Typical Voltages for non-DCC layouts


Eddystone

Eddystone

in Eddystone, PA
I'm new here, so I hope it's okay to post this question in this section.

I'm getting back into the hobby after a long break. Most of my locos are mid-90's, and none of it is DCC. I have set up a temporary oval of Atlas track (the original stuff with the black roadbed under the ties) on which to test some of the locos and rolling stock. I've cleaned the silver rails, but they don't look like high quality nickel silver. I have a power supply that I built based on a design in a hobby book, and frankly I need to dig up that book to recall what the design of this thing is. It has a wired cab control with brake and momentum and may even be pulse width modulation. It is powered by an extremely high quality regulated supply that came out of a piece of medical imaging equipment.

Here's the question: When this supply is maxed out, there is about 13.0 or 13.6 volts DC available at the rails with the loco running. I've heard this is correct for HO, but the engines seem to run a bit slow, even at max, and the headlights are somewhat dim. Basic power supplies like the MRC Rail Power 1300 are rated at 15 volts DC, and with that voltage at the tracks, the engines seem to run at speeds I would expect with the headlamps at the proper brightness. (On some engines, this is probably above prototype speeds.)

Bearing in mind that this is NOT DCC, can I get some feedback on the maximum track voltages people are running, please?
 
Thanks for the reply. Would you say that the 12v you quote is for current state of the art stuff? I'm finding that I need to catch up on newer technology, and sometimes what was good for my original series Proto 2000 locos is not what's good for today's new engines. Locos designed with DCC and pulse width modulation are sometimes not optimized for older power supplies.

Why do you suppose companies like MRC are still selling basic units that put out 15 VDC if loco manufacturers recommend 12 VDC? I suppose there is a division between "serious" power supplies and "toy train" power supplies, but MRC doesn't seem to make that distinction.
 
The manufacturers didn't set the voltage. It was the NMRA, National Model Railroad Association. It has a series of Standards that cover this subject specifically, (and many, many others as well). The Standard for Electrical is S9 and can be found here: http://nmra.org/index-nmra-standards-and-recommended-practices Go down the list to Electrical-S9 and click on it, and it will open up the Standard that starts with, "I. POWER A. Full throttle voltage available at railhead shall not be less than 12 volts direct current at maximum anticipated load. (1)" Different Standards for DCC and etc have their own standard number.

The NMRA website, http://nmra.org , is a prime reference that all RR modelers should use, not just for the Standards and Recommended Practices.

I have also read in several RR model mags, that if the power supply puts out filtered DC, the locos will run slower at 12 volts than when using a non-filtered supply. You medical power supply is probably filtered.
 
Last edited by a moderator:
Thanks, Cary!

Interesting that the standard only sates that at least 12v should be available but doesn't mention an upper limit.

RP-9 Electrical, however states that supplies must "produce between 12v and 16v while delivering rated current." So technically, that 16v should be the upper limit for DC operation. There are pulse width modulation waveform diagrams in the standards section that seem to show the upper limit of the pulses at 15 volts. There's some sort of discrepancy between loco manufacturers REPORTEDLY stating that voltages should max at 12v and the NMRA allowing up to 16v. I read some threads about Kato engines burning up with more than 12v supplied.

From an electrical standpoint, the NMRA does not seem to be sufficiently specific about what they mean by DC because should be a constant voltage level which implies filtering or voltage regulation to remove instantaneous variations in level that occur with unfiltered half-wave or full-wave rectification.

I need to dig out the magazine with the schematics for the power supply that I built to see what the circuitry is. It's been a long time. I used to have an oscilloscope that I used every day in field service, and that would answer all of the questions. The medical supply I am using is probably filtered and regulated, as you mentioned, to yield a virtually flat DC voltage with no ripple at all. I gather that supplies like the MRC Railpower 1300 and 1370 are either full-wave rectified or half-wave rectified which is like 100% ripple. It's possible that my supply may even be current-regulated to some extent. I guess I need to find some answers at this end before asking any more questions.
 
All the technical stuff aside .... do you really run your trains even at 12 volts ? Back when I was using DC on my older layouts, even a mainline train was running at only 6 to 8 volts max.. But then, my layout wasn't big enough to warrant running them any faster between points A and B ! ;)


Mark.
 
Mark,

My layout consists of a 300 ft long straight shelf with turntables at each end, so I need the speed! ;-)

But seriously, folks, right now I am just running on an oval about six feet end to end with 18" curves. The trains just look slow at 13 volts and the headlights are somewhat dim. At 15 volts, the better engines are marginally faster while the cheaper engines are zipping around like toys.

I got an email back from someone at MRC regarding the Railpower 1370, and he said that that unit puts out 15 volts with no load and drops to 12-13 volts under load. Sounds like a big drop to me, and that is not what I am seeing on my little oval.

Glen
 
Glen,

Keep in mine that the RP you quoted is a Recommended Practice and not a Standard. Some have taken that RP and brought out locos that are designed to run best at 18-24 volts DC, (mth). Also keep in mind that a Standard is simply a minimum level of performance and not necessarily the peak.

The Railpower 1370, is a rather small pack, designed for a small layout with one or two engines running at the most.
 
Eddystone:

What is the mechanical condition of the locos? Are the armatures clean? The truck wheelsets and track clean? If you have Athearn locos, are they hard-wired? Is there a headlight shining on the loco while running? How are your tracks connected? Rail joiners only, or rail joiners and track soldered at some joints?

I think you may also need to use a volt meter on the track to determine what the voltage is without a loco running and then with one running to get accurate readings to help you figure out what is going on and what your loss is.

I fixed some of my railroads's voltage problems just by soldering some of my rail joints. It eliminated a lot of jerkiness and power loss. Good luck!

Photoman475
 
I have an around-the-wall with return loops (continuous running, not reverse loops) and a 3% maximum grade. I run both DC and DCC (by switching between an MRC 260 and an MRC Tech 6 6.0 DCC, depending on the locomotive). On DC, going uphill, depending on the "tonnage" and whether I'm running one or two Athearn "Blue Box" diesels, I seldom run more than 10volts DC indicated by a DC volt meter permanently wired on the DC bus. Amperage under that load may run 1.5 - 2.0, depending on the lashup and the load. That is seldom more than 50-75% throttle. Once on the level I usually back off to about 40% throttle to keep the trains from looking unprototypically fast. I don't have meters on my DCC bus, but my heaviest train is the Denver Zephyr with a Walthers Proto2000 E5A (was an E6) and E-8/9 pulling six passenger cars, including three that are old extruded aluminum, with the others Athearn Blue Box streamliners. On the grade, I do have to turn the knob to 83 as the grade has a 22" radius curve at both the top and bottom of the grade! Have no idea what voltage nor current that corresponds to. I'm no electrical genius (my aerospace career involved mechanical stuff), but I'd recommend wiring in DC volt and ammeters to see what kind of loads those slow engines are creating. Could be they need lubing and cleaning.
 
You must log in or register to reply here.



Back
Top