LED wiring in DC and DCC

[donhalshanks]

I want to wire an LED to a panel to show whether I have power on in a spur track.  I can't remember whether an LED wired in series with a resistor across the DC will light (when spur has power) when the direction of the DC (+,-) is changed with a direction switch..... or do I have to wire two separate LED's in parallel so that I always have one that lights?

If the latter, is their a type of an LED that lights for both directions of polarity?

In all cases, can either DC or DCC be used to power the LED.

Thanks. Hal

[cacole]

LEDs are polarized and will light only when they received the correct polarity, so on a DC layout when you reverse the polarity on the track the LED will either light or stay dark.  The variable voltage on a DC track will also cause the LED to not light at slow speeds and glow very brightly, and possibly burn out, at high speeds.

For a DCC layout, the LED will use only half of the waveform and will glow consistently bright regardless of the direction of travel of the locomotive.

A solution to the polarity reversal problem on a DC layout is to use a small bridge rectifier connected to the track so the LED receives the correct polarity regardless of the direction of travel; however, you're still faced with the problem of variable voltage on the track causing variable brightness of the LED.

Although it requires more wiring, I use 4PDT toggle switches to turn siding tracks on and off, with one side of the switch connected to the track and the other side to a constant-voltage DC power supply for the LED.  This arrangement keeps the LED burning consistently bright regardless of the polarity or speed setting of the power pack, and it goes off when the track's power is turned off with the toggle switch.

[CSX Robert]

A brdige rectifier is not a good solution to the polarity problem because it adds a voltage drop that exasperates the problem of the varying brightness of the LED because it will take a hgher voltage to even turn it on. Two LED's wired in parallel but opposite polarity will work, or you can use a bipolar red/green LED(red with one polarity, green with the opposite polarity).

[donhalshanks]

Any chance someone can show me a wring diagram for the solution "cacole" gave in his response using a 4PDT switch?  I have never wired a 4PDT.

Hal

[gandydancer19]

A 4PDT is just like two DPDT switches mounted side by side but in the same package with one handle.