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Thread: Digitrax PM42 question..

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    Default Digitrax PM42 question..

    The PM42 allows for 4 seperate sections, each of which can either be short circuit or auto-reversing.. is it possible to set it up so that section 1 is short-circuit protection, but have it power section 2 that is auto-reversing? i figure that i would need to speed up or slow down either the auto-reversing section, or the short-circuit detection, but, in theory, should it work? is it necessary? thoughts?

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    I *think* that when configured for auto-reversing, the PM42 section does *both* auto-reverse and short circuit, so there' s no need to "cascade" sections like you seem to be suggesting.

    That is, each subsection is always short-circuit protecting, but the auto-reverse "feature" can be enabled or disabled independently for each section...

    I'm not 100% sure I'm right about that, though... hoping one of the DCC experts will either back me up or correct me here...
    Never mistake a guy who talks a lot for a guy who has something to say...

    CH&FR Site and Blog: http://www.chfrrailroad.net and http://blog.chfrrailroad.net
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    I believe your correct TD. I would say that the PM42 has 2 actions when a short is detected, shut down the section or swap the polarity. Cascading the action seems a bit redundant.

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    Yes you can. Here is the documentation right from Digitrax.

    http://ikm.digitrax.com/questions/60...+a+Single+PM42
    Sean McC

    "No man is a failure ...

    who has friends." -- Clarence

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    Thanks, Sean, thats what i thought i could do, but couldnt see anything about it.

    Jeff

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    Make sure you read their notes. It tells you this is possible but users have had trouble with it in the field.
    Sean McC

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    who has friends." -- Clarence

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    The ones that I wired for auto reverse also had the short circuit protection enabled automatically.
    I did not need to do any thing to get it.
    Ken Price
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    It's around 1996-1999. UP, MP, SP. South Valley Railroad. Some where in the west of Texas. Near San Angelo.
    Started in 2007, Super Empire Builder with radio throttles.

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    Quote Originally Posted by vikingservices View Post
    I believe your correct TD. I would say that the PM42 has 2 actions when a short is detected, shut down the section or swap the polarity. Cascading the action seems a bit redundant.
    At the risk of venturing astray from practical application of the PM42, to theory, there *is* a difference between an auto-reverse and a short circuit... the auto-reverse will appear as a short, but will immediately correct itself as soon as the polarity is reversed. A true short, will remain after the polarity reversal has been attempted.

    Thus -- and I don't know what the PM42 actually does -- it could treat each short as a reversal, detect the failure of the reversal to correct the short, and then shut down.
    Never mistake a guy who talks a lot for a guy who has something to say...

    CH&FR Site and Blog: http://www.chfrrailroad.net and http://blog.chfrrailroad.net
    Appalachian Railroad Technology: http://www.apprailtech.com


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    Each PM42 section can be configured as short circuit protection OR auto-reverse, BUT NOT BOTH. Digitrax originally described a cascaded configuration where the first section was configured to provide short protection, with the second configured for auto-reverse. Due to interaction between the sections, they no longer recommend this configuration on the same board and references to it have been removed from the documentation.

    For an overview of PM42 function, se "PM42.pdf" (no hyphen) in the Yahoo Digitrax group files area.
    Doug Stuard,

    In the wilds of Northern Virginia

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    Hello,
    I am new at this. Have started building my simple DCC track plan with Kato, N scale, using JMRI, DecoderPro throttles. The track plan has a self loop. So I am told that it needs something like a PM42 for auto-reversing. But I also understand that the PM42 needs to be configured and it cannot be configured through JMRI. It needs a Digitrax Command Throttle which I do not intend to have. Does it also need a break-out board to connect it to anything?

    I wrote to Digitrax and they got back saying that they do not provide technical support for using PM42 with JMRI.

    I intend using PM42 because it takes care of future expansion plans.

    I did try to read online about using PM42 with JMRI but I didn't understand something about it needing the LocoNet or at least LocoNet Data Signal termination. I am confused. I have no LocoNet, the only other item from Digitrax that I have is DS64 turnout controller and it works well on JMRI DCC as is.

    Is there a simpler way to take care of auto-reversal? Or rather, which is the right way for a not too complex layout.

    Thanks,
    EsK

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    DCC Specialties has an auto-reverser of some sort. Their products tend to be pricier than Digitrax but given my experience with the Digitrax AR-1 I'd not recommend it. If you have a Digitrax command station, the PM42 can be programmed using it (e.g., Zephyr). Unfortunately, I don't know if one can use JMRI to program the PM42, and my brief search at the JMRI groups.io site didn't yield anything.

    edited to add: if you are bent on getting a PM42, get a breakout board as well.

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    If all you want is the auto-reverser then I'd go with the Digitrax AR-1 as there is no configuration.

    I have two of them and they do the trick. I have a Zephyr Extra (DS51) and did need to adjust the 'short circuit' timing on the command station - to give the AR-1 time to deal with the temporary short. The command station will still occasionally cut out before the AR-1 has done its job.

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