Sort of a reborn railroader, started adding lighting to my scale (street lights, block signals, etc)
I have not installed any reistors which I just learned about, am I going to have a problem with bulbs burning out premature. When do you need them, if their is enough lighting hooked up wont it spread the power out enough not to damage any one light?
For incandescent bulbs, the simplest thing to do is to run them at a slightly lower voltage than their rating. So, I run 16-volt bulbs at 10 or 12 volts. This gives a dimmer light, which I find more pleasing anyway, and it makes the bulbs last a lot longer.
If you put 2 16-volt bulbs in series (connected end-to-end) then each of them only gets 1/2 of the voltage. So, if you are powering them with a 20-volt source, each would only get 10 volts.
You can use resistors to cut the voltage down as well, but then you need to know the resistance of each bulb, which is generally not going to be on the package.
For Light Emitting Diodes (LEDs,) though, you must use resistors. LEDs themselves have very little internal resistance, and connecting one directly to your power supply will convert them very quickly into Darkness Emitting Diodes, or DEDs.
It takes an iron man to play with a toy iron horse.
Here is some info concerning LEDs and lamps. Read carefully before attempting to use the resistors.
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
You can find more info by searching with Google for dcc resistors, leds resistors, 1.5 volt lamps resistors.
The info is valid for using DCC decoders or DC voltage out of a power supply.
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.
Northernwoodwstarted adding lighting to my scale (street lights, block signals, etc) I have not installed any reistors which I just learned about, am I going to have a problem with bulbs burning out premature. When do you need them, if their is enough lighting hooked up wont it spread the power out enough not to damage any one light?
The simplest thing to do is to get a power supply that matches the power rating of the lights. If the light bulb is rated at 6 volts, run it from a 6 volt or less power supply and there is no issue. You don't have to worry about prematurely burning out bulbs or spreading out power, or learning equations (see below).
On the other hand if the bulbs are rated at 6 volts then one can put them in series (end to end) with a 12 volt power supply. This spits the 12 volts in half giving each of them 6 volts. Or four 3 volt bulbs, etc. It is simple mathematics of adding up the volts in series (the voltage rating of the light bulbs) to match or be slightly higher than the voltage rating of the power supply. Each light bulb is actually acting as a resistor for the other light bulb.
A resistor is used when the power supply does not match the rating of the light bulb and there are no other bulbs to use (or don't want them to use) to balance the power. For example if one had only a 1.5V light bulb and a 12 volt power supply the bulb would burn out faster than one could blink. So a resistor that consumes 10.5V would have to be added in series with the light bulb. To calculate the size of the resistor one has to measure the current (amperage) draw of the bulb and do a calculation. R = E/I or Resistance is equal to the voltage (10.5) divided by the Current. So if the current is 0.025 amps 10.5 / 0.025 = 420 ohms.
This equation (E=IR) is called Ohms law. It is essential to understand for those wishing to work with electricity.
LED type lights are a whole different story, and hooking them in series will not spread the power like regular light bulbs do.
The simplest way is to set up a separate power supply, and layout lighting circuit. Get an old DC power supply. Get out the voltmeter, and dial up whatever voltage you want, or need. Running 12 volt bulbs at 11 volts gives sufficient brightness, and prolongs bulb life.
You can also buy cheap Wal Warts, in just about any desired voltage these days.
If you put a bunch of bulbs in series, and one burns out, it's like the old christmas lights. You have a problem finding the burned out bulb.
Ok, I'm trying not to be confused and yet, want to do things right. Please someone help me with this. I want to learn this so much.
I have a Tomar HO scale dwarf signal. It has two LEDs, red and green, and a white wire. The litertaure that came with the signal says that both bulbs have an LED voltage of 2.2. The red has a LED current of 20.00 and the green has 30, whatever this means. No resistors were included with the package. Using Ohms law or what have you, what size resistors do I need for each bulb and can I get these from an on-line model rairoad supply source such at Internet Model Trains, Discount Trains online, etc.
