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What size of bulb for motor load on stationary decoder?

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  • Member since
    January 2007
  • 180 posts
What size of bulb for motor load on stationary decoder?
Posted by Otis on Thursday, February 21, 2008 10:52 AM

I am still designing my experimental stationary sound system using Soundtraxx DSXs and LCs (just now awaiting arrival of correct transformers in the mail)

I have heard that the LC series decoders (not usually used as stationary) may require a motor load to respond.  A light or resistor would do this.  I would like a light to signal the decoder in use on the sound board I am making.

What voltage and mA would be best?....one close to the lighting used by the decoder (1.5 V) or higher in voltage?  I am going to put the bulbs in Radio Shack E-10 bases (as I have nothing like a socket for the grain of wheat sizes) so this gives me a choice of these Radio Shack bulbs:

2.5 V & 300mA
7.5 V & 220mA
14 V & 200mA
2.5V & 360 mA
14.5 V & 100mA
6.3 V & 150mA or 250mA

Soundtraxx is yet to respond.  In the meantime, does anyone have a good idea?

Thanks

  • Member since
    December 2005
  • From: East Granby, CT, USA
  • 505 posts
Posted by jim22 on Thursday, February 21, 2008 9:08 PM

Assuming the decoders use the motor as a load to communicate  back to the command station (i.e. for reading back CV values) you need to simulate a motor.  I don't know if a bulb would be a good simulation for this.  Bulbs are basically resistive loads, but have a large inrush current.  When first turned on while the filaments are cold, a bulb may take 10 times it's hot current.  Motors, on the other hand, are inductive loads, and also have a back-emf which goes up with motor speed.  I think I would try a resistor across the motor leads of about 12V/.1A = 120 Ohms.  For experimental purposes, how about hooking up a real motor and getting the decoder communicating.  The substute a resistor for the motor with a rather high value, maybe 220 ohms, and reduce the resistor value until the decoder will communicate.  I wouldn't go lower than 68 ohms or so.  If you try a bulb, make it a much lower current one, like 12V 30ma.  That should not pull much more than .3A at startup.

Jim 

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