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Effect of diodes on DCC

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  • Member since
    August 2013
  • From: Richmond, VA
  • 1,890 posts
Posted by carl425 on Saturday, January 10, 2015 1:49 PM

rrinker
One input line to the processor connects before the bridge

That makes much more sense.  It's what I would have guessed, but guessing gets me in trouble. Smile

"A man's got to know his limitations" Dirty Harry

I have the right to remain silent.  By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.

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Posted by betamax on Saturday, January 10, 2015 2:14 PM

CSX Robert

 

 
betamax
If you look at the diagram and remove the 4 diode block, leaving the single one, the waveform will still look the same, except one will not have a 2.8V drop, while the other will still have a 0.7V drop in amplitude.

 

No it won't.  With the assymtrical DCC module you have two paths for the two phases to take.  One phase will be blocked by the four diodes and pass through the one diode, creating the 0.7 volt drop.The other phase will be blocked by the one diode and pass throught the four diodes, creating the 2.8 volt drop.  Without the second path, the phase that is blocked by the one diode wlil not have any way of passing through.

 

 

You are correct, I made a mistake.  I started thinking of current flows from HV measurements I've been doing lately and accidently applied that to diodes. Diodes conduct the current, if the diode is reverse biased the current can't flow.  I was thinking of capacitors with respect to current flows to measure high voltages (by which I mean 100,000V or more).

Since it is exacting work, sometimes you forget you are not doing that when looking at something else. 

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Posted by Iansa on Saturday, January 10, 2015 8:36 PM

AS the op has DC and DCC the simple answer is fit a DPDT switch to each isolated section so each section can be powered by DC or DCC.

Turn DC op off in all decoders in CV 29 and when op DCC  switch DPDT switch to DC power.

When the decoder see's DC power the loco will stop. To power loco by DCC again just switch to DCC power and off you go.

What happens when loco bridges the DCC & DC current " NOTHING" no damge will be done to decoder.

I once had an automatic signalling system using a variation of this method.

Loco/train would automatically stop at red signal when isolated section, actvated by train in block in front, was changed from DCC to DC.

It was done with block detection and relays but that is another story.

BTW, get rid of the diodes if using this method.

Cheers

Ian

 

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Posted by maxman on Saturday, January 10, 2015 8:49 PM

Iansa
What happens when loco bridges the DCC & DC current " NOTHING" no damge will be done to decoder.

I confess that I don't understand any of what's being discussed here.  But I'm willing to accept that there will be no damage to the decoder if the loco bridges the gap.  But what effect, if any, will there be to all the DCC components connected to the track on the DCC side of the gap when they get backfed DC?

  • Member since
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  • From: Reading, PA
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Posted by rrinker on Saturday, January 10, 2015 9:30 PM

 That is 'bad' That's why this is not a good method - either the whole layout runs DC, or the whole layout runs DCC, it's the only safe method to use both on the same layout. At some point, someone will not be paying attention and cross a block boundary between DC and DCC and cause problems.

               --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
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  • From: Brisbane Australia
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Posted by Alantrains on Sunday, January 11, 2015 6:23 AM

That's exactly what I do Randy,

even though my layout is wired for twin cab control (Old DC system) I only ever connect one controller to the layout at a time. There can never be DC and DCC connected to the layout at the same time. As I only use a PowerCab which has an upper limit of 2 amps for DCC, my existing wiring works fine. 

The diodes are only connected to power dead ends such that DC engines can be backed out, they stop automatically on their way in due to the diode blocking the current flow once the engine has all power pickup wheels inside the dioded end section. This prevents DC engines from going off the end of the track (and crashing to the floor in some cases). 

Guess I'll just have to put better stops (Piles of dirt etc), at the dangerous dead ends.

Alan Jones in Sunny Queensland (Oz)

 

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