one feature of DCC that i don’t see mentioned is the decoder monitoring BEMF to estimate motor rpm and adjust voltage to maintain it, especially at low speeds.
i’m not aware of any DC throttle that does this and not sure how practical it would be over a length of track and wire, the affect of lights or when running multiple locos
also not sure how a length of track affects PWM or pulse power. i think there’s a big advantage driving the motor directly with just an inch or so of wiring between the motor and drive circuit
Creg, For what its worth and that may not be worth a hill of beans MTH DCC locomotives will slow down while going down hill when operated in DC.
As I mention on page one of this topic I adjust the start volt,speed step and start/stop mometum.
If the decoder has “throttle notching” you can make DCC engines sound like they are working hard.I seen this once and was told speed step and momentum made this possible.
BEMF does in some cases out perform DC PWM delivered thru the track. But based on my experiance and testing with the ARISTO TRAIN ENGINEER, the difference is small or unmeasurable with most high quality locos.
I have been using the TRAIN ENGINEER for nearly two decades, I installed a version of my Advanced Cab Control on the layout of a friend about 15 years ago, also using the TRAIN ENGINEER throttles.
That layout was the subject of operating sessions by a round robin group, many of the members are DCC users. They liked the TRAIN ENGINEER and many noted it performaance to be basically equal to DCC.
My old layout had blocks as long as 60’ with a single feeder, the other layout had blocks 20’ to 30’ with single feeders. That seemed to have no negative effect on the performance of the locos.
My new layout will also have blocks in the 60’ range.
I use filtered and regulated power supplies at 13.8 volts. The TRAIN ENGINEER does not come with its own power supply. And I would suspect the quality of power in effects the quality of power out…
Both on my layout, and on my friend’s layout, we use a #12 throttle buss to distribute the throttle power around the layout. Relay panels that connect the throttles to the blocks are located near the block in question and are conncected to the tra
A few more thoughts, BEMF is not a universal feature of DCC, as not all decoders have it, and some modelers report problems with it in some locos and have to turn it off.
Likewise PWM is by no means a universal feature of DC, with only a handful of PWM DC throttles ever being on the market.
But both cases likely represent premium motor control for their respective systems.
The mechanical quality of the loco is still an important factor here. BEMF and PWM will not fix a bad driveline, but will bring out the best in a good driveline.
it makes sense that a DC motor under load (going uphill) and with constant drive voltage will reduce rpm which reduces bemf allowing more current and torque to adjust to the load.
a DCC decoder that uses bemf to maintain speed in that same loco will increase the drive voltage to maintain a constant bemf and rpm
since you said your loco slows down using DC, it sounds like the DCC decoder uses bemf to maintain the speed going uphill.
Linn Westcott discussed his current sensing circuit in the TAT-V(?) saying it could be adjust to actually increase speed going uphill and visa versa. there are multiple approaches, both analog and digital/firmware to manage speed
One thing I have not seen mentioned–“Imagination.” All my years as a kid and now as a 73 year old I can “hear” the bells and whistles and “see” the lights without the need for expensive DCC operation. If you want it fine but we already deprive kids of using their imaginations for so many things.
as i mentioned earlier with multiple locos, bemf does not accurately indicate the load the motor is expected to pull. i’ve read that it’s often recommended to disable bemf when consisting locos because the control algorithms in each decoder are not synchronized.
when one decoder lowers the drive voltage the other may see a greater load and increase the voltage.
I think Thomas Edison had a similar problem with his first generators until he realized he needed to mechanically link the govenors on all the generators
And so, as a practical matter, as it applies to my modeling, nearly every train on my layout is pulled by more than one powered unit.
I model a big Class I in the early 50’s. Steam powered trains are typically double headed, diesel powered trains have two, three and four unit consists, sometimes more, even switching is often two SW’s or ALCO S’s back to back.
And I have grades, and pull long trains that actually require this power. How often would BEMF actually work?
