bulbs

[grumpy]

I recently purchased a Proto 2000 GP9 DCC ready in box from lhs for one very good price . With the intent to do the install myself I also purchased the decoder for the loco.Upon disassembly I find I have to change the 1.5 v bulbs for 12v 50 mil amp bulbs.Do I need the specific bulb rating or can I use any 12v bulb that will fit.I am not very familiar  with electronics and the wiring of same .
Don

[Yampa Bob]

You should stay with the recommended bulb.  It's good policy to stay within the manufacturer's specs as close as possible, and a 50ma should be readily available. 

To give you an idea of power requirements of the bulb, it would be equivalent to about 1/2 watt. 

Bob

[r.cprmier]

Bob;
Why not forgo lamps and use diodes?  simpler, easier on the wattage, and the longevity beats resistive loads (lamps) many times over.  Now if you only feel funny about doing electrical work...

Rich

[grumpy]

How would I translate that bulb to a diode.
Don

[Jim Banner]

How would I translate that bulb to a diode.
Don

For an LED headlight, connect the LED's cathode (identified by a shorter lead and/or a flat on the base of the diode) to the blue wire.  Connect the LED's anode (the other wire) to a 1000 ohm 1/4 watt resistor.  Connect the other end of the resistor to the decoder's white wire.

For an LED rear light, do exactly as above but connect its resistor to the decoder's yellow wire.

Note that you want to use LEDs (Light Emitting Diodes.)  Of the thousands of types of diodes, only LEDs emit light.  LEDs include red, yellow, green, blue and white.  You want white ones.  White ones come in blue-white, cool white, ultra white, and warm white.  Most of us prefer warm white LED's for most steam and all diesel locomotives.  Most hobby shops stock warm white LEDs in 3mm and 5mm sizes.

[grumpy]

Jim
Thanks for the info.
Don

[r.cprmier]

Jim;
A couple of things left out here are:
Diodes are not lamps; they are semi-conductors which emit light.
The amount of light a diode emits is commensurate with the ohms/watt
rating of the resistor.  !,000 watt is going to give a brighter light than I think is right for a headlight; I generally go with about 700-750 ohm@1/4 watt, using a yello-glo type diode.
The diode is going to act as its own polarity switch", in that if wired correctly, it will glow in the foward position. or the reverse position; whichever way your engine is running.

They will last a lot longer than incandescent lamps under the same conditions, thus pretty much leaving you alone.

Diodes can also be used for other lighting applications.  F'rinstance, I am working on a coaling tower that is loosely based on the New Haven facility at New Haven, Ct.  On this tower are two sets of arc lamps set pretty high up on the structure, serving as yard lights.  They face either direction on the track, and blue-white LEDS; resistor at around 600 Ohms, would be really neat here!!

Rich

The old Reprobate

[Jim Banner]

Jim;
A couple of things left out here are:
Diodes are not lamps; they are semi-conductors which emit light

There definitely are some things left out.  But there are also some errors creeping in.  I hope you don't mind if I take the opportunity to correct some misinformation that has been going around on this site and others.

Diodes are devices that conduct electricity in one direction only.  They include semi-conductor diodes, vacuum tube diodes, selenium, copper oxide and other rectifiers, and even galena crystals used with cats whiskers.  Only a small percentage of semi-conductor diodes also produce light.  These include Light Emitting Diodes (LEDs) and Laser Diodes.

The amount of light a diode emits is commensurate with the ohms/watt
rating of the resistor.  !,000 watt is going to give a brighter light than I think is right for a headlight; I generally go with about 700-750 ohm@1/4 watt, using a yello-glo type diode.

