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Power level to track on MRC Prodigy Express 2

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  • Member since
    May, 2005
  • From: North Carolina
  • 235 posts
Power level to track on MRC Prodigy Express 2
Posted by trnj on Saturday, June 02, 2018 5:47 PM

I just replaced my MRC Prodigy Express with a new one, after the other one served me for 12+ years without a problem.  But I noticed that the power supply for the old Prodigy Express puts out 14.3-5 volts while the new "wart" applies only 13.1-3) volts to the track.  Would it be harmful to continue to use the older power supply (wired into an off-on switch) or is there a reason for the decreased voltage to the track?  The user's manual says the output is 14.5 v and and 1.6 amps but the power supply is listed at 13.8 v and 2 amps.  The old supply is 15 v. at 1.6 amps.  ??

  • Member since
    January, 2009
  • 3,052 posts
Posted by RR_Mel on Saturday, June 02, 2018 6:19 PM

I have a Prodigy Advance and it reads 15.6 volts on the DCC output using my Fluke meter but differently on cheapo meters, from just under 14 volts to over 16 on the Harbor Freight meters.  I have one A830L meter I bought off eBay that reads slightly less than my Fluke.
 
I have found that cheapo meters can be ±1 volt compared to my Fluke on straight DC.
 
I seriously doubt if a one volt difference would cause you problems.
 
 
Mel
 
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
  • Member since
    January, 2015
  • 228 posts
Posted by RR Baron on Saturday, June 02, 2018 7:10 PM

DCC is DC PWM thus it is an AC square waveform.

Experimenting revealed the Harbor Freight CEN-TECH 7 function digital multimeter AC reading of DCC was closest (surprisingly close) to the actual DCC voltage than readout from several models of Fluke and Extech True RMS mulitimeter.

The Harbor Freight meter has a pod inside, which end user can use to calibrate the meter.


Regarding MRC Prodigy Express2 power supply - go with what MRC tells you. 

 

RR Baron

 

  • Member since
    October, 2006
  • From: Western, MA
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Posted by richg1998 on Saturday, June 02, 2018 8:12 PM

For a comparison, my NCE Power Cab power pack is 13.9 vdc. The DCC output is 13.6 vac. I have four Harbor Freight multimeters.

About the same at the club that uses the NCE five amp Power Pro.

Rich

N

  • Member since
    February, 2002
  • From: Reading, PA
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Posted by rrinker on Saturday, June 02, 2018 11:56 PM

 Does one power supply say AC and the other DC? Many DCC systems have switched to DC power supplies even if the system can handle either, simply because 13.8V DC is a VERY common power supply available in quantities cheaply. If the power supply puts out DC voltage, thent here's no way the track voltage can be higher than the power supply, if fed with AC, this is typically rectified and filtered inside the system and the result is a slightly higher output because the spec on the power supply is RMS and when rectified and filtered you get peak, which is square root of 2 times the RMS. Less some internal losses and you get the same or greater than you started with.

 The HF meters work because DCC is a square wave. It reads the peak and that's it. A plain RMS meter (that doesn;t say True RMS) assumes a sine wave, so it will read low for the DCC square wave. A True RMS meter can read correct for various wave forms, like sine, square, and triangle, but there is a caveat - they usually only work up to a certain frequency, usually fairly low - well under 1KHz. DCC is a much higher frequency, therefore even a fancy True RMS meter will read incorrectly. I do have one old Fluke that specifies True RMS up to 20KHz (it was designed for audio engineers), I haven't checked DCC voltage with that one to see how accurate it is, but my fancy bench meters and even my fancy handheld definitely read low. The HF cheapo meters though - they work for this. Only other thing that can read an accurate voltage is my oscilloscope.

                                 --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
    May, 2005
  • From: North Carolina
  • 235 posts
Posted by trnj on Sunday, June 03, 2018 4:54 AM

I appreciate all the input.  I use a "RRampMeter" which seems to measure DCC well.  It is quite sensitive and changes milliamps momentarily used even when one of my "Frog Juicer" circuits is triggered.  I think the fact that the 13.8 v power supplies are cheaper is the main reason MRC has begun to use them!  I intend to continue to use the older "wart" which is already wired into my system (with on-off swich on panel) and keep the newer supply as backup.   

Thanks to all who responded.  The Prodigy Express fits by budget as well as my "one man," one engine (at a time) layout, a point-to-point switching layout.

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