Slowing down a locomotive

[leewal]

I have a new locomotive that I'd like to lash up with another. However, it runs so much faster than the other it's impossible. Is there a way to slow it down. I know DCC would make it work, but I run DC and have no plans to change at this late date in my life.

[RR_Mel]

You can use diodes in series between the rail power pickup and the motor.  Because of the reversing DC for forward and reverse you would have to use them in pairs paralleled + to – and – to +.  There will be .7 volts drop across each pair.  I would suggest 1N4001 diodes, they are rated at 1 amp.

 

Two pair in series will drop the voltage going to the motor 1.4 volts and so on at .7 volts per pair.

 

 

 

 

Mel

 

 

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

 

I'm beginning to realize that aging is not for wimps.

 

[dstarr]

I don't believe I have ever had that problem.  I run straight DC.  I lashup a lot of diesels.  I will confess that I am usually lashing up diesels from the same manufacturer.  Was it me, I would take a good look at the slower locomotive and see if some tuning would speed it up.  It is worth taking the gear towers on the trucks apart, cleaning out all the old grease with solvent, brushing each tooth of each gear with a pipecleaner to pick up the odd bit of flash.  Relube with a dab of molly grease from the auto parts store.  The gears are made from slippery engineering plastic and don't need much lube. Give the motor one (just one) drop of light oil on each bearing.  Check wheel gauge, coupler height.  Look for rotating parts rubbing on the inside of the shell.  Check that the motor is mounted flat, not cocked up at an angle and the U-joints are running with a very small angle, almost straight.  On Athearn BB locomotives current is carried to the motor thru a springy metal strip clipped to the top of the motor.  Better is to hard wire the motor.  Get a couple of 1/4 inch "Fastons" from your hardware store.  They will slip onto the strips coming up from the trucks.  Crimp wire into the Fastons and solder the other end to the springy strip. 

   If nothing gets the slow locomotive up the speed, you can place one or more ordinary diodes in series with the motor of the faster locomotive.  Each diode will reduce the voltage to the motor by 0.7 volts.  You need two stacks of diodes, one for each direction.  You might try the classic constant head lamp brightness circuit.  That uses four diodes  (two diodes in each direction) to rob 1.4 volts from the motor to light a grain of wheat lamp.  With this circuit I can crack the throttle and have full headlamp brightness long before the motor starts to move the locomotive.  Headlamps stay good and bright for all throttle setting from creep to highball.

[tankertoad135]

When I ran DC, I used a resistor between the poles of my motors to slow down lokies.

[leewal]

You and me both.  Thanks for the reply.

[Canalligators]

If you need to have the response curve (speed v. voltage) the same shape, but start up at a higher supply voltage, use the diodes.  If you want the curve to be flatter but respond less, use the resistor.

My grandson has a Thomas engine that just plain runs too fast.  It starts out fast and maxes out way too fast.  We want the speed v. voltage curve to not be any flatter, but to moved down overall.  This would call for diodes.  Well, I tried a resistor and played with a lot of resistor values, and if I got the max speed down into subsonic, it took 3/4 throttle to get it moving.  I need to retry with diodes.