Associated Products:

PX112-10, SDH166D, SDXH166D

KB1015: Power Xtender Q & A

This article was last updated on Nov. 18, 2013, 3:50 p.m. | Print Article | Leave Feedback

My sound decoder has a capacitor, why do I need a PX112?

The capacitor that came with your Digitrax sound decoder is designed to hold up sound operation in the presence of brief power interruptions.  It is not designed to keep the locomotive’s motor and lights running.  Our ears are very sensitive to sound interruptions so, the capacitor on your sound decoder will prevent most of these drop outs on average quality track.  Most people don’t even notice the small pauses in a locomotive’s movement and the small flashes of the lights when the track power is interrupted.  If you are experiencing problems with power dropouts, you should consider adding a Power Xtender to smooth out operations.

How long with the PX112 keep a locomotive and sound going when track power is interrupted?

The PX112 will typically hold up sound for about 30 seconds on an HO loco that is stationary.  By default after about 6 seconds the diesel prime mover will make the “shutdown sound” due to packet loss timeout (CV11).  Even though the decoder is still powered by the PX112 it is no longer receiving information from the Command Station.  CV11 controls the Packet Timeout interval, this is the amount of time the decoder will remain active after it stops receiving commands (packets) from the command station.  This value can be set from 0-255 and has a default of 6.  If CV11 is set to 00 packet timeout will be disabled and the decoder will stay on as long as it has power even after the loco is dispatched.  

A moving locomotive will continue to run from 6 to 15 seconds depending on motor load, activated functions (lights, etc.), and sound volume.  The PX-112 is intended to allow the decoder to continue to run in the presence of brief power interruptions of no more than one to two seconds.  It is not a battery, and will not run a loco for extended periods of time.

With Scalable speed stabilization (BEMF) ON the loco will be able to hold speed for longer than when it is OFF.

In bench testing of an SDXH166D Premium Sound Decoder with a PX112-10 installed we observed the following:

If the locomotive with the decoder installed is stationary on the track and the bell/F1 is left ON, approx. 6 seconds after the track is disconnected, the diesel scheme will execute the prime mover shutdown sound (set by CV11 value, Packet Timeout  CV), and the bell will continue to sound for a total of about 25 seconds.

If additional functions are activated, this sound holdup time will decrease.

With a DC motor at about 15% speed, the motor will hold up approx.  5 seconds, depending on locomotive load and sound volume.

How Long Does It Take to Charge the PX112?

The PX112 may take a couple of seconds to charge up on the applied track, to full voltage, and this is longer when it is connected to a programming track with current limiting and different voltages.
The minimum motor run voltage is about 7 Volts, maximum track voltage is 15V.

Programming and Reading Back Decoder CVs with PX112

Because of large charging currents and the time it takes to charge the PX112, it may take 2 attempts to program or read back CVs from your PX112 decoder.  If possible during programming and configuration it is recommended that the PX112 be unplugged from your decoder.  If that is not possible follow the simple steps below to program and configure your PX112 equipped decoder. 

With PR3 & SoundLoader 2.XX

Because of the charge and time needed to charge the PX112 to capacity, Soundloader may fail to read the decoder on the first attempt.  When this happens the Manufacturer ID will show "00" instead of "Digitrax".

In order to re-read decoder ID properly and enable SoundLoader’s functionality simply press the “Get Detailed Info” button

Once SoundLoader has correctly identified the decoder and reads Digitrax as the manufacturer, you should be able to use the CV editor to read back and program CVs. If you have issues reading or programming a second attempt will almost always resolve the issue.

With a Digitrax Command Station

Using a DSC100 and a DT4XX throttle the first read of DIRECT CVs on the programming track may fail when using a PX112, if this occurs simply re-read the CV and the value will read. 

When available mainline programming is recommended when using a PX112.

Loading New Sound projects into my sound decoder with the PX112

When loading a new sound project into a Digitrax sound decoder equipped with the PX112 is it recommended that the manual programming method be used.  Clicking the Green “Download this Sound Project to SFX Decoder” may cause some files to not be loaded.  The manual programming method is very simple and outlines below.

Click Erase Flash and wait for the process to finish

Click Program SDF and wait for the process to finish

Click Program .WAVs and wait for the process to finish

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