300 LED Rope Light Question

That's why I bought two

All kidding aside, the positive output of the bridge is connected to the longer lead, opposite the side marked with an "-".

As for the LM317, I'm reading the pins left to right, positive-from-bridge to #1, resistor to #2, and #3 is tied to the end of the resistor before heading to the output connector.

--PCJ

Facing the front of the regulator, from left to right, it's as follows.

Left: Adjustment terminal

Center: Output terminal

Right: Input terminal

It sounds like you have it backwards, the input from the bridge should go into the input terminal.  Here's the picture from the data sheet, this is looking at the front of the part.

"Front" means the heatsink fin is facing away from you like in my photo of the breadboard above, correct?

---PCJ

I picked up a long roll of this light strip while on a visit to the local electrical shop.

I have 18.7 volts AC on the rails for DCS/TMCC constant voltage.

Running through a full wave bridge rectifier I come out at 18 volts DC.

If I cut the light strips to wire in series will this not give me 9 volts DC per light strip??

For passenger car lighting??

At 9 volts they have a nice glow not to bright??.

Correct, if you can read the silk-screen on the part, that's the front.

You can do that, I prefer to control the current with a constant current source.  If you use the LM117, you can adjust the brightness, a nice feature.  For me, 9 volts DC on the strip was way too bright!

If you're happy with that, it's fine.

Now modified at the LM317 as follows:


---PCJ

Time to plug it in and see if you get any smoke!

Remember, you need a load on it to actually see it regulate the current.  Try a resistor in the 100-500 ohm range to start, measure the voltage across it, and we can calculate the current to see if it's working properly.

All I need is a decent multimeter. Got a recommendation

Should I be able to light up a carbody's worth of LED strip (or the whole string?) with this as-is and determine from the brightness whether any further adjustments are needed?

---PCJ

DECENT multimeters will cost a lot. I have one from Radio Shack bought about 6 years ago. cost me $90. Worth every penny. Radio shack sells a few models from cheap to  expensive. the one that they have now that's comparable to mine costs $95.

you can get cheaper ones, but the quality and accuracy suffers. 

HTH----

For casual use, you can do fine with a Harbor Freight model for less than $20.  you can pay hundreds of dollars for one, but for most of the uses around model trains, it's not necessary to spend that kind of money.

The whole strip will take several amps, so you probably won't be able to light all of those.  Cut out what you're putting in one car and light those.

Well, it certainly works

(Bonus: the cap didn't go PAF! when I hooked it to the unfiltered Z-brick)

By the way, that's on the minimum output of a Z-1000 with the controller attached. If I crank it up, it gets a little brighter, but even as is, (and as predicted, I might add) it's a bit on the "needs welding goggles" side of the brightness scale. Now, let's bring on the adjustments  

I ended up using 15 LED's on the strip in a group of cars, and I ran them all on a 20ma CL-2 constant current regulator.  They were plenty bright for me.

Any suggestions on how to dim the string a little? (I'm guessing it's the (value of) resistor bridged across the LM317) It looks like 12-15 lights will suffice for a Superliner.

---PCJ

I have used the LED light strips in my Williams 16 & 18 inch cars.  I put 18 leds in the 16 " cars & 24 Leds in the 18 " cars, using the 20ma Cl-2 current regulator . See pictures

The resistor across the LM317 determines the total current output on the constant current configuration.  There is a simple formula for the resistor value to vary the current, see below.

what is the difference between a :  lm317   lm317l  317t  and  317lz ?    jrg? 

The LM317L(anything) is a 100ma maximum current part in a TO-92 package, looks like a plastic transistor.

The LM317T is a TO-220 package looks like one of the large power driver Triac or FET packages on the motor driver boards.  These are rated at 1A or 1.5A, depending on who makes it.

The LM317K is a TO-3 round power package with two ears for screws, it handles 3A.

A plain LM317 doesn't really exist, they normally have a package type specified.  Here's the sheet with many of the types.

thanks grj.   that clarifies it to me.  i wasnt sure if the   h  k  l  s  t  designator  was case type  or power factor..   [maybe im dyslexsic as i orig meant grj].   i only use   

to-220 type.

I noticed that the L package wasn't on that page, but apparently you got the idea I was trying to convey.

One other wrinkle:

I bought some other resistors to experiment. Right now I have a 330 ohm ( 1/2 watt) resistor on the "ADJ" lead of the LM317T. As before I have bright lighting at the minimum output of the Z-1000 (somewhat like really strong fluorescent bulbs). It can run like this for more than an hour and no component is more than slightly warm, if at all. If I turn the Z1000 controller up, the string gets significantly brighter, up to about 1/4 of the controller's travel. At that point the LED string stops getting brighter, but the LED's start getting really warm in a matter of seconds. This...doesn't seem quite right.

---PCJ

Are you wiring the 317T in the constant current configuration as I posted previously?  If so, a 330 ohm resistor there should barely light the LED's at all!  That would be putting out about 4ma.

