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When I've done PS3 steam conversions on my Premier steam locomotives I've run all the LEDs for lighting off the headlamp circuit, up to 8 total, without issue. I use 3mm LEDs with a 470 ohm resistor for the headlight and the other LEDs get 560 ohm resistors. I have a Premier GS4 that I bought a few years ago that was converted from PS1 to PS2 by the previous owner using the PS2 upgrade kit with the PS2 3V board. I'd like to convert it to all LED lighting off the headlamp circuit like on the PS3 steam upgrades I've done. Can the PS2 3V board support 7 or 8 LEDs on the headlamp circuit like the PS32 board used in the PS3 upgrade kits? I just want to make sure before I go ahead with the LED conversion. 

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Both the PS32 board and the PS/2 use the same FET to drive the lights, and they'll handle the same amount of current.  Eight LED's won't make them break a sweat.  I've put four 6ma bulbs on the PS/2 and PS32 board lighting output and had no problems.

Do you mean four 6V bulbs (incandescent)?

The point though is a PS2 3V board's 6V output should easily support 8 LEDs.  560 Ohms per LED would be a good starting point.  As with the PS3, you can mix/match resistor values for multiple LEDs to tune individual brightness.  The brightness will be different between PS2 3V and PS3 with the same resistor so some experimentation is in order.  A simple calculation (not technically correct but good enough for matter at hand) is to think of the PS2 3V lighting output as 6V DC.  Then, using say ~3V as the LED voltage, the resistor drops 3V.  So the LED current is 3V / Resistor or ~5 mA (i.e., 3V / 560 Ohms = 0.005 Amps).

This has been discussed in previous OGR threads but what can be confusing in an LED conversion is if you measure the DC output voltage (using a DC voltmeter) from a PS2 lighting circuit you'll only read maybe 2 or 3V DC.  How can that be?!

So as GRJ points out, the PS2 lighting circuit bulb outputs are really pulses of ~20V.  Then the techno-babble takes over with RMS voltage vs. average voltage and away we go down the rabbit-hole.

As mentioned previously, a good starting point is to just assume you're starting from a 6V DC output and calculate your LED resistor value(s) accordingly.  Yes, there may be an oddball application which pushes the boundaries and requires doing more math...but I can't recall such a situation here on OGR.

 

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