Judging from a quick search, I know there has been quite a bit of discussion on
this topic in these fora. The question of what is the optimal track voltage for DCC
operation in different scales, and, in particular, N scale.
I have a Prodigy Advance system which puts out 14.5V to the track. Will this hurt
my N scale locos? I’ve tried a few locos on the track and they work fine, so I guess
my question has to do with the long term wear and tear on the equipment.
As I do more research into this, I’m realizing that there are few if any DCC systems
that less than about 14V to the track. If I’m wrong here, please let me know.
The bottom line is that I’m transitioning from HO to N and I’d like to use the same
DCC system - the Prodigy Advance system. Do you think this is wise?
I don’t think it should be a problem. My NCE Power Cab is set up to run both HO and N and has an output that is slightly less than your MRC PA @ 13.5VA. I think you’re fine until you start exceeding 16VA or so.
I will be curious to hear from those who actually have a DCC system that has a separate terminal or switch for selecting the different scales and what those outputs are.
Thanks Tom. Yes, those are the people I’d like to hear from - those with a switch on their DCC systems
that changes the voltage from one appropriate for HO scale to a lower voltage for N scale.
You have to be careful measuring AC voltage (which is what DCC is). The frequency matters. So you get an incorrect reading using the AC voltage on a your meter to measure DCC. The meter is setup to correctly measure 60 cycle house current in RMS (root mean squared, NOT peak to peak). It’s not radically off, just not accurate with a more than a few volts, I suspect.
The best way to measure it would be with an oscillosope. Then take the peak to peak and divide by 1.4, I believe to get RMS.
The Digitrax DB 150 does have a three-position toggle for each of the scales. I inadvertently flipped mine up to the top O scale position when feeling blindly for the power toggle very close to it one time. I didn’t notice until perhaps days later…not sure when I did this… but I happened to measure the track voltage with a digital meter and got over 19 volts. To this day, I have had no troubles with any of the decoders.
As Tom says, though, an accurate measurement in N scale output should not be much over 15 volts, maybe 16 tops.
When DCC voltage is measured at the track, it is the peak to peak measurement of the bipolar DC voltage. does alternate, but I think I’d say it really has more characteristics of a DC voltage than AC, but that’s a totally different discussion. Antway, the thing is, that what is important is what can get to the motor, and that is going to be at most about 1.5 Volts less than the voltage to the tracks. So it you have 14.5V at the tracks, you won’t have any more than about 13V (and probably less) at the motor, at the most. If you want to, you can measure the effective voltage by measuring a function output (at least for most decoders) or you could measure the voltage at the motor at full speed. There’s an NMRA spec of the minimum maximum (I hope that makes sense) that a decoder should be able to handle for N scale, unfortunately, all that does is say your decoder should be safe. The motor could be another issue, but in general, it won’t be.
Well, the thing that made me ask this question of myself and also do some research on this topic
is the realization that Tony’s Train Exchange will consider the warranty on their DCC decoder
installations void if an N scale loco is operated on a voltage greater than 12 Volts. Judging from
what is available out there for DCC systems, it seems that finding one that produces a track voltage
of 12 volts is not so easy. For example, the Digitrax Zephyr produces 12.8V on the track.
Has anyone had a problem with Tony’s in this regard?
The NMRA DCC Standards and Recommended Practices makes no distinction between Z, N, and HO scale as far as track voltage is concerned. The RP is 14.5 Volts for all scales, so there will be 12 Volts available to supply to the motor, until you get up to O. That’s why you can use Z, N, and HO scale decoders interchangeably as long as they have sufficient Amperage rating for the current draw of the locomotive.
If that’t the case they are just being overly conservative and covering themselves. Here’s the NMRA bit I mentioned earlier. It does differentiate between scales, but only on the max allowable voltage:
C: Power Transmission and Voltage Limits For Transmitting
Power Through the Rails
The baseline method for providing the power to operate locomotives and accessories, which shall be
supported by all Digital Command Stations and Digital Decoders, is by full-wave rectification of the
bipolar NMRA digital signal within the Digital Decoder7. In order to maintain power to the Digital
65 Decoders, gaps in bit transmission are only allowed at specified times (see S-9.2, Section C). The RMS
value of NMRA digital signal, measured at the track, shall not exceed by more than 2 volts8 the voltage
specified in standard S9 for the applicable scale9. In no case should the peak amplitude of the command
control signal exceed +/- 22 volts. The minimum peak value of th