I think there's a wiring issue somewhere here, the LED brightness should not be varying, and the LED's should CERTAINLY not be getting hot!

Railride,

Move the wire as shown below.  In the LM317 constant-current configuration, the output to the LEDs connects to the leftmost ADJ pin...not to the middle OUT pin as one would logically think.

If each strip-of-3 is electrically identical, then the voltage will divide equally to 9V each. In reality, they vary slightly so you might get 9.1V on one and 8.9V on another.  On another pair they might be 9.0V and 9.0V.  

Refer to the plot in my 3/28 post which shows LED current vs. applied voltage. LED brightness as measured in, say, lumens is exactly proportional to LED current. Half the current is half the light output. As shown for one measured strip-of-3, at 9VDC the strip current was 2.5mA. I think this might be a bit on the low side but you need to decide that. 

Note how the current does not vary much between 9.1V and 8.9V. So you won't be able to perceive the strip-to-strip imbalance in the above example.

I used a 5-foot and a 6-foot section of the 300-LED reel to illuminate the subway shopping center I added recently. I power them with 12CDV.

The 5-foot section is behind the store fronts and shines through the cut-outs in the foam-core board I used for the store fronts. The store fronts themselves are Google images printed on regular paper and glued to the foam-core board.

The 6-foot section is in front and over the stores and illuminates the walkway and the shoppers. The problem was that the outer 6-foot section was so bright that it overwhelmed the shine-through store front effect. To make these outer LED's dimmer, I added four 1N4002 diodes (had them already) in series with the power lead to the 6-foot section, and this did the trick. (BTW, I tried 1, 2, 3 4, and 5 diodes and 4 worked best.)

Results (click image to enlarge):

Alex

Here's the choke I'm using.

All Electronics CC-15 15uh Choke

Speaking of All Electronics, I was looking at their new catalog and do I have this right?  $155 for a strip of 300 warm-whites?   

Wow, that is crazy pricing

Yes that is insane pricing! $1.55 for 1 3" 3 led segment! I just bought another reel of 100 segments(300 led) from Ebay for 16$. It's very odd that AllElectronics is charging so much for the LED strips.  

This just reenforces the requirement that you check around for the best deal on stuff.  All Electronics has good deals on some things, obviously NOT on those LED strips!

I'm also into g gauge and have some very power hungry passenger trains..like 20+ amps per train. Each car has 14 incandescent bulbs in it and takes 1 amp to power them.

Switching over to these Led's look like the way to go.

What I do is buy these buck converters on ebay and that way I can adjust the voltage out..that way it won't matter if I'm running on a 20 volt display layout or my at home 24-30 volt layout.

 And I'm lazy when it comes to building circuits as I like things modular. I'll start with some inductors as I'm a DCS guy, bridge rectifier with some 4700uF caps across the outputs to control flicker straight into a buck converter then out to the lights..simple quick and easy! Forgot that I'll install some poly-fuses incase something shorts out internally.

Here's the Buck's on ebay..maybe folks on here could use them as they only measure about 1-1/2" square?

U:US:1123">http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170792570361&ssPageName=ADME:LU:US:1123

Price is right, and it should be easy.  Of course, a three terminal regulator would do the same job for less than a buck, and there's be no more wiring.  Look at the LM7812 in the TO220 package.

so, ok,  for a string of 12 led's,   which would be better,  one  lm317t  or one  cl2n3 ?   can a cl2n3  handle 12 led's ?   need a heat sink on either ?   

The LM317T would probably be my choice.  For 12 LED's, the maximum current would be 80ma at full current for the three LED groups on a strip, no HS required for the LM317T.  The CL2N3 only handles 20ma, so you'd have to parallel them for more current.  They also have a much more limited power dissipation in the TO-92 package, so at a high input voltage you may need a clip-on HS.  It's all about the voltage drop across the CL2 and what current is being supplied.

Future doesn't seem to have much in the way of suitable RF chokes.

Ah well, I've ordered from AE before (back before on-line shopping )

---PCJ

In your LM317T configuration, the voltage across the resistor is 1.25V.  Since Power = V x V / R, the power for a 330 ohm resistor is only 0.005 Watts.  The SMT resistor suggested earlier has a rating of 0.125 Watts.  You don't need a 1 Watt resistor there.  Also, the resistor is a 0805 type which is 0.08" x 0.05 inches.  I suggest 0805 because the leads between the LM317T are exactly 0.1".  So as the photo shows, the 0.08" length of an 0805 resistor makes for a tidy assembly job.

If the inductor is the only thing you're ordering from All, then consider this 17 cent inductor from DigiKey.  If you do eBay, I recall another thread on an LED conversion asking about inductor specs and he ended up getting them for IIRC 5 or 10 cents each in small quantity (free shipping but delay from Asia).

If you plan to do more electronics tinkering, considering the $9 shipping charge, Future has some nice pricing on semiconductors if you can navigate their site.  For example, the 1N400x diodes for 2 cents in small quantity. Or the 555 timer chip for 15 cents in small quantity.  I'd say these are in the top few parts that come up this forum.