optimizing contact of Märklin F7 locos

doclouis Jul 11, 2018

  1. doclouis

    doclouis New Member

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    Hello guys,

    while converting my layout to DCC, a serious problem came up concerning the electrical contact of my Märklin F7 engines. I have never had these problems with running them analogue.

    All these engines do have quite a few years on their backs: The oldest (Amtrak) from 1981, the youngest (SP Daylight) from 1997, most of them are bought preowned. I use drop-in decoders from Velmo, all locos have been to a "ultrasonic bath" and cleaned with Qtips/isopropanol. All the tracks (Märklin) have been cleaned with isopropanol as well, for the switches I used a toothbrush. While MTL and AZL locos run very fine, smooth and without Problems on the same tracks, the Märklin locos get stuck every 20-30cm and have to be pushed to gain contact again. Well okay, all Märklin locos have traction tires installed to 2 of 8 wheels. These two wheels do not make contact, but the AZL engines have tractions wheels as well, so this should not be a big issue, as These run fine.

    I am wondering what causes this lousy contact. As I used the Gaugemaster HF1 before in analogue mode, I can imagine that it caused micropits on the wheels, which worsen the contact. An exchange of the wheels might help.

    Does anyone of you have made experience with Märklin locos and lousy eletrical contact using DCC? What did you do to optimize the contact?

    Cheers,
    Lutz
     
  2. SJ Z-man

    SJ Z-man TrainBoard Supporter

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    Hmmm. The decoder is more sensitive to dirt on the wheels. Each time there is enough drop, the microprocessor has to restart. Milliseconds, but still noticeable. And, decoders from some suppliers, like Digitrax, have 'Momentum" be default. That means, each time the decoder restarts from a dropout, it has to ramp up the Speed Steps and this is several seconds. (set CV3 and 4 to '0' to disable).
    Also, if the motor current is high (I have seen many märklins with 250 ma or more. Even though the decoders handle 500 to 1000 ma (1 Amp), the decoder could still shut down (over current or overheat), then restart.

    Make sure your wheel are clean. Not the brass Trix brush but alcohol. Paper towel, one truck on, other on the track.
     
  3. doclouis

    doclouis New Member

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    Hello Jeff,

    I've already set CVs 3&4 to 0. But it's good to know that this was a right decision. What's interesting is the thing about the brass brush. In fact I have been using such a brush for years, I guess I bought it by the end of the 1990s. Does this drive pits in the wheels as well? Now it's no wonder having contact problems, when wheels and rails have thousands of micropits caused by Gaugemaster HF1 and such a brush. I am excited, if the brandnew wheels I ordered from Märklin will bring a better contact.

    Cheers,
    Lutz
     
  4. ViperBugloss

    ViperBugloss TrainBoard Supporter

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    I have tried converting a few Marklin locomotives to DCC using Velmo decoders with not very good results, as they tend to have the same erratic behaviour as you report. Rather than the problem being the wheel to rail contact, I have wondered if the problem is the contact point between the brass strips on the Velmo decoders and the capacitor in the locomotive. I have considered attempting to solder this connection but have never been brave enough to try.

    I also have some Rokuhan locomotives with Velmo decoders. These are the German locomotives that were developed as a cooperative effort between Rokuhan and Noch, with Velmo also involved from the start. In these locomotives the contact point is a screw fitting. I had the decoders fitted by the supplier in Germany. (I live in the UK). They are more reliable but again do require a clean track. One feature of the Velmo decoders is that on occasions the lights will go out, but the locomotive keeps running. The lights have to be then switched off and on again from the DCC handset. I use NCE equipment.

    Rob Pearce (aka Viper Bugloss)
     
  5. doclouis

    doclouis New Member

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    Hello Rob,

    I tend to believe that it is a wheel/track problem, as Märklin-Velmo-locos will stop on the same sections of the layout and especially on turnouts. But before going back to analogue I can try a soldering.

    Cheers,
    Lutz
     

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