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RE: [WiringForDCC] Power Supply Question

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  • John Bishop
    Thanks to everyone for the advice. One concern is diversity of equipment.  I have a GG1 equipped with a Magnum decoder that will handle up to 35 volt peak,
    Message 1 of 15 , Dec 1, 2011
      Thanks to everyone for the advice.

      One concern is diversity of equipment.  I have a GG1 equipped with a Magnum decoder that will handle up to 35 volt peak, and I will use those in my other locos.  On the other hand, I also run trolleys and smaller engines which don't need such big decoders, but perhaps I should for safety although they are more expensive.

      The real answer, I expect, is to hurry up and finish more track, install DCC on my layout, and not run any DCC stuff on it until I do.

      John Bishop



      --- On Tue, 11/29/11, Max Maginness <m.maginness@...> wrote:

      From: Max Maginness <m.maginness@...>
      Subject: RE: [WiringForDCC] Power Supply Question
      To: WiringForDCC@yahoogroups.com
      Date: Tuesday, November 29, 2011, 7:24 PM
















       









      Your eye to brain to hand on the knob response time – about 2 seconds



      Your AC power line time to a spike - 8 milliseconds ( maybe a bit more with capacitors)



      Spike to decoder death – about 200 microseconds



      Enough said?



      Max



      From: WiringForDCC@yahoogroups.com [mailto:WiringForDCC@yahoogroups.com] On Behalf Of John Bishop

      Sent: Tuesday, November 29, 2011 4:55 PM

      To: WiringForDCC@yahoogroups.com

      Subject: Re: [WiringForDCC] Power Supply Question



      Thanks.



      I will reconnect the big can condensers I was using.



      I have a voltmeter (and ammeter) installed as a part of my power supply. This is partly because some O scale motors can use up to 18 volts, but smaller motors can't. I realize that the limiting factor is the decoder voltage rating, not that of the motor, but only some of my engines currently have decoders.



      As long as I keep an eye on the volt meter, can I safely omit linear regulator?



      John Bishop



      --- On Mon, 11/28/11, Mark Gurries <gurriesm@... <mailto:gurriesm%40comcast.net> > wrote:



      From: Mark Gurries <gurriesm@... <mailto:gurriesm%40comcast.net> >

      Subject: Re: [WiringForDCC] Power Supply Question

      To: WiringForDCC@yahoogroups.com <mailto:WiringForDCC%40yahoogroups.com>

      Date: Monday, November 28, 2011, 11:34 AM



      On 11/23/11 at 10:38 AM, snboy2001@... <mailto:snboy2001%40yahoo.com> (John) wrote:



      >Hi guys,



      >



      >I have installed decoders in some of my O scale engines to run



      >on a friend's DCC layout.



      >My own layout will eventually be DCC, but I'm not there yet,



      >and it is now powered by a homemade power supply consisting of



      >a Variac, together with twin transformers and rectifiers. At



      >one time I had a couple of large can condensers in the circuit,



      >but they are now disconnected.



      >A couple of the decoders have failed operating on my layout,



      >and a friend suggested that DCC decoders might be destroyed by



      >use with unfiltered DC, that I should reconnect the condensers.



      >



      >What do you guys think?



      >



      >Thanks,



      >



      >John Bishop



      >



      Not recommended way of running you decoder equipped engines.



      Unfiltered DC generated from a transformer and rectifier has:



      1) a very high peak DC voltage than what you read with a



      meter. To be more precise, the peak voltage is about 1.414



      time higher. (Peak of the AC sine wave voltage) So if you



      putting out unfiltered 12VDC on the track, the peak voltage is



      close to 17V.



      2) the consequence of passing any form of AC noise or voltage



      spikes right to the track. The bridge rectifier will not stop



      this from happening. All it does if rectify the AC spike and



      noise into DC spike and noise.



      These two factors in combination may create a situation where



      you are presenting to high of a peak DC voltage to the decoder



      which will destroy it because you exceeded it maximum voltage



      rating of the decoder.



      Solution?



      Filtering the rectified voltage with a large capacitor/condenser



      will greatly address the spike and noise voltage stuff.



      However, by adding the capacitor, it will also raise the now



      filtered DC voltage to be 1.414 times higher than what you had



      unfiltered. You can see that effect with a DC voltmeter. You



      will also need to "clamp" the maximum/peak voltage seen at the



      track level to guarantee you never exceed the maximum voltage



      rating of the decoders. A linear regulator can do that for



      you. Just get a 15VDC regulator of suitable current rating



      installed before the reversing switch. May need a heatsink for



      the linear regulator.



      With this done, the variac speed control function will still



      work as before but the track voltage range will now be protected



      and clamped. The down side is the variac knob control range



      will become vary sensitive in the sense that to achieve a given



      operating speed as before, you will be using a lower knob dial



      (position) setting than before. You will also noticed that past



      a certain point, no matter how high you turn the variac knob up,



      there will not be any speed increase.



      Best Regards,



      Mark Gurries



      Electrical Engineer



      DCC Website & NMRA DCC Clinics: www.markgurries.com



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    • Steve
      In case you are looking for another one I have a XFR 10&12 transformer I got from Tony s Train exchange in 1998 that s never been used and its on e-bay right
      Message 2 of 15 , Dec 2, 2011
        In case you are looking for another one I have a XFR 10&12 transformer I got from Tony's Train exchange in 1998 that's never been used and its on e-bay right now. The label says output of 18v ac and 8 amps but when I measured it I got 19.8 volts, Steve.
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