Hello I have lights. RRMel helped me offline get the right stuff and helped me set it up and explained how things worked so I could understand. So now my lights run off a 20amp power supply with a DC-DC converter I have more power then I need but thats ok. Here is a photo of part of the light's the rest are to spred out and wont showup. I have these brighter for the photo. Thanks for all the help
Have a nice day Frank
Mark R. hon30critter GrandTrunk-HO Warning Each and every LED will require a Resistor. Not so. If you use a power supply with the correct voltage for the LED you don't require a resistor. Dave Actually you do for any kind of permanent installation. A quick check with a couple batteries is ok for testing purposes only.
hon30critter GrandTrunk-HO Warning Each and every LED will require a Resistor. Not so. If you use a power supply with the correct voltage for the LED you don't require a resistor. Dave
GrandTrunk-HO Warning Each and every LED will require a Resistor.
Not so. If you use a power supply with the correct voltage for the LED you don't require a resistor.
Dave
Actually you do for any kind of permanent installation. A quick check with a couple batteries is ok for testing purposes only.
While I agree that you should always use a resistor with LEDs if you don't have a current regulated power supply, that doesn't necessarily mean every LED needs a resistor. If your voltage is more than twice the LED voltage you can run LEDs in series off of one resistor.
rrinker ...... I've been saying that forever but now you found a site that backs up what I've always known (probably actually learned exactly what they say there 30 years ago but have forgotten the exact math).. There is exactly ONE case when no limiting resistor is needed - when you have a constant CURRENT power supply. Of course that's a lot more complex than just a resistor. For example, I can set my lab power supply to 15ma and set the voltage to anything it can do and hook an LED directly to the terminals. Even if I set the voltage to 30 volts, the LED will be fine because the constant current mode will allow no more than the 15ma I set it to. There are constant current LED drive ICs you can use that accept a wide input voltage range but will only allow the LED a proper current. --Randy
...... I've been saying that forever but now you found a site that backs up what I've always known
(probably actually learned exactly what they say there 30 years ago but have forgotten the exact math)..
There is exactly ONE case when no limiting resistor is needed - when you have a constant CURRENT power supply.
Of course that's a lot more complex than just a resistor.
For example, I can set my lab power supply to 15ma and set the voltage to anything it can do and hook an LED directly to the terminals.
Even if I set the voltage to 30 volts, the LED will be fine because the constant current mode will allow no more than the 15ma I set it to.
There are constant current LED drive ICs you can use that accept a wide input voltage range but will only allow the LED a proper current.
--Randy
I presently have a lab digital (x2) meter, PS613U V-DC power supply.
I use this unit to check many of my minimum V-DC supply and minimum Amperage requirements.
The Amperage setting (Current - I) on a lab power supply will set the maximum Amperage (Current - I) output.
No matter what the V-DC setting is set on the a lab power supply, the Amperage setting (Current - I) will determine the maximum V-DC output.
Calculations: (LED)
- LED 15.mA (Current - I)
- V-DC power supply (30.V-DC)
LED Calculator:
- 30 (source voltage)
- 3 (diode forward voltage) --> example
- 15 (diode forward current mA)
Results: (From Above Calculations)
With a supply voltage of more than 24V, you'll dissipate excessive heat in a current-limiting resistor.
rrinkerThere is exactly ONE case when no limiting resistor is needed - when you have a constant CURRENT power supply.
there are 20 ma LED drivers. bit more expensive than resistors. I think they are just an lm317 in current mode.
greg - Philadelphia & Reading / Reading
Nice find Mark. I've been saying that forever but now you found a site that backs up what I've always known (probably actually learned exactly what they say there 30 years ago but have forgotten the exact math)..
There is exactly ONE case when no limiting resistor is needed - when you have a constant CURRENT power supply. Of course that's a lot more complex than just a resistor. For example, I can set my lab power supply to 15ma and set the voltage to anything it can do and hook an LED directly to the terminals. Even if I set the voltage to 30 volts, the LED will be fine because the constant current mode will allow no more than the 15ma I set it to. There are constant current LED drive ICs you can use that accept a wide input voltage range but will only allow the LED a proper current. Again, more complex than just using a resistor. The drive ICs are great when you want to run the LED right to the limit without any chance of going over. When sizing a resistor, if you size it for half or less of the LED's maximum current, even a relatively large voltage swing won;t cause the currrent limit to be exceeded - example is typical use of a 1K resistor for white LEDs on DCC. For mose, that reults in a nominal 9ma to the LED. Most white LEDs are good for 20-25ma. So even if the voltage to the rails should increase to say 20V, the LED would still get less than 20ma. It's always good to leave a safety margin in any design.
