Flicker Free Coach Lighting.
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Lights in passenger coaches and vans have the annoying tendency due to their light weight and poorer Track Pick Ups, to flicker while operating in a moving train. The previous circuit that I used from my mate Jim in the U.S, while it worked for Guards Vans but when using 6 or so LEDs to illuminate a Passenger Coach, as soon as there is a loss of power, the LEDs dim. While the LEDs did not extinguish altogether, this continual dimming of the LEDs as the train/Coaches negotiated dirty track etc. just looks like flickering.
Operation of the previous Circuit. The rectified D.C. is “clamped” to 5.1 Volts DC due to the Zener Diode as the voltage rating of the Super Capacitor is 5.5 Volts. This 5.1 Volts supplies the power to the LEDs. The 1,000 Ohm resistor restricts the Inrush Current so DCC system do not shutdown.
With a loss of track power, the LEDs are powered from the Super Capacitor but the voltage drops causing the LEDs to dim. The longer the time of no power, the number of LEDs (load) & the size of the Capacitor determine how much of a drop in the LEDs brilliance.
Restoration of power restores full brilliance to the LEDs. This dimming & back to full brilliance is seen as a flicker. Depending on Pick Up design & dirty track, this flicker can be annoying.
Operation of the above Revised Circuit. The rectified 12 to 14 Volts D.C. charges up the Capacitor & supplies power to the 5 Volt Regulator that provides a constant 5 volts to the all LED/resistor combinations.
A loss of power, the discharging Capacitor supplies power to the Regulator that still supplies a constant 5 Volts the LEDs and the LEDs remain at a constant brilliance until the Capacitor’s voltage drop low enough that the Regulator cannot “regulate” any longer & the LEDs start to dim.
The time the LEDs stay at FULL brilliance is determined the same as above – Capacitor size, load & how long is the loss of power.
The difference between the two circuits the LED’s brilliance drops as soon as there is a loss of power where in the revised one, the brilliance drops after some time period, determined by mainly the size of the Capacitor. A 1,000 uF 16 Volt Electrolytic Capacitor can hold a constant brilliance for more than a second, enough to eliminate any flicker. This will depend on the quality of the pickups and the number of LEDs (load).
Capacitor C1 Value. Using Capacitors larger than 1,000 uF, there needs to be a “Current Limiter” installed in the connection to the Capacitor to eliminate the “Inrush Current” tripping the DCC Booster’s Internal Circuit Breaker on powering up the layout of after a short circuit. This Current Limiter comprises of a 1.0 Amp Diode (1N4004) and a 150 Ohm ½ Watt resistor wired in “parallel”. The end of the Resistor/Diode combination with the Diode’s “Band (Cathode)” is connected to the Bridge Rectifier POSITIVE Output and the other end of the Diode/Resistor combination, connected to the + of the Capacitor/s.
Building the Light Board. I built my own DIY Light Boards using Veroboard and 5 x 3 mm Prototype White LEDs & 1,000 Ohm resistors. I mounted the Bridge Rectifier, 5 Volt Regulator & 470 uF Electrolytic Capacitor on one end, see below. If you were to make a few of these, maybe source some Surface Mount LEDs and resistors from Ebay but remember the quality & colour may not be what you want.
“Test build” one & see if the supplied colour & number of LEDs, illuminates the Passengers in the Coach, to your desired level of brilliance. The brilliance can be adjusted by changing the value the LED Voltage Dropping Resistor. In my initial version I used 1,000 Ohm resistors where the Current drawn was 3.5 mAs. I replaced the 1,000 Ohm resistor with 500 Ohms to increase the brilliance but the current draw increased to 25 mAs. This high current “demand” was too high a 470 uF Capacitor. I replaced the Capacitor with one of my “home made” 200,000 uF Stay Alives.
The white Marks on the Centre Strip of the Veroboard below, highlight where you need to cut the Copper Strip to isolate the LEDs/Resistor connection otherwise the Board will not work.
A close up the electronic components.
I have included the original Flicker Free circuit below.