RailPro > RailPro Specific Help & Discussion
Keep Alive installation w/ Railpro
Dean:
Seriously considering adding Keep Alive to my RailPro fleet. I understand how it works with DC, but what about DCC? You need a true RMS meter to measure the track voltage because of the DCC waveform. Will this affect the rectifier? Will the DCC signals being sent over the track have any affect?
Digitrax has a keep alive module that is much cheaper than the TCS module. Will it work using the same circuit?
Thanks
Alan:
Not being a user of either brand keep alive nor a DCC user, the best I can do is offer a bit of general information.
Keep alives use supercapacitors, sometimes called ultracapacitors, which are a type of super high density electrolytic capacitor. Large value capacitors, especially electrolytic, are slow changing devices on electrical timescales. They are sluggish. Because of this they do not smooth out high frequencies very well if at all. The DCC square wave is somewhere around 10kHz if I recall correctly. That may very well be above the effective frequency range of the capacitors used in these two commercial keep alive products.
Common in electrical circuits is a combination of a large capacitor and a small capacitor together to filter electrical noise on a supply line. The big slow capacitor supplies large current during the long dips while the little fast capacitor supplies current during the short quick dips. i.e. the big cap takes care of low frequencies, the little cap takes care of high frequencies. Here is a practical example used in my detection boards:
In this circuit the 555 timer chip produces both low and high frequency noise on the supply line every time it changes state. Equate that to losing rail contact (low freq) and DCC signal (high freq). The big electrolytic on the board carries the load for the long slow changing dips. The little ceramic cap next to it reacts fast carrying the load during the short fast dips. The result is noise-free supply line. This big cap little cap combination is extensively used in electronics. If the little cap were not present then the the high frequency noise would still be on the supply line. I suspect the keep alives work the same way.
TwinStar:
This setup will work whether you're applying DC or DCC to the rail, correct?
William Brillinger:
Yes, this will wok with DC and DCC power.
William Brillinger:
Here is a nice overview of available Keep Alive options:
https://sites.google.com/site/markgurries/home/decoders/keep-alive-compatibility
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