# Multiple DCC Booster question



## DonR (Oct 18, 2012)

I get emails of posts to Wiring for DCC forum.

There was a thread there that discussed problems with more
than one booster powering a large layout.

One poster responded that it is necessary to keep the boosters
IN PHASE. 

I understand phase but how does one do that in DCC? Is that similar
to matching the a/c polarity of the Booster output, or must the AC 
input also be in phase?

I don't have any boosters, but am aware that many members do. I
wonder if anyone on the Forum has experience with multiboster
operations.

There have been a couple of our Forum members who had problems with
boosters of different makes. I wonder if this 'phase' sync may have
been the culprit.

Don


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## RT_Coker (Dec 6, 2012)

Don,
The Bachmann 5 Amp booster goes into “short” mode when it is out of DCC +- phase with the Dynamis (when a locomotive “shorts” the track gaps between the two districts). Defiantly not the best way to find the phase match; but probable the simplest in this case. I have a meter that measures the DCC voltage across the track, but doesn’t seem to be able to directly detect an out of phase condition for this power combination. I image that one could put a couple of resistors (~1 Kilo-ohm) across the gaps, measurethe DCC voltage across one of the resistors (in effect a current measurement under a slight load), and then select the +- polarity with the lowest voltage (current) as the correct +- phase match. 
Bob


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## DonR (Oct 18, 2012)

Bob

What is confusing about this is that there is no obvious +/- markings
on wires from the Bachmann controller, or reverse loop controller that I have. 
Thus I have to assume that on the Bachmann booster that you mention, 
there is the same red 2 conductor wire to the track. If you use the Bachmann
system complete with their plugs and jacks all would be well. But I, and
I would guess a lot of others, whack those plugs off and connect to
a buss. 

What polarity guards are there on Boosters and controllers of other makes?

How do we find the polarity of the DCC- AC for the purpose of avoiding the phase short when going from one district to another?

Again I don't have a booster...Yet. But this problem has been the subject of
at least 2 threads in the last several weeks. So I wanted to explore it for
the benefit of the others who may encounter the problem in the future.

Don


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## JerryH (Nov 18, 2012)

Measure the ac voltage across the gap on the same rail. If it is in phase, you won't get much reading. If it is out of phase, you will get the same voltage as between the A and B rails.


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## RT_Coker (Dec 6, 2012)

DonR said:


> Bob
> What is confusing about this is that there is no obvious +/- markings
> on wires from the Bachmann controller, or reverse loop controller that I have.
> Don


Don,
Yes, my controller’s (and manuals) do not identify the phase +- of their track/booster outputs. I can only assume that making it look “easy” was more important to somebody than following the NMRA recommendations. Based on my experience, I would not assume that their controllers/booster/reverser are going to work with each other, unless it is a combination specifically shown in one of their manuals. 
To my knowledge, the phase on a “reverse loop controller” is not important. It is supposed to flip the phase of its output to avoid the phase mismatch.

Bob


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## DonR (Oct 18, 2012)

THANK YOU JerryH.

That is so simple and so important. You get voltage reading if out of
phase...and little if any if in phase...

That should solve many problems in the future.

Bob

After I wrote that it dawned on me how stooped it was...of course,
that's what a Reverse controller is supposed to do...match phase. 

Don


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## Brakeman Jake (Mar 8, 2009)

I can't discuss how all DCC manufacturers deal with this issue.However,I strongly believe that Digitrax designers have thought of this.When you install more than one Digitrax components (of any type),they require that they are linked with the Loconet cable (six leads) AND their common GROUND terminals for reference.

Although there aren't definite + or - polarities in DCC,tracks still have to be identified through the layout (A & B or North & South or whatever) so that no short situation is created within the trackage itself.Then its only a matter of connecting these identified leads to the same booster track ports (either right or left) to have polarities taken care of without the use of any polarity reversing device.I haven't installed a booster yet,but it only would make sense to me if the components were engineered this way.It's my theory though,standing to be corrected...

Easier still,Digitrax Power Stations and Boosters can be set as reversing units if desired when used as auxiliary boosters so no additional polarity reversing device is needed to go from a district to another.They are needed only when you need reversed polarity within a district,like a return loop in most cases.


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## DonR (Oct 18, 2012)

Jake

What happens when you have a large layout with several booster districts and
you run a Buss. An HO club here in N Florida has a modular layout
that is about a block long and half that wide.
Digitrax doesn't expect you to use their cable for that do
they? I have only experirence with Bachmann...they also have only the
ports and a single pair cable with plugs at either end. 
Bachmann does not show any polarity. You just have
to cut off their plug and connect to their cable with color coded wire to
maintain polarity throughout the layout.

