Power feeds in a circular arrangement

[cromptonnut]

Hi all

 

Wanted to pick your brains as to whether one answer is better than another here   It happens to be DCC (yes I read the forum title) but in this case I don't believe it makes a difference. as it's just a power supply.

 

I have 8 boards arranged in a circular fashion.  Each board has a pair of banana sockets for power feed to that individual board.

 

I have one power feed that will go to all boards which will be connected via banana plugs.

 

I believe I have two options:

1. 8 pairs of banana plugs with cables going to one place (chock blocks, tag strips or whatever) and one pair of wires to the power source
2. Daisy chain the wires in a circular fashion with two pairs of wires going to each pair of banana plugs making a complete loop with another pair of wires from one position going to the power source.

I'm still using the same number of banana plugs and sockets regardless of which method I use.  I just didn't know whether there was a "preferred" way of doing this or both are equally suitable?

 

Or is there an option C (or D, or ...) that I haven't thought about?

 

Many thanks

 

'Nut

[peter220950]

Option C is to feed from one end, but not complete the loop, as I seem to recall that with DCC this is not encouraged, I think there are issues with interference and attracting alien spaceships.

 

On a larger scale I put two feeds on our club roundy round  (16ft x 40ft ) that feed from each end but don't connect in the middle (option D)

 

It's certainly easier to roll up a pair of wires with plugs in it than a spiders web that radiates out, and also it can be hung from the layout boards. I would loop wires in and out of the plugs without cutting the wires as well, to reduce the number of mechanical joins/connections.

 

EDIT

 

Found what I was searching for

 

http://www.brian-lambert.co.uk/DCC.html

[cromptonnut]

In the absence of any real strong opinions either way I went for the simple option of (2) and have a complete circle for testing - if it seems that being a circle creates problems I can easily cut it.

[SHMD]

Hi cromptonnut,

 

Option 1 would be a "Star" configuration and the 2nd option is a "daisy chain" which returns and creates a loop. (As you know.)

 

For the size of this Network, for that us what it is, is not really relevant. Even the returns - forming a loop - are not really a problem. (Just unplug 2 leads to see if any problems are related to the "return loop".

 

What's the maximum current you envisage through the Bus?

The disadvantage of "daisy chaining" is the accumulation of series connections. Each connection has a resistance - say 0.1 ohms. This doesn'tsound much but they DO add up. The more current then the higher the voltage drop. 5 modules at 1 amp = 0.5volts dropped. 12 modules at 1.5 amps = 1.8volts. But that's with good wiring and quality parts.

 

Having said that, "daisy chaining" is a good choice here.

 

 

Kev.

[cromptonnut]

Hi SHMD, thanks for the technical interpretation of my attempt to explain something   Yep its a daisy chain.

 

The circle itself is a single track (there's a double to two single track junctions on boards outside of this circle, so trains come from a double track and can go either left or right to single track "branches"  which are of course the loop, so I am guessing that the current will only ever be one or two locos, plus potentially a rake of lit coaches.  An O gauge MPD it is not

 

Within the plugs I have twisted the two wires together and soldered all connections to help reduce resistance.  Each of the 8 boards has its own power supply - from the daisy chain - so I would expect there to be minimal loss to the point of not being relevant. 

[Izzy]

In the absence of any real strong opinions either way I went for the simple option of (2) and have a complete circle for testing - if it seems that being a circle creates problems I can easily cut it.

The circle will be completed every time a Loco crosses the joint.

 

Izzy

[cromptonnut]

After the pointwork, there are insulating fishplates on both rails on both sides, and all of that track is fed through a reverse loop module, and as the track between those points is about 18ft long I would be incredibly surprised if we ever have a train covering both ends and trying to trigger both sides of the reverse loop at the same time.

 

I did think that far ahead

[Andy Reichert]

I have DCC wired around an  oval of about 70 ft circumference, with no intentional (known) rail breaks and no problems seen..

 

There is however at least one practical issue to consider.  And one theoretical one too far fetched to worry about.

 

1. If there is one rail connection overlooked or bad rail joint you won't know until you get a second one on the same rail. Only than can you find where both are .

2. In theory, if the DCC data frequency was a lot faster, or the loop far, far  longer, then you could lose signal reception when a loco is close to the power feed location. The data signal travels at around  the speed of light or approx 2 NS per ft. So the pulses going around the long way can arrive later than those coming the short way. And the resultant not quite overlapped pulse distortion can become unreadable.  But while this can and does upset some computer LAN's, it's not going to happen on normal layouts.

 

Andy