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KA/Stay-Alive Devices

The process of keeping a decoder running on power after power has been known as a Stay Alive that used the very old Aluminum Capacitor technology to store energy. Technology has advanced and a new type of capacitor called a Super Capacitor capable of both huge energy storage and do so while supporting high charge and discharge current rating suitable to power a DC motor.  The term KA/Stay-Alive will refer to the SuperCapacitor version of the Stay-Alive.

The first Super Capacitor KA/Stay-Alive product was introduced by Lenz but was only compatible with Lenz decoders and other DCC manufactures that signed up with Lenz (QSI is one).  It has remained a mostly European solution and is expensive.  The first Lenz decoders that supported it were NOT sound decoders.

Latter generic KA/Stay-Alive products were introduced by TCS as a direct response to solving power problems with sound decoders.  The two wire, small, non decode specific, low cost product that was in stock at time of introduction made it a instant hit that all of the other DCC manufactures quickly copied in one form or another.   Most of these KA/Stay-Alive devices are sold as an "Add On" devices you purchase and install yourself for any decoder you want.  This is the reason behind this web page existence.

The technology behind KA/Stay-Alive devices are what are called "Super Capacitors" by electronic industry marketing terms.  These capacitors can have up to 1000x or more capacitance inside the same space as compared to a traditional large value capacitor (Aluminum or AL Type).   The specific subtype of super capacitors used in KA  have a very low internal resistance so they can directly power a motor successfully.

Before the TCS Super Capacitor version Stay-Alive came along, the term "Stay Alive" was used.   The name "Stay Alive" referred to an equivalent "home built" circuit that used standard and old (AL or Aluminum) capacitor technology.   The Stay Alive circuit was popularized by Marcus Ammann on his website.  If you had room in your locomotive for the large capacitor, it could help.  But space limitation really limited the Stay Alive solutions success.  I use the term "Stay Alive" for the old capacitor technology.

With KA's, we can use smaller capacitors allowing it to fit more locomotives while storing more energy than a Stay Alive device can do.

1) SUPER CAPACITOR KA/STAY-ALIVE PRODUCT LIST
2) WHAT ARE THE BENEFITS OF USING A KA/STAY-ALIVE?
3) WHAT IS A SUPER CAPACITOR?
4) WHAT IS THE DIFFERENCE BETWEEN A REGULATED AND UNREGULATED KA/STAY-ALIVE DESIGN.
5) WHY DOES USING A BEMF DECODER MAKE A DIFFERENCE WITH KA/STAY-ALIVE?
6) ARE THERE ANY COMPATIBILITY ISSUES USING KA/STAY-ALIVE's?
7) HOW CAN I TELL IF A DECODER WAS DESIGNED BEFORE KA/STAY-ALIVE's WERE INTRODUCED?
8) WHAT PRE-KA DECODERS WORK WELL WITH KA/STAY-ALIVE's
9) WHAT ABOUT THE CAPACITOR THAT COMES WITH MY SOUND DECODER?
10) WHERE CAN I FIND DETAILS ON HOW TO INSTALL A KA/STAY-ALIVE ON MY PRE-KA/STAY-ALIVE DECODER?
11) HOW LONG DOES IT TAKE TO CHARGE A KA/STAY-ALIVE?
12) WHY IS THERE A DIFFERENCE IN KA/STAY-ALIVE RUN TIME PERFORMANCE WHEN THE SAME KA/STAY-ALIVE IS USED ON DIFFERENT ENGINES AND DECODERS
13) COMPARING KA/STAY-ALIVE VIDEOS.



1) SUPER CAPACITOR KA/STAY-ALIVE PRODUCT LIST (7/17/16)
Here is the complete list KA products offered by the above date from various DCC manufactures.  Not in any specific order.  (Note numbers)


Manufacture
Name
 Model
Name
Model
Number
and/or
Part
Number
Visible
Number
of Super Capacitors
Effective
Total
Capacitance
in uF
(1)
Estimated
Energy
Capacity
in Joules
(2)
Available
Voltage &
Reg vs
Unreg
(3)
Track
Voltage
Range
(4)
HO scale
Run
(5)
Wire
Count
(6)
Wire
Color
Code
(7)
Charge
Method
(8)
Advertised
Decoder
Compatibility
Size
L x W x H
in mm
(Rounded)
Space
Volume
mm^3
Product Notes
TCS
Keep
Alive
KA1
KA1-C

1454
1455
6
36,700
[0.22F x 6s]
@2.5V/Cap
4.13
15V
Unreg
12-16V2-5
Sec
 2+ Blue
- Blk/Wht
Resistor
150 Ohms
TCS Keep Alive Ready &
most non TCS decoders
27 x 17 x 8
3672TCS Decoders need to have CV182 set to a value of 2.  TCS decoders built after 2/2012 are keep alive compatible.  C=2 pin connector included.
TCS
Keep
Alive
KA2
KA2-C

