GANDY DANCER - (suppression ?)

[fenderman]

I have just purchased one of these Gandy Dancer's as a novelty item on a projet layout.
I did have a few problems getting it up and running at first (very jerky and intermittent) but I had been warned about this, and read a few of the forum threads about it, and after some meticulous attention, it runs as sweet as a nut now.
So what's the problem you may ask, well, after checking with an EMC meter, there MAY NOT be any suppression on the motor on this little gem, but wanted to qualify this before I started to go about the task of attempting to fit one, some other electronic bits that are around on the layout seem to be effected when this runs, but not with any of the normal loco's, which of course do have suppression capacitors fitted.
Any info would be appreciated.

[Jim Banner]

RFI standards are more relaxed on this side of the pond and many (most?) locomotives have no suppression built in.  Those that are meant for the international market, such as Bachmann products, often have to have the RFI suppression capacitors removed in order to work correctly with Digital Command Control.  I suspect that this does not greatly increase the RFI emitted as the radiating antenna length is short, just the wiring between the DCC decoder and the motor whereas with dc control and no suppression, all the wiring and track between the motor and the controller can radiate RFI.  If you are having problems with excessive RFI, I suspect you are using dc to run your gandy dancer, and the following applies:

There are various levels of suppression you can apply until you conform to EDC standards.  The first is simply a small capacitor across the motor terminals, something like a .001 microfarad disc ceramic.  If that does not do the job, add two chokes, one in series with each motor lead.  Something like 20 turns of #28 magnet wire wound around a 3 mm rod then slid off the rod and mounted on a scrap of perforated circuit board, or if there is no room for that, wound around a soda straw and glued to the straw to make a self supporting coil.  Alternately, there are any number of small commercial chokes wound on ferrite rods.  Buy the greatest inductance that will carry the motor current and will physically fit.  If this still does not work, add two more disc capacitors, one from each motor terminal to the motor's case.  Still not good enough?  Add another capacitor across the inputs to the chokes, that is, the ends of the chokes that go to the wheels.

I for one would be very interested to hear how you make out with this.

Jim