fixed resistor and you're down to 8 ma when the pot it all the way to 100 ohms.  1K would turn the lights out totally, that would only be 1.25ma to the LED's.

As far as the cap, I have indeed done that, I put it on the input to the regulator for flicker-free lighting.  Also, add a 22uh choke to the center rail lead for DCS compatibility.

Thank you John

Nice we have you EEs on the Forum to ask questions.

One last thing,I assume the .1 uf NP cap is for spike suppression. If you add the 1000uf polarized capacitor do you still need the NP one?

Dale H

Actually, the .1uf cap is just recommended for the input to three terminal regulators to keep the internal circuit from oscillating.  Many times it can be omitted, it's just easier to always put it there for me. You'll notice on the datasheets, most of the typical applications include the .1uf on the input.

If you have a large cap there, you can leave out the .1uf cap.

The large cap has too much inductance to be of any help if the circuit tends to oscillate so the .1 may be necessary. A ceramic capacitor for the .1 is all thats needed if needed (in addition to the large cap).

Perhaps true Chuck, but I've never seen any issue with tons of circuits similar to this.  I wonder if the design of the more modern regulators has removed the issue, my intelligence on that problem is at least 20 years old.

Yes, I've never had one oscillate, I probably wasted .1uF ceramics over the years.

hey john, didnt you redo some southern lionel crescent cars with LED strips and circuits? something cool to show how you did that setup. 

chris

Yep, those were the first cars I did with LED's, kinda' my "trial" run.  I used the CL2 in those, I think the pictures are in the long thread on passenger car lighting.