Is the max speed set by the decoder the same in DC as in DCC?
In other words does the decoder speed management also operate while the locomotive is operating on a DC powered circuit?
Just curious, do you have a snail? If so what is it?
in DC mode, a decoder simply passes track voltage to the motor, minus the voltage drop from the rectification in the decoder (The current still goes through the rectifiers.)
So in this case max speed is a function of the track voltage. The “decoder speed management” doesn’t come into play because there are no DCC packets tellling it what to do.
That’s why a DCC loco will sometimes take off at top speed if there’s a short or other event that “scrambles” the DCC signal - It thinks it’s on DC, so it applies full track power to the motor.
That’s also why I turn off analog on all my locos…
Great point. [bow][Y]
Newish Athearn RTR GP35 seemed to run at approximately the same speed as the same model from 20 years ago before plugging in the T1. Putting the decoder in seemed to slow the newer model. Speed difference is slight but also varied with throttle setting: start speed voltage is lower for the older (a well run in model) and the newer model catches up at mid speed only to be beaten out again at top speed. Gearing is surely unchanged over the years, one would think.
Operative word is “seemed”. Before putting the dummy plug back in to verify this “observed” effect I thought I’d ask.
Logically, a dual mode decoder would simply bypass the software in the decoder but not necessarily. Sound decoders utilize some of the software while in DC mode.
The T1 is motor-only two function.
I’ve now experienced the interesting runaway phenomenon with two Soundtraxx equipped locomotives. A Bachmann Sound Value and an Athearn Tsunami2. Not with ESU or TCS, so far. Early days. I just either grab the locomotive or switch off the power.
Completely correct from what I have seen.
The DCC locomotives I have removed decoders from do run faster on real DC power than that silly “Dual Mode” garbage where the decoder rectifies the signal. There is a voltage drop in the decoder, and the motor does not run as well in DCC decoder dual DC mode.
If your layout is DC, remove the decoder.
-Kevin
I’m sure some decoders, maybe even most, do just pass the volatge through when in analog mode, but I also know for a fact that modern Digitrax decoders do apply momentum and speed settings when in analog mode. While I do have a few TCS, NCE, MRC, and BLI decoders, the vast majority of mine are Digitrax and they are only ones I’ve used much on DC, so they are the only ones I’m sure about.
Time for a little experiment. I have some other brand motor only decoders also. I am trying to standardize to TCS and ESU.
There are a lot of variables to consider. Track wiring, track itself (sectional/flex), DC transformers, locomotive circuitry, and more.
It’s a given that a large buss and tons of feeders are better than a pair of wires to a single connection on a loop of track. How clean the transformer puts out DC current. I once had a transformer that put out pulsed DC and some of the early decoders were confused and act strange or not go at all. The pulsed DC was designed to kick start locomotives and the pulses would decrease as voltage increased.
Decoders plugged into a factory board with any RF circuit will act differently than one hardwired in. Any caps, resistors and diodes can have an affect on how clean the decoder sees the voltage.
Pete.
Model trains do not run well on pure filtered smooth DC.
I have an expensive smooth DC power source at my workbench I can use for testing, and a Troller Autopulse or MRC 2500 (PWM) produce “DC” that makes the models run much better.
A dual mode decoder will never be as good (on DC) as an MRC 2500 or Aristocraft wireless throttle without a decoder.
I have a Ken’s Varipulse throttle that Dr. Wayne recommended, but I have not tried it yet. It is PWM in a handheld unit.
As always, if you run DC, I would recommend ditching the decoder.
-Kevin
that’s interesting and makes sense.
in DC mode, the decoder needs to recognize the polarity of the DC voltage and swap the H-bridge connections to the motor to change the direction of the motor.
applying momentum suggests the decoder is them using PWM to ramp up/down the track voltage when it sees it changing
My Bachmann EM-1, the only locomotive I have that still has its decoder, definitely has electronic momentum built into the functionality when operating on DC.
Someday I will figure out how to get the tender open and get that decoder out of there!
-Kevin
It looks like you remove four screws on the bottom and the body just lifts off:
https://www.bachmanntrains.com/home-usa/dwg/dwgs/N%20SCALE%20EM-1%202-8-8-4.BODY%20&%20DECODER.pdf
Hi Robert… there have been a few threads about my EM-1 before. My problem is that I accidentally glued the tender floor to the tender body while applying details, and now the model is painted and I am afraid of damaging it. The body will not come off no matter what I have tried.
It is entirely because of one of my mistakes, and is just another Kevin-Induced problem of my own making.
[(-D]
There are many, many of those.
-Photographs by Kevin Parson
Thank you for trying to help out. I appreciate that effort.
-Kevin
Have you tried popping that tender in the freezer for a couple hours? That sometimes works for breaking glue bonds. Different rates of contraction, I suppose.
FWIW an engine with a green lightboard is going to slow the engine down when running on DC, whether there’s a decoder or not. The lightboard shifts the first say 1.5 volts applied to the engine to the lights (for “constant lighting” effect), then only the power over that amount goes to the motor. If you remove the lightboard and hardwire things together, the engine will start at lower voltage and run faster at full power. I did that with some of my HO engines when they first started putting lightboards in; of course it meant when I converted to DCC I didn’t have receptacles to plug decoders into so had to hardwire them in.
Beautiful job on that loco, I can see why you don’t want to risk damaging it. Another option if you haven’t already considered: How hard is it to remove the body from the engine itself (I can’t really tell from the diagram) and do you think you could do it without damaging anythig? According to Spoookshow’s EM-1 page it looks like the right and left rail pickups and both motor leads are brought to a curcuit board at the back of the engine. If you desoldered the motor leads from the board and soldered them to the left and right rail pickups the motor would run straight from rail power, although the decoder would still do sound and lights.
That might be the difference. However, our impression is that the two locomotives ran at approximately the same speed when the decoder was not installed. One might expect the same lightboard effect to occur either way.
Experiment is required. I have another use for that T1 anyway and more are on order. I can change it out and fit a replacement later once the issue is resolved by testing the relative speeds without a decoder in the way.