rrinkerZero stretching got an old but never before run Bowser loco moving - on a DC power pack all it did was sit there until the power pack overload tripped. Use address 0 on the DCC system, which was only slightly more powerful than the DC power pack being tried, got the loco to move and allowed it to break in a bit, after which is then worked on the DC power pack.
while the alternating DCC voltage is not good for a DC motor long term because of unproductive heat buildup, it has a similar effect as PWM to help overcome the friction of a motor to keep it turning. (I wonder how that Bowser loco would have run with a PWM throttle)
while i've read about stiction, i was unaware of a dithering feature supported in some decoders (CVs 56 & 57).
mbinsewiThe Athearn DC BB locos I have run on my Digitrax, the zinging seems to quiet as the speed increases ...
the "zinging" is the alternating voltage of the DCC signal which occurs for a smaller percent of time as a pulse is stretched longer to increase speed.
greg - Philadelphia & Reading / Reading
The Athearn DC BB locos I have run on my Digitrax, the zinging seems to quiet as the speed increases, but they still run smooth, with no jerking.
I don't make a habit of doing this, but I have run a few on DCC, for short periods of time. Especially before I started installing decoders. I just had to do it, to see if it works, as the Digitrax manual says it would.
The last time I did this was to see if I had individual control over a DC loco, on the track with a DCC loco, which I did.
It just sounds "wrong", with the zinging.
Mike.
My You Tube
Possibly. My locos I've tried never run as fast as they would with a real DC powerpack, and some can be noisy, but they aren;t real jerky, they are fairly smooth moving once you get past the singing that even the better motors do
I don;t regular run locos like this. I'll just put soomething on for a quick test to make sure it actually runs. If I could jump the throttle between speeds, you could probably play the motor like a musical instrument
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy,
You have better luck than my friends and I do with zero stretching. My stuff always runs pretty jerky on zero stretch - Spectrum steam, Bli steam, Atlas, P2K, Athearn steam and lots of old brass....Perhaps Digitrax has a better zero stretch than CVP?
Guy
see stuff at: the Willoughby Line Site
trainnut1250 To operate a DC locomotive on a DCC system, a technique called "Zero Stretching" is used. Usually referred to as Address 0, an address isn't allowed in DCC. I just wanted to point out that while zero strectching will work, the loco performance is pretty poor. Many systems dropped the zero strecthing feature in subsequent updates after it was generally agreed that the option wasn't really useful as more than a "parlor trick" or a way to see if your recent DC purchase will run. Its not good enough to know how well the loco will run, just to confirm that it will. My system has the zero stretch option but I never use it because of the poor loco performance. Guy
To operate a DC locomotive on a DCC system, a technique called "Zero Stretching" is used. Usually referred to as Address 0, an address isn't allowed in DCC.
I just wanted to point out that while zero strectching will work, the loco performance is pretty poor. Many systems dropped the zero strecthing feature in subsequent updates after it was generally agreed that the option wasn't really useful as more than a "parlor trick" or a way to see if your recent DC purchase will run. Its not good enough to know how well the loco will run, just to confirm that it will.
My system has the zero stretch option but I never use it because of the poor loco performance.
Depends on the loco Athearn Ble Box locos with their loosely built motors (magnets aren't glued in, ends are held on by the top and bottom clips) buzz like crazy. Zero stretching got an old but never before run Bowser loco moving - on a DC power pack all it did was sit there until the power pack overload tripped. Use address 0 on the DCC system, which was only slightly more powerful than the DC power pack being tried, got the loco to move and allowed it to break in a bit, after which is then worked on the DC power pack. Other motors 'sing' a bit, which changes pitch as you advance the throttle. Top speed is never great, but they are locomotives and not slot cars.
Like I said - not something I would do for permanent running, but for the occasional test run, it's fine. Haven't burnt anything up yet.
One thing to consider is that if you actually don;t follow the recommendations and hookt he ground lead of the DCC system to earth ground like the ground pin of a wall socket, and you are using an AC powered oscilloscope, you are risking blowing it up.
The DCC output is an example of a floating voltage, at least in some booster designs. Neither side is tied to a ground point. This is pretty much the same way switch mode power supplies work. You really have a differential signal the correct wya to measure this is with a differential probe, the alligator clip ground pin on a standard scope probe goes right through to earth ground.
Most boosters work by outputting through an H bridge, so there will be no center reference available. The output is as close to a square wave as can be generated, but there is a finite switching time in the H bridge.