1456
1457
5
200,000
[1F x 5s]
@2.7V/Cap
18.23
13.5V
Unreg
12-16V6-15
Sec
2
+ Blue
- Blk/Wht
Resistor
150 Ohms
TCS Keep Alive Ready &
most non TCS decoders
33 x 12 x 9
3564TCS Decoders need to have CV182 set to a value of 2.  TCS decoders built after 2/2012 are keep alive compatible.  C=2 pin connector included.
TCSKeep 
Alive
KA3
KA3-C

2000
2001
4160,000
[0.64F x 4s]
@2.7V/Cap*
9.33*??
Reg*
12-16V6-20
Sec
2+ Blue
- Blk/Wht
?TCS Keep Alive Ready &
most non TCS decoders
26 x 11 x 92574TCS Decoders need to have CV182 set to a value of 2.  TCS decoders built after 2/2012 are keep alive compatible.  C=2 pin connector included.
TCSKeep 
Alive
KA4
KA4-C

1668
1667
4160,000
[0.64F x 4s]
@2.7V/Cap*
9.33*??
Reg*
12-16V6-20 Sec2+ Blue
- Blk/Wht
?TCS Keep Alive Ready &
most non TCS decoders
13 x 13 x 122028TCS Decoders need to have CV182 set to a value of 2.  TCS decoders built after 2/2012 are keep alive compatible.  C=2 pin connector included.
Lenz
Power
Power 1
1
1,000,000*
@2.7V/Cap
3.65
Regulated
(boost Converter)

1 sec
@
250mA
3
+ Blue
- Brn

Pink
?
Lenz Gold
QSI
22 x 13 x 10
2860Power 3 has been discontinued. Must set CV112 to run duration.
Digitrax
Power
Xtender
PX112-xx
See note
4160,000
[0.64F x 4s]
@2.7V/Cap
9.33
??
Reg*
12 - 15V
??
2
Plug Only
+ Red
- BLk
?
Digitrax 6 Series
1Amp
N and HO
26 x 16 x 9
3744XX = number of wires in digitrax "plug and play" harness.
-2 = 2 wires
-6 = 6 wires
-10 = 10 wires
NCE
No Halt Insurance
Small
524148
6
36,700*
[0.22F x 6s]
@2.5V/Cap
4.13
15V
Unreg
up to 15V
4 Feet
or
2-6 Sec
2
+ Blue
- Blk/Wht
CC
Manual shows how to install it on NCE decoders
32 x 16 x 8
4096You can order a D13 series decoder with a factory installed No Halt.
NCENo Halt Insurance
Medium
524149
2
1,500,000
[3F x 2s]
@2.7V/Cap 
5.4715V
Reg*

12 Feet
2
+ Blue
- Blk/Wht
CC
No manual published.16 x 32 x 168192There are two versions of this product.  Decoder like PCB board design.  Product Not Released on NCE website.  Some dealers stock it but is is NOT listed for sale on NCE's store.
NCE
No Halt Insurance
Medium
524149
6
166,667*
[1F x 6s]
@2.7V/Cap
21.87
15V
Unreg
Up to 15V??
2
+ Blue
- Blk/Wht
CC
No manual published.54 x 16 x 108640There are two version of this product.  Long stick like design with blue shrink wrap. Product Not Released on NCE website.  Some dealers stock it and it is listed for sale on NCE's store.  Intended for larger locomotives.
Soundtraxx
Current
Keeper
810140
5
200,000
[1F x 5s]
@2.7V/Cap
18.2313.5V
Unreg
up to 22V
up to 10 Seconds
2
Plug Only
+ Blue

- Blk
CC*
Tsunami
40 x 11 x 6
2640It is believed to be electrically the same as a TCS KA2
ESU
Mini
Power
Pack
54670
1
1,000,000
[1F x 1s]
@2.7V/Cap 
3.65
??
Reg
 3
Sec
3
+ Red
- Blk
&
White
?
LokSound &
LokPilot
22 x 14 x 10
3080Believed to be same basic design as Lenz Power 1  Must Set CV113 to run duration.
DISCONTINUED
ESU
Mini
Power Pack5467111,000,000
[1F x 1s]
@2.7V/Cap
3.65??
Reg

3
Sec 
3+ Red
- Blk
&
White

LokSound & 
LokPilot
16 x 10 x 132080Smaller version of above discontinued version. 33% reduction in volume.
ESU
Maxi
Power Pack5467222,500,000
[5F x 2s]
@2.7V/Cap
36.54??
Reg


3+ Red
- Blk
&
White
?LokSound & 
LokPilot
28 x 16 x 135824Must Set CV113 to run duration.
* = Need more investigation to verify 100%.

