What's the correct DCC voltage ?

Garden Railroading
1

So, I finally got my 10 amp NCE DCC system hooked up to my outdoor layout. So far, I have successfully run an LGB Mikado and a AML K-4 Pacific. The question I have is what voltage should I be putting on the track?

The NCE instructions recommend no more than 18 volts so that not too great a load is placed on the train lights. The problem so far is that these loco’s don’t move very fast without getting them up to about 20 volts. 20 volts is where I have set the booster now and still am not getting much speed out of the AML K-4 Pacific with it’s new lower gear ratio motor. (Greg E., I know you warned me about this but Accucraft only offers two choices).

I additionally have a USA Trains Hudson loco (decoder to be added), and dual USA F-3’s that I will run in a consist. Included are Aristocraft heavyweight cars and a couple of USA cabooses with lights.

Do I have to worry about burning out lights or are all these lights rated for 24 volts? The K-4 Pacific has LEDs with proper dropping resistors.

Thanks for any input,

Tom

2

For N and HO scale, the usual voltage setting is 14.5 Volts; for G scale, 20-21 Volts. DCC equipped locomotives will run slower than straight DC versions due to the decoder’s conversion of the DCC signal to DC power for the motor.

You may be able to increase the top speed by adjusting the decoder’s CV 5, Vmax, to a value of 255 if it is not already set at that value.

Here’s some good information about power requirements for the different scales:

http://www.loystoys.com/info/power-supply.html

3

Most large scale train electronics (locos, lights, smoke units, etc.) are designed to run off of 24 volts to the track, as that’s kind of the “unofficial” standard for track voltage. In many cases, the on-board electronics contain voltage regulators to control the voltage to the lights, smoke units, etc. It’s rare that I’ve seen a large scale train with electronics that went “poof” at 24 volts. I know many folks who run DCC with 24-volt power supplies without much worry. You will want to make sure that the particular decoder you’re using can handle it, though. Most large scale decoders can, but–again–there are the odd ones out that cannot.

Later,

K

4

You need to read each mfg spec on max voltage.

Zimo rates many decoders at 30 volts with some surge ratings up to 50 volts.

MRC had 21 volts on the older G decoders.

Just saying NMRA compliant is not enough, one needs real voltage values to be safe.

I set my Zimo system ot 24 volts and run zimo, MRC, LGB, Massoth, digitrax decoders and my only failure was a MRC 1818 blew the mosfets.

5

In addition to what Dan said, I have to counter what Kevin said.

While many manufactures may SAY their trains run up to 24 volts, you would rarely run the train at 24 volts for any length of time.

DCC having constant voltage will often burn out small incandescent lamps in locos unless you put some voltage dropping in.

For example, the marker lights on Aristo steamers are 18 volt… leave them on 21 volts and they won’t last long, and will die really quickly on 24 volts DCC.

So, you cannot compare a “maximum DC voltage specification” from the manufacturer to a constant DCC voltage applied to lamps that are just getting track voltage.

Also, there may be things like unregulated smoke units.

All of these things should be taken into consideration if your DCC voltage is higher than about 18 volts.

When you buy an NCE system, unmodified, it can normally be adjusted up to 20.1 to 20.3 volts.

I’ve had mine modified to get really close to 24 volts and this made an appreciable difference in top speed on several locos, BUT it will not be enough for your K4 with that lower gearing, it will NEVER achieve a prototypical top speed. I’m bummed too, I have two of them. I’m working on getting the gearing between the stupid ratio supplied, and the way too low gearing the replacement motors have.

I have been happy with the decision to standardize on 24 volts to the rails, and I’ve been contemplating a Zimo system and I’ve made sure I can get 24 volts to the rails.

Sorry I can’t be of more help… if I find some magic for the 1:48 gear drive to change it to 1:30, I’ll publish it on my web site. I have a mill and lathe and it looks promising.

