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DCC System Programming Track Output - Is it Necessary?

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krs

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Discussion starter · #1 ·
Posted By mbendebba on 20 Aug 2011 04:23 PM
Posted By krs on 20 Aug 2011 03:19 PM
Posted By Greg Elmassian on 20 Aug 2011 02:55 PM
Not defending NCE, since it's a nice feature on the Zimo, but they have always had the philosophy that a current limited (low current) programming track was a good way to make sure you did not damage a decoder if you had an installation problem.

If you have a programming track that can source 3 amps, then a defective installation can damage hardware with a 3 amp short...

There's pros and cons to each way of thinking, one way is extra convenience, and the other way is extra safety in my opinion. I'm fine with the second way.

Knut, I reread what Kenny posted and you quoted... I see no evidence in there that the cv programming did not take, because the statements "defaults to 255" means he was never able to READ the CV, not that he could not PROGRAM the CV. The test would be to go to the programming track. Use direct mode to program CV 1 to a new address (and assuming he is configured for short addresses) see if the new address is responsive on the main.

An easy, quick test, whose results would be interesting.

I've programmed many a decoder that I could never read back... some old LGB ones, ones from C.T. Elektronik, and certain accessory decoders.


Regards, Greg
Greg,

I actually see both extra convenience AND extra safety by having a separate programming track output.
The downside of having a separate output only for the programming track is the extra cost the manufacturer incurs........but that should really only be pennies.

On the Piko Central Station I can see that - they aim for low cost to keep the price low.
But I don't really understand Zimo's rationale to eliminate the programming track output.

There was an "explanation" as to why on the Zimo website but that has now disappeared.
In the current description of the new Central Station, Zimo provides a secondary out put which is listed as being usable to drive a programming track but the current limiting on it is set at 5 amps.
However..........that design is not completed yet - at least I don't think it is, so Zimo could still make changes before the product is shipped.

Anyway - that's a side discussion.




Knut: There is no question in my mind that a programming track is essential, and I would not buy a system that does not have one (2AMP MAX, is more than plenty).A programming track has many uses. For instance, I will never let anyone put a loco on my layout until I checked it out on the programming track. There are many times when I forget how I configured a particular locomotive, especially when I have not played with it for quite some time. Pull the loco of the shelf, pop it on the programming track, read off a few cv and I am ready to go.



Mohammed -

A programming track can be added very easily and inexpensively to any DCC system that does not have one. NCE actually makes a current liniting unit just for that purpose - other DCC Central Station manufacurers just suggest to add some current limiting resistors and use the main DCC output.

If I remember right, Zimo's logic was that most people use POM for programming now-a-days so that a programming track is no longer necessary.


I like a programming track with current limiting as well but it wouldn't stop me from uying a specific DCC system if that was the only issue.
Current limiting at 2 amps I think is far too much btw, I'm thinking more like 500ma.


But I have never really thought about what the current limit should be and how it should be implemented.
That might be an interesting discussion so I started a new topic; let's focus on the Zimo decoder NCE system issue in the other thread,

Knut
 
#2 ·
It does not usually come up, the max current needed to program, but there are "boosters" available.

It would be a fun experiment to see what current was used by various various decoders during programming, and also "trapping" the signals on the readback of data.

I have a scope, although measuring DCC current would be tricky, maybe have to measure the waveform over a resistor in series to calculate the current.

Greg
 
#3 ·
Knut: I agree 2amps is probably a bit too much, and like you I have no idea whtat the limit should be and how it should be implemented. I have been saved by the programming track a number of time, particularly when I tried to install decoders in very old LGB lomotives. I cannot live without a programming track, I spend as much time on it as i do on the main. With that said, I would prefer to have the manufacturer make provision for one instead of me trying to figure out how to do it. I have other fish to fry. I really use the programming track mostly to inquire about the status of a decoder. 95% of the time, I use a computer and a programming module to program decoders, for me the term programming track is a misnomer.
 