How exactly Digitrax builds theirs I don't know, but their recommended way to test track voltage is between the ground pin and rail A, and then ground and rail B, and adding the two. The ground is not really earth ground, it is a common reference point int he circuit. It is not tied to either the ail A or Rail B outputs. You'll measure say 7.5 volts between ground and either rail, when the track voltage is 15 volts. That ground is artificially generated in the middle of the waveform - I suspect via a couple of diodes. I suppose I could tear my DB150 apart and examine the circuit. Even more reason to never tie that terminal to the earth ground.
All I know is the full wave bridge rectifier produces pulsating DC voltage to be filtered by the filter capacitor. Looks just like an AC signal but flat topped and crosses thru zero with each transition which makes it an AC signal.
Good enough for me but I guess not good enough for those who count all the rivets.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
betamaxSince the booster only has two wires supplying power to it, it cannot create a negative voltage. One of those wires is the common, the other is the "positive". To create a +/- 14V output, you would need a 28V power supply to create those voltages internally, or an external 14V power supply with plus, minus and common wires.
I think what you're trying to say is that if you measured the voltage between either rail and the common (less positive wire providing DC power to the booster) you would measure (half) the supply voltage on one rail and zero volts on the other. You would never measure a negative voltage.
but the decoder in the locomotive only sees the voltages between the rails and it sees the polarity of that voltage changing -- the voltage on one rail alternately becoming larger and then lesser (minus) with respect to the other rail.
betamaxSince decoders pick off the digital stream via a diode, how would that affect operation if a negative pulse is on the rails?
are you suggesting that the DCC signal on the rails simply changes between zero and some positive voltage? Zero volts is not at the bottom of each waveform below, zero volts is the dotted line thru the middle. From S-9.1
The NMRA baseline digital command control signal consists of a stream of transitions between two equal voltage levels that have opposite polarity.
richg1998 Quote. In a DCC system there are no AC voltages, nor are there positive and negative voltages. Just a sequence of high and low voltages on each rail, where one is energized (high) and the other is not (low). It is a digital system, after all. The full wave bridge rectifier in the decoder produces DC voltage because there is AC voltage. The filter caps smooths out the pulses like any rectifier circuit. Alternating current. Not what we see from our outlets in the house because of the digital data. Use your definition. I will use mine. Just a higher frequency power supply feeding more electronic circuits. The digital data is sent to the microprocessor. Equal Positive and negative going pulses like AC has. I have used my Scope many times. Before our power gets here the AC looks pretty bad also. Rich
Quote. In a DCC system there are no AC voltages, nor are there positive and negative voltages. Just a sequence of high and low voltages on each rail, where one is energized (high) and the other is not (low). It is a digital system, after all.
The full wave bridge rectifier in the decoder produces DC voltage because there is AC voltage. The filter caps smooths out the pulses like any rectifier circuit. Alternating current. Not what we see from our outlets in the house because of the digital data. Use your definition. I will use mine. Just a higher frequency power supply feeding more electronic circuits. The digital data is sent to the microprocessor.
Equal Positive and negative going pulses like AC has. I have used my Scope many times.
Before our power gets here the AC looks pretty bad also.
Your scope is fooling you. But it isn't lying either.
You clip the "common" (reference) lead (usually the one with the gator clip) to rail B , and clip the probe to rail A.
Rail A is energized to +14V, current flows from the probe through the scope and returns to B, as it should. The display shows a trace moving in the positive direction.
Then Rail A is held to "0" and B is energized to +14V. The probe is less positive than the common and current flows in reverse through the scope, resulting in a negative trending trace.
Since the booster only has two wires supplying power to it, it cannot create a negative voltage. One of those wires is the common, the other is the "positive". To create a +/- 14V output, you would need a 28V power supply to create those voltages internally, or an external 14V power supply with plus, minus and common wires.
Since decoders pick off the digital stream via a diode, how would that affect operation if a negative pulse is on the rails?
mbinsewi Easy now.... ....there are things electronic about all of this that I may never get to the top of the learning curve, and it doesn't bother me at all!
Easy now.... ....there are things electronic about all of this that I may never get to the top of the learning curve, and it doesn't bother me at all!
Just joking around! I honestly don’t want to stick around on stereotypes of different generations. While I might quickly understand how to program CVs, that doesn’t mean I like it, sometimes I feel like people assume my generation are tech wizards, and while that mostly true, I detest CVs! Can’t wait till I learn how to use JMRI!
mbinsewi As long as we're all haveing fun, getting along, helping each other, and doing just what your signature lines says..... It's all good.
As long as we're all haveing fun, getting along, helping each other, and doing just what your signature lines says..... It's all good.
Can’t agree with you more (hey, we’re getting along!). No offense intended, just having fun!
I wrote that signature just in case something came off too harsh, glad someone caught on to it!