Greg

6

Greg, are you referring to the bulbs themselves? Very well may be the case. With the stock wiring, the Aristo locos I’ve worked with seem to be regulated to around 5 volts so to be more-or-less constant brightness at all but the slowest throttle setting. Gut the stock wiring, and yeah, all bets are off on whether the bulbs are up to 24 volts. (Which I can say ain’t likely, given my experience.)

Later,

K

7

Yes, I took care to be specific as to the brand, model, and the particular lights.

Quite a few lights run straight from the rails, and there are still incandescent bulbs out there.

Just something to be aware of when converting… for me the advantages of 24 volts far outweighs the disadvantages.

Regards, Greg

8

No doubt, there are plenty of locos out there that have unregulated incandescent bulbs for the lights. That’s been SOP since the dawn of time until just recently when LEDs started taking over, and the incandescents that are being used have to maintain similar performance. Anyone doing any kind of electronics installation needs to know what the lights in the locomotive are rated at, and plan accordingly–either by including the necessary electronics so not to blow the lights, or by swapping out the lights with something that will stand up to the voltages they’re using.

I’m still a bit confused about your statement “…the marker lights on Aristo steamers are 18 volt…” The Aristo steamers I’ve worked on and/or reviewed recently have all had markers/class lamps fed by a 5-volt voltage regulator. What the bulb itself is rated at is immaterial, so long as it’s more than 5 volts. The bulb and the regulator work in tandem, much as an LED and its dropping resistor.

As I’m reading your statement, you’re asserting that Aristo steamers have unregulated 18-volt bulbs in a 24-volt world, and this is causing the bulbs to blow when run at full throttle. Since this isn’t the case on the most recent production Aristo locos, which specific Aristo steamers have exhibited this behavior? I looked on your web site, but could find no references. I think this is something our readers here would like to know more specifics about so they can take appropriate steps to correct the issue. (And should be included in your web pages with your other tips about improving Aristo’s locos.)

Later,

K

9

First run mallet

10

Also, those analog/DC engines had heat sinks for regulators that do not have enough mass for the extra watts that 24 volts needs for heat dissipation. I just looked at the new Bachmann 3 truck shay DCC sound version and tied it to the zimo system and the 7812 100ma regulators were so hot you could not touch them.

So, I will remove the original board and rewire this engine.

11

I just got my computer working again this a.m. (Friday) since getting hit with lightning Monday morning. So - just getting caught up on this thread. Based on what I am seeing from you experts, I need to talk to Aristocraft about their lights in my heavyweight passenger cars, USA Trains about their lights in their cabooses, and the decoder manufactures if I have hooked my loco lights up directly to the decoder - right??

Tom

12

If you’re going to be powering your lights from the decoder, the first step would be to measure the voltage coming out of the decoder. Some decoders allow you to set the intensity of the lights (vary the output voltage) on the decoder itself, so the rating of the lights in the cars is easy to accommodate.

Next would be to see if there’s a voltage regulator in the cars by sitting them on the track and slowly increasing the voltage going to them. If they stop getting brighter after a certain point (usually around 5 - 8 volts) then there’s a regulator inside, and you shouldn’t have to worry. Just hook the wires going to the track to the decoder instead.

If they keep getting brighter and brighter the more voltage you apply (no regulator), then you have a few options…

  1. find out from the manufacturer what the bulbs are rated at, and make sure your decoder output doesn’t exceed that.

  2. If you can’t control the output of the decoder, install a voltage regulator circuit in the car to control the voltage instead. Radio Shack sells a variable voltage regulator. That, a capacitor and a potentiometer is all you need to build that circuit. Last time I bought one, the circuit was printed on the card for the variable voltage regulator, and RS had all the parts. (You can also use a “preset” voltage regulator; they typically come in 5 and 12-volt flavors, but others may be available. That’s why the variable ones are cool, though - you can customize it to exactly what you need.

  3. replace the lights in the cars with more suitable lights (either incandescent or LED, though I’d look at LEDs.)

Those three steps would work if you’re not controlling the lights via a decoder but straight from the track voltage as well.

Later,

K