TIU Active vs Passive Mode DCS Signal Voltage

WOW, good to know.  I'll lay in a stock of chokes!

If those are the 10 amp variety, could you post a link to the ones you use? I will add it to the list of PTCs and TVSs that no one ever looks at. Actually I will look at it and have the choke part for reference too. 

I will put this TIU Active vs Passive Mode DCS Signal Voltage information in my college text book.  I kept this book around just for days like this or for when “HeathKit” has a big comeback.

Thanks: Gary

rtr12 posted:

If those are the 10 amp variety, could you post a link to the ones you use? I will add it to the list of PTCs and TVSs that no one ever looks at. Actually I will look at it and have the choke part for reference too. 

Digikey used to have some thru-hole ones that I've used, but they're no longer stocked.  Here's a suitable replacement, you just have to solder to the mounting pads.

Bourns Inc. SRP1770TA-220M

Okay, how this this revelation on voltage impact affect my power setup?  I'm running passive mode on my two mainlines to get more than 10 amps to the track.  I use a 34A 22uH choke.  Here is my setup:

The PSX-AC is set at 15.8 amps because that is all I need for the passenger train I plan to run (about 11-12 amps).  

I did a less technical test of this setup on the affect on the DCS signal only.  Without either the PSX or choke, the signal strength was 8.  With the PSX but without the choke the signal strength dropped to 5.  Adding in the choke with the PSX the signal strength increased to 9.  Used two different engines.

So, the way I read Dr. Tang's scope readouts adding the choke does two things for me: 1) increases voltage to the track, and 2) increases DCS signal.  Is that correct?

NOTE: John and the rest of you anti-more than 10 amps folks, I have no plans to go to power districts

CAPPilot posted:

Okay, how this this revelation on voltage impact affect my power setup?  I'm running passive mode on my two mainlines to get more than 10 amps to the track.  I use a 34A 22uH choke.  Here is my setup:

The PSX-AC is set at 15.8 amps because that is all I need for the passenger train I plan to run (about 11-12 amps).  

I did a less technical test of this setup on the affect on the DCS signal only.  Without either the PSX or choke, the signal strength was 8.  With the PSX but without the choke the signal strength dropped to 5.  Adding in the choke with the PSX the signal strength increased to 9.  Used two different engines.

So, the way I read Dr. Tang's scope readouts adding the choke does two things for me: 1) increases voltage to the track, and 2) increases DCS signal.  Is that correct?

NOTE: John and the rest of you anti-more than 10 amps folks, I have no plans to go to power districts

Hi there,

You're right the DCS signal should increase with the choke becasue it the PSX won't load the output of the TIU. 

The choke works by frequency selectively providing an impedance to to the TIU output port that allows AC 60 Hz to pass but not the DCS signal.

A 22 uH choke is going to provide an impedance of Zchk=j X (freq) X 2pi X L

L = 22e-6        Freq = 60    pi   = 3.14159...

At 60 Hz power this is about 0.5 ohms. Which means the power signal can go right through it without much issue as it's basically a short.

The DCS signal is at about 3.7 MHz

the impedance is Zchk=j X (freq) X 2pi X L

L = 22e-6        Freq = 3.7e6    pi   = 3.14159...

At 3.7 MHz the impedance is 30.6K...basically like an open circuit.. so it won't affect the DCS at all.

Since the 60Hz behavior is basically a short, its unlikely the choke can increase the track voltage... only the DCS signal. Also I don't know how we all arrived at 22uH... any high value.. like 10-500uH will work as long as it can handle the current. Don't go too high though or the series resistance will become a problem...

Like you say, the higher the impedance of the choke, the more resistance typically you have to deal with. 

Thanks GRJ, list has been updated in the Electrical Forum > Electrical Reference Materials & Manuals 'sticky' thread.

What problem(s) is this resolving? My head is thick this morning ...

Weaker DCS signal strength on the track in passive mode as opposed to active mode.

Can these be soldered in without a SM board?

Sure, just solder a wire to the contacts.

On this issue of Active voltage • Passive voltage. As an end user I am more interested in track voltage.  The MTH Premium APP shows track voltage.  What should be the high's and low's of track voltage?

This is a screenshot from my iPhone, with one engines on this line, with eight lighted passenger cars.

Thanks: Gary

trainroomgary posted:

On this issue of Active voltage • Passive voltage. As an end user I am more interested in track voltage.  The MTH Premium APP shows track voltage.  What should be the high's and low's of track voltage?

Track voltage has nothing to do with the strength of the DCS signal, which is what we've been discussing.  Track voltage is a product of the transformer voltage, how good your power wiring is, and how clean the track and your wheels and pickups are.

gunrunnerjohn posted:

trainroomgary posted:

On this issue of Active voltage • Passive voltage. As an end user I am more interested in track voltage.  The MTH Premium APP shows track voltage.  What should be the high's and low's of track voltage?

Track voltage has nothing to do with the strength of the DCS signal, which is what we've been discussing.  Track voltage is a product of the transformer voltage, how good your power wiring is, and how clean the track and your wheels and pickups are.

Thanks John: Got it......

but can you help me to understand what is a safe range for track voltage?

Gary

There really isn't a truly "unsafe" voltage.  Generally, I like to keep the track voltage somewhere close to 18 volts as I run Legacy/TMCC and DCS.  However, DCS runs pretty good down to 12-13 volts on the track as long as there's sufficient current available.  The other constraint is TMCC/Legacy doesn't want to see more than 19 volts on the track, DCS around 22 volts.

Hi John: Thanks for the information.

I have 4 main lines with one Lionel Brick for each main lines.  Just checked the Lionel Track & Power Catalog. They say it puts out 10 AMPS / 180 Watts. but does not give the high end for the voltage.

Do you know what is the starting point on these Lionel Bricks are for the voltage?

Thanks: Gary

My two PH-180s put out around 18.3 - 18.4 volts with no load on them.