Re: Large Gauge Ground Wire in Parallel with Loconet Gound Wires == Groundloop?

Mark Gurries
 

A true ground loop requires the following.

1) Two parallel current paths.

2) The mixing of two independent currents that should not be mixed together.

Eliminate one or the other eliminates the problem.

The current we do not want to be shared on the Loconet ground is the locomotive current. Fortunately we know that the undesirable locomotive currents originate and end only at the booster locations.

So the solution is to find a way for the locomotive current to flow down the booster ground wire and not the loconet ground.

Additional interesting facts are

1) Booster do not use the Loconet signals. They only monitor the RailSync signals on the Loconet cable during normal operation.

2) Railsync is a lot less sensitive to the problems related to ground current

We can use these two pieces of information to help identify the solution.

To eliminate the "ground loop" would require Splitting the loconet cable right at the command station location into two separate Loconet busses.

a) A Loconet bus for all devices other than the boosters. Call this Throttle Loconet.
b) A Loconet bus for just the boosters. Call this Booster Loconet

With the Throttle Loconet bus and the Booster Loconet bus only tied to each other at a SINGLE point where the command station is located, the two Loconet bus grounds are connected but they will not have the same paths and therefor will not have the same currents on their respective ground wires.

With the Throttle Loconet, we know we only have Railsync signal current and Loconet signal current on the ground.
With the Booster Loconet, we know we only have Railsync signal current and Locomotive current on the ground.

Now you run the Booster Loconet ONLY between Boosters. Do not connect it to any other type of Loconet Device. It only connect to the Command Station at the command station location with a RJ splitter. Now there is no reason for locomotive current to flow down the Throttle Loconet Bus because there is no booster connected to it. It is an Open Circuit as far a Locomotive current goes.

Just doing that one step alone breaks the locomotive current off the Throttle Loconet bus for all the devices that need the reliable loconet signal communication. Technically we now no longer have a ground loop since we are not mixing independent currents much anymore. The only remaining problem is the fact that on the Booster Loconet we can still have momentarily high DC current flowing down the small gauge wires. We solve that by running our large wire gauge wire between the booster grounds. Yes the wires are in parallel, but they are NOW carrying the same current at the same time between the exact same locations. There is no ground loop.

One could cut the ground wires out of the Booster Loconet cable to force 100% of the locomotive ground current to run on the large wire but with reasons to do so are greatly diminished. The locomotive current will naturally choose the large gauge wire since it the path of least resistance.




On Dec 24, 2017, at 9:50 AM, nwsteamer modelrr@... [WiringForDCC] <WiringForDCC@...> wrote:

Mark,

The way I read this statement the large gauge wire in parallel to the
Loconet 'ground' wires does constitute a 'loop' and could cause a
reliability problem.

Thus, the recommendation in Allan Gartner's website to cut the Loconet
'grounds' at the boosters is valid. Do you agree?


On 12/24/2017 05:03 AM, Mark Gurries gurriesm@... [WiringForDCC]
wrote:
Adding the large gauge parallel ground wire permitting a ground loop
to be establish is the LESSER of the two evils.


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Posted by: nwsteamer <modelrr@...>
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Best Regards,

Mark Gurries
Electrical Engineer
DCC Website & NMRA DCC Clinics: www.markgurries.com

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