PowerCab with PSX and PSX-AR

[nickelplate759]

I've got a problem with reversing sections on my layout.  Power comes from an NCE PowerCab.  Power blocks (there are 2) are protected with DCC Specialities PSX, and reversing blocks (also 2, coincidentally) have DCC Specialities PSX-AR.

Because the PowerCab is rated for 2 amp, the trip current for all the PSX and PSX-AR is set to 1.27 A  (CV49=1).  The PSX and PSX-AR manuals say that this setting must be used with the PowerCab.

The reversing sections work properly (meaning they reverse), but I have a persistent problem as locos leave the reversing section when the polarity of the reverse section does NOT match the polarity of the power district - the loco pauses for about 2 seconds before restarting.        This does not seem to happen when the loco goes from the power district into the reversing section, even if the polarity doesn't match.

The PSX manual suggests that if this happens I should raise the trip current on the PSX (power district), but the next power trip level  (CV49=2) is 2.54 A, which exceeds the rating of the PowerCab.

So - what should I do?
A. is there another way to address this problem other than raising the power trip levels?
B.  is raising the PSX trip level to 2.54 A OK even with a PowerCab and I'm worrying for nothing?
C. Get a booster for the Powercab, like the NCE SB5?

[peteski]

George, are your sure your Power Cab can supply 2.0A?
I own a Power Cab and mine came with a wall-wart rated for only 13.8V 1.35A.  If yours is like that too, then the reverser will not work reliably.

[RBrodzinsky]

Have you watched the LEDs on the PSX and PSX-AR to see which one is tripping when the loco stalls?  But, I have found these to not work very well with either the PowerCab or the older Digitrax Zephyr (DCS50).  The trip current steps just don't seem to let you set them for those units well

[nickelplate759]

Have you watched the LEDs on the PSX and PSX-AR to see which one is tripping when the loco stalls?  But, I have found these to not work very well with either the PowerCab or the older Digitrax Zephyr (DCS50).  The trip current steps just don't seem to let you set them for those units well

I've watched the LEDs until I see little red spots when I'm trying to sleep!    Neither fault light (on the PSX nor the PSX-AR) ever seems to go on, and the PSX-AR "reverse blink" happens (or stops) as expected - at the beginning of the stall.

So - would the SB5 (5 amps) fix this?

[nickelplate759]

George, are your sure your Power Cab can supply 2.0A?
I own a Power Cab and mine came with a wall-wart rated for only 13.8V 1.35A.  If yours is like that too, then the reverser will not work reliably.

No, I'm not - but the documentation claims it can.   I haven't checked the wall wart (it's tucked away under the layout where it's hard to see).

[peteski]

No, I'm not - but the documentation claims it can.   I haven't checked the wall wart (it's tucked away under the layout where it's hard to see).

I suspect it is just like mine and it does not supply enough current for the reverser to work reliably.  While the Power Cab unit itself might be rated for 2A, the wall wart they supply with it does not live up to that rating. 

But you might be able to solve the problem by getting a wall-wart with more amperage (to squeeze the full 2A out of the Power Cab's internal  booster). It it should be cheaper than SB5 (unless you're planning on going that route anyway).

[Steveruger45]

I just checked my power cab wall wart.
It’s 13.8v and 1.8 amp. [ Guests cannot view attachments ]

[peteski]

I guess they were not consistent in their wall wart specs. Still less than 2A, and I suspect the low amperage output of the booster is causing the strange reverser behavior.

[nickelplate759]

My wall-wart matches @Steveruger45

I tried bumping up the threshold on the PSX (not the PSX-AR) and it didn't help - which makes sense since the threshold is now over 2A.

I'd spend the $$ for the SP5 IFF I knew it would fix the problem.

[Steveruger45]

My wall-wart matches @Steveruger45

I tried bumping up the threshold on the PSX (not the PSX-AR) and it didn't help - which makes sense since the threshold is now over 2A.

I'd spend the $$ for the SP5 IFF I knew it would fix the problem.

Not sure if this will help you but take a look at this link which discusses an issue and provides a fix for it and may be what you’re experiencing.
http://www.sbs4dcc.com/tutorialstipstricks/psxandfrogjuicersshortcircuitconflict.html

[nickelplate759]

Well - more experiments yielded more data.
The problem only occurs with SOME of my engines.   The only thing they seem to have in common is that they are the engines that are fussy about electrical contact - engines with KeepAlives, or just good all-wheel pickup (like my Atlas c420, for example)  seem to be find.

The problem has appeared with a few different brands of decoders (MRC, Digitrax, TCS) so I don't think it's specific to one brand.

So - the things in common are:
1. engine with iffy electrical contact AND
2. short stall on transition from reversing section into power district when the polarities do not match in advance (so the reverser will trip - which it does).

Any ideas on what I can do besides improve the contact of all affected engines?  For example, move the block boundary away from switches and other areas of troublesome contact?  Stagger the ends of the block boundary (DCC Specialities recommends this in general, but I haven't done it).

