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ESU LokSound 

52400 V3.5 "Keep-Alive"


There has been a lot of discussion on the internet about adding "Keep-Alive" capacitors to motor and sound decoders to improve performance on dirty rails or areas with poor continuity like frogs and dead rail sections.

ESU LokSound decoders tend to be less sensitive to these problems but can be affected by poor continuity none the less.

Many V3.5 and prior models of ESU LokPilot and LokSound decoders can have a "Keep-Alive" capacitor installed to improve performance.

It is important to note that the ESU LokSound V3.5 and previous models require a different type of KA than is currently available today.  

You can use an ESU Power PackTCS KA, Tsunami CurrentKeeper, or Digitrax Power Xtender but the solution requires additional components to work effectively.

It is also important to note that the common method of connecting a KA to the rectified output of the input power diodes as used on nearly every decoder design will not work.  

In some instances, it may be necessary to solder directly to the circuit board.  Know your abilities and work carefully, it's not hard.  A stray bit of solder will release the smoke from your decoder.

ESU LokPilot & LokSound Connection Diagrams

The manuals for ESU decoders include a wealth of information about installing the decoders and adding ancillary components like external chuff sensors, headlights, speakers as well as capacitors.

This illustration was taken from a respective manual and shows the appropriate pads on the decoder where the capacitors are connected.

You may notice they specify a 470uF 6.3V and a 2200uF 25V capacitor.  Why two caps?

In testing to determine if it can be done I tried many different configurations of capacitors.

I concluded that the early models of LokSounds actually have two seperate "keep-alive" circuits already on-board.

This is no doubt one of the reasons the ESU brand performs so well.

The first circuit is a low-voltage circuit that provides power to the processor.  On most models I could access, there is a large black capacitor in the center of the board.

ESU LokSound V3.5 Processor Capacitor

The second circuit is a standard track voltage circuit that provides power to the drive and function outputs.  On most models I have seen, this is a large yellow block near the end of the board.

ESU LokSound V3.5 Drive Capacitor

You may also notice they specify a 2200uF capacitor.  Is that too much or not enough?  It just depends...

A good rule of thumb is to add as much as you can fit in the unit.  Anything more than zero is better than nothing and currently the TCS KA-series Keep-Alives are the most powerful units available.

The bottom line here is the more capacitance you add, the better the unit will perform as continuity degrades.

You may also notice that ESU recommends including a resistor-diode pair in the positive leg of the capacitor.

This design is also referred to as an Inrush Current Protection circuit.  It is included to prevent false short-circuit detection by DCC circuit breakers and command stations.

Is it required?  It just depends on your application.

Do you or will you ever use a DCC circuit breaker?  If yes, you should probably include it.

How much total capacitance do you have installed in all of your locos and rolling stock?  If you have big caps in every loco and lighted passenger car on your layout, you should probably include it.

It is not required for all applications however.  The TCS KA's and ESU Power-Packs include Inrush Current Protection on-board the device.

The ESU LokSound V3.5 "Keep-Alive"

This photo shows the actual connections described in the wiring diagram on the decoder.

ESU LokSound V3.5 "Keep-Alive" Solder Pad Connections

The 2200uF drive capacitor called out in the ESU circuit diagram can be replaced by any of the previously mentioned "Keep-Alive" devices without any additional modification.  

Typical KA devices are ten times more powerful than the 2200uF capacitor and will make a dramatic difference in the performance of the loco... so long as the process has power.

You will not need the diode and resistor for the drive cap since these devices will already have them on-board.

To improve this circuit and take advantage of the power of the KA devices, we also need to upgrade the 470uF processor cap to a "super cap".

I recommend using a SBS4DCC 470 mF 5.5V Radial Super Capacitor but any 5.5V or 6.3V Super Cap will work.  The higher the farad rating, the better the installation will perform.

You will note I also added a diode - resistor pair to the positive lead.  You can get these from SBS4DCC also.

The 73700 Select Direct is really just a 73800 Select Micro with a 
> Next18 connector and adapter board.  The small decoder unplugs from 
> the main board to reveal additional solder pads on the bottom side.  
> To add a keep alive, use the board layout in the manual for the Select Micro

The 73700 Select Direct is really just a 73800 Select Micro with a 
> Next18 connector and adapter board.  The small decoder unplugs from 
> the main board to reveal additional solder pads on the bottom side.  
> To add a keep alive, use the board layout in the manual for the Select Micro
5.5V 0.47F Super Caps for Processor "Keep-Alive"

You can still add a "Keep-Alive" if your board does not have the requisite solder pads but does have the on-board keep-alive capacitors.

Simply locate the processor and drive capacitors as shown in the previous illustrations on your circuit board then connect the capacitor positive to the marked end (red or silver stripe in this case) and the cap negative to the opposite end.

The ESU LokSound V3.5 "Keep-Alive" In Action
They a picture is worth...

And a video even more.

Here is a brief demonstration of the effect this will have on your loco when installed correctly.



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