Model Railroading > How to mount detection resistors

Asking this for a friend...

He has 500+ cars that need detection resistors, so buying Jaybee resistor wheelsets is out of the question(but it\'s MY plan, FWIW)

He\'s experimented with soldering 1/8 W resistors to the metal wheels, but the wheels won\'t take solder and the plastic axles melted. He has a conductive paint pen, but doesn\'t quite grasp the concept of surface mount resistors, and is afraid of painting a short circuit.

Anyone have experience with homemade detection wheelsets?

VunderBob

I am in the process of mounting resistors on wheelset right now. I am using P2K wheels, 10K ohms surface mount resistors, and a conductor pen. I glue the resistor in the middle of the axle with a small amount of gel ACC glue. Then I draw a trace of silver with the conductor pen from each end of the resistor across the axle and onto the hub of the wheel. I then do the other end. After the silver has cured I test each wheel set with an ohm meter to make sure I have a good connection. If I don\'t I reapply the silver trace. When everything checks out I paint the silver with black paint to hide its brightness. I then mount one wheelset per truck. Thank goodness I don\'t have 500+ cars to do. The 100 plus I am doing is more than enough.

The thing that I have had a problem with is getting the silver to flow from the tube. I ended up cutting the tip a little. Also, I really have to squeeze the tube to get it to flow. I also have to shake the tube frequently and clean the end of the tip.

Don\'t worry about creating a short curcuit. If you test each wheel set and make sure that the resistance is approximately 10K ohms, then you won\'t have a short circuit.

I admit that I have not tried this myself, but I have seen one modeler who drilled a press-fit size hole in each wheel, near the axle. Then, just push the leads of the 1/8 watt resistor into the holes. You may need to experiment a little to find the size drill that works best.

Hmm! I must be missing something here. What is wrong with using conductive paint across only the insulation between the wheel and axle and then using a razorknife to trim the width down til you get to the desired resistance?

I haven\'t done any this way in a long time but it used to be standard procedure.

Also, if you don\'t mind, I suspect that 10K ohms per axle, two axles per car giving 5K ohms is a bit high. If your detection system can detect 5K ohms, I suspect that it can detect humidity and lots of RF interference as well. I may be wrong here but my experience says that about 1K ohm detection is about the highest safe value for HO blocks that run, say, 6-8 lineal feet. Maybe its just that you are in Arizona and we\'re here in Michigan!

<<Hmm! I must be missing something here. What is wrong with using conductive paint across only the insulation between the wheel and axle and then using a razorknife to trim the width down til you get to the desired resistance?
<<

The reason to use surface mount resistors is it is a lot faster and easier than trying to scratch away just the right amount of conductive paint. The surface mount resistors only cost about $0.02 a piece and have a know resistance value. They are very small and don\'t interfere with the axle clearance.

<<Also, if you don\'t mind, I suspect that 10K ohms per axle, two axles per car giving 5K ohms is a bit high. If your detection system can detect 5K ohms, I suspect that it can detect humidity and lots of RF interference as well. I may be wrong here but my experience says that about 1K ohm detection is about the highest safe value for HO blocks that run, say, 6-8 lineal feet. Maybe its just that you are in Arizona and we\'re here in Michigan!>>

I use the Digitrax BDL16 which is very sensitive. It actually has two detection levels, 22K and 10K. The default is the 22K ohms setting and with that I haven\'t had any problems. Some of my blocks are over 20 feet log and I haven\'t had any problem with false detections and I live in the rainy NW. Maybe it is because with DCC there is always current on the rails as opposed to regular DC which uses a background voltage for detection.

I just sent Terry this set of instructions.

Remember, he\'s trying this with traditional resistor that have wire leads.
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How to mount the resistors...

This is a variation of the surface mount method.

1. Superglue the resistor to the axle.

2. Bend the leads to touch the axle, and tack wire with glue near the resistor body.

3. Trim leads to leave wire past the tack points.

4. Using paint pen, complete circuit between leads and wheels.

No solder, and should go quickly.

Bob