This is a pretty simple task but my question is do I need to add a load resistor or is that covered on the PS-2 5V board? The leds are tiny 2mm wired in series and don't appear to have a resistor inline. This is the pre-wired MTH led harness that is included with PS-2 upgrade kits PN# CE0000005.
Thanks, Rod
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No resistor needed, the PS2 lighting outputs are already current limited.
What voltage LED is needed for 5v PS2 ?
Jim,
LEDs are always rated first by current, then by voltage. In other words you feed them a current, they light up, and in doing so they then settle on an appropriate voltage for that current. (This is the opposite of how we normally handle incandescent lamps, where you apply a specific voltage and the lamp, when at that voltage, draws a resulting current.)
In this situation Rod described how the LEDs were wired, i.e. in series and fed by a specific LED drive circuit in the PS board set, which provides the precise current necessary. This is probably somewhere around 25 mA, which is common to many red LEDs.
You don't need to worry about voltage -- the board provides the correct current so that the LEDs both light up and reach that voltage, whatever it is.
Mike
@Freight Train Jim posted:What voltage LED is needed for 5v PS2 ?
Edit- basically following what was just said above.
Dedicated outputs are designed for LEDs- so if using one of those- 2 LEDs in series- is the correct "voltage" for the 2 marker outputs and single LED for Beacon. Since color of LED is related to voltage and both red and green work- again voltage is not how to best describe the LED.
If replacing an incandescent bulb output - totally different ballgame- you need a current limiting resistor in series with the LED as PV is an unregulated source.
@Jeff_the_Coaster_Guy posted:No resistor needed, the PS2 lighting outputs are already current limited.
Correction, the marker and beacon lighting outputs are current limited for PS/2. If you put an LED directly on the headlights, number boards, ditch lights, or cab light outputs, they'll be toast in seconds.
OK thanks guys, good stuff. So Vernon that schematic is for the 5V boards I guess because it shows headlights etc as incandescent. It also shows markers as pairs of series leds with no inline resistors so that agrees pretty well with what we are saying here.
And John good point on adding resistors if converting any bulb outputs to leds!
Thanks all.
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