Decoder Installation Considerations

[richg]

If anyone here enjoys following instructions, here is a PDF you can download and save to your PC. The fellow is from South Africa so some some items he mentions you might not be familiar with. I correspond with him via some Yahoo DCC Groups and he is very knowledgeable with DCC & Sound.
Be advised, with this info, you need a multimeter, good soldering iron and proper tools.
For just a Plug & Play motor control loco only, probably just a meter but if the loco is DCC ready, not even a meter. Yes, I know, DCC ready sometimes has different meanings depending on the loco  such as a Spectrum 4-4-0 and Spectrum 44 tonner. One a plug, one soldering wires.

http://www.herman.rula.co.za/pdf/dcc_decoders.pdf

One thing I noticed in the document, Take Your Time.

Rich

[Jim Banner]

Good instructions.  Along with Take Your Time, the author also suggests do not skip a step.  That includes measuring the locked rotor current draw for each and every motor.  This is a step all too often skipped by neophyte and experienced installer alike.  And sooner or later, an out of spec motor shows up and smokes a brand new decoder.  All too often, the installer blames it on a bad decoder because he/his friend/someone he read about once installed the same decoder in the same locomotive and never had a problem.  He would know for sure whether or not it was a bad decoder if he had pretested it, but people who skip checking the motor current usually skip pretesting the decoders too.  So he sends the decoder in for warranty replacement and waits.  And waits.  Or more likely, he buys a new decoder because people who skip the tests are usually in too much of a hurry to wait.  Want to guess what happens?  With all the time he wasted so far, he again skips the motor test and the decoder pretest.  He misses that the out of spec motor is is still out of spec.  And he has the pleasure of watching another decoder go up in smoke.  That is when his locomotive ends up on my workbench.

Sorry about the rant.  Funny thing is, I believe in freedom of choice in many things, including the freedom to smoke decoders if that is what you want to do.  Trouble is, not one of the people who have asked for help have ever said that smoking decoders is what they wanted to do.

One factual problem I have with these instructions is the suggestion that you can use resistors as low as 100 ohms with GOW and GOR bulbs.  Some GOR bulbs draw as little as 15 milliamps at 1.5 volts.  But a 100 ohm resistor will drop only 1.5 volts at 15 milliamps, not nearly enough to drop 12 volts down to 1.5 volts.  More likely, under those conditions, the bulb will receive about 7 volts and be passing about 50 milliamps.  The 100 ohm resistor at 50 milliamps will be dropping about 5 volts.  At 7 volts, that bulb will have a life expectancy of about 7 milliseconds, based on a rated life of 1000 hours at 1.5 volts.  A minimum resistance for use with this bulb would be 700 to 750 ohms.

Jim