# Keep Alive



## spdaylightfan (Nov 15, 2009)

I found several, I believe Soundtrax, purple heat shrink wrapped stacks of capacitors at a garage sale for five bucks. No instructions! I want to use them as keep alive devices in my lighted passenger cars. Is it simple enough just to hook them across the lines from the trucks to the lights. Observing polarity of course

Thanks


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## gregc (Apr 25, 2015)

spdaylightfan said:


> I want to use them as keep alive devices in my lighted passenger cars. Is it simple enough just to hook them across the lines from the trucks to the lights. Observing polarity of course


in what respect does polarity matter? how are you wiring your lights?


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## Lemonhawk (Sep 24, 2013)

Probably not. If its just stacked capacitors, and your using DCC, the caps will most likely "smooth" out the DCC signal making the decoders no respond. If your running DC, then the caps will follow the DC voltage and keep the whole railroad powered for a few milliseconds. Also, what circuitry is used to power your lights in the passenger cars? Do the lights respond to the throttle in terms of brightness, or are they independent of the throttle position. I think you need to know how the lights are wired in the car before adding any keep alive caps.


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## BMK (Sep 13, 2011)

You will find this article interesting on passenger car lights.

https://www.nmra.org/sites/default/files/sr201509_lighting.pdf


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## wvgca (Jan 21, 2013)

you may need a bridge rectifier as well ... they are DC devices that don't tolerate reverse voltage that well


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## gregc (Apr 25, 2015)

spdaylightfan said:


> Is it simple enough just to hook them across the lines from the trucks to the lights. Observing polarity of course


keep alives are added to the decoder after the bridge rectifier.

i believe a single diode would be sufficient in a passenger car application


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## D&J Railroad (Oct 4, 2013)

All the keep alives I have seen will keep a locomotive running for about 10 seconds after it leaves powered track. Quite a novelty, but when ya want to put one of those into a switcher, the size of it creates a problem. If they could be made in a smaller size by limiting the length of time they will run, that would be a practical device. The objective in the keep alive should be to run over an occasional bit of dirty track, not impress your friends with a locomotive that will keep its lights on after ya lift it off the track for a while.


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## gregc (Apr 25, 2015)

keep alives aren't difficult to make: diode, resistor and some # of caps. I've built some and just strapped them to the back of a 0-6-0. A more permanent solution would be to put them in the tender


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