LEDs For Downtown Buildings

OK, here's what I've drawn so far:



Each building has LEDs (1 to 3 depending on the number of stories in each building) wired in parallel and each building is then wired to the next building in parallel.

Again, the LEDS came wired in parallel on the Christmas light string so I would prefer to keep them that way.

The LED "Wizard" I used didn't allow for this "parallel/parallel" design, instead it came up with a parallel/series design of parallel banks of LEDS wired in series within each bank.

It also determined the values for resistors based on this parallel/series design. I'm not sure if I should use what was determined, because I'm thinking that 1 resistor may work for this large parallel circuit. I've shown the various values for the resistors for each building:

single LED - 470 ohm 1/2 watt

double LEDs - 220 ohm 1 watt

triple LEDs - 150 ohm 1 watt

Should I:

1) calculate the values for the resistors using the values determined by the wizard
2) determine them for each building LED bank
or
3) determine the value for a single resistor for the entire circuit.

My electronic training was so long ago that I've forgotten most if not all of it.

Should I keep the buildings wired in parallel to one another or should I wire each building in series with the power source?

Bob what is your power supply? I'm curious as I have to start scheming up an LED light circuit as well for the buildings I will have.

If you wanted to wire the houses in series, you would need to have the same number of LEDs in each house/building. You don't.

I didn't see your supply voltage.

You are using one resistor to limit the current to multiple LEDs. If the LEDs are very similar, that can work. If the original lighting string was all parallel, it is worth a try. You might also be able to use just one resistor for everything, but the power in that resistor might be fairly high.

I was going to use a wall wart rated at 12vdc and 300 Ma output, IF this circuit will allow it.

All LEDs are white, 3mm. I used 3.3 for the forward voltage and 20 mA for the forward current.

The wall wart is a variable type, going from 3, 4.5, 6, 7.5, 9.0, and 12 vdc using a slide switch.

One resistor would be the easy way out. Would a single 470 ohm 1/2 watt resistor work? The battery box that the LEDs came attached to has a single resistor inside, but I can't make out the value.

The wall wart may not handle the amperage, but I'm not sure how to calculate the value in the circuit I drew.

The total should be 20 mA times the number of LEDs.

^ Dale, the power supply that Bob is proposing to use; does that mean it could supply a maximum of 15 leds? 300mA divided my 20mA per led?


http://www.ebay.ca/itm/12-Volt...&hash=item35b5163b6b

What do you think of this power supply? Is that over-kill, too expensive etc... ?

That switcher supply will work, but it is probably overkill.

I would recommend trying the LEDs at 20 mA first. The ones I am using for illuminating passenger cars are VERY bright at 20 mA.

^ Dale, what do you use for power supply to your LED circuits?

I scrounged around in the back and found a 12vdc transformer for a desktop PC speaker set. Basically junk so I cut the (speaker) plug off, spliced it onto a couple leds I have wired up and it works perfectly (of course).

These things are a dime-a-dozen at the 'Repeat Botique'. I'm going down there when the store is open and see if they might have a bunch of these. I can likely pick them up for next to nothing there.

I believe with just a few of these I could power all of the building lighting on my small layout.

Thanks Dale!

I'm going ahead with the wiring, about the worst thing that can happen is that it doesn't work (concerned about the amperage output of the wall wart), but I have other wall warts that have higher ratings. I also have a couple of AC wall warts, so I'd need a rectifier to use them.

Bob, I suggest using 15 ma or even 12 ma instead of 20 ma. The light output will be reduced some, but there will still be sufficent brightness. If the variable supply has 300 ma or more of output, i'd use that one set at 6 or 7.5V. This would allow you to use 1/4 watt resistors-- you would have to recalculate the resistor values of course---

quote:

If the variable supply has 300 ma or more of output, i'd use that one set at 6 or 7.5V.

LOL! Shows how "Tunnel-Vision" comes into play...I had forgotten all about being able to vary the voltage

What I'll do is wire the circuit starting with the wart set at 6 vdc and go from there.

Bob,

A word of caution to you and all the folks out there wanting to use one resistor for an entire string of LED's.If you remember that coal tower I showed you?
Well it has 17 LED's in it and they were very difficult to wire in.

I originally figured the wrong value resistor and with the flip of a switch lost all the LED's . Now I use one LED and one resistor and because I'm always dealing with 12 volts I know I can buy just one value resistor and it'll be fine for everything I have.3 wouldn't be so bad but don't put all your eggs in one basket.

