Stay Alives for Decoders.


Note: When using Keep/Stay Alives, make sure you disable DC operation in CV 29.


I have found with DC enabled (I always disable DC), the operation of the loco with no power (under Stay Alive), is very much reduced and the loco movement is jerky, using Soundtraxx Tsunami TSU-750/1000 & Econami steam decoders with Soundtraxx Current Keepers or TCS KA2s.



Stay Alives Modules are available from TCS, NCE & Soundtraxx provide power to the decoder & motor during power interruptions caused by dirty track, dead sections around Turnouts (Frogs) etc, making stalls/hesitations, a thing of the past. The amount of time the loco can “run” will depend on the amount of current the Motor, Lights & sound draw and the amount of capacitance of the Stay Alive. Shown below are the approximate “relative” sizes of the TCS, NCE and Soundtraxx units for comparison.


TCS Keep Alives: KA1 Size L26.7 x W16.4 x H7.5 mm KA2 Size L33.0 x W11.6 x H8.8 mm









NCE: Small No Halt Size: 1.25" x .64" x .29" (32 x 16 x 7.5 mm) Medium No Halt Size 2.14" x 0.640” x 0.400" (54 x 16 x 10 mm)










Soundtraxx Current Keeper - 40mm x 6mm x 11mm.








All versions of the above Stay Alives connect to the decoder with 2 wires, where:


1.  The BLUE wire is connected to the Function Common - DC Positive (Blue wire). 


2.  The BLACK wire is connected to the DC Negative of the decoder.


Many decoders do not provide a “DC Negative” connection. The DC Negative is easily found at the at the Anode ends of the two Input Diodes (Bridge Rectifier), that have their Cathodes (Band) Ends, connected to the Track Input. More details below.


I have fitted TCS KA2s to HO locos equipped with Soundtraxx Tsunami (TSU-1000, TSU-750 & AT-1000), Soundtraxx DSD100-LC etc, Loksound, TCS, NCE and other decoders (shown below), that provides between 5 and 60 seconds of stay alive, depending on Motor current draw etc.


The TCS documentation says when connecting these units to TCS decoders, program the TCS decoder’s CV 182 to a value of 2. When fitting the KA1/2s to other brands like Soundtraxx, there is no need to program CV 182.


Everybody's experience with power interruptions varies, thus the size of the necessary Stay Alives also varies. Some will be happy using the KA1 but on my layout with 40 – 50 mm “Dead Frog” at the Turnouts, I need the KA2s with their greater capacitance. The KA1 is wider but shorter than the KA2. The available space in a loco may determine which one to use. See below for how I cut a KA2 in “two”.


See Bruce Patrarca aka Mr DCC, demonstrating the benefits of these Stay Alives on his Club layout.


For more technical details on Stay/Keep Alive, see Mark Gurries page.



Connecting the Stay Alives.


Note: For any decoder not mentioned below, use the method explained at the bottom of this page to find the DC NEGATIVE connection.


The following photos and details of how to connect Stay Alives were done using TCS’s KA2 Keep Alive. As the TCS, NCE & Soundtraxx all use two wires to connect to the decoder and is identical. The Lenz and ESU Stay Alives use 3 wires and if installing either of these, leave the “Control” wire disconnected.


Soundtraxx Tsunami Decoders.


1. Do NOT connect the BLUE wire to the RED Capacitor wire. If you do, the Stay Alive will only provide power for the sound but NO Motor Stay Alive. The loco will stall/stop, immediately the loco experiences a power interruption (dirty track).


2. I have found that if you remove the supplied 220 uF Capacitor altogether, I could not read CVs of the Tsunamis on the Program Track. Replacing the 220 uF with a smaller 100 uF 16 Volt Electrolytic Capacitor, I was able to read CVs.


3. If you are having problems finding space for the 200 uF Capacitor in your particular loco installation, replace the it with a 100 uF 16 Volt Capacitor soldered directly to the two + & - pads of the AT-1000 Tsunami.


