Resistor Wheels for Block Detection

[rbryce1]

Just wanted to pass this little tid-bit along for others who may be planning to do this.

I have finished setting up my railroad for block detection so I can see where my trains are.  The last thing I need to do is install the small resistors on my freight car axles so the system can see them.

I researched the task and found I need to glue 10K ohm resistors, 1/8 watt, to the axle so it creates a very small current path across the wheel's insulator.  This small amount of current allows my BD20 to detect that a car is on the block.

I ordered 200 resistors on eBay, and was surprised at what I received.  I needed a magnifying glass to SEE the resistors, and it was impossible to install them on the axles with the conductive paint.

It turns out, that one of the long list of codes in the part number was the number 0201.  Not knowing what that meant, I did not pay that much attention to it, as I thought all the chip resistors were similar except for resistance and wattage.

Well, the 0201 was a size code, which, had I looked into it earlier, meant this resistor was .024" in length, .012" in width and .01" in height !!!   In metric that is 0.6 mm in length, 0.3 mm in width and 0.25 mm in height.

What I should have ordered (and did so this evening) was resistor size code 1206, which is the exact same resistor only about 5 times that size.

The below link is to a sizing table showing resistor sizes.  If you are contemplating doing this, I suggest you refer to the table on this web site before ordering.  You may wish to order sizes
1206, or the even larger 2010.

Hope this helps someone!

http://www.resistorguide.com/resistor-sizes-and-packages/