Common Ground

[Anonymous]

I have 2 4x8ft leftover homasote modules with a lot of yard and spur trackage on them from my old HO layout. The track is wired for standard DC operation, 8 separate blocks with a common ground (one track completely without any insulated rail joiners). I plan to introduce DCC to isolated parts of the layout, starting with the main line and adding spurs and yards as I get decoders installed in more of my locos. Now for my question:

Since AC power is being applied to the DCC-enabled track, do I have to separate both sides of the track on the areas that I want to keep as standard DC? Or can I continue with separted rail sections on only 1 side?

Thanx in advance....

[Jetrock]

Why are you applying AC power to the track??

[Anonymous]

QUOTE: Originally posted by Jetrock

Why are you applying AC power to the track??

OK, maybe it's NOT AC? It's whatever is going from the command station to the track (I thought that was AC). I haven't actually tried to wire the layout yet (I last experimented with a programmimg track about a year ago), I'll cross that bridge [and follow the diagrams of course] when I get there. My main worry right now is that I don't want to have to split apart all of my existing common-rail connections.

But if what's coming out of the DCC power supply isn't AC, then it shouldn't be a problem....right?

[Jetrock]

What is coming out of the DCC generator is a modulated DCC signal, which is technically DC but not the same as the analog DC that comes from a DC powerpack. You DON'T want it common-railed with a DC power supply.

[Fergmiester]

Hi Ken

If I read you correctly. If you keep your sections isolated from each other then you won't have any problems running DCC on one section and DC on another. But you will have to keep your sections seperate (Cut both rails).

Hopefully this answers your question.

Fergie

[cacole]

One clinker in your question is the statement that your layouts are wired for common ground -- DCC doesn't like common ground wiring and you're going to have trouble isolating one section from another with that type of wiring. If you had two separate wires going to all of the existing blocks, using DCC would be a simple matter of connecting the DCC booster to whatever tracks you wanted to run under DCC, and you could leave the others connected to straight DC and run both at the same time provided they were properly insulated from each other. The common ground wire makes this isolation impossible.
.

[rrinker]

ABSOLUTELY do not mix DC and DCC with a common ground. Not EVER. Go here: http://www.wiringfordcc.com and read up on the subject.

IF and only IF you have ONE booster only, and never add another, you can get away with common ground. Add a second booster - and you're back to potential trouble. Therefore the simple answer is to simply NOT use common ground under any circumstances.
There are ways around it, but they are generally for large layouts being converted where it is wholly impractical to rewire everything. On a small home layout - just wire it up the right way and never have to worry about it again. The loco you save might be your own. The hair you'll otherwise pull out, as well.

--Randy

[ericsp]

I think that calling traditional method to deliver power to the track "DC" confuses people into thinking DCC is AC. It would be better to call it analog instead of DC, since the difference is analog and digital, not AC and DC.

[Anonymous]

Guys,

Ken is right, It is AC on the rails, not DC.

Read up at Allan's site for specifics. From Allan's site, "Another complication is that the DCC voltage on the rails is AC rather than DC. However, this is not quite the same as the smooth cycle constant low frequency 50/60 Hz AC available at the local utility wall outlet"

[ericsp]

QUOTE: Originally posted by Trainnut1250

Guys,

Ken is right, It is AC on the rails, not DC.

Read up at Allan's site for specifics. From Allan's site, "Another complication is that the DCC voltage on the rails is AC rather than DC. However, this is not quite the same as the smooth cycle constant low frequency 50/60 Hz AC available at the local utility wall outlet"

I am not an electrical engineer, however, I am pretty sure one cannot run a DC motor on AC power.
The NMRA says this about DCC, "The DCC signal is an alternating DC waveform, which contains the digital information. . ." (http://www.nmra.org/beginner/dccbasic.html).

[Anonymous]

Eric,

I believe that the decoder has a rectifier or diode bridge to provide the motor with DC current. The answer is in your quote" alternating DC waveform" the keyword there is alternating......

[Anonymous]

QUOTE: ericsp stated:
I am not an electrical engineer, however, I am pretty sure one cannot run a DC motor on AC power.

This is true since the AC source cannot generate the polarized field necessary to power the motor, unless, of course a rectifier is used. Like Eric, I am not an electrical engineer, but have worked in that industry for nearly twenty years, and I understand the following to be true: Since our locomotive motors are DC motors, they need a DC supply to run. The decoders we install are basically small motor controllers that convert a DCC (whether it be considered AC or modulated DC) supply to variable voltage DC to power the motor. This is really the same concept as using a motor control circuit to take 480V AC from the source and supplying variable DC voltage for use in a variable speed drive mechanism, which is not uncommon in industry today.

[ericsp]

QUOTE: Originally posted by Trainnut1250

Eric,

I believe that the decoder has a rectifier or diode bridge to provide the motor with DC current. The answer is in your quote" alternating DC waveform" the keyword there is alternating......

If the decoder has a rectifier then the rail can have AC power. However, the author could not have been refering to AC. AC and DC are mutually exclusive. To describe AC as "alternating DC" would be ridiculous.

[Anonymous]

Thank you guys,

My question is answered - except not the answer i'd been hoping to hear[sigh]! Appears that now I'll have to rip out a lot of track that has been encrusted in solidified ballast to insert those insulated rail joiners on the other side.

[Jacktal]

I don't think you have to rip out any track if they are solidly held to their roadbed.Simply cut gaps with a fine metal saw blade or a Dremel cutting wheel where necessary.The only purpose of the insulated joiners is to ensure non-conductivity and proper alignment of the rails.If your tracks are firmly held,alignment will be retained.

Depending on where your gaps will be needed,you may have to add a few feeders but it's not too hard to do without damaging your scenery.

[Anonymous]

QUOTE: Originally posted by Jacktal
I don't think you have to rip out any track if they are solidly held to their roadbed.Simply cut gaps with a fine metal saw blade or a Dremel cutting wheel where necessary....If your tracks are firmly held,alignment will be retained.

That's hopeful news! The 'new' feeder wires are, in many cases, already there - I installed them to eliminate dependence on the rail joiners for reliable electrical contact, so maybe only a few new ones will have to be added.

The main challenge will be to make sure that I have good, SOLID alignment on each side of wherever I need to cut.

[Fergmiester]

QUOTE: Originally posted by KenLarsen

QUOTE: Originally posted by Jacktal
I don't think you have to rip out any track if they are solidly held to their roadbed.Simply cut gaps with a fine metal saw blade or a Dremel cutting wheel where necessary....If your tracks are firmly held,alignment will be retained.

That's hopeful news! The 'new' feeder wires are, in many cases, already there - I installed them to eliminate dependence on the rail joiners for reliable electrical contact, so maybe only a few new ones will have to be added.

The main challenge will be to make sure that I have good, SOLID alignment on each side of wherever I need to cut.

If the place where you are going to cut is on straight and level ground you will have no problems what so ever. However if your on a curve or grade transition then it could get vey tricky. And at best will have to use rail nails.

Fergie

[retsignalmtr]

you can put an insulated joint anywhere you want to without ripping up the track and ballast. cut a slot with a snapsaw or cutoff wheel in a dremel tool. then put a piece of styrene into the slot and then put a drop of acc on it to bond it to the rail. after the acc sets up trim the styrene to the profile of the rail. i have just installed digitrax dcc on my layout last week. the manual recommends feeders on both rails but also says that if you are going to use common rail wiring you have to special order a booster that is set up for it. the double rail wiring is better for troubleshooting and for adding reversing sections. if you are going to install dcc you won't need insulated joints except if you are going to use a programing track and as a place to store you loco's that do not have dcc installed.