Table Notes:

1) Effective Total Capacitance in uF:  Accounts for the application circuit (series/parallel) where more than one capacitor is involved. 
Individual capacitor capacitance values are so high, they are rated in units of Farads. 
1F (Farad) =1,000,000uF (micro Farads) hence a 0.1F = 100,000uF and 1000uF = 0.0001F

2) Estimated Energy Storage in J (Joules):  Result of calculation using equation E(J)= 1/2*C*V^2. 
C in Farads as defined by circuit (series or parallel).  V = Total voltage of the series capacitors. 
Super Caps with both 2.5V and 2.7V ratings are used in different KA/Stay-Alive designs. 
This energy storage calculation removes both the motor load variable and the KA/Stay-Alive design variables when comparing KA/Stay-Alive's.
This energy storage calculation assumes the capacitor(s) start fully charged and are then fully discharged down to 0V. 
In reality, the capacitors are never completely discharged to 0V because the KA/Stay-Alive circuit OR the decoders themselves quit running when the voltage drops down to low.
Another indication of how long the KA/Stay-Alive will last is found in the HO Scale Run category.

3) Available Voltage:  The max potential voltage available to run the decoder a the very start of discharge (Loss of track power). 
Unreg = Unregulated design is where the KA/Stay-Alive output voltage drops with discharge.   
Reg = Regulated design where the output voltage is maintained during KA/Stay-Alive discharge until capacitor is depleted.  Output voltage is independent of the track voltage.
See section 4 for more information.

4) Track Voltage Range:  The range of DCC track voltage the Super Capacitor KA/Stay-Alive can operate over.  KA/Stay-Alive's have very simple or limited over voltage protection.  Hence greatly exceeding the maximum track voltage can damage the KA/Stay-Alive.   Max voltage information is based on manufacturing data or by inspection of circuit design.  If no data given, assume typical HO scale track voltages are acceptable since that is the target marker for most of these KA/Stay-Alive devices..

5) HO Scale Run:  This is the published information about the potential run times or distance achieved by the KA/Stay-Alive.  However since there are no standards governing the load conditions in which the test is conducted, this information is not very useful.  Big motor or small?  Old Motor or New?  Most test typically involved a light HO engine move.  Another indication of the KA/Stay-Alive run time capability is the "Estimated Energy Capacity" category which removes the motor load as a variable. 

6) Wire Count:  This is the number of wires used by the KA/Stay-Alive all by itself.   The most basic KA/Stay-Alive connections are simple PLUS and MINUS DC connections which only takes 2 wires going to the decoder.  Some more advanced KA's have a 3rd wire which allows the decoder to control the KA/Stay-Alive in terms of turning it on or off.   Example: Lenz Power and ESU PowerPack KA/Stay-Alive is disabled during programming track operation so it does not cause a compatibility issues during reading CV values.   This requires the decoder becoming aware of the KA existence which typically involves setting a decoder CV value.

7) Wire Color Code:  All KA/Stay-Alive have at a minimum of two wire connection that carry both Positive and Negative power.  The wire colors used to represent the polarity of the power connection does not consistently follow the NMRA color code.   The best that can be said is any wire with Black (including striped black) or Brown are the negative terminal colors.   Blue and Red are the Positive terminal colors.  If the KA/Stay-Alive has a 3rd wire it is always the control wire and it any color other than used for polarity.   PLUGs are not standard.  In most cases, the plugs can only be used when BOTH the decoder and the KA/STAY-ALIVE brands are the same.  Otherwise you will have to cut off the plug on the KA/Stay-Alive and hardwire it to the decoder assuming you know what your doing.

8) Charge Method:  There are two ways to charge these large capacitors.   Resistor or "RES" and a Constant Current Source or "CC".   A resistor is a cheap passive current limiting method where as the Constant Current is a semiconductor active current limiting method.   When comparing the two methods with the same charge current, the Constant Current source is far faster than the resistor method but comes at a slightly higher cost.  Why?  While at the very start of a charge cycle with a fully discharged capacitor, the charge current is the same, but past that they become very different.

8a) The Resistor method mean the current that charges the capacitor is a function of the difference in voltage between the applied (track) voltage and the voltage on the capacitor.  As the capacitor is charging up, the voltage rises.  When it is fully charged, the capacitor voltage is the same as the applied voltage and the charge current is zero.  But given the voltage is rising as the capacitor is charged up, the amount of current going into the capacitor goes proportionally down.  It is like filling a glass of water at rate X but as the water rises in the glass, you reduce the rate the water filling the glass.  The rate of water filling the glass is reduced from heavy stream to a small stream to multiple large drops to just a few really small drops as you reach a full glass.  It is taking you longer and longer to fill the glass.  See section 11 below for more information on charge time.

8b) The Constant Current method means the current that is charging the capacitor is constant just as its name implies.  The current going into the capacitor is the same when the capacitor that is empty as it is when it reaches full.   When the capacitor gets full, yes the current goes to zero.  But the time it takes is a lot less.  Using the same glass analogy, you fill the glass at rate X but you never change the rate until the glass reaches full.  Your going as fast as possible all the way to full.  See section 11 below for more information on charge time.


