RailPro > RailPro Specific Help & Discussion

RailPro and DCC discussion on Model Train Forum

<< < (2/2)

William Brillinger:

--- Quote ---And then there is the question of whether the AR-1 would even work on AC.
--- End quote ---

The answer is no. The RailPro AR's and such are only designed to work with a DC power supply, such as the PWR-56.

It is my understanding that many DCC systems are AC on the track, which is why I said the LM's are ok on AC or DC. The LM Manual does not specify DC that I can find.

Alan:

--- Quote ---But the peak voltage of an AC sine wave (the instantaneous max and min of the sine wave) is the RMS value times the square root of 2.
--- End quote ---

Assuming when we say AC we are referring to the AC wave of a DCC system...

You are speaking to sinusoidal wave AC. DCC is square wave variable frequency AC centered around 10kHz. Root mean square still applies just that you cannot use the sine of the wave. The reciprocal of the frequency 1/f is used to calculate RMS voltage of square wave AC. Since a DCC signal is variable frequency (long pulses / short pulses) the effective DC RMS voltage varies constantly however it tends to be very close to the peak voltage because of DCC signal peak dwell. Within the context of RailPro it doesn't matter. The high frequency DCC power is easily rectified and filtered internally by the LM.

With respect to 50Hz or 60Hz house current your explanation is spot on. I surely hope no one is trying to run their train track on such. They won't for very long!

Alan:

--- Quote ---thereby eliminating the reverse loop requirement
--- End quote ---

As stated earlier, as long as we have only two rails reverse loop requirements will be with us. Reverse loops and frogs - one of the few advantages of battery power.

Alan:
There may be some confusion about nomenclature. The model railroading community means old style variable throttle pack when they say DC. With RailPro we mean steady state voltage when we say DC.

Michael's AC explanation is applicable to throttle pack DC output since those units have no filtering or regulation. Even though the rheostat (throttle lever) varies the voltage/current, it does not smooth out the highly rippled waveform that is produced by the transformer inside the throttle pack. This works for DC motors because they don't need a filtered supply. The mass and momentum of the armature provides all the smoothing needed. Precise voltages (peak or RMS) are almost useless specs because the user simply moves the throttle until the train is moving at the desired speed i.e. getting the required voltage. If a second locomotive is placed on the same track it will reduce the speed of the first locomotive because the supply voltage is not regulated, it is throttled. Voltage varies with throttle position and load on a throttle pack DC layout.

For RailPro and DCC we are not directly powering motors. We are sending power to electronics that in turn power motors. The electronics require clean, steady state DC voltage. A RP layout has this available on the rails, a DCC layout has high frequency on the rails which is smoothed to steady state with small capacitors inside the LM. Additionally, with RP or DCC we expect one locomotive to not affect the operation of another locomotive. Therefore, the supply voltage must remain constant as load is varied. That is why both RP and DCC use regulated power supplies. Voltage does not vary with load.

The model railroad world generalizes into 3 categories: DC, DCC, and RailPro (or alt). All 3 use DC. The difference is what the DC waveform looks like. I whipped up an illustration to help:

melarson:
I'm getting the sense that because DCC is an alternating current signal, we tend to use the terms DCC and AC interchangeably.  But electrically they are two totally different animals, as Alan has clearly shown.

Actually, all I wanted to do (in my typically long-winded way) was to keep people from using [traditional] AC on the rails.  We suggest to people that they can give RailPro a try with minimal investment by purchasing a CI-1 and one or more LMs.  They can use a power supply they probably already have on hand to power the rails.  So they look in their train closet and grab, for example, that DCC Specialties MF-615 power supply they used with their Digitrax command station.  They see its output is 15VAC, they compare it to the guideline they saw (12 to 18 volts DC or AC), see a match and off they go, never suspecting that it could be a problem.

Would it not be better to tell people that they can use 12 to 18 volts DC or DCC.  It's a small, but important, difference, and Ring's specification.  Hopefully that would alleviate any concerns about the compatibility of a particular power supply and keep people's LMs from over-heating, operating erratically, or possibly failing.

Michael

Navigation

[0] Message Index

[*] Previous page