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Hello Guy's thanks for the info on led's but I do not paln to use any. I like the look of a bulb better. I should be done getting my lights in parallel this weekend. I will be able to only hook up 45 for now waiting on lamp shades. Then back to the power supply. Thanks Frank
Mel sent you a email
Mark R. Enjoy the show guys .... I ran out of troll food on that other forum .... Mark.
Enjoy the show guys .... I ran out of troll food on that other forum ....
Mark.
I found the Abuse button, far left bottom corner.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
He's back
Is a resistor required for a LED (Light Emitting Diode)?
hon30critter Not so. If you use a power supply with the correct voltage for the LED you don't require a resistor. Dave
Dave is totally correct if you use a power supply with the correct (exact) required voltage.
I have a large stock of many different types of LED's from 3.MM (.118" Dia.) to 5.MM (.196" Dia.) from the standard round head LED's, to the flat top LED's, in many different colors. These LED's operate in many different V-DC power supply that ranges from 1.8V-DC --> 3.2V-DC mostly determined by the size of the LED.
LED's of the same exact type and size, will also have a Different V-DC power supply determined by the Color of the LED used.
Also each different manufacture will also have a different V-DC power supply determined by the Color of the LED.
LED's operate at very low limited V-DC power supply ranges and also require correct polarity connections.
Hate to be that "copy-n-paste guy", but this link will give you the reasons why ....
https://electronics.stackexchange.com/questions/12865/is-a-current-limiting-resistor-required-for-leds-if-the-forward-voltage-and-supp
GrandTrunk-HOWarning Each and every LED will require a Resistor.
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Small Tiny Light Bulbs
Between (2002-2004) I purchased may different sizes of light bulbs from Miniatronics (Micro Miniature Bulbs).
At that time, there were many different choices of sizes and many different choices of voltage.
Now Miniatronics is only selling one type of 1.5V 1.34MM (.053") Dia. 25mA incandescent bulb.
Code: 18-025-10 [10 pcs] Price = $15.95 and Code: 18-025-20 Price = $28.95
Miniature Light Bulbs
Any and all types of small model railroading Bulbs use an electrical filament. Just like any regular light bulb using an electrical filament, has an expiration usage time date. Any type of Constant vibration on a bulb will in time will break the wire tungsten filament.
Question?
How much longer will miniature light bulbs be manufactured?
Why Not Convert To LED's?
An LED using the correct Current (voltage and amperage) will last for ever. LED's being sold on Ebay, only cost pennies each and there are Thousands of different choices.
Ebay search = LED --> Model Railroads & Trains
Caution
"White" LED's give off a soft blue color tint, while "Warm White" LED's give off a soft yellowish color tint.
Fact
LED's are also used as lighted Diodes, to control V-DC voltage direction.
Warning
Each and every LED will require a Resistor. I use this excellent location for required calculation. (LED = Diode Forward Voltage)
http://led.linear1.org/1led.wiz
Example Connection
My Model Train Structures
I will be using small soft yellowish color tint LED's inside all of my buildings, that will never ever require replacement.
18 Gauge is fine and Yes to Your other questions.
Take Care!
Frank
Hello ok I think I found two problems with my wiring. Some of my lights were not wired in parallel so I'll fix that first. How big should the wire be feeding the lights? Mine is solid 18ga by my striper's. Is this to small? I used phone line form there to the light's it is the same size as the wire on the light is this wrong to? Can there be a light at the end of the parallel feeder's ? Thanks Frank
You don;t even need Ohm's Law. You don't even need to know who's law it is, but in this case it's Kirchoff. If you put light bulbs in parallel, the total current is the sum of each current. so if they are 30ma bulbs and you have 50 of them, that's 1.5 amps. 50 x .030. So you need a power supply capable fo supplying at least 1.5 amps, and good practice says the total load should be no more than 75-80% of the capacity of the power supply. SO you really want a 1.9-2.0 amp power supply. You can always go higher - amps are drawn by the load not pushed in by the power supply, so a 10 amp power supply wont blow up your light bulbs that draw 1.5 amps. You would however want to provide some sort of fuse or circuit breaker because 10 amps at 12 volts is 120 watts which is a lot of heat.
