Passenger Car Lighting

[TwinStar]

I thought I had seen a simple dual DC/DCC circuit to power interior passenger car lights. I'm open to any style/design but I'm running into walls on finding a simple, and hopefully cheap, solution to light a LOT of passenger cars.

I could have sworn I saw a rectified capacitor circuit somewhere.

[G8B4Life]

Something like this?


From http://cs.trains.com/mrr/f/744/t/251747.aspx?sortorder=desc

Adjusting the values for the required brightness for H0 shouldn't be too hard, just don't ask me how as I don't know 

There are plenty of circuits out there, a Google search for "passenger car lighting circuit" brings up quite a few. In fact there's probably more than a couple of commercially available circuits if you want to spend the time looking.

Edit: Depending on how many is "a LOT" of passenger cars you'd probably need a lighting circuit for each car. It is probable you could use a circuit like the above to light a few cars in a set but something like a 10 to 14 car streamliner set the current draw of all the LED strips is likely going to make the component size and inter-car connecting wire become too big and cumbersome.

- Tim

[TwinStar]

Something like that Tim. I finally found what I had buried in the back of my mind:

https://www.scalesoundsystems.com/product-page/basic-stay-alive-kit

Two things may be missing on this though. I need the ability to run on fixed DC and DCC and I'd like a on/off switch (reed perhaps). I also do not want to interconnect cars as my passenger consists will vary and actively be switched out.

The C1 in your diagram is the capacitor?

[TwinStar]

I think I'd want it switched between one power lead and the rectifier to prevent too much in rush current for cars that are off but on the track.

Capacitor capability would only need to be 2-5 seconds just get over intermittent track and keep the lights from flickering.

[G8B4Life]

I guess a stay-alive would work. To get it to be DC and DCC capable you'd need to put a bridge rectifier in. Wiring the car's up like the way we have to wire an LM-2 up for keep alive should work, feeding lights instead of a module.

There are latching reed switches around, some models here came with them for exactly the same purpose, turning the lights on an off with a little magnetic wand. I guess where you put the reed switch is up top you (I've put the reed switch inbetween the bridge rectifier and the rest of the stay alive) as long as it's between the track and the keep alive.

Hopefully Alan will come along and poke any holes that need to be poked in this idea.



I hope to use this circuit one day; I've got a LED light bar here that uses it and it's very effective, plus it has a pin on the IC to turn the whole thing on and off which might be able to be controlled with an LM.


www.diodes.com/assets/Datasheets/PAM2861.pdf

- Tim

[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]

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

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]

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.

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

[Alan]

Capacitor discharge voltage curve.

[TwinStar]

Got it, thanks.