2) WHAT ARE THE BENEFITS OF USING A KA/Stay-Alive?

For all decoders, sound or not, it offers improved smooth running especially on less than ideal track with less than ideal wheel pickup.  It cannot make up for a mechanically bad drive mechanism but it can make up for your typical electrical pickup problems.  The best way to think of a KA/Stay-Alive is as an electronic version of a mega flywheel WITH the extra benefits of powering more than just the motor.  It can also power all the lights and the sound system of a sound decoder.

For a sound decoder, it goes a long way to preventing sound dropouts and engine stalling.  Some sound decoders are designed such that when the loose enough power they shutdown and must go through a "engine restart" sequence before it can start moving again.  If this happens in the middle of a moving train, the engine will stop hard and drag the train to a stop or a slow speed with the worse being it will cause the train to derail.  Newer sound decoders are getting smarter in addressing this specific problem.  But if you got an old decoder and the existing wheel pickup is operating at the best it can do, then adding a KA is the best next step solution.


3) WHAT IS A SUPER CAPACITOR?

Super Capacitors have been around for a long time.   The common characteristic between both is the capacitance ratings are in F or Farads.   1F (Farad) =1,000,000uF (micro Farads).   Most common capacitors are rated in uF.  Non Super Capacitor KA/Stay-Alive use capacitors in multiples of 1000uF.  However a 1000uF capacitor is only 0.0001F.  In other words, Super Capacitors have about 10,000 times more capacitance than a standard capacitor.

What has recently happened is a new generation of Super Capacitors are now offered with high charge and discharge current formats suitable to power motors.   Hence the recent introduction of Super Capacitor KA/Stay-Alive to the hobby.   However even today it still "appears" to be available in limited quantities at this time since there have been shortages and out of stock issues with KA/Stay-Alives.  NCE has not even shipped their version to date and it been announce for over a year.   A common voltage characteristic of these new super capacitors is each capacitor is limited in voltage between 2.5V and 2.7V.  There are 5V version but they are simply two 2.5V capacitors wired in series and packaged together.   In other words, you cannot get a single 6.3V, 10V, 16V or 25V super cap.  (What makes these caps better than the orginal is the electrical parameter called ESR or Equivalent Series Resistance is very low.)

The original Super Capacitors are still around but have been and still are only suitable as a alternatives to battery backup on ultra low current consuming devices such as static memory and/or "Time and Date" keeping devices often found in old PC's.  You can get one and try it, but it will not work at all.  (ESR is way way to high.)


4) WHAT IS THE DIFFERENCE BETWEEN A REGULATED AND UNREGULATED KEEP ALIVE DESIGN.

UNREGULATED: A unregulated KA/Stay-Alive design typically involves the capacitors directly driving the decoder as a raw DC power source.   As the KA/Stay-Alive discharges, the voltage supplied to the decoder falls.  

What is the maximum KA/Stay-Alive output voltage at the start of discharge?

Simplistically a fully charged KA/Stay-Alive output voltage at the start of discharge will be the same as the DCC booster voltage powering the track it is sitting on provided the booster voltage itself does not exceed the maximum rated output voltage of the KA/Stay-Alive.   Furthermore, the output voltage can never be greater than the track voltage.

Unregulated Examples:  

a) 15V Output Rated KA/Stay-Alive.
IF the given KA has a maximum rated 15V output but is charge by a 12V booster driving the track, then actual start voltage from the KA will be 12V and not 15V.
IF the track voltage is 15V, then the actual KA output voltage will be 15V.

b) 13.5V Output Rated KA/Stay-Alive.
IF the given KA/Stay-Alive has a maximum rated 13.5V output but is charge by a 12V booster driving the track, then actual start voltage from the KA will be 12V and not 13.5V.
IF the track voltage is 13.5V, then the actual KA/Stay-Alive output voltage will be 13.5V.
IF the track voltage is 15V, then the actual KA/Stay-Alive output voltage will STILL BE 13.5V.  Why?  The voltage protection circuit has clamped the capacitor voltage.  The operational consequence of this situation is a non BEMF decoder will experience an instant drop in motor speed based on the difference between the track voltage and the KA voltage.  In this example, it will be a sudden 1.5V drop which can translate to an INSTANT 15% speed drop.  

Regardless of the actual available output voltage of the KA/Stay-Alive, the decoder will keep running on the KA/Stay-Alive until the decoder decides to quit.  Since decoders quit working any where between 5V and 7V, this leaves between 15% to 29% of the stored energy in a unregulated KA/Stay-Alive unused.  (Energy vs Voltage are not the same ratio.) 