Regards, Isaac
I model my railroad and you model yours! I model my way and you model yours!
SPSOT fanSome of the “Old Heads” seem to take forever to understand even the smallest things about electronics!
I can handle CV's and run my trains. And if I get tired of all the DCC stuff (not), I can easy flip a switch, unplug my Digitrax, plug in my MRC 2500, and go back to DC.
But I digress,
mbinsewi Your Grandpa is telling your this? I guess your much, much younger than I thought you were. , or, lets say, had an idea of. I'm 70, well entrenched in the grandpa age, kid.... Mike.
Your Grandpa is telling your this? I guess your much, much younger than I thought you were. , or, lets say, had an idea of.
I'm 70, well entrenched in the grandpa age, kid....
Yes, I am very young (I’m in my latter teens). Your not the first person to tell me I seem older, I usually babble so much about trains people interpret from my knowledge of railroads (and a cornucopia of other random topics) that I’m much older! I’d assume my grandpa couldn’t understand how you could run both a DC engine and a DCC engine simultaneously. Some of the “Old Heads” seem to take forever to understand even the smallest things about electronics! Though even I didn’t get how you ran a DC loco on DCC until just now...
Wow, I had no idea you could run a DC loco and a DCC loco at the same time. My grandpa told me you couldn’t run DCC locos while you used address zero. Thanks for the info everyone, very informative!
betamaxNot all systems support Zero Stretching, as it not part of the DCC standard.
stretched "0" bit is described in S-9.1
betamaxAll the DCC locomotives will continue what they are doing, as they just ignore that packet.
a stretched 0 bit is allowed in a valid packet. No need to "just ignore the packet". The width of a zero-bit half-cycle (time between polarity reversal) needs to be >= 100 usec, so it can be as long as necessary to establish the desired DC voltage.
betamaxIn a DCC system there are no AC voltages
betamaxthe direction of current flow changes rapidly.
while DCC is certainly not like the old Lionel AC transformers and is not sinusoidal, the fact is that current to each rail does alternate direction and is therefore AC.
betamaxnor are there positive and negative voltages.
when describing a voltage, it helps to define the reference that the voltage is between. (this is why high voltage line worker can touch 765,000 volt lines).
So while there is just 12V between the terminals of the booster supply, the H-bridge in the booster continually alternates the routing of current from the supply (+) to the rails such that with reference to one (either) rail, the voltage on the other rail is changing polarity from + (higher) to - (less than).
betamaxWhen address 0 is in use, it generates a lot of packet traffic which can bog down system response. Even when set to speed step 0. To power a DC locomotive a lot of packets have to be sent at address 0.
no additional packets (at least one) are sent. By stretching a zero-bit, one packet can be very long.
As I said I would do yesterday, today, I put an Athearn loco, no decoder, on the lay out, set it's address at 00, on the same track, I had a loco with a decoder, with address set at 03, and I had independant control of both locos.
Moving the throttle on one, did not affect the other, as it would be if I had 2 locos on the track, with seperate addresses.
I use an old Digitrax (2004) SEB set, with a DB150 and a DT400 throttle, which gives me seperate control of 2 locos, using 2 throttle knobs.
To operate a DC locomotive on a DCC system, a technique called "Zero Stretching" is used. Usually referred to as Address 0, an address isn't allowed in DCC. All the DCC locomotives will continue what they are doing, as they just ignore that packet.
Not all systems support Zero Stretching, as it not part of the DCC standard. For those that do, they simply alter a null packet by making one rail high (energized) for a longer period of time than it would normally be. The longer it is held high, the faster the DC motor will turn. Speed is determined not by voltage, but by time.
In a DCC system there are no AC voltages, nor are there positive and negative voltages. Just a sequence of high and low voltages on each rail, where one is energized (high) and the other is not (low). It is a digital system, after all.
While Rail A is high, the current flows through the motor to Rail B (at zero volts), and it turns, providing motion to the locomotive. In this case, Rail A is more positive than Rail B, so current flows from the energized Rail A to B and back to the source. To reverse direction, Rail B is held high, current flows from B to A and the motor turns in reverse. Rail B is now more positive than Rail A, so it will turn in reverse. Repeating this packet this fast enough keeps the motor turning.
When address 0 is in use, it generates a lot of packet traffic which can bog down system response. Even when set to speed step 0. To power a DC locomotive a lot of packets have to be sent at address 0.
Under normal DCC operation, the high frequency of the pulses on the rails cause the effective flux in the motor to cancel, as the direction of current flow changes rapidly. This can result in overheating, and some motors, such as coreless types, can be quickly damaged. The motor is also going to make some noise as the torque vector keeps reversing, causing the amature to vibrate.
