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. (Table Note number) = See notes below the table for explanation)

* = 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

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