4. I have found that programming a Tsunami fitted with a TCS KA2 on the Program Track using a Soundtraxx PTB100 Booster with my NCE Power Pro unit, there are instances when reading CVs, returns a value of 255 for the CV. See below for more details.


Connecting the Stay Alives.


Econami 100.


        1. The Blue wire to the decoder’s Blue Function Common wire.

        2. The Black/White wire to the decoder’s Green/Yellow wire.


Tsunami TSU-1000


1.  The Blue wire to the Blue Function Common wire.

2.  The Black wire to the Black wire connecting the 220 uF Capacitor (not the Black “Pick Up” wire).


Tsunami TSU-750


        1. The Blue wire to the Blue Function Common wire and

2. The Black/White trace wire to the Green/Yellow wire.


Tsunami AT-1000 shown below.


        1. The Blue wire to the Blue Function Common Pad (Pads 2 or 9).

2. The Black wire to the Black wire connected to the 220 uF Capacitor (not the Black Pick Up wire).


    To the Anodes of either of the 2 Diodes with the Cathodes (bands) ends connected to the Track Pick Up wires.





Tsunami GN-1000


The GN-1000 is different than other Tsunamis in that they have:


1. On Board 1.5 Volt Regulator for 1.5 Incandescent lamps. Do NOT connect to Tabs 2 and 11 like that on the AT-1000.

2. The “+14 Volt” Pad near the Input Diodes is isolated from the Motor. If you use this connection there will be NO stay alive for the Motor.


Connect the Stay Alive’s wires:


        Blue: to the Cathode (Band) end of the Track Input Diode adjacent to Tab 11 as shown below.


Black: to the Anode (NOT the band/stripe) end of the Track Input Diode adjacent to Tab 12 as shown below.














Schematic is courtesy of Ulrich Models.




Soundtraxx in Bachmann, Intermountain & Proto. 


Stay Alive connections for a Soundtraxx equipped Bachmann RS-3 with the TSU-WW56 Circuit Board courtesy Glen Duke. Marty C suggested that Intermountain and Proto locos have this same TSU-WW56 Circuit Board.




QSI Revolution A. 


NOTE: The Revolution A has a 5.0 Volt regulator and 220 Ohm resistors included on the Board for LEDs or 1.5 Volt Incandescent Lamps. You CANNOT connect the Stay/Keep Alive’s BLUE wire to this 5.0 Volt Tab. Connect the Stay/Keep Alive as shown below:


1. The Blue wire to the Cathode (Stripe) end of the Diode with the Anode connected to either Track Pick Up.

2. The Black wire to the Anode end of the Diode with the Cathode (Stripe) end, connected to either Track Pick Up.



QSI Revolution U 


1. Connect the BLUE wire to the BLUE decoder wire.

2. Connect the BLACK wire to the Capacitor’s BLACK wire.


Loksound V3.5 


See Bryann at SBS4DCC Streamlined Backshop Notes at:


Loksound V4.0


See Bryann at SBS4DCC Streamlined Backshop’s Notes at:



Soundtraxx DSD100-LC


        1. Remove the heat shrink from the decoder by slicing down one edge with a Razor Blade etc.

        2. Connect the BLUE wire to the BLUE decoder wire.

        3. Connect the BLACK/White trace wire to the Anode as shown with the yellow wire.

        4. Re-install Heat Shrink.







1. Connect the BLUE wire to the Function Common Tab or to the positive connection as shown

2. Connect the BLACK/White trace wire to Anode as shown below.







1. Connect the BLUE wire to the Function Common - Pin 7 or to the positive connection as shown

2. Connect the BLACK/White trace wire to Negative connection at the Anode as shown below.






1. Connect the BLUE wire to the Function Common (Pin 7) or to the positive connection as shown

2. Connect the BLACK/White trace wire to Anode of the Diode as shown below.






1.  Peel back the shrink wrap from the 9 Pin Socket end, as shown.

2.  Connect the Blue wire to the decoder Function Common BLUE wire.

3.  Connect the Black wire to the Diode (Anode end), as shown below.






NON Sound Decoders. 



