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using decoder as cab control throttle

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  • Member since
    February 2002
  • From: Mpls/St.Paul
  • 13,892 posts
Posted by wjstix on Sunday, January 12, 2014 9:58 PM

It would probably be easier to get one of those roller gizmos to run the engine at the workbench on DC first, or to add a DPDT toggle to the layout allowing you to change power from DCC to DC when needed. I do the latter on my layout, no big problem.

Stix
  • Member since
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  • From: Back in the PNW
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Posted by alco_fan on Sunday, January 12, 2014 9:53 PM

rrinker

 This is another one that comes up now and again. General consensus is that it theoretically will work, but is probably a bad idea as even the slightest short on the rails powered by the decoder motor output will fry the decoder. 

+1

The decoder has no protection on that side.

  • Member since
    October 2006
  • From: Western, MA
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Posted by richg1998 on Sunday, January 12, 2014 9:09 PM

All the suggestions are good.

 I think you know but will mention it anyway. The motor will get PWM. Twelve to fourteen volt pulse with varying pulse width. No pulse, motor stopped. First speed step with be a narrow positive pulse for forward, negative pulse for reverse. The pulse will widen for more speed and the pulse level will remain the same. Motor will see this as a DC voltage. Same with a voltmeter. The beauty of DCC is this pulse will help start a DC motor. Just like the old DC power packs with pulse control.

Rich

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

  • Member since
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  • From: Reading, PA
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Posted by rrinker on Sunday, January 12, 2014 11:27 AM

 This is another one that comes up now and again. General consensus is that it theoretically will work, but is probably a bad idea as even the slightest short on the rails powered by the decoder motor output will fry the decoder. Perhaps using an appropriate lamp in the circuit (an 1157 needs too much current for most decoders, unless you use a large scale decoder) would help, but the response time of the cold filament might be too slow to prevent damage to the decoder.

                       --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    July 2008
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Posted by mfm37 on Sunday, January 12, 2014 10:47 AM

It will work as long as the decoder is powering a completely isolated block. Yes it's been done before. The gotcha is if you use more then one decoder. One each powering its own block. The problem occurs when crossing block boundaries. Decoders have no protection on their output bwires. So as soon as the wheels bridge the gap, both decoders get current from the opposite block  into their motor and outputs. The decoders fry instantly. Only difference between small scale decoders and large scale is they large scale ones make more smoke when they fry.

Martin Myers

  • Member since
    February 2013
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Posted by AGSB on Sunday, January 12, 2014 9:36 AM

It could work, in theory, but you would have to use a decoder equipped with the DC Plug. DC engines don't like to run on DCC and if you are testing their performance before installing a decoder you don't want anything getting in the way. How would you set up an ammeter and volt meter to measure stall current? If the stall current was beyond the limits of the decoder, you may be replacing a lot of decoders.

I have a length of flex track set up to be easily operated with DC or DCC. I test my engines on DC and if all checks out, then I disconnect the DC, install the decoder and connect the DCC and program the decoder. A set of test leads with aligator clips is all that's needed.

  • Member since
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  • From: Sierra Vista, Arizona
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Posted by cacole on Sunday, January 12, 2014 9:28 AM

Using a decoder as a substitute for a DC power pack could work IF you used a decoder made for G-scale with a 5 or 10 Amp power output.  Anything less would probably be burned out very quickly by a heavy current draw motor, short circuit, or mechanical defect in the locomotive.

  • Member since
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  • From: Collinwood, Ohio, USA
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Posted by gmpullman on Sunday, January 12, 2014 8:40 AM

I don't see why it wouldn't work. Red & Black wires connected to your DCC buss and gray & orange wires to a length of test track. Downside is, if there is a short or if your locomotive you are testing draws more current than the decoder can handle you would run the risk of cooking the decoder. The total load would be on the motor outputs as well so if you had any lights they would add to the decoder's load.

I have an older MRC Tech2 or 3 with an ammeter and voltmeter on my test track. It paid off when I found one of my P2K PAs with the Hi Amp motor that was drawing 4.5 amps! That would have put an early end to any decoder.

The decoder relys on the DCC booster for short protection and you wouldn't necessarily have that on a decoder motor output.

Hope this helps, Ed

  • Member since
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  • From: lavale, md
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using decoder as cab control throttle
Posted by gregc on Sunday, January 12, 2014 7:42 AM

the various threads discussing DC/DCC control and my own needs to check DC locos before adding a decoder make me wonder about just using a decode intended to be installed in a loco as a throttle to power the track directly in place of conventional DC throttle.

Not sure how complicated the wiring woudl get.  Cab control would be used to route the external decoder output to only that section of track with the DC loco and would therefore only need to drive a single loco.

has this been discussed before?   what are the pro and cons?

greg - Philadelphia & Reading / Reading

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