RailPro > RailPro Specific Help & Discussion

Keep Alive installation w/ Railpro

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Alan:
Not that it really matters but be aware there is a 1.4V drop across a bridge rectifier. Assuming you are using the 14.8V RP power supply, your loco is now actually running on 13.4V. The HC1 throttle knob is not marked in volts so the motor voltage doesn't matter much in actual use. You just turn the knob a pinch more. However, the missing 1.4V will ever so slightly change the start and top speed of a loco. If you are picky about how your locos perform then some fine tuning of your RP start and max settings may be in order after installing a bridge rectifier.

KPack:
Sorry, I should clarify my question a bit.  I know that coming into the rectifier it doesn't matter what wire goes where, but coming out it is polarized.  My confusion had to do with TCS's wiring instructions, which say to attach the blue wire from the KA to the positive on the decoder, which in our case is the blue wire on the decoder.  I'm assuming the external bridge rectifier makes it so we can just hook the KA to the black and red power wires after the bridge rectifier going into the decoder?  As long as the +/- on the KA is the same as the polarity on the exit of the rectifier.  Am I making any sense?

-Kevin

Alan:
Sorry Rob. I was posting while you were. By sheer accident almost answered your question. Sure, RP will run fine on 12.5V. Top speed may suffer.

A case could be made that if one loco has keep alive capacitors then all your locomotives should also. It would be interesting to study the MUing function between KA'ed and non-KA'ed. I am sure it will still work but am curious if there is an observable deterioration in function.

Alan:

--- Quote ---As long as the +/- on the KA is the same as the polarity on the exit of the rectifier.
--- End quote ---

Correct.

The keep alive deal is nothing more than fundamental power supply smoothing. At the heart of virtually every power supply out there. Perhaps you have seen an illustration like this:



The capacitor supplies current to fill in during the AC polarity changeover. This smooths the output voltage. The KA application functions the same except the periods of no supplied current (loss of connection to the track) are unpredictable in frequency or duration so a larger capacitor is needed to make sure there is sufficient current available to cover the longest interruption at maximum load. Electrolytic is a type of capacitor that can store a lot of energy in a small space. They are used in power supplies and KA for this reason. Electrolytic capacitors, with few odd exceptions, are polarized. Hence the + and - markings and why the KA has color coded wire leads. + must always be connected to + with an electrolytic capacitor. Hooked up backwards they explode. Sometimes violently.

TwinStar:
Fantastic!! I've been begging Tim for these for over a year now and I'm about to start wiring my E units for power and sound. This couldn't have come at a bette time. Hardware is being ordered now.

Thanks!

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