Soundtraxx MC2


Stay Alive connections for the MC2 thanks to Detlef Kurpanek







1. Connect the BLUE wire to the Function Common Blue wire

2. Connect the BLACK/White trace wire to the Negative connection of the decoder’s Bridge Rectifier shown with the Green wire.







1. Connect the BLUE wire to the Function Common Blue wire

2. Connect the BLACK/White trace wire to Diode/Capacitor junction as shown with the Green wire.




NCE D408SR Decoder.


Connect the Stay/Keep Alive leads to the on board large Electrolytic capacitor as shown in the below photo. Details thanks to Mark Gurries and Pete Mulvany.





To find the DC Negative of ANY decoder not shown above:


1.  On the decoder, locate the 4 Diodes (Black rectangular blocks) used to rectify the DCC from the track, generally on one end of the decoder where the wires from the track pick-ups are secured/soldered to the decoder.


2.  The ANODE ends of the two Diodes that have their Cathodes (Band) Ends connected to the Track Input, form the DC NEGATIVE.


3.  The TCS T1 has a Bridge Rectifier. Connect the Black wire to the Negative Pad of this Bridge Rectifier.


4.  Smaller N/Z Scale decoders like the TCS M1, have really small Diodes or with decoders that you cannot identify the Input Diodes, to locate the DC Negative:

a.  With the decoder powered

b.  Connect your Multimeter’s RED Lead to the decoder’s Function COMMON.

c.   With the Multimeter’s BLACK Lead “Probe around” the large (well compared to the rest of the components), Orange or Brown “block” a Capacitor.

d.  One end should be the DC Negative, like what is shown on the NCE D14SR decoder above.  

5.  Hopefully you’ll find the DC Negative.


Perceived issues when using Keep Alives.


If there is communication with a Stay/Keep Alive (e.g. KA2) equipped loco, it WILL stop when commanded to. The loco will stop at the station, stop when switching loads, not end up in the Turntable Pit etc.




Locos will keep running when an un-powered block is encountered like when using signals etc. You have to take this into consideration if you are using a Keep Alive.


Using Service mode of programming may be difficult, see next.


Programming on the Program Track with KA1/2s.


I have found that programming a decoder (Tsunami) with a KA2 installed, on the Program Track using a Soundtraxx PTB100 Booster with my NCE Power Pro unit, there are instances when reading CVs, returns a value of 255 for the CV.


The theory to read CVs, is that the Command Station instructs the decoder to pulse the Motor according to the stored CV value. From these pulses of current from the Command Station, the value is displayed. The only problem is a charged up KA2 or the Command Station may supply the pulses of current. If it is the KA2 supplying the power and not the Command Station, then there will be no pulses of current from the Command Station pulses to interpret to display the CV value, hence the 255 display.


When using the Program Track, if you get a 255 when you read a CV (programming), then try again with a discharged KA2. A good practice if using the Program Track, disconnect the Stay Alive. This could be very inconvenient so a “link or switch may be installed.


Except for the initial read of a decoder after installation or troubleshooting why a decoder does not work, I use “On the Main – POM” mode of programming using Decoder Pro, where there is no issue.


More details of the Stay/Keep Alives.


I have been using SIMPLE Stay Alive on some of my problematic running locos, for years, comprising of the largest value capacitor I could fit into a HO loco, namely a 4,700 microfarad 16 Volt Electrolytic capacitor, a 100 Ohm resistor to limit the charging Inrush Current and a 1.0 Amp Diode to bypass the resistor, when the Capacitor discharges (supplying Stay Alive).


Components have become smaller and cheaper. The size of a 1.0 Farad 2.7 Volt Super Capacitors is 10 mm x 6.3 mm, making it possible to have large reservoirs of power (capacitance) like how TCS, NCE and Soundtraxx have provided.


To use the 2.7 Volt 1.0 Farad super capacitor in our 12.0 volt models:


Connect 5 or 6 Capacitors in SERIES as to what TCS have done OR


Electronics are used to convert this low voltage energy into what the model needs, as Lenz has done with the USP, see below.