SPSOT fanthe speed the DC locomotive is running at would determine the maximun voltage either could recieve (as DC locos speed is controlled by the amount of colts applied to the track).
A DCC system changes the polarity of the track voltage to send packets. The average voltage is normally zero.
It can control a DC locomotive by stetching a positive or negative cycle so that the average voltage is not zero. While a DC locomotive may run, there's a lot of wasted AC current (the signalling for DCC decoders). Address 0 is used to control this DC value.
Tell ya what, when I get back here later this am, i'll set it up and try it. I have two throttles on the DT400, so I can control 2 seperate locos.
mbinsewi SPSOT fan When running with address 0 the layout becomes DC and the DCC equipped locomotives don’t run at all. Wrong. On my Digitrax DCC DB150 with the DT400 throttle, I can run a loco without a decoder on one throttle, and a DCC loco on the other. The DCC system does not become DC. Mike.
SPSOT fan When running with address 0 the layout becomes DC and the DCC equipped locomotives don’t run at all.
Wrong. On my Digitrax DCC DB150 with the DT400 throttle, I can run a loco without a decoder on one throttle, and a DCC loco on the other.
The DCC system does not become DC.
I had no idea you could run a DC locomotive and DCC locomotive at the same time! Are you sure that would work well? The speed the DC locomotive is running at would determine the maximun voltage either could recieve (as DC locos speed is controlled by the amount of colts applied to the track). So if the DC is running slowly the DCC locomotive could only run the same speed as the other DC engine or less. Correct me if I’m wrong, hope I make sense...
nope ..
the DCC system sends out packet information for DCC first, which the decoder can accept ..
it is only after this that it sends out the DC information, which if the DCC was valid, the decoder cannot accept .. simple ..
i thought it was your statement that the system/layout becomes DC and DCC equiped locos no longer work that was inaccurate.
SPSOT fanNow most DCC systems can become ‘DC’ systems by running with address one. When running with address 0 the layout becomes DC and the DCC equipped locomotives don’t run at all.
A DCC decoder can work on a DC layout if enabled to operate in DC mode.
floridaflyer Address one on a digitrax will not operate a DC loco, only 00 will. I have a DCC loco with address 01 and it runs on DCC. I'm not sure fan has his facts straight.
Address one on a digitrax will not operate a DC loco, only 00 will. I have a DCC loco with address 01 and it runs on DCC. I'm not sure fan has his facts straight.
It seams I have caused some confusion by accidently saying address one instead of address zero. I am aware that address zero is the one that runs DC locomotives (at least on a Digitrax system). Apologies for any confusion, the title has been corrected.
A DCC system does not become DC. You can run a DC loco on DCC, as I stated, Digitrax says to set the address to "00".
But the system does not "change" into DC, and a DCC loco will run, as it should.
SPSOT fan ... So today many DCC decoders are dual mode, meaning they run on but DC and DCC. Now most DCC systems can become ‘DC’ systems by running with address one.
...
So today many DCC decoders are dual mode, meaning they run on but DC and DCC. Now most DCC systems can become ‘DC’ systems by running with address one.
I have never seen this stated. I can't disagree, but I have yet to see a thread on this forum, or on any other, where this is discussed and/or taken as a given. I do know that entering Add "00" on my Digitrax DT400 throttles with a DB150 backing them will allow me to run DC-only locomotives. I only tried it once. That was plenty. No, really...
SPSOT fan When running with address 0 the layout becomes DC and the DCC equipped locomotives don’t run at all. What I’m wondering is what a dual mode decoder will do when you run address 0. Will it run as a DC loco, or will it ignore the DC signal and sit still doing nothing.
When running with address 0 the layout becomes DC and the DCC equipped locomotives don’t run at all. What I’m wondering is what a dual mode decoder will do when you run address 0. Will it run as a DC loco, or will it ignore the DC signal and sit still doing nothing.
I don't know about "0", but "00" is what we are asked to enter for an address if we want to run a strictly DC motor using the Digitrax systems. I don't think our systems support the address "0" or "00" for DCC operations because the default for all decoders that are NMRA compliant is "03". So, to address your question, a DCC-enabled decoder (set in CV29), should do nothing if you go to Add "0" or even "00" and attempt to get any powered decoders to do something...anything. They will power up, and do everything in neutral that you had them doing the last session (I'm pretty sure), but they should not turn lights off/on, sound the horn, turn the drive mechanism, consist, etc.
SPSOT fan Again just a curiosity, I don’t actually have a DCC system at the moment, though I do run on others systems.
Again just a curiosity, I don’t actually have a DCC system at the moment, though I do run on others systems.