David

I am putting LEDs inside passenger cars. I use the tape strips of LEDs driven by a fullwave bridge rectifier and the CL-2 constant current integrated circuit. I am running multiple groups of 3 series LEDs in parallel, with a total of 20 mA split among the parallel groups. A car has an 18" strip of LEDs consisting of 9 paralllel groups of 3 series LEDs each. That means that each LED is running with 20/9 mA, just a bit over 2 mA/LED.

I utilized some common white copier paper to make a white floor in the cars, rather than the painted black frame with black wires that soaked up the light from the LEDs like a sponge.

If I ran these LEDs at 20 mA each, the cars would be way too bright!

The tape strips are great - not very expensive and very convenient to wire and attach. (The first batch that I bought from Mouser Electronics was much more expensive that an online seller.)

I wired my cars up the same way Dale, and I also discovered that for 15 LED's on a strip, 20MA was plenty bright. I had tinfoil on the car floor, but maybe the white would yield a softer light, I'll have to try that. I bought a 5 meter reel of the warm white ones for $15 on eBay.

David,

I plan on putting a resistor in at each building. If one of them goes out that's not a big deal to fix.

The LED's and resistors should outlive you.

My bro' designs electronics satellite communications equipment; unfortunately he lives 2500 miles away, or I could get his technical expertise on my layout.
Anyway, I asked him about a 12v power supply for LEDs and his recommendation is to use an old PC power supply.

So anybody ever use an old PC power supply for this application?

I found this video on YouTube. It's awesome if you are interested in this.

http://www.youtube.com/watch?v...h_Uw&feature=related

Demo,

You got me thinking , I may have used one on my garage layout but I can't recall now. I have 2 I took out of old computers, one of them I cut a hole in the case and mounted an On/Off switch in it so I wouldn't have to unplug it or use a power strip.

Seems like it has +12, -12, +5, and -5 vdc outputs. Time to dig it out of the garage!

Actually, you can light a host of LED's from an old wall-wart power supply, no need for a PC power supply! That's an overkill unless you're lighting thousands of LED's!

I have a box of old wall-warts that I toss any from dead appliances and the like. I looked, and there are several that have 12 volt 1.5A outputs. If you series string several LED's in individual buildings, you could power several hundred LED's from that power supply.

Figure each white LED at a 3V operating voltage, you can have up to three of them in series with a current limiting resistor running on 12V at 20ma. Taken to the max, that 1.5V power supply will run up to 225 LED's. Even if you run each single LED with a resistor, you can run 75 LED's from that wall-wart.

Do you really want a PC power supply with the noisy fan and it's power consumption running to light a few LED's? Remember also, that the PC power supply has to have a minimum load to run at all, so typically that will require some load resistors or incandescent lamps. LED's don't present the proper load to kick start the PC power supply.

I wouldn't go out and buy a PC power supply for this use, but if you have one on hand and it is free, go for it! Some PC supplies require that at least some minimum current is drawn from the output before they will operate properly.

I also strip out dead PC supplies and use those nice metal enclosures for other projects. For example, I used one enclosure to hold my custom-wound toroid transformer that I use to power my switches and accessories.

Don't know weather anybody thought about this or not but I just happened to look under my work bench to see what size wall warts I had and I saw one of my trickle chargers.I've got several of the Battery Tender brand but this one is a single outlet made by Schumacher .It's a 3 amp charger with a selector for 6 and 12 volts.

I know I didn't pay much for it and at 3 amps it'd be about all you need for a good while and trickle chargers are continuous duty made to be plugged in and forgotten.

You can also buy additional ends for them so you can wire a female plug on your light output for your layout.If you need the charger just unplug it and plug it up to your lawnmower LOL

David

quote:

Originally posted by DPC:
Don't know weather anybody thought about this or not ...

Like I said, old wall-warts are great for LED lighting.

If you are using a battery charger, or even a wall wart for that matter, check the actual terminal voltage with a load similar to what you expect to have. Unloaded voltages can be much higher, and battery chargers typically charge at about 14.4V.

quote:

Originally posted by Dale Manquen:
If you are using a battery charger, or even a wall wart for that matter, check the actual terminal voltage with a load similar to what you expect to have. Unloaded voltages can be much higher, and battery chargers typically charge at about 14.4V.

Dale's right,

I'm sure most of you know this but for those who just don't think.There is more than one reason you DO NOT put an engine on the track with the throttle turned up to 18 volts or especially using a brick with no other engine or load present aside from the obvious which would be that you might short something out.