One other observation - if something happens to cause a short on the layout (like some idiot runs through the wrong side of a turnout), the PowerCab trips, not the PSX.  Pretty sure that's not the way I want it   

[Maletrain]

This has my attention because I have a PowerCab with a wall wart rated at 1.44 amps, and have bought but not installed some PSXs and PSX-ARs for a layout I am finally putting together.

I am wondering if your PSX has a trip delay set in its CVs.

The trip delay on the PSXs is enabled by CV55.  With CV55 = 0, the trip delay is less than 1 ms.  With CV55 = 1, the length of the delay is set by CV65.  CV55 default value is 0, so no delay is the default.

CV65 can have values from 1 to 255, equating to delay in ms equal to the CV65 value divided by 8 (e,g., a value of 80 = 10 ms delay).  There is some words in the manual that "a value of 128 should work with almost all layout problems" that result in nuisance trips" but that the value should be set as low as it can be for your layout. (A value of 128 would be a delay of 16 ms, which is probably slower than the PowerCab.)

The CV65 default value is 24, which equates to a 3 ms delay.  The PSX instructions say that this 3 ms delay is the minumum to use with a PSX-AR and that some layouts may require a longer delay.

So, I am wondering what values you currently have for CV55 and CV65 in the PSX that does not trip before the PowerCab.  Unfortunately, the PSX manual says to use programming-on-the-main to change CVs, so I do not know if you can use programming-track to just read the existing CV values.

Another issue is that you just posted that the problem seems to only occur with locomotives that have keep-alives.  The PSX literature says that the PSX has logic that determines if the load is a true short or just an overload due to a discharged capacitor.  That is a wild card that is not explained further.

But, because you posted that a true short circuit causes the PowerCab to shut down instead of the PSX, I suspect that it is either in the time delay CVs or the PowerCab is just shutting down on a current below 1.25 amps. 

But, some other things to consider are:
1.  You posted that you set the trip current to 1.27 amps by setting CV49 = 1.  The other way to do it is to put a jumper between pins 1 and 2 on contact block J6.  There is a warning in red print to not do both.  So, make sure you don't have a jumper on J6.
2. Since you can't read CV49 with POM, are you positive that it value is 1?  If it is any other number, including zero, then your trip current is 2.54 amps or higher.  It might be useful to try reprogramming CV49 to zero and putting a jumper on J6 to see if that makes any difference. 
3. A way to test that your trip set point is really the issue would be to find a load that draws right at 1.3 amps, and see if the PSX trips and the PowerCab does not.  A variable resistor should work for that test.
4.  I can't find any info in the PowerCab manual that describes its overcurrent trip features.  I am thinking that should be in the PowerCab, not its wall wart, but I am continuing to look for the answer to that.

[peteski]

4.  I can't find any info in the PowerCab manual that describes its overcurrent trip features.  I am thinking that should be in the PowerCab, not its wall wart, but I am continuing to look for the answer to that.

I'm speculating the following scenarios:
Even if the Power Cab circuitry can supply 2A of track power, if the current draw exceed what the wall-wart is capable of supplying then either the short circuit protection inside the wall-wart kicks in (if the wall-wart is so equipped).

Or if the wall-wart has no such protection, then exceeding the wall-wart's current rating will likely cause its output voltage to drop (below what the Power Cab needs to operate), thus shutting the Power Cab down.

[carlso]

Very Interesting !

My Power Cab wall wart is 1.35 amps. I only use it on my program track with JMRI.

carl

[Maletrain]

I asked about PowerCab short circuit response on the NCE group, and apparently things are not well documented and variable among different vintages of PowerCabs.  Here is what I got in response from that group:

My understanding initially was that the Power Cab basically relied on the wall wart shutting down and restarting with an overload.

However I believe one of the Marks (Gurries or Schutzer) did post contrary and correct information. I don't have it to hand...

You are correct.  Very early PowerCabs relied on the wall wart as you describe but after incidents of the damaged FETs when some users substituted a different power supply Jim also added overcurrent shutdown in the software.

I can’t remember exactly which software version this was added to, but I think it was around 1.28c or so.    Anyway the current software will shut down the track voltage in the case of an overload, but it’s still sort of a race condition as to whether the wall wart or the software shuts it down first.

Not all PowerCabs behave the same way as there were several different suppliers of wall warts over the years the PowerCab has been in production so some may shut down at lower currents than others due to the overload current capacity of the wall wart.

When I acquired mine, version 1.28c, It would shut down for shorts, then attempt to restart until the short was cleared. The OEM wall wart is marked as a switching power supply. When I tried a power supply not marked that way (sold as compatible with a higher current ceiling by a prominent DCC dealer) the PowerCab would still shut down but would not restart.  It required unplugging the cable from the throttle to restart.
I have since mellowed from my apprehension about a power shortage and the original wall wart has performed perfectly. I Now use the after market WW to supply my auxiliary DC bus.

So, from this, I am thinking that Nickelplate759 is seeing his wall wart shut down before his PSX breaks the circuit.  It would be helpful to know what version of the PowerCab software and amp capacity wall wart he is using.