I found two old power packs that I was planning on using as dedicated power supplies for my block signal lights and crossing signals. One is an old TYCO which says 18V DC and 20 V AC. The other is an old AHM which says, "16.5 VDC and 10 VA, whatever that means. I am assuming all of my signal lights would run off of the DC, or do some go off of AC? . Is that where most lighted accessories, if not all, run off from a power pack? Maybe I should dump both power packs and get something on Ebay or at Radio Shack that would be "safer" to use, but I'm not sure. But, given what I do have, what size or type resistors should I order online to help me run theses LEDs safely?
I went to You Tube and saw where and how you solder the resistor directly to the LED leads. According to my dwarf signal instructions, after I add the required resistors, I hook up the white wire to positive and the LEDS to negative. But on a power pack, it doesn't say what is positive or negative for "trains" or "accessories." How can you tell??
Using OHM's Law or some other homegorwn easier rule of thumb to work with, could you show me how to plug in the numbers for what I have in LEDs and power packs, to refernce to for other accesories.
Thank you so much to anyone who has the patience and care to help me.
Mark
wingmanOk, I'm trying not to be confused and yet, want to do things right. Please someone help me with this. I want to learn this so much. I have a Tomar HO scale dwarf signal. It has two LEDs, red and green, and a white wire.
I have a Tomar HO scale dwarf signal. It has two LEDs, red and green, and a white wire.
wingman The litertaure that came with the signal says that both bulbs (not bulbs LEDs) have an LED voltage of 2.2. The red has a LED current of 20.00 and the green has 30, whatever this means. No resistors were included with the package. Using Ohms law or what have you, what size resistors do I need for each bulb (not bulbs LEDs)
can I get these from an on-line model rairoad supply source such at Internet Model Trains, Discount Trains online, etc.
Personally I don't believe the numbers. Most LEDs will light on 1.4V so unless they already have a resistor built into that LED it seems a funny number to me. I would throw in a 1000 ohm (1K) resistor in the circut and see what happens. If it is too dim then go to a lower resistance value.
The difference you see isn't that necessarily that the LED lights at 1.4 volts, it's that the current rating of an LED is the MAX current it can handle. So when doing the calculation with Ohm's Law, you want ot use LESS than the 20 or 30ma that the LEDs are rated for. Usually half is MORE than sufficient - the more current, the brighter the LED. The forward voltage drop is the spec givne when they say the LED is "2.2V" and that is the absolute, so when doing an Ohm's Law calculation for an LED you have a known voltage and have to adjust the resistor to allow the proper amount of current.
Incandescent bulbs have a current rating - but that is the absolute current they will draw at the rated voltage. Not "up to", if the bulb is rated for 30ma at 1.5 volts, it will draw 30ma at 1.5 volts. The voltage is what varies with a bulb. The rating is the max it can handle while giving a reasonable life. You can apply 12V to a 1.5 volt bulb - and it will do a fair imitation of a one time use flashbulb. You can also apply 9 volts to a 12V bulb and get a nice glow plus a bulb that will last decades. When calculating resistors for light bulbs, the current is what's fixed and you have to size the resistor to allow the desired voltage.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Another solution is to use the Train Control Systems voltage regulator (VR-1 ??).
They enable the decoder to put out 1.5 volts to the bulbs without you using the resistors which generate heat.
They have a harness to attach to their decoders or you can cut these off and handwire to your decoder.
I have used these with TCS, Lok Sound, Tsunami decoders.
To answer the power pack question. The reason there is no polarity marking, the polarity will change with the direction switch. That is what you have a multimeter for.
Texas Zepher LED type lights are a whole different story, and hooking them in series will not spread the power like regular light bulbs do.
To confuse things even more, you can connect LED's in series and get the same effect as incandescent lamps in series, you just need to observe polarity. I did it lighting my roundhouse with LED's I pulled out of a Christmas light string. Three in series and connected each group in parallel with a 9 volt wall wart. No resistors in the circuit at all.
Thank you all for your responses. I aopologize for being in the wrong thread with my question. But, you have been all helpful with your information. I am hoping to not buy any block signals or any other lighted accesories that require resistors as they seem a little problematic, but necessary with LEDs.
I did take Texas Zephyr's advice and bought some 1/4 watt resistors, with some at 1K and some at 470mw
Now, to the soldering.