LCS Power Limitations Through PDI ?

From MartyE's Legacy User Group meeting summary:

PDI network “coupler”. This small passive device will allow 2 PDI cables to be joined without needing an LCS device. This will come in handy to extend a PDI cable or when a LCS device is removed the cable can be joined up. This is available through Lionel parts. The PN is 691JOINA00.

I recall a a more recent thread (that I can't find) that shows a newer version with provisions to inject 12v DC power.  You have to call Lionel Service to order these.

Barry, I have done a number of posts on this subject in the past. For convenience here are two pictures. One is the single line diagram of my LCS system showing all the devices and cable lengths. The rose colored dots are the amplifier locations. In this system 5 were needed for flawless system operation. Also included is a picture of the amplifier, Lionel calls it a bus joiner. These are only available by calling Lionel.

As Tracker John states a regulated 12VDC power supply is required for the joiners to work as an amplifier. That is provided by the barrel jack connector that plugs in at the top.

The Lionel Parts website shows the current model:

691JOINB00

PCB / PDI BUS JOINER WITH POWER JACK (NO DISCOUNT)

$16.00

Must contact Lionel to order.

AmFlyer, are you using a single 12V regulated supply with sufficient amps or multiple supplies?

That is the version in the picture above. With these bus joiners there is no reason to change the Lionel provided system power supply. At least in my LCS setup the issues were voltage drop in the DB-9 cables, not a power supply current limitation.

I have a 12VDC accessory bus that runs around the layout. As shown in this picture on the left there is an adjustable regulator that connects to that bus and powers the Joiner. There is a regulator for each of the joiner/amplifiers.

Ignore the Joiner in this picture, it is an old handmade prototype Lionel R&D sent us 4 years ago. Works the same but looks different.

Barry, since you may not be able to order the joiner until we all get back to work, you can cut a PDI cable in half and build your own breakout box to inject power.  Pinouts are:

PDI Cable
1. Serial common      (Black)
2. Power ground       (Brown)
3.  PDI TxData           (Orange)
4.  PDI RxData           (Red)
5. +v power               (Yellow)

You will note the wire gauge is not appropriate to maintain voltage over long runs per AmFlyer's comment.

Here is a better picture with the LCS powered on.

The gauge wire used in the Lionel DB-9 cables was only intended for very short runs. 

Good thread!  

@Tracker John posted:

Barry, since you may not be able to order the joiner until we all get back to work, you can cut a PDI cable in half and build your own breakout box to inject power.  Pinouts are:

PDI Cable
1. Serial common      (Black)
2. Power ground       (Brown)
3.  PDI TxData           (Orange)
4.  PDI RxData           (Red)
5. +v power               (Yellow)

You will note the wire gauge is not appropriate to maintain voltage over long runs per AmFlyer's comment.

Tracker John et al:

First, thanks for the replies/advice.  This is my first post to the Forum and I certainly appreciate the sage advice.

My LCS modules are mounted on a pullout panel in three columns with five or six modules each plus the SER2 and WiFI mounted separately on the same mounting panel. Each module is basically connected to the next with a 12" PDI cable.  The longest cable is the 10 ft. cable from the power supply to the WiFi module, then 12" cable to the SER2, then a 3ft. cable to the first ASC2.  where it becomes 12" cables to the top of the column and then a 12" cable to the top of the next column then 12 " cable down the column, etc. See attached photo.

In other words, voltage drop due to PDI cable length is mitigated by the short runs of PDI interconnecting the modules.

While the breakbox approach would certainly help if it were inserted between say between the 8th and 9th module, I'm still wondering why not simply replace the 1A power source with a 2A power source and be done with it?  I understand that small gauge wire  can cause a voltage drop, but given the relatively short overall total PDI length (e.g. no more than 26 ft. total including the initial 10 ft from the Legacy Base) is there a concern that the last module would not receive sufficient current even if the input current source was doubled?  Given that I had no problems prior to adding the WiFi and SER2 modules, the question is whether adding those two modules (totaling 450 ma of additional power consumption) and three feet of additional PDI cable would mean having to use a breakout box rather than simply increasing the total available current. 

Consequently, is there any thought about the number of interconnections between modules as being a voltage drop concern as well as the overall footage of PDI cable that should drive the decision as to whether use a breakout box versus simply using a larger power supply?

Thanks,

Barry

Given the compact arrangement of your LCS modules, I think a 2A power supply may be the solution given your calculations show your total current draw exceeds 1A.  My LCS use has been on modular layouts where the cable snakes around the perimeter - a lot of 20ft cables in use.  Voltage drop is an issue.

If the 2A power supply doesn't solve the problem, inject power at the tail end of the chain.

Tracker John:

Given your comment to inject power at the tail end of the chain, that would be an easy thing to do using your prior post about cutting a PDI cable to gain access to the two power leads (Yellow power plus/Brown power ground) and simply connecting them to the 2A power supply I have that has the traditional red/black binding posts.  Thus, I would not touch the original 1A supply and add the second 2A supply at the tail.  I would expect that the amount of actual current provided by the 2A supply to be the amount needed to compensate for whatever additional current is needed.

Unless you see an issue with this arrangement, I'll work on this in the morning. I have a 3 ft. PDI cable that would be a perfect 'victim' for this application and would avoid having to take what is already installed apart.

Thanks!

Barry 

i would not inject power into the head and tail ends of the lcs chain. i believe the bus joiner interrupts the power supply at that point in the chain. just try the   higher capacity supply by itself.

rudy

also this video:

https://youtu.be/St8FkSYb7nw

Rudy, power ground (brown), +12v (yellow), and serial common (black) are electrically contiguous on the modules (ASC2 and SER2) I tested.   Power injected into either end should propagate through all modules in the chain.  According to Jon Z, the serial i/o in each module re-transmits packets to the next leg - point-to-point comms.  (the original ASC & other modules used multi-drop serial comms).  This diagram was drawn before I learned which pins were Tx and Tx comms.

OK if Jon Z said it is good, it is good!

(editing this) In re-reading your note, it's not clear to me what exactly Jon Z said regarding an additional power supply. In an abundance of caution, I would recommend using two power supplies only in conjunction with the Lionel bus-joiner PCB, or use a single higher-current supply at one end of the chain.

Barry, that is top end work, your LCS setup looks great. A couple of thoughts on solving your issues. First I have had two ASC2's fail. One would loose its programming when the power was turned off and one just stopped working. So one of the LCS components could be bad. I now have some spares of each type just in case. Four years ago Lionel R&D gave us a copy of their development software so they could see why my system was not working correctly. At the time there were 38 LCS devices and all would work but not reliably. The system behavior leads me to believe the stated ma current requirement for the devices is not continuous, just when the device is performing a function. As I recall, the voltage at the end of the line was a bit over 3V. Adding 3 joiner/amps solved it. Last year I added 6 more BPC2's plus interconnecting cable to the system so two more joiner/amps were added. At $19 these are a cheap, proven and tested fix by Lionel.

I agree with Rudy.  If you use two (or more) supplies with out breaking the power buss then I feel you leave yourselves open for a ground loop situation which could inject noise and spurious signals into the communications.  At the price of the joiners as AmFlyer points out this is the way to go in my opinion.  I have found this thread very informative because I too have a large network (16 devices) and a 40' run.  I had to disconnect my serial connection because it was loading down the network and now thanks to you all I am going to go back and take another stab at it.

dick