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Ampere Requirements for DCC vs DC

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  • Member since
    December 2004
  • From: Bedford, MA, USA
  • 21,481 posts
Posted by MisterBeasley on Thursday, December 10, 2015 11:10 AM

Arto
Should these reversing sections (blocks) be on a separate power district?

Reversing sections in DCC must be isolated with gaps at both ends, just like in DC.  You can even use a DPDT toggle to do the polarity flip, if you'd like, but most DCC users opt for an auto-reverse unit which makes the whole operation seamless.  In a DCC reverse section the polarity is flipped for the reverse region itself while the train is in the loop.  In DC, you keep the loop polarity the same while flipping the polarity on the main line.

Although it's not always thought of as a power district, in effect an auto-reverser controlled region is just that.  It's isolated, and the auto-reverse circuit is a short-circuit detector which first tries to "resolve" the short by flipping polarity.  When you wire an auto-reverser, you do it the same as you would a circuit breaker, with its power input directly from the primary power bus and the output to the isolated track section.  You wouldn't put a breaker between the primary bus and the auto-reverse circuit.

It takes an iron man to play with a toy iron horse. 

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Posted by mlehman on Thursday, December 10, 2015 11:04 AM

Stevert
They can be, but they don't have to. What you'd need to do is determine if they should be separate power districts if they were NOT reversing sections, and proceed accordingly. Alternately, it may be easier to handle them as separate districts even if they don't need to be. In the end it boils down to your overall power and wiring philosophy...

Good way of thinking about it.

I did notice recently that at least one mfg is making an autoreverser combined with a circuit breaker. Heck, maybe they have been along and I just noticed that? In any case, that might be more cost effective than doing both on separate boards.

Mike Lehman

Urbana, IL

  • Member since
    December 2001
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Posted by Stevert on Thursday, December 10, 2015 9:43 AM

Arto

 

 
MisterBeasley

I've got my layout divided into 6 power districts.  4 of these are simple breakers, and two others are auto-reverse sections which are actually power districts with polarity-flip capabilities. 

 

 

 

You've brought up another interesting issue for me. On the inside mainline track I've decided to use to open space in the middle of the layout for two reversing sections. This is a future project but the turnouts to do this were already installed as part of the layout rehab/expansion.

Should these reversing sections (blocks) be on a separate power district?

 

They can be, but they don't have to. 

What you'd need to do is determine if they should be separate power districts if they were NOT reversing sections, and proceed accordingly.

Alternately, it may be easier to handle them as separate districts even if they don't need to be.

In the end it boils down to your overall power and wiring philosophy... 

  • Member since
    January 2014
  • From: Chicago area
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Posted by Arto on Thursday, December 10, 2015 9:29 AM

MisterBeasley

I've got my layout divided into 6 power districts.  4 of these are simple breakers, and two others are auto-reverse sections which are actually power districts with polarity-flip capabilities. 

 

You've brought up another interesting issue for me. On the inside mainline track I've decided to use to open space in the middle of the layout for two reversing sections. This is a future project but the turnouts to do this were already installed as part of the layout rehab/expansion.

Should these reversing sections (blocks) be on a separate power district?

  • Member since
    December 2004
  • From: Bedford, MA, USA
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Posted by MisterBeasley on Thursday, December 10, 2015 9:11 AM

It will be about the same.  Sound engines take more power than non-sound engines.  They also use power when they're idling, because they are making noises.  Compared to old engines, though, even sound engines will draw less than some of the ancient blue-box Athearns I used to run.  (FYI, I gutted a few of those "old friends" and they now run as dummy "honorary" engines or as "sound dummies" with sound-only decoders in consists.)

I have a decent-sized layout that runs around 3 walls of a 24x24 foot room above my 2-car garage.  Most of my engines have sound.  I run the whole thing with a single 5-amp supply driving my Lenz DCC system.

By rewiring the way you already have, you've made the best possible improvements you could for power distribution.  If you've already got your tracks "block-wired" for DC, you've done most of the work needed to add a few circuit breakers to divide the layout into power districts.  I like the solid-state products from DCC Specialties, but there are other good breakers on the market as well.

I've got my layout divided into 6 power districts.  4 of these are simple breakers, and two others are auto-reverse sections which are actually power districts with polarity-flip capabilities. 

It takes an iron man to play with a toy iron horse. 

  • Member since
    September 2003
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Posted by mlehman on Thursday, December 10, 2015 9:05 AM

If the amps drawn stay roughly the same, i.e. same locos, lighting, etc, then you're only adding whatever gets wasted as heat from the decoders you install. That will be very little and not enough to make any effective difference to rate needing further improvement.

With DC block wiring, you send the power from the supply to the block the locos run in. When they aren't running, the amp draw is virtually nil.

With DCC, you have a "base load" that's on all the time, but so long as everything is standing still it's very light. As you increase power to get things moving, then the amps drawn increases.

That's in very simple terms, of course. How it acts is somewhat tied to how your circuits are arranged, so hard to be more specific other than to say if it is working well for DC now, it should be adequate for DCC.

Mike Lehman

Urbana, IL

  • Member since
    January 2014
  • From: Chicago area
  • 335 posts
Ampere Requirements for DCC vs DC
Posted by Arto on Thursday, December 10, 2015 8:38 AM
Background:
 
When I originally built my layout 30+ years ago I hastily wired it up with whatever I had laying around. In retrospect this turned out Not to be a good idea since the wire I used for both bus and feeders was 28 gauge. Some of the bus runs were 20 to 40 feet long. I was getting significant voltage drop in blocks with the longest bus wire. To make matters worse, the terminal blocks at the control panel used even thinner un-insulated wire to bridge the common across the terminal blocks. Needless to say, I had a lot of current draw using the older Athearn, Model Power, etc locomotives, three to six units per train (two 100’ mainlines, so sometimes 3 trains).
 
This led me to believe I needed more “power” in the form higher amperage power supply. What I had done was basically created something close to a very large toaster.
 
After rebuilding the layout and re-wiring in preparation for DCC (10 gauge throughput throughout) I noticed the amperage draw fell dramatically, and I no longer had any voltage drops at the far end of the layout.
 
I’m still using DC. Lately I’ve been running newer DCC locos with sound (Athearn Genesis & Broadway Limited).
 
I’m wondering what the net result is when I install DCC in the next month or so. With the higher constant voltage going through the rails will my DCC amperage requirements for locos/car lights be reduced further or will it remain about the same as running them on DC?

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