RECOMMENDATION 12-3: Lighting Passenger Cars
Considerations of Using Lighted Passenger Cars:
Be sure if you are using lighted passenger cars, that reversing
sections are longer than the longest train you will be running. You have probably
heard that if a train is entering a reversing section at the same time as one
is leaving, this will cause a short and shut the booster down. A lighted passenger
car will do the same thing. So make sure your reversing sections are long enough.
How many passenger cars can be run on DCC?
If you only have a dozen or less passenger cars, you probably
don't need to worry much about the load the passenger cars will be putting
on the booster(s). However, should you be so fortunate to have many more than
that, the math is simple.
Booster current (usually 3.5 or 5 A) - the load of the locomotives
(usually approx 3/4 A) - (# of lit cars x their current draw (maybe .2A))
My estimates above should be a bit on the high side.
Definitely buy the 5A boosters. You can even buy the 8A boosters,
but I don't recommend them for HO or smaller unless you really need to. Instead,
break the layout into smaller sections that can be handled by a 5A booster.
Note: Idle locomotives only may draw .2A or less. Idle, lights off, and no
sound, definitely less.
Do you want every car lit?
Or only those part of an active train, or soon to be active. If
you want them off, you may want to go as far as putting a decoder into each
car. That's convienent, if not inexpensive. You could hook them the cars to
save money on decoders, but I find that wires between cars are a fair amount
of trouble. If you can afford decoders, I'd go that way.
Or you could park them on tracks in a yard or whatever and use
a toggle switch to kill the power to that track.
You should figure out how much current your cars will draw. I
haven't done a lighted passenger car yet, but I suspect the average modeler
would want it dimmer than the average toy passenger cars that I had when I
was a kid. So light a car any way you want that gives you the desired effect
and measure how much power it draws at about 14V.
What if I don't want to use a decoder?
You, for the most part, can simply run a lighted passenger car
directly from the DCC track! In HO and smaller, it's that simple!
Those running O or G, may want to use 19V LGB lightbulbs; if you
can find them. Or you can use 14V bulbs and put resistors in series with them.
To figure the resistor value = (19V[track voltage]-14V[bulb voltage])/0.06A[bulb
amperage] = 83 ohms. Use any standard value from 82 ohms to 100 ohms should
work fine. The wattage rating of the resistor needs to be 1/2 watt.
If you want to use 12V or lower voltage bulbs and want something
that will keep the lights from flickering when you hit a dirty spot, use the
12V power supply circuit described below.
RECOMMENDATION 12-4: 12V Power Supply Circuit - Millions of
Uses!
Do you need a circuit that will power sound systems, light cars,
anything you can think of, from DCC or 12VAC? Here it is, in this example,
it is used to power a sound system. It consists of Z1, C3, C4, C5, and usually
a 7812 voltage regulator. The red and black wires have the 12VDC on them. This
circuit can produce up to one amp.
C4 and C5 are 0.01uF capacitors rated at typically 50V - they are
common. Z1 is rated at 1A and 50V - also common. C3 is usually rated at 25V
and for starters, is a 1000uF capacitor.
There are a lot of variations on this circuit.
This is very compact and can fit in a Z-scale car if you are determined
enough. There are many ways to make it smaller. Many of your uses don't draw
anywhere near one amp. Therefore, you can forget putting a heatsink on the
voltage regulator. Another way to make the circuit smaller is use components
that are rated closer to the voltage you will be applying to the circuit. For
example, C4 and C5 can be gotten in 25V and sometimes lower voltage ratings.
C3 can definitely be gotten in 16V ratings. Don't worry about Z1. It's size
isn't affected by applied voltage.
There are few cautions I must give you.
1. If you are running this from a 12V transformer: You
probably aren't concerned about size. So use 25V or higher components. Without
getting into the technical details, a 12V transformer, usually puts out, as
far as these components are concerned, almost 18V. Note: With DCC, this isn't
an issue.
2. If the voltage rating of C3 is below the applied voltage
IT WILL EXPLODE: Got your attention, did I? There is a safety margin
built into these devices. But if you apply too much voltage to C3, an electrolytic
capacitor, IT WILL EXPLODE WITH INJURY, ESPECIALLY TO YOUR EYES, POSSIBLE.
3. If you hook up C3 backwards, IT WILL EXPLODE regardless
of whether you applied too much voltage or not.
So whatever you do, don't undersize C3. It's okay to have it just
big enough, but don't make it too small. Also consider whether you will be
taking your car with this circuit in it to another layout running a higher
voltage.
Another size choice you can make is using a lower value of capacitance
for C3. If you are running the circuit off of 12VAC and you want an amp, use
the 1000uF capacitor. But at DCC frequencies, a smaller capacitor can still
produce an amp. If you are putting this inside a car, you probably don't need
anywhere close to an amp. So you can probably use a 100uF or a 47uF or maybe
even a 22uF or a 10uF and get the results you want.