#4 ·
Knut: I agree 2amps is probably a bit too much, and like you I have no idea whtat the limit should be and how it should be implemented. I have been saved by the programming track a number of times, particularly when I tried to install decoders in very old LGB locomotives. I cannot live without a programming track, I spend as much time on it as i do on the main. With that said, I would prefer to have the manufacturer make provision for one instead of me trying to figure out how to do it. I have other fish to fry. I really use the programming track mostly to inquire about the status of a decoder. 95% of the time, I use a computer and a programming module to program decoders, for me the term programming track is a misnomer.
 
Discussion starter · #5 ·
Don't know how I missed that last time I looked at the service mode RP, but it does spell out the current limit on the programming track:

Service Mode operations should be performed in an environment with limited energy to prevent damage to decoders during programming. For the purposes of this RP, limited energy is defined as 250 mA, sustained for more than 100 ms. A programmer may further limit the energy via a current limiting resistor, if it is clearly documented that not all compatible DCC devices may be programmed by this programmer.
 
Discussion starter · #7 ·
Then I read this:

How PowerPax Works

PowerPax is microprocessor controlled. When hooked up for programming, the PowerPax initially provides power to the programming track to charge-up decoder components like capacitors that would otherwise reduce programming energy and cause a programming failure. When you initiate the programming sequence through your DCC System, the PowerPax also boosts and controls the programming energy to about 200 mA. In the event of an overload or short the PowerPax instantly shuts down to protect the decoder and your DCC System’s programming circuits.

I gather from this and the NMRA spec that the current to the programming track should be between 200 and 250ma - best arrangement would probably be a constant current source to guarantee that under all conditions.

If I now go back to Axel's earlier comment:
What we also know for certain is that the MX695 needs 150-200mA more current than the older MX690s

I can see that from a "spec" point of view we can easily have a problem with the MX695 requiring more than the 250 ma maximum allowed by the NMRA spec.
 
#8 ·
Yep, violating the spec for programming current.

There's really no excuse, since modern micros draw less power, and can shut off all external things like the audio amp, etc.

I've found other things where there was no good reason to make it difficult to program... when I find that kind of stuff, I stop buying... there's too much technology available to justify any real excuse.

Some manufacturers seem to do this stuff so you have to use their equipment... then I strongly vote with my wallet...

Greg
 
Discussion starter · #9 ·
Posted By mbendebba on 20 Aug 2011 09:03 PM
I cannot live without a programming track, I spend as much time on it as i do on the main. With that said, I would prefer to have the manufacturer make provision for one instead of me trying to figure out how to do it.

Mohammed,

With the Central Stations I have seen so far that do not have a separat programming track output, the manual will give you the details on how to set one up.

So you don't have to figure out anything but you do need to buya few extra components and hook them up.
 
Discussion starter · #10 ·
Axel,

Where does this information come from?

"What we also know for certain is that the MX695 needs 150-200mA more current than the older MX690s"

I find it hard to believe that Zimo of all people would not meet the NMRA spec.
I flipped through the MX 695 manual but couldn't find anything that suggested that more than normal programming current is required for this decoder.

Knut
 
#11 ·
Posted By krs on 20 Aug 2011 10:28 PM
Posted By mbendebba on 20 Aug 2011 09:03 PM
I cannot live without a programming track, I spend as much time on it as i do on the main. With that said, I would prefer to have the manufacturer make provision for one instead of me trying to figure out how to do it.

Mohammed,

With the Central Stations I have seen so far that do not have a separat programming track output, the manual will give you the details on how to set one up.

So you don't have to figure out anything but you do need to buya few extra components and hook them up.


Knut: I am curious enough to want to know more, would you please provide some source information. thanks
 
Discussion starter · #12 ·
Posted By mbendebba on 20 Aug 2011 10:58 PM
Knut: I am curious enough to want to know more, would you please provide some source information. thanks


Mohammed,

I'd love to "show" some of the options here but this forum just makes it too time consuming since I can't post pictures directly.


