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You don't need a relay Dave, the headlight power will handle at least three and probably four 60ma incandescent bulbs.  If you use LED's, you can handle a fistful more!  I've wired the markers, flickering firebox and headlight to the headlight power with no issues at all.  I normally use LED's in any case for upgrades, so I'm probably using less power than many "stock" installations.

 

FWIW, the FET's that drive the headlights are rated at .7A or better continuous current.  The limitation of power for lighting is probably the available power, not the switching of the headlight itself.

 

Last edited by gunrunnerjohn

MTH recommends only 2 bulbs, but acknowledges some factory come with 3 bulbs on a circuit.  As far as powering a CV board that has far more components on it than just the bulbs so you are power other circuits that may not be efficient.

 

Dave's idea is correct and what has been done before.  Some guys just take the relay off the PS-1 bottom board, or a PS-2 5V board for upgrades and use it.   G

I've seen more than one PS/2 locomotive with three bulbs on the headlight circuit, so I suspect that is possible.  If you restrict it to the current for three bulbs, that's 180ma.

 

As I mentioned, I use LED's for upgrades, so I can use eight or nine of them and still be under that value.  Also, I typically use higher resistance for the markers for even less current, as running them at 20ma typically makes them unrealistically bright.

 

Since the CV board expects track voltage AC, the relay would be necessary if you wanted to drive it from the headlight circuit.  I just prefer to dispense with it in most cases and run the lights directly.  Since you already have constant voltage from the PS/2 board, using the CV board is kind of redundant in any case.

Originally Posted by CRH:

In the October/ November 2007 issue of O Gauge RR magazine there is an article written by Jim Wolsiffer  on how to do this with a relay and some other components. 

Keep in mind the PS2 bulb signals are pulsed to deliver constant power to a filament.  At high track voltages, the pulses are quite narrow and the voltage is applied maybe 10% on, 90% off.  Relays behave differently than bulbs in terms of "output" in response to pulsed inputs.  So if you're driving the relay coil with the PS2 headlight signal, I'd take a look at that article or have CRH summarize the "other components"... I'd think a capacitor would be involved.

Originally Posted by gunrunnerjohn:

I've seen more than one PS/2 locomotive with three bulbs on the headlight circuit, so I suspect that is possible.  If you restrict it to the current for three bulbs, that's 180ma.

 

As I mentioned, I use LED's for upgrades, so I can use eight or nine of them and still be under that value.  Also, I typically use higher resistance for the markers for even less current, as running them at 20ma typically makes them unrealistically bright.

 

Since the CV board expects track voltage AC, the relay would be necessary if you wanted to drive it from the headlight circuit.  I just prefer to dispense with it in most cases and run the lights directly.  Since you already have constant voltage from the PS/2 board, using the CV board is kind of redundant in any case.


If you are doing an upgrade to a premier engine, and the board is in the tender, you don't have sufficient wires to power all the engine light features.  G

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