On the other hand, the larger the value of C3, the more immune
the circuit will be to dirty track. In that case, you may want to stick with
the 1000uF or go up to 2200uF, 3300uF or larger. Larger values, especially
when you are drawing much less than an amp, may allow something, like lights
or a sound system, to stay on for a few seconds upon loosing DCC power. Maybe
you want that.
The voltage regulator shown is a 12V one, but you can get them
in other voltages as well from the same company you would buy the 12V regulator
from.
SUGGESTION 12-5: How to Get 1.5VAC to Run Grain of Rice Bulbs
This has nothing to do with DCC. Call this one a bonus.
1.5V is somewhat of problem to get. Common voltage regulators
don't go this low. Modelers have come up with some interesting ways to get
1.5V. Because they often had some sort of drawback, I came up with my own way
of doing it. It's simple!
This idea works great and is easy to implement in countries using
120VAC out of the wall or approximately that amount. This idea can still be
used in other countries, but it's ease of implementation will depend on what
voltage transformers are available.
ONLY
do this if you FULLY understand what I am talking about. If not, get with
an electronics friend of yours to help you out. Before putting this circuit
into operation, test it with a voltage meter connected by clips. DO NOT be
touching any of the wires with your fingers when testing it. FAILURE TO HEED
MY WARNINGS COULD BE FATAL.
What I am about to suggest is common. It's how power gets from
a power plant to your house - through the use of multiple transformers. However,
even if you have done electronics projects before, you may have never hooked
multiple transformers together. So this may seem odd or confusing to you. If
it is, DO NOT DO IT. IT COULD KILL YOU if hooked up wrong.
Here's the idea. Take two transformers, each with 120V in, and
12.6V out. Each has a voltage transformation ratio of less than 10.
1. With a fuse and a switch, wire the first one up so you can
plug it in the wall. You will get 12.6VAC out.
2. Take the second transformer. Instead of connecting it's wires
that are labelled 120V to 120V, connect them to the 12.6VAC of the first transformer.
You will get about 1.3VAC!
Note: You could have one transformer putting out 12.6VAC. You
could run this 12.6VAC around your layout. You could then have a small transformer
in each town to produce the 1.3VAC to light that town. Or you could just run
the 1.3VAC around your layout. Which way to do it, is up to you and what you
are modeling.
If you are in a 110/120V country, T1 and T2 should be 120V:12.6V
transformers. In a 220/240V country, T1 should be a 220:25.2V transformer.
T2 should be a 220:12.6V transformer or the nearest equivalent. The fuse, F1
should be no larger than ¼ amp.
Using Lamps and LEDs with Dropping Resistors.
If you are using a 1.5V lamp or a LED, you will need a series dropping
resistor. Here are the equations for computing the values for that resistor.
These equations have a lot of uses. It is not the purpose here
to describe all those uses. The intent is to provide the equations for those
that know
how to use them. I do provide two common and useful examples below.
| |
Where:
VPS
VL
VD
IL
R
W |
is voltage provided by power source.
is the voltage rating of the lamp or LED.
is the forward voltage drop of a diode if used.
is the nominal current in amps for lamp.
value found for resistor in ohms.
wattage value found for resistor |
|
The term VD is 0.7V if you are using a series protection diode.
Otherwise it is 0V.
The term IL is the nominal operating current in amps. If 20mA, then use 0.02.
If 100mA, then use 0.1.
The term VL is the nominal operating voltage of the bulb or LED. The nominal
operating voltage for an LED is typically 2.6V. Blue LEDs are typically 3.7V.
You will find that resistors are not typically available in every possible
value. Therefore, use the commercially available value that is close to or
higher than the value you calculated.
In determining the wattage of the resistor, use the value for R that you decided
to buy. Once you determine the wattage, use a resistor with a wattage rating
that is higher than the value you calculated.
See the two circuits below for examples.
Using a grain-of-rice light bulb in a locomotive.
You will need a voltage-dropping resistor in series with grain-of-rice bulb.
Use the equation above. For HO:
VPS = 13V
VL = 1.5V
VD = 0 (since you have no diode)
IL = 15mA = 0.015A
R = 767 ohms. You can use XXX ohms from Radio Shack.
Using a 100 and 680 from Radio Shack in series, W computes to be 0.165. Use
a ¼W
resistor or larger. Radio Shack has a better selection of ½W resistors.
Using an LED to indicate to DCC track power on.
You will need a voltage-dropping resistor in series with the LED. You will
also need a reverse polarity protection diode.
VPS = 14.4V
VL = 2.6V
VD = 0.7V
IL = 20mA = 0.02A
R = 555 ohms. You can use 560 ohms from Radio Shack.
Using a 560 from Radio Shack, W computes to be 0.224. Use a 1/4W resistor or
larger. Radio Shack has 560 available in ½W size. Use that.