The TCS KA1 uses 6 x 220,000 uF 2.5 Volt Capacitors connected in series and the KA2 uses 5 X 1.0 Farad 2.7 Volt Capacitors in series. Connecting Capacitors in SERIES, using similar value Capacitors the effective capacitance Ct = C/n and the operating voltage of the package, resulting in:


        KA1: 36,667 uF (microfarads) at 15.0 Volts.


        KA2: 200,000 uF (microfarads) at 13.5 Volts making the KA2 5.5 times larger than the KA1.


The charging current when using the above KA1 and KA2, due to their high value of capacitance, has to be reduced otherwise the Booster may sense that there is a short circuit, more so when there are a few KA1/2, when the power is first applied or when a Circuit Breakers is trying to reset. A 100 to 200 Ohm resistor is used to keep this changing current at manageable levels and a Diode is connected in parallel to this resistor to short out the resistor when the Capacitors are being discharged to provide power for the loco during the power loss.

But the best thing yet, the KA1 and KA2 can be used with ANY decoder.


Lenz Power 1 Module (USP) can ONLY be used on decoders that support USP, like the Lenz Gold and the QSI Titan. The energy stored at 2.7 Volts on the 1.0 Farad Capacitor has to made into a voltage that is suitable for a 12 Volt Motor, by some electronics comprising of what I can see, a small Coil, 2 x 6 Pin ICs, an 8 Pin IC, a Diode a Transistor/FET and numerous other components, provide the stay alive power. The high impedance input of the Gold decoder allows packet information, changes in direction, speed etc to get through to the decoder while running on stay alive (dead track) as evidenced on the Gold/USP YouTube video.


Some years ago a modeller friend asked me to install Lenz decoders into his Bemo HOn3 fleet of locos. One unit a 4 wheel Tractor/Shunter was a real problematic runner continually stalling/stopping in the Yard on his Exhibition layout. I installed a Lenz Gold/USB combination, resulting in smooth running through the Yard. He was ecstatic. This installation was a real challenge, fitting in the Gold plus USP into the small Cab but was worth it. I have since installed USPs into a few of his problem runners with similar great results.


Why do we need Stay/Keep Alive.


Dirt has been the enemy of model railroaders since we used electricity to operate locos. We have been able to put up with it, what has changed.


The introduction of SOUND locos.


Many modellers are building their dream layout in un-sealed environments where the air quality is not as clean as we would like it to be.


When a NON Sound loco experiences a power interruption from dirty track, gaps at turnout frogs etc, there would be a slight hesitation that in many cases would go un-noticed but with SOUND locos, you hear this hesitation with the sound disappearing then coming back on as the processor in the decoder stopped and started up again. This becomes quite annoying. Track cleaning isn’t the model railroader’s favourite chore, so I would persevere until it became unbearable. Applying CRC 2-26 sparingly to my track has reduced these sound reset interruptions.


Locos without flywheels and that is more than half of my steam locos, would most probably stop at these power interruptions, making this inconvenience a real hassle now.


On top of dirty track/wheels there are plenty of other things that contribute to a loss (interruptions), like:


Track geometry/alignment.

Gaps/Insulation at Points/Turnouts Crossings etc. Many chose Peco Electrofrogs or similar to reduce the unpowered area around the Frog.

Locos with small numbers of wheels and pick-ups, no Tender Pick-ups etc.

Brass, Brass/White Metal DJH Kits etc where one side Drivers/One Bogie picked up positive and Tender/ other Bogie picked up the negative.

Poor contact at Drawbar and the Bogie Bolster.

The material wheels are made from can have an effect on pick up. Some materials are better than others and I am not into replacing them.

While the weight of a loco may be enough, due to where it is located, the loco may be un-balanced effecting traction and pick up, especially when over Points/Turnouts etc.

Tender Pick-ups seem to be unreliable (example C32 and C35).


Rectifying some of these issues is possible but some are way out of league of many modellers and fitting a Keep Alive will hide these issues and result is better running.


Fitting Keep Alives does not mean you can eliminate track/rolling stock maintenance.


Regularly clean your track.


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