Bachmann does use a special cable to connect to walkaround controllers that
comes as a spring coil...I didn't like that and found that Home Depot sells
made up cables of various lengths for computer/TV connections with identical
plugs to Bachmann. 

Don


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## Brakeman Jake (Mar 8, 2009)

Boosters don't need to be physically installed within each districts.They can all be installed near the command station and all have their specific buss wires going to the target districts they power.With sufficiently big buss wires like 14 ga.,there shouldn't be any problem.

Then,boosters can be installed in a string,with Loconet cables from one to the next and so on.

The other way is to make your own loconet cables of proper lengths and bring them all to the command station but...command stations have only two Loconet ports...


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## DonR (Oct 18, 2012)

Coincidentally...a guy just posted a question on the Forum Wiring
for DCC that is similar to my original post..
How do you know when one district is out of phase to the next...
Those guys should visit this thread and get the simple method.

Don


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## RT_Coker (Dec 6, 2012)

Checking DCC +- phase between HO track districts for the correct phase match: [The following assumes you have a multi-meter that can read the DCC voltage and give a reasonable reading.] [Also the track districts should first be able to correctly run a locomotive in the individual districts without crossing the gap between the districts.

For both rails gapped (no Common Rail and no Power Station Common): Measure DCC voltage across the one rail gap while the other rail gap is shorted out.

For only one rail gapped (Common Rail): Measure DCC voltage across the one rail gap. 

For Power Station Common: ??? 

Voltage should be less than 4 volts. [If DCC phase is mismatch, the voltage should be around 24 volts or more.]

Bob


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## fcwilt (Sep 27, 2013)

I made a little device with a red LED, green LED, a couple of resistors and a couple of insulated alligator clips. 

I soldered one lead of one resistor to the anode of one LED.

I soldered one lead of the other resistor to the cathode of the other LED.

I soldered the remaining leads of the resistors together with a piece of flexible wire which connected to one of the clips. 

I soldered the remaining LED leads together with a piece of flexible wire which connected to the other clip. 

I used heat shrink tubing as needed to prevent shorts and enclose the finished device, arranging the parts with the LEDs sticking out one end and the two wires sticking out the other.

Attach one clip to each rail on DC and you will get either RED or GREEN depending on polarity (assuming enough voltage is present to light the LEDs).

Attach one clip to each rail on DCC and you will get both RED and GREEN (assuming enough voltage is present to light the LEDs).

Attach one clip to each rail on a DCC system across a rail gap between blocks/power districts will show both RED and GREEN if out of phase, nothing if in phase.

There is a type of two color (red/green) LED you can get which is connected internally such that you could use it in such a device, in which case you would get sort of a YELLOW color when both the RED and GREEN LEDs were on. I didn't have one so I just used what I had on hand.


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## RT_Coker (Dec 6, 2012)

fcwilt said:


> Attach one clip to each rail on a DCC system across a rail gap between blocks/power districts will show both RED and GREEN if out of phase, nothing if in phase.


Fcwilt,
That is a neat test circuit!

However, I believe it is possible to get a “nothing” indication between out-of-phase power districts, if the power side of the boosters are independent (floating or otherwise not connected). In other words the test circuit is not completed without a “Common Rail”, “Power Station Common”, or the second district gap shorted.
Bob


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## fcwilt (Sep 27, 2013)

RT_Coker said:


> Fcwilt,
> That is a neat test circuit!
> 
> However, I believe it is possible to get a “nothing” indication between out-of-phase power districts, if the power side of the boosters are independent (floating or otherwise not connected). In other words the test circuit is not completed without a “Common Rail”, “Power Station Common”, or the second district gap shorted.
> Bob


Yes that would be true but if memory serves me (and it may not) aren't all command stations/boosters supposed to be wired to a common ground? Are there brands that don't recommend this? 

Seems to be I remember reading about possible decoder destruction when a loco crossed from one power district to another IF there was NOT a common ground.


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## RT_Coker (Dec 6, 2012)

fcwilt said:


> Yes that would be true but if memory serves me (and it may not) aren't all command stations/boosters supposed to be wired to a common ground? Are there brands that don't recommend this?
> 
> Seems to be I remember reading about possible decoder destruction when a loco crossed from one power district to another IF there was NOT a common ground.


Fcwilt,
I have a self contain 2.3 amp system that “can be used with” the manufacturer’s 5 amp booster. This apparently is construed by the manufacturer to mean that you can have one 5 amp district. I found this unacceptable, so I have a configuration (2.3 amp district & 5 amp district) that is not supported by the manufacture. The 2.3 amp system does not have an identifiable “Power Station Common”, so my setup does not have a “Power Station Common”. I don’t recommend my setup, but it works well for me and does not destroy decoders. There may be others out there that have made compromises like this. I would hate for them to destroy something.
Bob


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