The amount of light a Light Emitting Diode (LED) produces is directly proportional to the current passing through it.  This current in turn is equal to the voltage across the resistor divided by the resistance of the resistor.  The voltage across the resistor is the difference between the supply voltage and the forward voltage drop of the LED.  This means that the more voltage that is supplied, the brighter the LED for a given value of resistor.  It also means that the higher the value of the resistor, the dimmer the LED for a given supply voltage.  For a given supply voltage, a 750 ohm resistor will give more light than a 1000 ohm resistor.  The wattage rating has no effect on the amount of light the LED puts out, at least until the resistor burns out because its rating is not high enough to dissipate the heat produced.

Lets look at a practical example that makes use of these concepts.  Typical dc voltage supplied by a decoder to a lighting circuit is 12 volts.  Typical forward voltage of a warm white diode is 3 volts.  So the voltage across the resistor is 12 -3 = 9 volts.  For a reasonably efficient diode, 10 milliamps (.01 amps) is plenty of current.  So the resistor value = 9 volts / .01 amps = 900 ohms.  Closest 5% value is 910 ohms.  But 1000 ohms is close enough.  It will give a current of 9 milliamps, which is just fine.

The wattage that the resistor has to dissipate is voltage across it times current through it.  For this example, that would be 9 volts x .009 amps = .081 watts.  We could use a 1/10 watt resistor but operating it at 81% of its maximum dissipation, it will heat up, probably enough to melt plastic.  A 1/4 watt resistor would be working at only 32% of its rating and will not get too hot, even if the track voltage is above normal.

They will last a lot longer than incandescent lamps under the same conditions, thus pretty much leaving you alone.

Absolutely true.  Typical rated life of an LED is about 100,000 at its rated current.  Typical rated current for a 3 mm white LED is 20 milliamps.  At 9 milliamps, we might well get double that.  That is about 23 years of continuous operation.

The diode is going to act as its own polarity switch", in that if wired correctly, it will glow in the foward position. or the reverse position; whichever way your engine is running.

An LED, being a diode (conducts only in one direction) will do exactly as you say.  But there is one danger in doing it this way.  LEDs have a rating known as maximum reverse voltage, and it is typically around 5 to 7 volts.  If you apply more voltage than this to the diode, it will start of conduct, even though the voltage is applied in the "non-conducting" direction.  The series resistor MAY limit reverse current to a safe value, in which case every thing is fine.  But if it does not, the life of the LED will be shortened.  In the extreme case that you apply too much reverse voltage and have no series resistor, the life will be reduced to a fraction of a second.  You will be okay if you connect two diodes in inverse parallel (one one direction, the other the opposite direction) and use a single series resistor.  If you need only one directional LED (such as headlight in a covered wagon) then the second diode can be a regular, non-LED diode (type number 1N4001 for example.)

Diodes can also be used for other lighting applications.  F'rinstance, I am working on a coaling tower that is loosely based on the New Haven facility at New Haven, Ct.  On this tower are two sets of arc lamps set pretty high up on the structure, serving as yard lights.  They face either direction on the track, and blue-white LEDS; resistor at around 600 Ohms, would be really neat here!!

Rich

The old Reprobate

I like LEDs for lighting and use lots of them.  The last few years, I have been buying sets of warm white Christmas LED lights and stripping the LEDs out of them.  3 mm, 5 mm, round end, inverted cone end, they all have their uses in model railroading and cost as little as 7 cents apiece.  I am presently retrofitting a G-scale engine house with LEDs, 11 inside and 4 more outside.  It is part of a program to replace all my outdoor lighting with LEDs, starting with the ones that stay on all night every night.  The real world flood lights will have to wait longer, or come down in price sooner.  Unfortunately, the fluorescent ones don't work worth a darn up here in the frozen north when the temperature hits -40.

[r.cprmier]

Jim and others;
The voltage across the resistor is the difference between the supply voltage and the forward voltage drop of the LED.  This means that the more voltage that is supplied, the brighter the LED for a given value of resistor.  It also means that the higher the value of the resistor, the dimmer the LED for a given supply voltage

I had the ohms ass-end-to; a typo.  My misteak.

Rich