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Ever since I (the webmaster) started out with digital, I have planned to convert my childhood locos to digital. I have been reluctant to do this, since I have been "emotional" about these and especially about my first loco ever, a 3003 that I got for Christmas in 1963. This loco has been with me since then, and every time I have taken it out it has worked as it should. It was stored away at my parents house for about 20 years but I got it back when my son got his first railroad a few years ago..       

And finally, I decided to convert it since I want to see it run also on a digital layout...

This is a loco with the SFCM motor, and there are 2 obvious choices to make a conversion. One is to install a Delta decoder, the other to install a 6090x decoder and a HAMO magnet. You can also do as described on Dr König's pages, but this seemed too drastic to me...

Since I have done the 6090 + HAMO conversion before and have blown decoder motor outputs, I was a bit reluctant to do it again. Also, I did not have a HAMO SFCM magnet at home...  What I had at home were a few Deltas and a Lenz LE900 decoder for DC motors....   So I decided to make down right dirty cheap conversion with the LE900 using 2 diodes to rectify the motor current....  The 2 diodes trick is a well known way to make a Märklin loco run with DC power...  You replace the electromagnetic reversing unit with 2 diodes and you can then use the loco as a DC loco instead...  The electromagnetic stator in a Märklin motor has 2 coils, one used for each direction. It has 3 leads, one is going to the motor and the 2 others are connected to the reverse unit. The connection setup is well described by this picture, taken from the Ames-Friberg-Loizeaux "Digital Command Control" book published by the Swedish Allt om Hobby publishing company. (BTW, this book is recommended even if it is about DC-digital, not Märklin digital).... 



The task

To convert a loco from 1963 with a SFCM motor with the Lenz LE900 and 2 diodes while keeping the original motor. This means that the motor had to be configured run as a DC motor, and then the decoder would be connected.

The procedure

  • Check the loco, and clean it up
  • Overcome the mental barrier of violating a childhood loco
  • Make the loco a DC-loco
  • Connect the decoder
  • See the loco run in Digital....

This is what I started with..  1 childhood loco, 2 1N4001 diodes, a Lenz LE900 decoder, a piece of clear plastic, some straps, "superglue" and of course a soldering iron....


First of all I had to clean the loco a bit, since it had about 30 years of stale oil, dust and cat hairs in it.... 
I dismounted the motor and other easily demountable parts and gave the chassis a bath in "Ajax" and then rinsed and dried it carefully....  When it was dry, re-oiling and mechanical "smoothness" testing was performed with satisfactory results. The picture is a "before cleaning" picture.....  



An electric toothbrush is a very handy tool to clean out the inner corners of the motor cover...
As you can see, "some" grime had been accumulated over the years.... 




I mounted the decoder on the clear plastic plate with "superglue" and then mounted it into the loco. I first tried to glue the plastic plate directly onto the chassis, but it dissolved the black paint, so I used the piece of double-sided tape that came with the decoder in the end...  The Lenz LE900 is much smaller than the Märklin decoders, but it was still quite difficult to find enough space for it without having any part of the decoder shorting components to the chassis...  Unlike the Märklin decoders, it comes "naked" without any plastic cover to insulate it from the chassis. 



Here you can see the plastic plate I glued the decoder to, the arrow shows an area that became very useful later, this is the area where I could "superglue" the diodes to...




The motor cover was stripped of "unnecessary components", I cut away the capacitors and cables. Only the "center tap" from the stator was preserved...
 

So now it was time to re-mount the motor, and connect it to the diode setup. I had some problems with the stator coil winding ends, since they were old and broke where they were connected, but I managed to connect cables to them after all...  Then I tested the motor in "DC mode" by connecting it temporarily to the digital test track...  The motor was ok.... It moved in both directions.... 

 

Ok, now it's time to hook up the cables...  The blue, green an violet cables are not used in this conversion, and the light cables (white and yellow) were connected together so the light would be on in either direction of operation since the 3003 doesn't have rear lights....  The cable hookup became quite easy, and the diodes were "superglued" onto the plastic plate I had mounted the decoder onto. Diodes are shown in the second picture... 



Finally, the loco was tested at what it is intended to do, and that is pulling a few "Thunderboxes" around on a digital layout.... 

 

Summary and peculiarities

The Lenz LE900 seems to have the same capabilities as a 6080 or a Delta, since it has no EMF speed regulation as 6090x.  However, it has adjustable acceleration an deceleration.  My test run was made with the factory default settings for the decoder and the loco ran very well indeed...  Actually far better than Delta. I will test with the programmable settings later on... I was rather impressed by it since it is a cheap decoder (about the same as Delta) compared to Märklin and Uhlenbrock decoders.

However, it seems like it is very sensitive to dirty tracks, and needs "perfect" conditions since it behaves like a 6090 when it momentarily looses current - a dead stop and then starts again...  This behavior is also reported on Uhlenbrock decoders, so I presume the decoder is more "sensitive" to dirty tracks. I have thought of adding a capacitor to overcome this....  

After some more testing, it seemed like it got some "overheating" problems, since the loco suddenly started to jump and at the same time it flashed the lights, even if the lights were turned off...  This could of course be a case of bad connection, or because I connected both light outputs to the front light, or it may be a general problem with the setup since 2 diodes do not provide perfect "DC-power"...  I will have to investigate it further.  A Märklin decoder would probably have been "fried" under the same circumstances....  Even if the speed is set to zero, the loco continues to jump....  But if it is lifted off the track and then immediately put back again, it runs normally for a while again.....  

Probably the decoder is ok, but the wiring might need an overhaul. I will investigate and test some more regarding this matter. Since the function outputs are protected, I have a suspicion that it doesn't like my wiring with both function outputs connected together.....  

This page will be updated as soon as I find the solution to the problems I have noticed... 

But in general, the decoder runs very well indeed and the peculiarities mentioned are noticed only after long-time continuous running...


Update regarding the "peculiarities":

After changing the slider to a brand-new one, the problem was reduced for a while. But "over-oiling" caused the problem to re-occur...  So, my conclusion was that "sparks" from the motor and maybe also unreliable connections to power & ground causing "spikes" were to blame for the behavior of the decoder...   The solution seems rather simple... Just re-install a non-polarized capacitor between the motor poles and it works flawlessly....  This smoothens those "spikes" generated by the brushes and the flat commutator, and as a result - the decoder does not misbehave anymore.... The loco runs absolutely perfectly now. I have also changed the acceleration settings and it is definitely better than Delta, but it does not have the torque that an EMF decoder has....  Since the decoder is rather cheap, it is still worth a closer look if you run "Märklin-Motorola" only with 6020/6021. If you have the Intellibox, maybe you should take closer look at the Lenz DCC decoders with EMF and run them in a multi-protocol environment. 

It was a simple solution to the peculiarities, but - in general, it is recommended in Lenz manuals to get rid of all capacitors when installing one of their decoders, so it was not the obvious choice. Since this is not a decoder with EMF load regulation, it doesn't matter.  With EMF decoders as e. g. the Lenz LE130 (NMRA-DCC) a similar solution would probably not be applicable due to the impact on the EMF signal.

 

 

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