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Passenger Car Lighting

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TwinStar:
Tim:

That looks like what I had in mind assuming I'm reading the schematic correctly. The next trick will be to see if I can etch a board that simplifies the assembly and installation. A board that 'snapped' into shorter sections to accommodate shorter RPO's would be useful as well. I think I remember a website that allowed you to draw and etch your own boards but I may be mistaken.

carrson:
I have some older Athearn blue box passenger cars that I have put LED's in to replace the bulbs..

I saw this video.. I think I will try this method

G8B4Life:

--- Quote ---I saw this video.. I think I will try this method

--- End quote ---

That's a very simple (but effective) way of doing it however there's a couple of gotcha's to be wary of.

LED strips are usually rated at 12v. RailPro puts out ~14v and a typical value for a DCC Command station / Booster output is ~16v. The bridge rectifier knocks ~1.2v out of that but is still greater than 12v so you would need to put in the extra resistor in as shown later in the video otherwise you could be shortening the lives of the LED's or resistors considerably depending on how much leeway the manufacturer has built into the LED strip.

On a conventional variable DC supply (trainset throttle) which is what it appears the guy in the video uses this system is fine. On RailPro or DCC for one or two cars it might be fine as well but for many cars (like Jacob needs) the RP or DCC supply might see the inrush current as a short (conventional variable DC supply likely does not have this type of protection built in) and may need to be taken into account. This is what those extra components in the Stay Alive kit prevent from happening.

Hmm, I wonder how many of these parts I have in my electronics bit's and bob's box? Might have to try an experiment or two.

- Tim

Alan:
First off you do not need all the complexity of the Scale Sound Systems keep-alive just for running LEDs. Tim's first schematic is all you need. A bridge rectifier and capacitor will get the job done. If you experience over-current shutdown then place resistor (R1) ahead of the capacitor to limit the in-rush current. Don't bother using a tantalum capacitor in this application unless space is at a premium. A garden variety electrolytic capacitor will work fine.

Secondly, LEDs are current devices so voltage is irrelevant. Simply use Ohm's Law to size the resistor for the desired current flow at whatever voltage you are using. If you are using strips they already include limiting resistors sized for 12V. You will only need to add an additional resistor (R2) if operating from a voltage higher than 12V. Remember, the bridge rectifier will drop the voltage by 1.4V.

The reed switch can be placed anywhere in the circuit.

All of this advice is based on the assumptions a) you need only a few seconds of stand by power; b) you don't mind a very slight brightness change. If either of these assumptions are false then you will need a much more complicated circuit more akin to Tim's constant current IC.

BTW you can build your own copy of the SSS keep-alive for a tiny fraction of their price. If you don't mind waiting 30 days to get the parts from eBay China you can probably build dozens for the price of one SSS keep-alive.

TwinStar:

--- Quote from: Alan on June 30, 2019, 05:42:53 PM ---First off you do not need all the complexity of the Scale Sound Systems keep-alive just for running LEDs. Tim's first schematic is all you need. A bridge rectifier and capacitor will get the job done. If you experience over-current shutdown then place resistor (R1) ahead of the capacitor to limit the in-rush current. Don't bother using a tantalum capacitor in this application unless space is at a premium. A garden variety electrolytic capacitor will work fine.

Secondly, LEDs are current devices so voltage is irrelevant. Simply use Ohm's Law to size the resistor for the desired current flow at whatever voltage you are using. If you are using strips they already include limiting resistors sized for 12V. You will only need to add an additional resistor (R2) if operating from a voltage higher than 12V. Remember, the bridge rectifier will drop the voltage by 1.4V.

The reed switch can be placed anywhere in the circuit.

All of this advice is based on the assumptions a) you need only a few seconds of stand by power; b) you don't mind a very slight brightness change. If either of these assumptions are false then you will need a much more complicated circuit more akin to Tim's constant current IC.

BTW you can build your own copy of the SSS keep-alive for a tiny fraction of their price. If you don't mind waiting 30 days to get the parts from eBay China you can probably build dozens for the price of one SSS keep-alive.

--- End quote ---

What would be the cause of the brightness change? Different voltage across the rails?

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