FW: [RFI] RR crossing lights

Ed - K0iL k0il@arrl.net" <k0il@arrl.net
Fri, 20 Dec 2002 07:23:27 -0600

As promised.  My connection in the RR business had some info on the RR 
crossing lights.  Looks like the LED displays are the future not only for 
traffic lights, but the RR business as well.

de ed -K0iL

-----Original Message-----
Subject:	Re: [RFI] RR crossing lights


We have been installing red LED lamp units in our crossing warning systems
for several years.  We would like to have LED lamp units at all of our
crossings, but with approximately 13,000 active warning systems it will be 
few more years before all of the old incandescent lamp units are replaced.
The LED lights will operate on AC or DC as most existing crossing warning
systems on our railroad and across the country use AC for normal operation
and DC as a backup when the commercial power is off.  Unlike traffic
signals, crossing warning systems must continue to operate when the
commercial power has failed.  AC operation doesn't necessarily indicate the
presence of a switching power supply, a bridge rectifier on the input will
provide for AC/DC operation. Most crossing warning systems use 10 volt 
operated by a 12 volt power system.  Some LED lamp units use a current
regulator and a low voltage stack of LEDs to allow operation directly from
12 volts.  Switching power supplies are used in some brands of LED lamp
units because the manufacturer has chosen to stack more LED's in series 
12 volts can drive directly.  One popular model uses a 70 volt stack of 
operated from a switching power supply.  The switching power supply 
are more efficient as no wattage in wasted in current regulating circuitry.

Power systems for railway signaling and crossing warning systems are never
grounded.  This is done to maintain the integrity of the low voltage DC
circuits which we use to control our wayside (train) signals and crossing
warning systems.  One byproduct of our "balanced" power systems is that any
RF hash we produce is not in reference to a ground plane, which reduces our
incidental radiation.  Likewise, any external RF that our systems are
exposed to ends up in common mode on both polarities of our power systems,
limiting the RF voltage appearing at the input terminals of our equipment.
When grounded equipment must be used, such as a VHF or UHF radio with a
grounded negative, we isolate the grounded equipment from our main power
system with a DC to DC converter.

Red LEDs were the first to be cost effective.  The development of yellow 
green LEDs has reached the point that we plan to start using them for
wayside signals next year.  Burned out signal lamps are one of our largest
(and most frustrating) causes of train delay.

Here are some links to manufacturers of railroad LED lamp units:




> -----Original Message-----
> From: Rob Atkinson, K5UJ
> I'm not yet calling this a problem, but in keeping with the earlier 
> on traffic signals, I noticed on the way home last night, when stopped at
> railroad crossing, that the big red flashing lights were big red LED
> lights.
> Rob Atkinson
> K5UJ
> k5uj@hotmail.com