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DCC Specialties PSX Circuit Breaker &

Tam Vally Depot Frog Juicers 

Short Circuit Detection Conflict

Last Updated 170812


Many Model Railroader using DCC choose to incorporate DCC-compatible Circuit Breakers to divide and distribute power on the layout and to provide short circuit protection to prevent damage to models and DCC Decoders when accidents happen.

The DCC Specialties PowerShield X (PSX) series of DCC Circuit Breakers are one of the most robust designs on the market and have been proven over time to perform exceptionally well in nearly any installation.

One very nice feature is the PSX is addressable like any other accessory so CV settings can be adjusted on the fly after installation.

Very handy... as you will read.

The Backstory

Model Railroaders have been faced with the quandry of switch frogs for decades.

Electro-frogs, energized frogs, Insul-frogs, dead frogs, frog polarity, power routing, frog juicer...

Recognize any of those phrases?

The first question when selecting and installing a switch is always whether to energize the frog or not.  A live frog is always better than a dead frog because model trains require a smooth, consistent flow of electricity to perform well.

It has been a known problem since the first switch was fabricated that an energized switch frog must change polarity based on the orientation of the switch points.

I won't digress into that subject here.  Please review the DCC Wiki on Turnouts for more information on the issue.

The introduction of DCC has only compounded these issues since DCC decoders do not respond well to interruptions of flow of electricity to the processor.

The best way to solve the problem is to use any one of a thousand techniques to route power to the frog directly from the track bus.

Unfortunately this can get complicated both mechanically and electrically and not everyone want to fool with it.

Another solution is to install a keep-alive device on the decoder which acts like a Uninterrupted Power Supply for a computer when the decoders looses power directly from the rail.

This is a nice fix and I am a big fan since the Keep-Alive hides a lot of nuisance issues and really does make DCC-equipped models run better but... keep-alives are very large and not every model or scale can incorporate them.

A third option is the Tam Valley Depot Frog Juicer.

The Tam Valley Depot Frog Juicer is a DCC accessory developed to simplify the task of energizing the frog AND set frog polarity with minimal effort.

It is essentially a simplified DCC auto-reverser.

Installation is quick and easy (it takes about five minutes), they require very little long term maintenance and they are very reasonably priced.

Faster, better, cheaper... an engineers mantra.

The Issue

Streamlined Backshop recently performed a complete wiring upgrade on a large layout to improve the reliability of train performance, DCC command control and to improve the utilization of the existing boosters and ancillary hardware.

The revised installation incorporated 12 PSX circuit breakers and 60(+) Dual Frog Juicers (DFJ) to divide and distribute power and control polarity.

In all cases, power is fed from booster to PSX to main track bus and input power to the DFJ is tapped off same main track bus as needed.

On startup, all 70 plus devices displayed short circuits and went into cyclical detection-reset pattern even though we knew they weren't shorted.

"What the..." 

"Shut it down"

"Where's the manual?"... nothing helpful...

"Google it..."

It turns out that by default, the PSX is set to detect shorts very, very quickly, much faster than the Frog Juicer for sure as evidenced by the detection conflict when the products are used together without adjustment.

A wheel contacts an energized frog with inverse polarity, the Frog Juicer changes polarity as required, the PSX detects the polarity change as a short circuit and trips and reset which the Frog Juicer sees as a short causing it to change polarity which causes the PSX to trip and reset which causes... ad infinitum.

The Frog Juicer detection rate has proven adequate over time so this is not to imply the Tam Valley Depot products are ineffective in any way, only that the PSX is much more sensitive when used with the default settings.

Hardware Identification

The DCC Specialties PSX boards have been subject to many hardware and software improvements and updates since their introduction many years ago.

Current production hardware having a date code 1114 or later (but best to contact DCC Specialties if this does not work on yours) incorporates software that implements CV65 to incorporate an adjustable time delay between short circuit detection and circuit interruption. 

Prior versions of hardware cannot be updated to incorporate this feature and should be replaced.

Software Identification

To verify that your PSX has a compatible version of software, place the program jumper to program and turn on power.

Observe LED D6.

When you turn on power, you should see four short flashes.

Any other flash pattern is the wrong software version.

Current versions of PSX hardware can be updated by DCC Specialties to a current software version that incorporates this feature.

PSX CV Settings

There are two undocumented (as of this writing) CV's to adjust the trip rate or sensitivity of the PSX Circuit Breaker.

As they are undocumented, they remain unnamed.

I believe CV55 enables CV65 and CV65 is trip time as measured in milliseconds.

Set CV55=1 and CV65=128.

Adjust CV65 in increments of 8 to fine tune the sensitivity to perform as desired in your installation.
Final Analysis

The PSX stands vigilantly on guard protecting the precious chips on a fleet of DCC decoders from short from short circuits.

The DFJ's work tirelessly energizing and polarizing the frogs that direct traffic across the pike.

The PSX and DFJ's have performed flawlessly together after applying these settings.

The PSX had been problematic in this installation from day one because of a large quantity of brass models that ply the rails.  

False short circuit detections from the inherent nature of operating older brass models made the PSX unusable.

As an added benefit, tuning the PSX using these undocumented CV's virtually eliminated the false detection problem as well.

Win. Win. Win.

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