One more note about the TRAIN ENGINEER performance. Not in all cases, but when I see a difference in performance between the TE and the same loco on DCC, the difference is this, a slightly, only slighly, higher starting speed from a dead stop.
Example, on DCC a given loco consistantly starts at 1.5 smph, on the TE it might not start until 2 or 2.5 smph. BUT, on the TE the chance for stalling after it does start is way less, almost zero.
I keep seeing this kind of discussion, but it doesn’t really seem to apply. [I apologize in advance if there is any wack content in the following opinions…]
Reading BEMF from a voltage-controlled motor ONLY gives you an idea of how quickly it is turning. (You can then pulse power, tinker with average or ‘wave formed’ voltage, etc. to modulate that SPEED). [Note that the other thing BEMF can be used, or abused, for is a rotational speed that can be manipulated for a sort of ‘chuff synchronization’ in sound generation, a thing perhaps safest restricted to short and well-characterized link between motor and controller!]
“Load” is a function of current, amperage, and I’d expect that while high amp draw can cause voltage sag this is insignificant with good feeders, so load control can be assumed related to amp draw. (Which can be sensed and used ‘in servo’ for voltage control of the motor for ‘cruise control’, etc. as per Westcott’s ‘load regulation’ that was supposedly not too well liked).
What doesn’t get helped is the inherent physical voltage drop from the throttle to the motor, which likely varies with distance and position on the layout, so would require a secondary measurement of calibrating resistance if BEMF were to work accurately for DC throttke implementation. I think it would be possible to adapt Linn Westcott’s idea of plugs with calibrated resistance, not in the throttle but in the locomotives, to let you match at least a reference level of BEMF for consisting, and I certainly see comments from people who say they are implementing BEMF on DC, so there may be a way. Personally I think an adjusted constant-current power circuit is more likely to give you ‘power control’ than the speed modulation
ATLANTIC CENTRAL
And I have grades, and pull long trains that actually require this power. How often would BEMF actually work?
I keep seeing this kind of discussion, but it doesn’t really apply.
Reading BEMF from a voltage-controlled motor ONLY gives you an idea of how quickly it is turning. (You can then pulse power, tinker with average or ‘wave formed’ voltage, etc. to modulate that SPEED). [Note that the other thing BEMF can be used, or abused, for is a rotational speed that can be manipulated for a sort of ‘chuff synchronization’ in sound generation, a thing perhaps safest restricted to short and well-characterized link between motor and controller!]
“Load” is a function of current, amperage, and I’d expect that while high amp draw can cause voltage sag this is insignificant with good feeders, so load control can be assumed related to amp draw. (Which can be sensed and used ‘in servo’ for voltage control of the motor for ‘cruise control’, etc. as per Westcott’s ‘load regulation’ that was supposedly not too well liked).
What doesn’t get helped is the inherent physical voltage drop from the throttle to the motor, which likely varies with distance and position on the layout, so would require a secondary measurement of calibrating resistance if BEMF were to work accurately for DC throttke implementation. I think it would be possible to adapt Linn Westcott’s idea of plugs with calibrated resistance, not in the throttle but in the locomotives, to let you match at least a reference level of BEMF for consisting, and I certainly see comments from people who say they are implementing BEMF on DC, so there may be a way
I hear and agree with you about imagination - especially when it comes to our younger population. That’s why I always recommend something like Brio for the 2-6 age group rather than an electric train set. I believe it allows kids to engage their imagination and hone their dexterity and handskills by taking apart and rearrange the train and the track to whatever configuration comes to mind. I call that “discovery and learning”.
While I do have sound in some of my locomotives, it’s not that important to me and I’ll mostly run them with F8 muted. When unmuted, I enjoy sound much more with steam locomotives than I do diesel.
OTOH, while I can “hear” the bell & whistle in my mind, I really enjoy lighting. For me, it adds a realism to operation and I like adding it to structures, light poles, and my locomotives. When I was able to install and operate a flashing gyralight to the rear taillight of my Con-Cor NYC Aerotrain using a separate TCS FL4 (light-function only) decoder, it took realism to another level for me. I’m not sure how practical or possible the latter would be in DC. Lighting on the layout, however, can easily be added and “adjusted” (for both realism and longevity) using the output of a spare DC power pack.
I faced the decision to possibly changing my DC/block controlled layout a couple of years ago. Based on the size of my motive power fleet, I decided that the initial cost of switching over to be more than I wanted to spend. I know that I could have had it DC/DCC controlled, but now that I’m getting older (read less flexible), working under the layout has become a major issue.
eaglescout
One thing I have not seen mentioned–“Imagination.” All my years as a kid and now as a 73 year old I can “hear” the bells and whistles and “see” the lights without the need for expensive DCC operation. If you want it fine but we already deprive kids of using their imaginations for so many things.
Eagle,
I hear and agree with you about imagination - especially when it comes to our younger population. That’s why I always recommend something like Brio for the 2-6 age group rather than an electric train set. I believe it allows kids to engage their imagination and hone their dexterity and handskills by taking apart and rearrange the train and the track to whatever configuration comes to mind. I call that “discovery and learning”.
While I do have sound in some of my locomotives, it’s not that important to me and I’ll mostly run them with F8 muted. When unmuted, I enjoy sound much more with steam locomotives than I do diesel.
OTOH, while I can “hear” the bell & whistle in my mind, I do really enjoy lighting. For me, it adds a realism to operation and I like adding it to structures, light poles, and my locomotives. When I was able to install and operate a flashing gyralight to the rear taillight of my Con-Cor NYC Aerotrain using a separate TCS FL4 (light-function only) decoder, it took realism to another level for me. I’m not sure how practical or possible the latter would be in DC. Lighting on the layout, however, can easily be added and “adjusted” (for both realism and longevity) using the output of a spare DC power pack.
Are lighting effects easily turned on/off or adjusted (e.g. pulse rate, type) using DC? Or, is that something that is pre-set by the factor boards that come with the locomotive? I’m guessing they are pre-set and cannont be adjusted or changed to another type.
Tom, I only have a few DC locomotives that have electronic lighting control boards in them. These are preset for their functions at the factory and as far as I know, cannot be adjusted.
With my old style 1950s fleet this is mostly just for directional/constant lighting.
There is only one I am not happy with. This one is set so the Mars Light only works when the locomotive is going backwards. That is a shame, because the Mars Light effect is spot-on.
I do not have any newer locomotive models with beacons, ditch lights, or working marker lights, so I cannot comment on these features in DC operation.
Sheldon can offer more information. I am sure he has more of these than I do.
The pulse rate of the Mars lights is constant no matter loco speed and is preset.
Depending on the throttles you use, lighting comes on full brightness (or very nearly so) as soon as the loco moves, or often before it moves.
With the PWM DC throttles I use, lighting comes on well before the locos move, and you can let the loco sit like that with no harm - I might not want to do that for hours…
There is no turning them off or on, they are automaticly on if the loco has power, off if it is completely off.
But in most cases the lighting is directional, headlights go off in reverse, backup or “B” end lights come on only in reverse, so the rear facing headlight of a back to back pair of A units is off when the train is moving forward.
I model the 50’s, no ditch lights, daytime running lights just becoming standard, some roads using Mars lights.
It works fine for me, I don’t really want to be bothered with turning headlights on and off…
I run TT&TO in dark territory. I need headlights that can be bright, dim, or off; I need some way to power the cab roof flasher; I need the ability to turn the class lights on and off; I need the ability to turn the numberboards on and off.
And I’m lucky; I model late enough that sections aren’t used, and a dim headlight counts as a marker, so the class lights don’t need to be able to be green or red.
After slicing computer DIP switches up and wiring a couple engines with switches in the battery boxes to turn all the lights on and off, I went to DCC gladly.
