Hints & Tips

Resistor Wheelsets

As I'm using DCC on my layout, my rolling stock has to be equipped with resistor wheelsets, in order to be detected, for train occupancy reporting to the dispatcher (Winlok). The technique I used to make my N scale resistor wheelsets can be used for DCC, as well as for any other detection system sensing track current, and in any scale.

Of course, the prerequisite, for making resistor wheelset is to get wheelsets with insulated metal wheels. Both wheels, or a single wheel, can be insulated, depending on the manufacturer.

In N scale (as well as in other larger scales), the resistor has to be very small to fit between wheels. I use 10 kohms - 1/8W surface mount resistors. They are really tiny and lightweight but, in return, are rather difficult to handle due to their small size, requiring tweezers, a magnifier and some patience... Not to mention that when one of them jumps from the tweezers, there is little chance to recover it...

The figure at right, shows how I installed the resistor on a wheelset (in this case, a wheelset insulated on both sides).

The resistor is first glued at an angle between the axle and one of the wheels, using a small drop of ACC. Installing the resistor at an angle is mandatory, to avoid shorting it with the metal axle.
After the glue has cured, the upper contact surfaces of the resistor are carefully scraped with a hobby knife, to remove excess glue and ensure a good electrical contact for the next operation. The same way, I recommend cleaning wheels in the area where the conductive paint will end at.

Then, using a toothpick, conductive paint is spread between resistor contacts and wheels, as shown on the diagram. I'm using a silver loaded paint which, when dry, has a zero resistance. It comes in tiny bottles and is rather expensive (as compared to the size of the bottle !) but goes a long way since one drop is enough for painting a wheelset.

When the paint is completely dry (not before !) check the resistance between both wheels, using a volt/ohm meter. The value read should be the resistor value (plus or minus 5% - resistor tolerance). If an "open" value is read, check for proper cleaning of the resistor/wheel contacts, add more paint, let dry and test again. If all this fails, check for continuity at various points, starting at one wheel, towards the other one.

One resistor wheelset per car gave me good results, for train occupancy detection, on my layout.

Good luck !

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Last update : 10/30/1998
© 1998, Jean-Louis Simonet