LEDs yield 10x power reduction in Realtrax lock-on and Switch bulb power
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stan
Joined: May 18, 2008
Topics: 17 Replies: 16
Topics: 17
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This is more a demonstration of applying LEDs than something practical to do given the triviality and required handiwork.
The stock bulb in an MTH Realtrax lock-on draws 1/2 Watt at 10V AC and doubles to 1 Watt at 18V AC. Apparently off-the-shelf 18V LED replacements with Christmas-light style press-in bases are not available at this time. Four white LEDs as used on 12V LED lighting strips popular for retrofitting passenger cars (about 5 cents per LED) can reduce power to less than 1/10 Watt per lock-on with no loss of brightness.
The idea is to mount the 4 LEDs at 90 degree angles aimed at the 4 lock-on lenses. The 3528 (3.5mm x 2.8mm footprint) surface-mount LED is one popular type used on 12V strips. The LEDs are mounted on 0.1" grid electronic prototyping project board. A 2.7k Ohm 1/8 Watt resistor limits the current into the 2 pairs of LEDs. Within each pair, the back-to-back (opposite polarity) wiring limits the reverse voltage across an LED since its mate will be forward conducting at 3 Volts.
The original 18V incandescent bulb has a wire diameter of 0.01" so #30 solid wire (also 0.01") is used to attach to the LED assembly.
As the photos show, even at less than 1/10th the power, the LEDs perform admirably. In fact, the LEDs hold there brightness at lower voltages better than the incandescent bulb.
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JohnBoy
Joined: May 14, 2008
Topics: 110 Replies: 517
Topics: 110
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Very nice project Stan. A vastly superior way to light these up. I'm betting you reduced the heat an order of magnitude as well.
John
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stan
Joined: May 18, 2008
Topics: 17 Replies: 16
Topics: 17
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Amending this to show the same 4-LED plus resistor design can replace the incandescent bulb in the Realtrax lever-switch control box. In this case the LEDs face upwards (rather than sideways) to illuminate the red or green lens. The components are the same as for the lock-on conversion.
Progress: