I am having a little problem with a P2K heavy 2-10-2. It is the dual mode engine running on straight DC.
At very low speeds, it has a little catch that occurs about twice in each driver revolution. At first I thought it might be something binding but on close observation I think it may be an electronic problem rather than a mechanical one. The binding occurs at different points in the revolution of the drivers and always at the moment of a "chuff" sound event. It is as if the power to make the sound robs current away from the motor momentarily.
Anybody noticed this phenomenon or have any ideas?
thanks,
grizlump
I owned one for a while. Always DCC and never that issue.
However, very low speed must be very marginal voltage power availible to keep the engine "Booted up" because it is a computer on wheels.
Just a thought.
DCC might be the only solution. Trying to run a decoder / sound equipped engine on DC power at slow speed causes the decoder to periodically shut down if the voltage is not high enough.
Having tested a number of different dual mode sound decoders on various DC control systems, I have to agree the problem is most likely low voltage, or, an output wave form that the decoder "sees" as low voltage at slow speeds.
I use Aristo Craft Train Engineer throttles and have experianced similar problems with DCC or DCC/sound locos.
For me it is not an issue since I do not use onboard sound. I have "decommissioned' the sound and decoders in all such equipment I have purchased. They all run much better now that they are analog and quiet.
Sheldon
i think sheldon may have hit the nail on the head. i too am using the train engineer control system. when i get the chance, i will try to operate this engine straight off the power pac and see if that makes a difference.
i will let you know what i learn.
thanks, sheldon
The Location: Forests of the Pacific Northwest, OregonThe Year: 1948The Scale: On30The Blog: http://bvlcorr.tumblr.com
thanks for the advice but i think this is all electronic. i have not torn into this beast yet but the sound event occurs at random driver positions and never at the exact same place so i would think the cam set up is not used since it would trigger the sound a the same 4 distinct locations each revolution.
Try lowering the volume - this will use less power to make the chuff noise. If it is indeed running at a voltage that is right at the threshold for operation there is little you can do about it other than bypass the decoder or switch to DCC. People like to call this a 'fault' in the sound decoder - well, how do you propose to have voltage available to run the electronics? This is common to all sound locos that run on DC, you need to get enough voltage to the track to activate the electronics to make the noises, then add more power to finally send some to the motor. You can't get around this without some way to have continuous power on the track. You usually lose range of control since with the common method of making the low end of the throttle range have gradual power increases (taper wound rheostats and the electronic equivalent), you end up near half throttle before you get enough power to activate the electroncis. But this is only about 5 volts or so. Now you only have half the normal range to control speed from stop to full - not much for fine control.
It's not a design flaw in sound decoders - it's simply the way things have to be to get this to work. The alternative would be powering the electronics from a battery - not yet practical for HO and smaller. It works great in large scale though. And how many peopel would complainwhen their loco sdtopped running because the battery was dead?
The PWM power of the Aristo system probably could be used to keep the sound on even when the loco is stopped, but a circuit to do that would not work other DC control systems that simply adjust the voltage to the track.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinker It's not a design flaw in sound decoders - it's simply the way things have to be to get this to work. The alternative would be powering the electronics from a battery - not yet practical for HO and smaller. It works great in large scale though. And how many peopel would complainwhen their loco sdtopped running because the battery was dead? The PWM power of the Aristo system probably could be used to keep the sound on even when the loco is stopped, but a circuit to do that would not work other DC control systems that simply adjust the voltage to the track.
Randy, no one said it was a design flaw, at least not in this thread.
The Aristo pulse width control makes it worse, not better. The Aristo system (and other full voltage pulse width modulation systems) use 12 volt square wave pulses to control motor speed. At slow speeds these pulses are full voltage but are short in duration and widely spaced, as the throttle is advanced the pulses get wider and the "off" space between them gets smaller.
Different kinds of circuits react differently to this. Regular lighting circuits with incandesent or LED lamps "see" the full voltage dispite the "off" periods and burn full brightness even at the lowest settings.
Motors, being inductive, resist the pulses until they are strong enought to start the motor, once started, the motor (similar to back EMF), reacts with the pulse allowing the motor to start/run smoothly at a slower speed than it would on any kind of pure DC wave form. But the net effect is still an "average" voltage that varies just like any other DC control system. Actually, the motor output from most DCC decoders is also pulse witdh modulation control.
Any additional circuit that would store voltage or buffer the effect of the pulse width modulation would negate its effectiveness in controling the motor.
Decoders can often "see" each off cycle at slow speeds and think the power has been turned off (actually it has for a very short time). This causes the decoder to shut down. This is the problem.
These are simply two non compatible technologies. Neither is flawed.
No not in this thread, but it's commonly mentioned as a 'flaw' in the way soudn decoders are designed to work on DC. There just isn't any other way, so it's not really a flaw.
Of course it doesn't work properly on the Aristo, the circuit is not designed for that. But it COULD be. I had a ditch light flasher that could work that way, storing the energy in a constant pulse that was too narrow to turn the motor over which allowed the lights to keep flashing even when the loco wasn't moving. It worked on the club layout ont he line connected tot he ControlMaster 20 but not the line run by the CMI Hogger - different pulse power methodologies. So, as i said, this would have limited appeal because it wouldn't work with ALL DC supplies and actually might make the problem worse for a more 'traditional' power pack.
We're actually in agreement here, maybe my post was misunderstood. And also about PWM - I've said it before, this is why neither your Aristo system nor DCC decoders like those inductors and capacitors in Bachmann locos. The signal reaching the motor is indeed the same with either control method. Only pure DC or those using low frequency smooth pulses are essentially unaffected. It's the sharp edges of the PWM square wave that those circuits are designed to filter out because they behave like the spikes that cause RF interference. Thus both DCC users and users of systems like yours get greatly improved performance by removing said capacitors from the circuit.
Randy,
Yes we are in agreement, about the cause of this problem at least, and yes I did slightly missunderstand your post, or at least part of it.
I think were we differ is in how we view this aspect of the current products. While I did not blame the sound decoder design in this thread, or ever really, I have said in the past that I do not find their operation satisfactory on DC - on any wave form. Not having any interest in onboard sound in HO makes this a non issue for me personally.
Personally I have no expectation of the industry in this area. I don't epect them to solve this "problem" and don't really think that they can. In fact I have advised many DC operators on this forum that if they want onboard sound they need DCC - at least based on the currently available technology.
One other note about the Train Engineer and lighting circuits, like the ditch light circuit you mentioned, ALL the factory installed lighting or home made constant lighting in all my various 100+ locos work very well on the TE. The lights light full brightness long before the loco moves and are easily kept lit after it stops. Mars lights, regular constant lighting, LED or incandesent, Intermountain, Proto, Bachmann, Genesis, etc - makes no difference. This trouble free, hands free, lighting effect is a real plus for me regarding the TE.
Since ditch lights are outside my 1954 era, I do not have any locos so equiped, but would suspect most such circuits would work the same as most of the mars light circuits currently in use.
Yes, the ditch light thing was for a 'regular' DC layout, not one with a PWM controller (and there are a few besides the Aristo system that are just like an ordinary single cab stationary throttle like a simple MRC power pack - or there used to be). Wasn;t for any of my stuff, I too model an era before ditch lights - I did it for the fellow member of the club I was in who was great at painting locos but not so much with electronics. He was going to paint my undec S-12 in exchange but I ended up moving away before that happened. I also model a railroad that didn't go for rotary beacons and Espee style christmas tree displays - which is how I get away with the lowest cost DCC decoders, I only need a headlight.
a belated thanks to all for your advice and input. after what i learned from you guys, i flipped the switch on the TE unit from pwc to linear when running the sound equipped engine and while not 100% perfect, it helped enough to satisfy me.
thanks again.