Hello Rich I looked at the ohm's calculator and I am not sure where to find the info to put in. I took a Altas power pack input 120vac 25w 0-14 vdc max 10va output 17vac max 15va. I took my meter and set to the train side turned the knob till I got 12v and 2.17a showing on the meter. When I hook up just one bulb I get 10.47v and 1.86a showing. So that means the bulb is using 1.53v and 0.31a? So if I want to light 50 of them at 100% I need 76.5 v and 15.5 a? I know I wont really need that much power. Because I wont have the light's that bright. Can I make that much power and what would I need? or am I still missing something.Thanks Frank
You don't need a book. Use an ohm's law online calculator.
What current do the bulbs draw at twelve volts DC.
I would suggest running them at nine volts DC for longer life.
Buy a step down 12 volt to nine volt volage regulator from Amazon for a few dollars if you do not know how to make one.
I recently saw a two amp and five amp at Amazon.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Hello Guy's I am kinda following. Electronics was always a tuff thing for me to follow. This is what I am trying to do I have 50 grain of rice 12 volt bulbs. This is buliding's,yard lights ect. My layout is a 13' x 15' horse shoe shape. Most of the lighting is on the right 15' side closest to the power about 38 light's this is where the yard round house and other bulidnig's are. The rest are buliding's spaced out over the 13' part and the left 15'. I would like to have them all work from one power source if I can ? I am not sure where to even start. Is there a book I can get at the library on something on line ? Or with this many lights am I going to need multiple power source's? I never worked with the power source from eather of the link's. Thanks Frank
Smart-aleck answer, less than 25, obviously. LOL.
If they are 16V buld,s a 9 or 12V supply would be perfect. They will last nearly forever on the lower voltage, and nothing will look like it has a nuclear reactor planted int eh middle of it (light shining through structure walls). 12V bulbs - a 9 or 6V supply will be good. Then all you need is a simple on.off switch, plus there is no chance you could bump the control and turn the power up too high for the bulbs.
I've standardized on 16 volt incandescents but I run them at 12 volts. This lets them run cooler and greatly extends bulb life.
It also gives a softer, "warmer" glow to the lamps, which better suits my Transition Era layout.
It takes an iron man to play with a toy iron horse.
One of several power supplies I use for "Hotel Power" on my layout is an MRC Controlmaster 20. Like the OP I have the lights wired to the throttle output and I usually like to have the voltage dialed down to about 8 volts unless there are visitors and I want the city lights to be a little brighter.
Normally at 11.5 volts I'm drawing 5.2 amps, well below the rated 8 amps (I never want to run anything close to the rated levels but about 15-20% below).
In my situation, If I leave the output at 11.5 volts and then turn on the C-M 20 the overload lamp will light and there will be no output. I have to dial down the throttle knob, turn on the power switch then dial up the voltage. This is my usual procedure anyway.
It may be a combination of the cold-inrush current of the incandescents and/or the circuitry of the transistorized throttle. Cold inrush current can be up to 14 times the usual resistance.
Other variable-voltage throttles (power-packs) may have similar behavior. You may have to bring the output up gradually.
Good Luck, Ed
I have a couple of 12 volt DC, 5 amp power supplies I got on eBay. They were about $8 each, shipping included from China. They arrived in a few days and work fine. Lots of power for my accessory lights.
But, they do not have circuit breakers, so for each lighting bus I add a fuse block and a 4-amp fuse. Better safe than sorry, and a fuse is cheaper than a power supply.
Hello ok It's a life like power pack the blue one. 120 v input output 16v dc 7va max output. When I put the meter on just the power pack train side this is set all the way open. I get 15.62v dc and 2.98a. When I hook up the lights I get 7.39v and 1.23a. The lights only stay on about a min. I can watch the meter count down. The accessory hook ups I get 4.1v and .01a with out lights. With the lights 2.2v and .01a. The lights do the same when hooked up there as well. I am not sure what all that means? Thanks Frank
Look at the power pack label for amps it can supply.
Put your amp meter in series at the highest DC amp scale and see what the bulbs are drawing. Very easy.
I have done that over the years with bulbs that I did not have the specs for.