REGULATED: A regulated KA/Stay-Alive design puts out a relatively constant voltage by using a "voltage boost converter" to step up the voltage from the capacitor level to a voltage that is suitable for the decoder.  The voltage remain constant until the boost converter fails because there is no longer enough voltage on the capacitor to allow the converter itself to remain running.  How much unused energy is left may be the same as the unregulated but the amount is NOT dependent on the decoder used but on the KA/Stay-Alive design.


5) WHY DOES USING A BEMF DECODER MAKE A DIFFERENCE WITH KA/STAY_ALIVE?

This only applies to UNREGULATED KA/Stay-Alive's.

Simplistically BEMF regulates mechanical motor speed by monitoring the motor speed electrically.  It can maintain a constant motor speed when that are changes in the load on the motor OR changes in the supply voltage feeding the motor.   Hence a given engine with a BEMF decoder can be running at a relatively slow speed and maintain that slow speed over long distance as the KA/Stay-Alive capacitors discharge.   However any incandescent based lights will dim over that same distance.  LEDs not so much.  Once the decoder sees the KA/Stay-Alive voltage drop below it's minimum operating voltage, the decoder will simply shutdown.

As a comparison, a non BEMF decoder engine cannot compensate the motor speed for the drop in voltage from an unregulated KA/Stay-Alive.  Instead the motor will start to slow down as soon as track power is lost and the speed will continue dropping.  It will behave a lot more like a GIANT flywheel.  Once the decoder sees a KA/Stay-Alive voltage that is below it's minimum operating voltage, the decoder will simply shutdown.

With a regulated KA/Stay-Alive, the existent of BEMF will not make any difference.  For the given motor load, the motor speed will be maintained until the KA/Stay-Alive itself quits.


6) ARE THERE ANY COMPATIBILITY ISSUES USING STAY-ALIVES OR KA/STAY_ALIVE's?

Yes in two key areas.

A) The response of the decoder when using a decoder that was designed BEFORE the existence of Stay-Alive or KA/Stay-Alive's.  

Why?  There is no DCC standard covering the response of a decoder in the presence of a KA/Stay-Alive.  It is an operating condition that was not accounted for because the DCC standard only worries about compatibility at the track level and not the decoder's detailed software and hardware design.  It represents an new operating state or condition that the decoder manufactures never had to work with before.  It may work perfectly by unrelated design choices or may not work well as you expect it to or may not work at all.  The point is you cannot complain about the results.  Your taking a chance.  

B) The Stay-Alive or KA/Stay-Alive can interfere with reading of CV's on the programming track.  

Why?   Decoders communicate with the command station by providing a pulse of load current on the programming track which is monitored by the command station.  (This is why a motor must be connect to the decoder to allowing reading CV's.)  The Programming Track is designed with the assumption that all power that is running the decoder is provided by the command station.  The presence of a KA/Stay-Alive during a pulse shift some current AWAY from command station and supplied by the KA/Stay-Alive itself.  If the current level of the pulse gets to low for the threshold of the command station, it will not be able to read the CV values even though the decoder is communicating correctly.  Another way the KA/Stay-Alive can interfere with the programming track is that when is power is first applied to the programming track, the KA/Stay-Alive will draw a low current (no standard for KA/Stay-Alive) from the programming track during charge.   It may confuse the programming station as a short or mask the response such that the decoder looks like it is acknowledging when it is not supposed to.  It all depends on the programming track circuit design which is vendor unique and the charge current chosen for the KA/Stay-Alive which is also vendor unique.

Of the two problems, in practice "B" is the most common problem.

It should be noted that some decoders that are designed to work with KA/Stay-Alive's may not work properly until you tell the decoder it has a KA/Stay-Alive connected.   It requires setting a CV value as documented in the decoder's manual or in the KA/Stay-Alive manual.  Most European Decoders manufactures and QSI have this option. 
 

7) HOW CAN I TELL IF A DECODER WAS DESIGNED BEFORE KA/STAY-ALIVE's WERE INTRODUCED?

European Decoders.  Any made before 2005.  Lenz Gold series decoders were the very first to support a motor KA/Stay-Alive.  Any brand of European decoder made before this date were not formally designed to support a KA/Stay-Alive.  Any Decoder made after this date were specifically design to support Lenz's version of a KA/Stay-Alive under a contract with Lenz.  If no Lenz KA/Stay-Alive connector was offered, then no formal support.  The "Lenz Power 1" KA/Stay-Alive were very expensive costing $50 each.  QSI was the only US decoder manufacture to support Lenz type.

US decoders: Any made before 2013.  TCS WOW series decoder were the very first US decoder manufacture to support it version of the KA/Stay-Alive called "Keep Alive".  "Keep Alive" is trademark of TCS.  Any brand of US decoder made before this date would have no formal support

"no formal support" simply mean the decoder was NEVER designed or specifically engineered to work with it.  Hence anything can happen when you add a KA/Stay-Alive.