Transformers with no load put out higher voltages so if you were to set your engine on the track with your brick at a no load voltage of 24 volts say bye bye to your electronics.

The nice thing I thought about the Schumacher was that it had a selectable 6 or 12 volts so even though the charging output was 14.4V @ 12 volts it'd be about 7 or 8 V with 6 volts selected so using a 3.5 volt LED with a 750 ohm 1/4 watt resistor it would still be plenty bright.

David

If you are going to use the 6V setting, do something to physically disable the switch so that it can't accidentally be bumped into the 12V position! I speak from experience....

One thing I do not think is mentioned here is if your power supply is pulsed current. Even if a Walwart is DC it may be pulsed current. In that case you should multiply AC input by 1.41 to calculated resistor size. Ditto if you use a toy train transformer with a bridge rectifier.

Pulsed current is explained here as it relates to LED wiring.

http://led.linear1.org/how-do-...alternating-current/

Dale H

quote:

Originally posted by Demo:
So anybody ever use an old PC power supply for this application?

JohnBoy describes such a project in the JC archive.

If you are considering that 5000 mA 12V supply for $40 or so, it appears ebay also has 1000 to 2000 mA wall-wart style regulated supplies for under $5 shipped albeit you'll wait to get them from Asia.

But whether PC supply or wall-wart, if starting from scratch, consider what others are suggesting about using groups of 3 LEDs in series with a 12V supply. The 12V lighting strips gunrunnerjohn mentions are attractively priced and he posted great photos on this passenger car lighting thread. When using the 12V LED lighting strips, you don't have to fuss with resistors since each strip-of-3-LEDs already includes the correct resistor for 12V operation. We can discuss ways to dim a strip if needed or because they run so cool (compared to incandescents) you can simply mask them.

Bob's LEDs are pre-wired in parallel so his situation is a bit different. So Bob, while I appreciate re-purposing a 12V supply, you might happen upon a regulated 5V wall-wart for a few bucks. That is, with a 12V supply powering 3V parallel LEDs via resistors, some 75% of the power goes into resistor heat. 5V supplies may be "disguised" as USB power adapters (which plug into wall AC and put out regulated 5V); I see some for as little as $1 shipped on eBay which is somewhat hard to grasp!

I would say that multiplying by 1.4 would only be appropriate for a rectifier when it is followed by a large capacitor. The average (DC) value of a fullwave rectified sinewave is only about 90% of the RMS value, and that isn't accounting for the diode voltage drops that will make it even smaller.

Many of the 5V wall-warts available are regulated, so if you want a simple solution, those do the trick just fine for single LED's with a current limiting resistor. I have a ton of those from stuff like Ethernet switches and routers that have passed on to electronics heaven.

I love the DIY project. When my brother told me to use an old PC power supply, and then I watched those Youtube videos and saw how easy it was... well I want to go that route. Then the fact that I was able to get 3 power supplies gratis, that's icing on the cake.
The small misc parts required to complete the thing are going to be in the $15 range. So I'm going to work on this thing tonight. Could not get the binder posts, but I have everything else.

As far as the various power outputs, my bro' recommends the 5vdc outlet. With 20mA bulbs, he says I just need 270 Ohm resistors and I'm good to go.

I'm thinking that running all my LEDs off a single power supply will be slick, neat, and even a bit professional looking. Seems like the way to go, although the simple wallwarts will do the job.

It's my thought that I will take 5vdc output to a terminal block, then route multiple lines out from that. I plan to install switches on all my buildings.

Carry on!

I'll look thru my box-o-wall warts/power supplies and pull out the ones that might do the job.

Report back when I do!

quote:

Originally posted by Demo:
As far as the various power outputs, my bro' recommends the 5vdc outlet. With 20mA bulbs, he says I just need 270 Ohm resistors and I'm good to go.

You'll get much less than 20mA through a typical white LED with 270 Ohm resistors and a 5V supply but it's a good starting point to choose a suitable brightness.

For those that don't want to bounce around for the infinite voltages available out there. I use a standard I've come up with for a single LED.I timed myself just a little while ago and it takes all of 4 minutes to make one.

I use LED's from Christmas lights ,the GE brand to be exact 3MM Warm White round top(Lowes)
Right after Christmas you can get a 200 light string for a couple bucks

I buy 100- 750 Ohm 1/4 watt resistors off the Bay $7.00 bucks
I buy a 50 foot roll of solid copper 4 conductor telephone wire from Lowes
I like it because I can bend the wire to position the LED exactly that way I want.

