S Scalers:

I am using the Zimo DCC system.  When trying to take advantage 
of its ability to feedback the position of turnouts I have ventured 
into the Land of Ignorance.  Perhaps those more familiar with 
electrons can help me out.

Here is the problem.  I am using Hankscraft turnout motors installed 
in Rix Rax II brackets. The Hankscraft motor is rated for 3 volts 
and supposedly draws less than 10 mA; I am bringing 12-14 volts.  So 
I need a resistor -- and a 1200 ohm resistor comes with the 
motor.  That works fine but the voltage drop over the motor is 5.5 
volts.  That's nearly double what's called for so I figure I need 
more resistance in the circuit.  So in my bench testing, I changed 
out the 1200, and replaced it with a 1000 ohm resistor, a 330 ohm 
resistor, and a diode I bought from Radio Shack (1N914/4148-Type 
Diode, described as popular silicon switching diode rated at 75V & 
450 mA)all in series.  Now the motor does not turn -- all the 
voltage is dissipated over the two resistors and the diode -- I 
might as well have replaced the motor with a wire.  [My application 
requires a diode.]  I am driving the test circuit with a Radio Shack 
12 volt DC 500 mA wall-mount transformer.  I also have a 12v, 1 amp 
DC transformer that delivers the same (non)results.  And I have the 
diode hooked up in the right direction.

I must confess I don't understand what is going on.  Why would adding
more resistance to the circuit knock out the motor?  Am I using the 
correct diode? It's just in there to regulate direction of current 
flow.

Any assistance would be swell.

Hilary Smith
Northern Virginia





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