8) WHAT PRE-KA SOUND DECODERS WORK WELL WITH KA/STAY-ALIVE's?

I have not heard of a Pre-Stay-Alive or KA/Stay-Alive sound decoder NOT working. Why?  Even though they were not designed to connect to a Large KA/Stay-Alive, their need for a small sound only Stay Alive capacitor forced the decoder designer to address the lack of power problem in some fashion.  In other words when properly connected, a KA/Stay-Alive device is to a sound decoder is just a very large version of small capacitor that also happens to provide power to the motor at the same time!

If it because the large KA/Stay-Alive capacitor devices provides power to the Motor that opens the door for unknown compatibility issue.  IF the decoder was not expecting power for the motor when running on the KA/Stay-Alive during a momentary power loss, it may stop driving the motor until true DCC power is restored.  Hence the KA/Stay-Alive may not extend the running of the locomotive but only keep the sound alive.  This is all vendor unique for it very detailed DCC decoder design dependent.  

For related information on this topic, see section 12.

We do not have access this this information which means trial and error is the only way to find out.  Fortunately nothing bad happens connecting a KA.   Fortunately again a lot of work has already been done in this area and information is available on the Web on how to do this.

For more information installing one, see section 10.


9) WHAT ABOUT THE CAPACITOR THAT COMES WITH MY SOUND DECODER?

Many, but not all, sound decoders come with a small external capacitor.   If it has an external capacitor the question becomes what type it is in terms of its function.  Not all capacitors are the same type.  Not all capacitors due exactly the same job too.  Fortunately unless you were a early adopter of 1st generation sound decoders, your small external capacitor is a Stay Alive class.

The first generation sound decoders were exclusively made by Soundtraxx.  The models lines were called the DSD, DSX and LC series all of which all had a small external capacitor EXCLUSIVELY for the speaker amplifier.  It used a special NP or Non Polarized capacitor.  The capacitor capacitance value was typically a low value of 33uF.  This is NOT Stay-Alive capacitor.   It is a DC blocking capacitor that does exactly what its name says it does.  It block the DC portion of the Amplifier power from reaching the Speaker.  Speaker only run on AC Audio power.  

With the introduction of the 2nd generation Tsunami Series of decoders, the need for a DC blocking capacitor disappeared when more modern and more powerful Audio Amplifiers became driven by advances in Cell Phone technology.  Now, the external capacitor became of Stay-Alive dedicated to the Sound System.  The sound decoders still depend on the locomotives Flywheels to keep the motor moving through the dirty track.

Flywheels where the first form of motor KA/Stay-Alive long before the electronic versions came along!   Flywheels stored rotational energy (angular momentum) that drives the motor shaft in parallel with the motor.  Flywheels + Stay-Alive will combine their energy together to make your engine run even longer long before KA/Stay-Alive's existed.


10) WHERE CAN I FIND DETAILS ON HOW TO INSTALL A KA/STAY-ALIVE ON MY PRE KA/STAY-ALIVE DECODER?

In concept, connecting a KA/Stay-Alive is very simple.  In practice it can be tricky depending on one electrical skills. 

Connecting a KA/Stay-Alive is the same for ALL decoders that are not designed to interface to a KA/Stay-Alive.  You need to find the raw DC power terminals of the decoder itself.  This is the same circuit point where the incoming DCC power is rectified to DC and splits up to feed the motor, the electronics and the function outputs.  At minimum there are only two connections:

PLUS:   Typically this is connecting the red KA/Stay-Alive wire (Blue for Soundtraxx) to the Blue Decoder wire.

MINUS:  This is the tricky part since all pre-KA/Stay-Alive standard decoders did not bring out a ground wire.  It is NOT the black wire.  Until 2003, there was no designated decoder wire color for decoder ground.  It is two color wire: Black with white stripe.  So if you do not have this color wire, you do not have this connection.  Therefore the ground connection must be found by circuit inspection by someone who knows what they are doing and involves soldering the black KA/Stay-Alive wire directly to one of the very small parts on the decoder.

It is simply impossible to document every combination of connecting a given KA/Stay-Alive to a given decoder.  As such there is no complete resource.  That said, one popular website page is dedicating itself to providing a lot of information on installing KA/Stay-Alives for various POPULAR pre-KA/Stay-Alive decoders with an emphasis on sound decoders.  It can be found here:

http://www.members.optusnet.com.au/mainnorth/alive.htm

Connecting a KA/Stay-Alive to the same wires used to connect the decoder supplied Sound only Stay Alive capacitor WILL NOT give you the extended motor running.  You can share negative wire, but you need to connect the positive lead of the KA/Stay-Alive to the decoder's "blue" decoder wire or it equivalent connection to power the motor.  Once you have connected the KA/Stay-Alive properly, you can choose to get rid of the Sound Only Stay Alive capacitor.  However if you do so, you must wait a few second for the KA/Stay-Alive to charge up.  Failure to wait can lead to starting out sound power failure problems since the KA/Stay-Alive has not charged up.  In practice it is not much of a problem since few people turn on DCC power and take off running a train instantly.


