Digitrax Frequently Asked Questions: Auto Reversing
Digitrax offers three ways of handling
auto reversing: AR1 AutoReversing Controller, PM42 Power Managers,
and/or DB100/200 series boosters. You can use these methods in any combination
on your layout.
Auto Reversing with AR1 AutoReversing
Controller
Cost effectively control a single automatic reversing section on you layout. Easy to set up. Works for DCC and DC applications.
Click Here for Link
to AR1 information
Auto Reversing with PM42 Power Manager
Get the benefits of sectioning your layout and auto reversing without adding more boosters!
PM42 Quad Power Manager lets you use a single booster and divide it's output into 4 sections for automatic reversing &/or to improve operation by preventing the large sections of your layout from stopping when a short circuit occurs. 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 sections off a single booster in any combination of regular sections and auto reversing sections.
Click Here for Link
to PM42 information
AutoReversing with DB100/200
series boosters
Digitrax's Intelligent AutoReversing works on detection of a brief over current when a metal wheel shorts out a single gap with opposite DCC polarities across it. This means that the total circuit must allow enough current for this brief short circuit to be seen.
If your booster is set up to AutoReverse and you are experiencing problems please check the following:
1)MODE: Be sure the booster’s Mode switch (right hand side looking at the booster) is in the center position before applying power to it. It only enters "auto reversing" based on this switch at power ON time.
2)POWER SUPPLY: Be sure the transformer/power supply can supply enough current for the booster to develop its maximum e.g. 5 amps for DB100 series boosters and 8 amps for DB200 series. Usually, even transformers less than this rated current will briefly allow enough current for short circuit detection. To test this, short circuit the Rail A/B terminals of the booster when it is running, i.e. Track Status lamp is yellow. The booster should "beep 5 times" and turn off its output within about 1/3 of a second of a solid short circuit. It should automatically restore track power within 1.5 secs of the removal of the short circuit. It should reliably do this at any time. If this does not happen then your input transformer probably does not have a high enough current rating or there is too much resistance in the input wires to the booster. Note that if the transformer Primary circuit safety fuse or the Secondary circuit breaker trip OFF, then you need to check the adequacy of your transformer/power supply. The transformer must be protected against short circuits or long term overloads that exceed its specified safety ratings.
3) FEEDER LOSSES: Excessive wiring resistance from the booster terminals to the reverse section gaps often lead to poor auto-reversing operation. If the booster cannot see a short at the gap then the AutoReversing strategy cannot work!. To test this, short the track across the rails next to the gap and be sure the booster beeps, shuts down and then recovers. Do this on both side of the gaps for each booster. If the booster does not reliably see the shorts next to the gaps, then you need to beef up the power feeds from the booster. Note that the "loop resistance" between boosters will need to be less than about 2 ohms for a 4.5amp rating with a 12V or N scale DCC booster setting. You do not need to measure this resistance since you can do the short circuit test which is a good indicator. The booster’s audible fault beeping was included to make it easier to use and debug!
4) BOOSTER RATING: Be sure that the booster with the lowest current rating is chosen to be the auto-reverse booster. This is very important when using boosters with different ratings. Also if the two boosters on either side of the Reverse section double gaps are both auto-reversing, there is no certainty about which unit will switch first to fix the gap polarity- i.e. auto-reverse. The first to autoreverse will fix the gap polarity.
5) MONITOR GAPS: On Digitrax layouts, if you connect a small 12V lamp across the isolating gap on one of the rails, it will then indicate whether the "gap polarity" is matching or not. If the lamp is lit, it means the gap is "mismatched" and if the lamp is off then the gap is matched and a loco can go through it. In this case you can easily see autoreversing in action by shorting across the rail gap with a screwdriver tip. The lamp should be off when the short is removed. You can alternate the lamp state by then shorting a gap at the other end of the reverse section. This clearly shows correct operation and gives confidence without need for complex tools. The boosters should be able to autoreverse within about 1/000 th of a second and so will never "beep" to show a fault when correct autoreversing occurs. With the connections you have to System One components, you will need a lamp across both gaps and need to short BOTH rail gaps simultaneously at one end of the reverse section to see this monitoring action correctly.
6) COMPATIBILITY: We have anecdotal reports of success using Digitrax boosters to autoreverse in most DCC systems made by other manufacturers. I have not personally been able to hook up and verify combinations that users may have in the field. At Digitrax, we follow the simpler wiring plans of "direct home" wiring as opposed to the other extreme of having a major "common bus" for all booster returns. We feel there are numerous technical advantages in doing this, especially on new DCC layouts with higher current loads. The isolated inputs of the Lenz and NCE boosters, and the way they connect them mean that there is no explicit return path in the double gapped autoreverse case until BOTH gaps have been reliably bridged. With moving wheels and dirty track you can see this is likely to be less reliable than a system that explicitly provides a return path that will work with any single bridged gap. This is one important reason we use "direct home" wiring. We also have several explict return connections between boosters in the Digitrax wiring scheme. The sensitivity to "steam locos" not working properly with boosters made by other DCC manufacturers may be related to the requirement for both gaps to be shorted. This is not the case with a pure Digitrax booster scheme. If you use two Digitrax boosters to accomplish auto-reversing, we can assure you of correct operation, and we have thousands of layouts that run steam and diesel locomotives that auto-reverse smoothly and reliably.
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This page, and all contents, are Copyright (C) 1996-2004 by Digitrax, Inc., Norcross, GA, USA.
Updated 05-04-04