Was just looking at Max Magliaro's power supply featured on Spookshow's site. Designed for bulbs, though. What would be a proper power supply for multiple LED's, used for street/structure lighting?? Joe D
I would also like to know more about this…. for me it is "LED's for Dummies"…. assume I know nothing and start there… thanks...
Depends on how many LEDs are in a "multiple". I have an NTRAK module with a street scene, and I use a simple 1 amp walwart I salvaged from some gadget that died around the house. It runs 12 LEDs for building lights, 8 LED street lights, a pair of crossing flashers and 2 incandescent bulds with no problem.
woodland scenics has 2 new light kits that have dimmable power supplies and 4 led's. they say it is o scale, but might be an option. http://woodlandscenics.woodlandscenics.com/show/Item/BA5790/page/1
Found this at a model led retailer I've used before. Does use surface mount resistors, which are very small. May not be up to everyones capabilities. But I'm 54 with bi-focals and have been very successful with surface mount led's, resistors, etc. http://www.ngineering.com/gen_lighting_kits.htm Joe D
The key is how many LEDs do you want to run off a single power supply. Wall warts are perfect for "contained" areas, but I wouldn't want to run long leads from them. The N-gineering link, above, is simply a wall wart to a distribution board. On the JACALAR I tap my auxiliary power 5V line, with the appropriate drop down resistor, or in some cases the 12V line. These are from a PC power supply that I have adapted to provide all the different voltages I need as auxiliary. On the FreeMoN modules, we run a DCC auxiliary buss. For the LEDs on my station module, I tape that buss and have a bridge rectifier and 9V regulator for the LEDs, all with proper resistors. The big key on LEDs is current regulation to the device, which is what the resistors are for. For most, you want between 10 to 20 milliamperes, but check the specs for the LED you are using. N-gineering also sells boards with current regulating devices, which in have used, as well.
What are the voltage and amperage requirements of your LEDs? That (along with how many you plan to light) will determine the power supply. FYI, there really isn't anything about Max's circuit that makes it "bulb specific". It would light the same number of LEDs provided they had similar amp/voltage requiments. Cheers, -Mark
Standard LEDs operate on 1.5v at 20 milliamps each, so it doesn't require much voltage. Taking into consideration the line loss you will incur across the wiring in your layout, 5v should do the trick. Add up the number of LEDs you are using, and you will get a good idea of how much current you will need. Unless you're modeling the Vegas strip, I daresay you won't need even an amp. If you're electronics savvy, solder up a 5v regulator to your 12v dc line, and feed the output to your LED load. A 7805 would do the trick.
I plan to use 3mm leds, some from older Atlas lightboards, and some surface mount chips for exterior fixtures. Don't have an idea of how many, but likely several dozen. Thanks, Joe D
You may need a heat sink on the 7805 when using it to regulate 12v. As an alternate to that, you can add a 7808 in series before the 7805. Be warned though, the 78xx regulators can only handle up to about one amp of current.
Here is another good calculator for LEDs: http://led.linear1.org/led.wiz It also shows you a diagram (schematic) on how to connect them and what resistor to use. I am using 3AAA battery holder from Radio Shack to power 15 LEDs. With rechargeable batteries I get about 3 hours of run time. If I used 3AA holder, I would get about 10 hours as the mAh rating on AAs is a lot higher.
Max here... hadn't noticed this thread until now, but in case anyone happens to read this, there are some dangerous misunderstandings still floating around in here that will lead to burned out LEDs and frustration. First, although LEDs do have a forward voltage specification, usually around 1.5 to 2 volts, stop thinking of feeding LEDs "volts". They are current-driven devices. This means that no matter what supply voltage you use, the key is to make sure that only 10 - 20 ma can flow through each LED. Whatever the LED's forward voltage spec is, rest assured, that's the voltage that will drop across that LED. Forget that. You need to limit the current. Some posts in here already touched on this, but from what I'm reading, I don't think it's getting through. For example, if you set up a circuit with a 5 volt regulator and just hook LEDs to that, they will all instantly fry because you have nothing limiting the current. If the regulator is capable of delivering 1 amp, then 1 amp is going to flow through those LEDs and burn them all out. Soooo..... you MUST put a current limiting resistor in series with each LED. Yes, you COULD put a single large resistor in place and then tap all the LEDs off of that, but I don't like that solution because the behavior of the LEDs will change as you add more of them. And if you remove some, you may have too much current flow through the remaining ones, burning them all out. My advice is... Start with a basic regulated supply, something that outputs, say, 5 volts or 12 volts, and has a a capacity of 1 amp. Wire each LED to it like this: (led) + --- R ---- -->|-- | | - -----------------| R can be a 1/4 watt or 1/8 watt resistor (you can use bigger, but it is totally unnecessary and they are bulkier). How many ohms? That depends on the voltage of your supply. If it's a 12v supply, and we want to limit the current to 10 mA, we use V = IR, so 12 = 0.010 x R, so R = 12/0.010 = 1200 ohms (or 1.2k ohms) (Actually, it's not 12 because the LED drops 1.7 or so, but I want to keep this simple). See how that looks to you. If you want it brighter, you could lower R, draw more current, and get a brighter LED, but don't push it over its maximum current. I wouldn't push it past 20 ma. So you could try a 620 ohm. That's it. Now, go buy a big bag of those resistors. Look on eBay. You can get 100 or 1000 resistors in 1/8w or 1/4w sizes of one resistance value very very cheaply.
I purchase power supplies, ect., from, http://www.allelectronics.com/ they have a 4 amp 5 volt DC supply that would light a ton of LEDs.
Check out: http://www.modeltrainsoftware.com/ He has excellent LED's and power supply. I have used many on my refinery scene. Carl
I find these to be very handy for some applications........... http://lighthouseleds.com/20ma-led-current-limiter-driver.html
