pm4

Digitrax Power Management System-PM42

PM4 Power Manager Get the benefits of short circuit management and auto reversing without adding more boosters!

PM42 Quad Power Manager lets you use a single booster and divide its output into 4 power sub-districts for automatic reversing &/or to improve operation by preempting booster shutdown when a short circuit is detected by the PM42. If you want to improve operation but don't need the added power (or expense) of adding a booster, the PM42 is the right answer for you. Each PM42 can run 4 sub-districts off a single booster in any combination of regular sub-districts and auto reversing sub-districts.

$79.95 msrp (Less than $20 per sub-district)

Click here for PM42 Manual

Click here for Application Note: Using PM42 with Zephyr/DCS50

PM4 to PM42 Upgrade Kit $9.99 msrp

Current PM4 users can upgrade their units for the new features of the PM42 by changing the chip on the board and re-programming the PM42 for their operation. The PM42 gives you 2 additional faster short circuit detection sensitivity settings.

If your existing PM4s are doing what you need them to do, there is no need to upgrade them.

Click here for PM4 to PM42 Upgrade Instructions

PM42 Questions and Troubleshooting:

Q. What’s the difference between the PM42 and the PM4?

A. The PM42 is an improved version of the PM4. We added 2 faster short circuit detection sensitivity settings and revamped the manual.

Q. Is there an upgrade to PM42 if I already have a PM4?

A. You can purchase the PM42 upgrade from your local dealer for $9.99 msrp. Simply remove the PM4’s chip and replace it with the PM42 chip, set up the new chip for your operation and you are good to go!

Q. When I get several locos in the same PM42 sub-district, the PM42 seems to shutdown at random times even though I am sure there is no short circuit, what is wrong?

A. The PM42 is set at the factory with a default current trip point of 3 amps for all 4 sub-districts. This is fine in most cases. If you plan to run more than two or three locomotives in a sub-district, you will need to increase the trip current. Use the minimum current set point that gives acceptable layout operation, i.e. minimum power interruptions when no short circuits are occurring. Be sure that all locos on the track that are not running have a throttle setting of "0." Locos that are sitting still with even a very low throttle setting can draw enough current to be detected by the PM42 and will add to the total current trip load.

Q. How do I increase the PM42's current limit?

A. Use a throttle to change the PM42's Option Switches 01, 02 and 09 as detailed in the PM42 instruction manual. The PM42's trip current threshold can be set at a value from 1.5amps to 12 amps. Always use the lowest possible setting, consistent with good operation and reliable short circuit detection and recovery. Higher current settings are not "better." We ship the PM42 with a moderate current trip threshold of 3amps so it will work on most DCC boosters and layouts with no changes.

This is because some boosters cannot supply enough current with the track feeder resistance to reliably allow short circuit detection. If this is the case with your booster, you will have to run with lower trip current levels and fewer locomotives or upgrade the track bus and feeder wiring for lower resistance.

Always be sure that the PM42 reliably detects a track short at the track furthest from it and be sure the PM42 operates before the booster shuts down. Use the "quarter test" to create a short circuit on the track at the furthest point from the PM42 to be sure of this.

Note that sometimes overlapped and recurring faults from multiple sources may still trip the Booster short circuit protection (Digitrax Boosters beep 5 times at this point!), even though the PM42s are operating properly. This is unlikely, but can occur depending on the decision and fault recovery logic used by the booster. The PM42 generally should operate slightly faster than the Booster.

Q. My PM42s seem to correctly trip on track shorts and auto-reverse reliably, but the power briefly drops out during these events, and when the PM42s attempt a fault recovery into a persistent short circuit, why is this?

A. No power on earth can stop the track voltage of the booster from collapsing to a low value when a true short circuit is present. This is simply Ohm’s law in action!

Actual track voltage seen depends on: the loop resistance of the short circuit, the current capacity of the booster and power supply and whether the Booster employs "smart" fault detection and recovery along with fault current management.

The PM42 works by sensing what it "believes" is fault current (determined by its trip current setting) in a sub-district of a whole district served by a single booster. When a fault is detected, the PM42 disconnects the short-circuited sub-district from the rest of the district. This allows the rest of the track served by the booster to return to proper operation very quickly.

The PM42 operates faster than the decision threshold of the booster in determining when a fault exists on the layout to shutdown the sub-district before any "welding" can occur! After a shutdown has occurred, the PM42 periodically checks to see if the fault is cleared so that it can "restart" the track area that was shut down. When the initial fault occurs and also during some "re-tries," the track will see a brief short. This is unavoidable. Most well designed decoders and equipment will work fine during these brief power interruptions.

Careful operation and maintenance of the track and plant, especially switches, and training operators not to foul turnouts set against them will address most track short circuit problems.

Q. Will the PM42 work with other DCC boosters and systems?

A. The PM42 was specifically designed to work with Digitrax Direct Home wired layouts. Any system that is configured this way will work with the PM42 with no interoperability issues. For example, CVP uses interoperable booster connections.

The PM42 can be used with a DC system if it is hooked up in the negative ground return path, or even a Marklin AC digital (trinary) booster. It is possible for the PM42 to be used with most DCC systems. Digitrax has no control or knowledge of each specific non-Digitrax system and how it may interact with the PM42.

Q. If I use a non-Digitrax compatible system, what features of the PM42 Auto reverse/Short Circuit Managers (SCM) will I lose?

A. The PM42 can be used as a stand alone Auto reversing unit and Short Circuit Manager with many other non-Digitrax systems, but for systems without LocoNet capability a number of networked management features will not be available.

For example, the PM42 sends out real-time, event driven (non-polled) information to the LocoNet about fault problems and resolution, auto reverse actions and also identifies the affected sub-districts. This allows other devices, such as PCs, the Digitrax Signaling system, Digitrax Transponding or other detection and sub-systems systems to know when sub-district is shut down. In addition, other network aware devices can influence the PM42 actions by programming the PM42's Option Switches and can turn ON and OFF or sequence power sub-districts as needed. The PM42 has is configurable through its Option Switches and a Digitrax throttle must be used to access these settings. A Digitrax Command station is not needed to access the Option Switches. A PC equipped with an MS100 and appropriate software can also access the PM42's management feature.

This option allows a PC to "bind" or combine some LocoNet resources with other systems, i.e. the PC is used a logical "bridge." This option is also available for the BDL16 Occupancy and Transponder detection system, which is also designed to operate and communicate stand alone without a DCC command station.

Exercise care when combining systems and their ground return or common legs. In particular be sure that the LocoNet common ground return is not energized to rail potential if it going to used with other equipment.

Q Can I combine the power input requirements for PM42s with other units for economy?

A. Digitrax does not recommend sharing power supplies used with PM42s with other devices. A supply of 12V-15V AC (A Digitrax PS515 is good choice!) or 13.8V to 15V DC will work in most cases. Do NOT share the power connections of PM42 with any booster.

Return to Digitrax Home Page

Return to Auto Reversing Page

Return to Online Catalog.

Page Updated 01-24-03.