11) HOW LONG DOES IT TAKE TO CHARGE A KA/STAY ALIVE?

KA/Stay-Alive device manufacture do not publish any official information on this.  The rate is a direct function of the final total capacitance value of the capacitor array and the current level used to charge the capacitor array.  I say array because low voltage Super Capacitors are wired in a series circuit.  Why?  When low voltage KA/Stay-Alive capacitors are wired up in series, the maximum operating voltage of the KA/Stay-Alive goes up but the usable KA/Stay Alive capacitance value goes down at the same time.  See table in section 1 for the column showing "effective total capacitance" vs Capacitor value. 

For a given array of capacitors, there are two ways to charge them.

1) With a simple resistor.

2) Electronic Circuit the charges with a Constant Current

For equal comparison of the two methods, we must establish a common starting charge current.   When the capacitor array is empty (0% charged) the full voltage is presented.  With a 100 Ohm resistor and 13V track voltage, that works out to be 130mA (0.13Amps)

100 Ohm Charging Resistor charge times. 0.13A start current. 13V
Individual Capacitor Value
Number in Series
Effective Capacitance Value
Time 63% Full
Time 100% Full
0.22F
6
36,600uF
3.66 Seconds
18.3 Seconds
1F
5
200,000uF
20 Seconds
100 Seconds
0.64F
6
108,333uF
10.8 Seconds
54.2 Seconds

Comparing voltage points: It take about 5 times longer to reach 100% full compared to reaching 63% full.

Constant Current charge times.  0.13A constant current. 13V
Individual Capacitor Value
Number in Series
Effective Capacitance Value
Time 63%
Full
Time 100% Full
0.22F
6
36,600uF
2.31
Seconds
3.66
Seconds
1F
5
200,000uF
12.6
Seconds
20
Seconds
0.64F
6
108,333uF
6.83
Seconds
10.83
S
econds

Comparing voltage points:  Charge time is linear with % value of full voltage.  It takes 1/2 the time to reach 6.5V compered to time required to reach 13V.


Comparing the two:   A Constant Current charge method is about:

1) 6 times faster reaching 100% full charge

2) 1.6 times faster reaching 63% full charge

than the simple resistor charge method.



12) WHY IS THERE A DIFFERENCE IN KA/StAY-ALIVE RUN TIME PERFORMANCE WHEN THE SAME KA/STAY-ALIVE IS USED ON DIFFERENT ENGINES AND DECODERS?

There are three electrical reasons why.  Current consumption, KA/Stay-Alive internal losses and minimum operating voltage.  There are a lot of variables.  Simply put, you cannot really predict what you will get.

12A) MOTOR CURRENT  Does the motor used in the Engine make a difference?

YES.  Motors by far consume the most power and will effect the KA/Stay-Alive performance more than any other function.  Different motor have different operating efficiency for the same load.  In other words the design quality of the motor's will greatly vary the amount of current the motor needs to draw to pull a given load.   A simple mans guide is generally any motors that draw less stall current for the same torque output that the other motor is more efficient.  More efficient motor historically are more expensive to make and hence have a high cost which is why they were not found in toys.  The lower the cost, the cheaper the motor.  Today most motors used in modern product engines are pretty efficient compared to late 1980 and older engines.  So this may not be a big factor depending if the motor is a 1990's motor or newer.

12A) SOUND CURRENT  Doesn't the decoder sound system consume a lot of power? 

NO.   It is true that the sound system consume some additional current/power.  But the audio sound systems does NOT consume a lot of continuous high current.   Audio Sound has a high "peak power" level or "crest factor" that does not happen continuously.  Most of the audio amplifiers on the sound decoder put out about 1 Watt PEAK of power into a 8 Ohm (some decoders put out even less).  The average or continuous audio power AT FULL "STORE DEMO" VOLUME LEVELS is WORSE CASE 10dB lower or 1/10W.  1/10W = 0.11Amps (110mA) when blowing a horn and the engine sound is playing its loud "high power" operating level.  The amplifier may be clipping its peaks but not at a level you can hear.  Unclipped real audio typically has a 20dB crest factor which lowers the continuous power even more to  1/100W = 0.035Amps (35mA). 

Most people think "Of course Sound Decoders do not last as long because they consume a lot more current!"   It is only partially true.  Why?  The only time sound decoder consume a lot of current is on power up.  The small Stay-Alive capacitors that a sound decoder needs to have to work draw a very BRIEF but a very "high inrush" current which is a direct consequence of charging capacitors up rapidly.   Once the small Stay-Alive capacitor is charged up, the current to charge it goes to 0 amps.  This "high inrush" current problem is usually discussed in a "power management" context relating to booster current ratings, the use of DCC circuit breakers and multiple sound decoders with their built in Stay Alive capacitors.  High inrush current problems are not related to the large external KA/Stay-Alive devices charging up because they have a resistor to limit the current inrush to a very low current.