This gives a voltage range from about 7 Volts to 18 Volts and a good size wall wart will run 100 or so of these.The battery charger would run 300 or so.
I bought my first 4 Ameritowne buildings and am making the LED's to go in them.
I'm also making some brass shepards hook style streetlights .
I'll post pictures when they're done

David

quote:

Originally posted by DPC:
For those that don't want to bounce around for the infinite voltages available out there. I use a standard I've come up with for a single LED.

So what is this, yet another of the many infinite choices?

quote:

Originally posted by Dale Manquen:
I would say that multiplying by 1.4 would only be appropriate for a rectifier when it is followed by a large capacitor. The average (DC) value of a fullwave rectified sinewave is only about 90% of the RMS value, and that isn't accounting for the diode voltage drops that will make it even smaller.

Dale M

I think what is being considered in the link below is the peak voltage going to the LED 120 times per second beyond what it is rated for. Even considering the drop from the bridge,the peak is over the formula for the resistor if it is not considered. I do not know whether or not during this brief intervals this would be sufficient to damage the LED. Maybe as an EE you can clear this up for me.

http://led.linear1.org/how-do-...alternating-current/

I have taken apart several LED Christmas light strings. Some were half waved with 2 diodes and others were full waved with a bridge made from 4 diodes. Then the LEDs were put in series,the resulting voltage is half waved or full waved pulsed DC peaking at around 170 volts from the wall. 50 LEDs in series on the string (or 100 on each half waved circuit), would drop 3.4 volts for each LED in series. That is about standard for a white LED. At least on these strings the engineering suggests peak voltage is considered even with pulsed DC without a capacitor. I am not an engineer ,I only observe how engineers do things. It is not clear to me if LEDs are like light bulbs and only RMS voltage is important. I do not know the answer to this I am just asking.

To all others

I do not understand the fascination here with all the Walwarts and other type power supplies. Here is how I do it. Any cheap starter set transformer would power all LEDs on most and even larger layouts. Run the variable or a fixed tap to a 25 amp bridge rectifier,the 2 AC leads. Run a bus for the DC and color code the wires. If a common bus is used for the layout hook one lead of the bridge to the common. Across the + and - of the bridge put a 4700 uf 35 volt capacitor across it. These parts would cost about $7 at Radio Shack. You now have a filtered DC power supply either variable or fixed. Fuse the circuit if desired to protect the wire. At 18 volts AC in you get 24 volts filtered DC out. This will provide maximum intensity for LEDs since the LEDs do not go on and off 60 or 120 times per second as it would with pulsed DC. With the 24 volts filtered DC up to 7, 3.2 volt LEDs can be put in series with a proper resistor or cl2-n3 chip. Usually 6 are enough to light most structures. Series wiring is always more efficient. If a variable tap is used and resistors are sized for 24 volts the LEDs can be dimmed as desired by lowering the throttle. Individual LEDs hooked to CL2-N3 chips would not dim if leaving them at full intensity was desired when others are dimmed.

Of course there are a lot of ways to do things. My method involves 1 or 2 wires running through the whole layout so I can not think of a simpler method.

Dale H

quote:

I do not understand the fascination here with all the Walwarts and other type power supplies.

Dale,

I think it's more of our "Hoarder" mentality than anything else . Why would a person SAVE a bunch of wall-warts in the first place? I had maybe a dozen at one time but can only find maybe 6 now.

I guess we're all looking at these as "free" sources of power.

Dale, I just took a look at the datasheet for a typical T-1 white LED by Kingbright. The maximum DC current is rated at 30 mA, and the peak current with 10% duty cycle is 100 mA.

In our typical operating range of 20 mA and less, I don't think the peak of the sinewave will cause any problems if we keep the average value at 20 mA or below.

One thing to keep in mind when working with LEDs is that our eyes respond logarithmically to light intensity. The LED's light output is linear as a function of current - half the current=half the light, but our eyes don't see it as only half as bright.

quote:

Originally posted by gunrunnerjohn:

quote:

Originally posted by DPC:
For those that don't want to bounce around for the infinite voltages available out there. I use a standard I've come up with for a single LED.

So what is this, yet another of the many infinite choices?

No it's 12 Volts something everyone has if they at least have an accessory output
but thanks for your "Infinite" input

David