So just a few examples and you can get the info directly via google.

On the Piko Central Station the instructions tell you to just disconnect the two feeds going to the main and connect the programming track instead.
For the Digitrax Empire builder they show a parallel connection to both the programming track and the main with a switch inserted into the mains feed to disconnect the mains when programming.
Don't know if either of these current limit in the programming mode.

If a user wants to play it safe, he could spend $20 and buy the NCE Auto-switch.

That way the programming track and mains stay connected permanently and the Auto-switch selects which one to power depending on the mode set up at the central station.
I have also seen set-ups where the programming track is the same connection as the main with two current-limiting resistors added in series, one on each leg.

Most of the Central Stations we use with Large Scale have a separate programming track output - the ones that don't are typically the small inexpensive ones for the smaller scale.
However - I don't recall any of the systems that do have a separate programming output to ever spell out if that output is actually current linited and if so what the value is.

Ironically, we have yet another situation here where a system that meets the specs could be perceived by the customer as having a problem whereas a system that does not meet the spec. could create the problem.

Knut
 
#13 ·
Knut, referring to your last sentence, I ran into that problem recently.

There was an accessory decoder I could not program, but it would program on another system. Of course my system was called into question. After all the analysis, it turns out the decoder REQUIRED a brief interruption in the programming track signal just before programming a certain CV.

This is not in the specification as a requirement on the programming track, but it took a while to show what was going on. There are then 2 points of view: the manufacturer of the system that can program this unit feels they have a superior product, the owner of the system that meets NMRA spec (me) believes this decoder should not be called DCC compatible, and should be made to work properly.

Yep, it happens...

Greg
 
#14 ·
There are other programming issues with certain decoders.

ESU LokSound Select decoders require a brief track power interruption AFTER CV48 is changed, even in OPS mode, for the change to take effect. I don't know if this is even covered in the NMRA spec. The decoder actually takes the programming, it just needs to be rebooted before the change is implemented.
 
#17 ·
Knut wrote that the new ZIMO system has a second output limited to 5A. This is actually a 2A improvement over the old system, becuase the traditional MX1 hat a 3A programming track output. On the test track we have oonly the 3A output connected. The nice part about a 3A or now even a 5A output is, that you can program and test all at the same time, on the same track, no swithcing around. Granted such as feater is most valuable for professional setups, on people who do a lot of installtions and modfications themselves.

Most hobbyists I know hardly use the programming track. However, currently, the only way to read back CV values is the Programming track, because on the main you have potentially many decoders installed which all would answer you. Same problem with address programming on the main, you can potentially set all the engines to the same address. (happens on a faulty power up on the MTS system)

ZIMO used to have an EC version that saved on several components and had only one output, but that one could easiliy be fed throught a DPDT switch and fire up a programming seperated from the main.

I persoannly see a huge value in a programming track, but I can also see the cosat savings for users which might never program.

As far as low current output to see if the decoder has a problem, I personally think that's what short circuit protection and Amp/Voltage readouts on the handheld are for.
 
#18 ·
Yes, but there is an important point, if you have a limit of 3 amps, and a short circuit of 2.9 amps, then you can cause damage. That's why the programming output is limited on a programming track.

Not all "short circuits" are zero ohms.

By the way, the QSI decoders have a feature that will announce the setting of any CV, so you can check things on the main if you want... set CV 64 to the CV number you wish to read back.

There are other solutions, and this is one of the nice things about DCC, is there's a lot of options.

Greg
 
Discussion starter · #20 ·
That makes a lot of sense.
Have the current limiting resistor in the circuit when programming and for initial testing and then short out the resistor to test run the engine.

Costs very little - every Central Station should have a capability something like that.
 
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Greg Elmassian
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