KEY POINT: Turning down the volume to more realistic usable levels reduces the power/current consumption even more.  The amount of power consumed by the audio amplifier is a lot less than you think.  This is why a small Stay Alive capacitor (220uF) is often used to address the most common track power pickup interruption problems successfully.

12B) KA/STAY-ALIVE PERFORMANCE   Does the Capacitor's ESR Value make a difference?

YES.   After the Motor, the next big variable is the super capacitor performance itself.  Different brands and models of Super Capacitors have different INTERNAL SERIES RESISTANCE values technically called ESR.   Equivalent Series Resistance.   The higher the ESR rating of the capacitor the worse it will perform for a given motor current.  So given two identical engine but have very different motors inside of them can have very different KA performance.

ESR represents an a INTERNAL VOLTAGE DROP term when high current is drawn from the capacitor(s).  Its Ohms law.  For a given motor current the following represent the voltage drop (loss) inside the capacitor for a given ESR of 6 super caps wired in series.

6 Series Super Cap: Internal Voltage Loss vs Motor Load Current. 
Ignores maximum capacitor voltage rating and discharge current capability of other support parts (discharge diode).
ESR/CAP10Ω


0.25Ω
TOTAL ESR
60 Ω
16Ω

1.5Ω
100mA Load
6.0V
1.6V
0.6V
0.15V
200mA Load
12V
3.2V
1.2V
0.30V
300mA Load
18V
4.8V
1.8V
0.45v
500mA Load
30V
8.0V
3.0V
0.75V
0.75A load
45V
12V
4.5V
1.13V
1A Load
60V16V6.0V1.50V
2A Load
120V
32V
12V
3.0V
3A Load
180V
48V
18V
4.5V
Any voltage in green means the capacitor can do something useful with a motor load.

So what does this mean in term of capacitor voltage available to run the motor?

6 Series Super Cap: Usable Capacitor Voltage vs Motor Load Current.  KA/Stay-Alive Capacitors charged to 13V.  
Ignores all other loss factors and discharge capability of other supporting parts (discharge diode).
ESR/CAP10Ω


0.25Ω
TOTAL ESR
60 Ω
16Ω

1.5Ω
100mA Load
7.0V
11.4V
12.4V
12.85V
200mA Load
1V
9.8V
11.8V
12.70V
300mA Load
0V
8.2V
11.2V
12.55V
500mA Load
0V
5.0V
10.0V
12.25V
0.75A load
0V
1.0V
8.5V11.87V
1A Load
0V
0V
7.0V
11.50V
2A Load
0V
0V
0V
10.00V
3A Load
0V
0V
0V
8.50V
Any voltage in red means the KA is useless in powering a motor..


12C) VOLTAGE  How does this effect performance?


Yes.  Capacitors when fully charge have a charge voltage very close to the track voltage.   As the capacitor discharges, it's voltage drops.   When the voltage drops below some decoder specific level, the level of functionality of the decoder is reduced or completely lost. In other words there are minimum operating voltages for the decoder.   The NMRA DCC standard only specifies the minimum operation voltage of a decoder is 7V.  Any operation below this voltage is 100% up to the decoder design by the manufacture.

This is really a decoder electrical design dependent variable. 

OLDER DECODERS:
Older decoders typically had a 5V minimum operating voltage at the chip/IC level.   When the KA/Stay Alive voltage fell to someplace between 8 and 6V, the 5V supply loses regulation and the electronics shutdown.   Sound or no sound does not matter.   Hence when the KA voltage falls to this point, the decoder stops motor and all leaving 6-8V of charge left on the capacitor unused the represents unrecoverable energy.  

NEW DECODERS: 
Newer decoder have 3.3V minimum operation voltage at the chip/IC level.    However the Sound still needs 5V to drive the speaker.  When the KA voltage falls to someplace between 8 and 6V, the 5V supply loses regulation HOWEVER ONLY the sound system of the decoder dies.  The motor continues to be driven by the KA allowing the engine to run farther until the 3.3V losses regulation.   That 3V difference means longer running but not at a fast speed.  

Conclusions:  The Older decoders require almost 2x higher minimum KA/Stay-Alive operating voltage than a new decoder.  A lot of the KA/Stay-Alive's potential energy is wasted.  Hence older decoders will never run as far as a newer decoder all else being even.


3) COMPARING KA/STAY-ALIVE's VIDEOS.

There are some Youtube video's available that illustrate these differences even between two sound decoders from two different decoder manufactures.

Here are a few examples.




6/22/15
9/9/15
10/20/15
2/12/16
7/17/16
9/19/16
12/22/16
4/6/17
7/21/18  Address TCS trademark concerns.