PSXX - AR Current Limit/Trip Value

[Chinapig]

Hi,
I've just installed a DCC Specialities PSSX-AR and everything appears to work perfectly except that when I put a Stay-Alive equipped loco on the Loop section of track, the unit "trips" and the Turnout at the end of the Loop throws.  I'm powering the layout with a 5 amp Digitrax DCS100.

All of my Stay-Alive equipped locos have the Diode/Resistor pair installed to slow down the surge of current when placed on the track.

I've managed to eradicate the problem by increasing the setting of the Current Limit/Trip Value to 6.3 amps.  Any settings below this, including the next one down of 5.4 amps, still give me the problem.  Even set at 6.3 amps, if I short the loop the PSSX still breaks the circuit and the DCS100 keeps operating.

The question is, am I likely to be putting anything in danger from short circuit induced meltdowns if I operate with it set like this?  Also, does anyone have any idea why I need to increase the Trip Level so much?

Cheers, Ted

[peteski]

So just placing a single loco equipped with the stay-alive circuit in that reverse-loop (?) section causes this?

Or there are multiple locos sitting on that loop and just adding one more loco with the stay-alive causes the problem?

What scale is the model?

Is this a home made stay-alive?  What is the total capacitance and what is the resistor value?

[Chinapig]

Thanks for responding.

Yes, it's just a single loco placed on the track with no other locos already on the track.

It's N Scale.

It's a home-made stay-alive with a capacitance of between 880uf and double that - I've tried the experiment with a few locos.  The resistance is 100 ohms.

I have used the PSX-AR before and don't recollect this problem.  This new PSXX appears to behave differently.

[mmagliaro]

My first thought would be to try bumping that resistor up to 220 ohm, and see if the problem goes away, just to prove that it is really the inrush current to that capacitor that is causing the problem.  I looked up the PSX-AR and it uses CV's 55 and 65 to control the delay before it trips.  Does the PSSX-AR allow this?  Maybe you could put in a delay of something like 10 or 20 mSec, which should be plenty to allow for the very brief inrush peak.

[peteski]

Ted, you mentioned you have  other locos with similar stay-alive circuit installed.  Do all of them trip the reverser, or just that singe loco?

But neither 5.4 or 6.3 Amps seems realistic.  Assuming that the track voltage is 12V (around 11V rectified DC inside the decoder), the maximum (inrush) current that 100 ohm resistor can pass is 11V / 100 ohms = 0.11A (110mA)  Add to that another 100mA that is consumed by a decoder (and I'm being generous), that is still much less than even 0.5A (not even remotely close to 5.4A trip current).   Something doesn't add up.

Are you sure the PSXX-AR is wired correctly?  That is a reverser circuit, but does it shut down completely when the loco is on the track, or keeps powering the tracek with thel loco on it, and just flips the polarity and throws the switch at the end of the reverse loop?

[Chinapig]

Sorted

CV58 is the equivalent CVs 55 and 65 in the PSX-AR.  It's described as "Reverse Delay Adjust" and the value you give it is "the value in ms added to the inherent delay from the short detection to the phase reversal of output" to the loop.

A value of 3 is all that's needed.

Thanks for your help guys.

[peteski]

Good deal in resolving what seemed to be an odd problem.

[mmagliaro]

I am glad that fixed it.  A little delay works wonders with brief surge currents.

But... am I the only one now dying to know what's really going on here?  An 880uF or 1760uf cap isn't THAT big, and as Peteski pointed out, a 100 ohm resistor would be limiting the inrush to way below 5 amps.

I reread the post.  So is it the actual moment you "put it on the track" that this happens?   If so, a spike is happening for some reason and it has to be something other than that keep-alive.  Maybe there's a partial short affecting your cap/resistor setup and it is bypassing that resistor.

Sorry... this is the way nerds think.  Must... know.... why....   LOL.

[peteski]

I was just going to let this go but now you did it Max! I am also puzzled but the description of the problem.

The device in question is an auto-reverser, and it obviously also controls the position of the points in a turnout at the entry/exit of the reverse loop.  The reverser is only supposed to flip the polarity of the track when it senses phase difference between the reversing section and the entry/exit section.  That should only get triggered when a loco enters the reverse loop through the turnout and it crosses the gap at the reversing section.  It is not supposed to kill the power to the reversing section.

I found it strange that just plopping the loco directly on the reversing section (not actually crossing the gap) should have any effect on that section. There is no phase mismatch occurring just by placing the loco within the reversing section.

Maybe I did not understand the original problem description, or it was incomplete?

[Maletrain]

Doesn't an auto reverser just measure current, and when it exceeds its setpoint, it first tries to reverse the phases, and then opens the circuit (both sides) if the current does not go below the trip setpoint.  I don't think it knows anything about "gaps" being "crossed", specifically.

[peteski]

Doesn't an auto reverser just measure current, and when it exceeds its setpoint, it first tries to reverse the phases, and then opens the circuit (both sides) if the current does not go below the trip setpoint.  I don't think it knows anything about "gaps" being "crossed", specifically.

Yes, most likely.  But that still doesn't seem to explain why a loco which does not consume more than 0.5A (even at inrush condition) placed on the reversing track would trip a 5A breaker.  It is probably some quirk in the reverser's firmware.

[Chinapig]

Yes, it's the actual moment I put the loco on the track that this happens and it's not a particular loco as it happens with all the ones I've tried.  It also happens when placing a caboose fitted with LEDs, a rectifier and a capacitor.

It is weird and I'm also interested in why it happens.  The loop is only meant to have its phasing reversed when it shorts with a track of opposite polarity - a short across its own two rails would activate the circuit breaker only and not cause the polarity to reverse.

This isn't what was happening.  Putting any of my stay-alive fitted locos on caused the polarity and the turnout to change.

[John]

Is your PSXX reverser upstream and in series of another circuit breaker .. you should put the reverser their own feed directly to the power out of the booster .. You may also want to look at this ..

[Chinapig]

John,
Yes, the PSXX is attached directly to the booster - it's not in a series with other circuit breakers.

I did view that video but I didn't think it was addressing my specific problem, unfortunately.

[peteski]

OK, so we will continue troubleshooting.  I was assuming that the reverser was wired according to best practices (which John mentioned). If not, make sure it is not connected downstream of another circuit breaker.  Never mind - you posted a minute before I did.  That part is all set.

If it is, the manual states that when the reverse loop senses short, it will shut down for short time, and then try to power  back up (this is a typical behavior of pretty much all DCC circuit breakers).  So when you place that loco in the middle of reversing track section (being careful lthat the wheels do not somehow cause accidental "real" short, and the reverser shuts down, does it try to power back up after the time delay, then powers back uop, or does it stay and cycle in the shut down state, trying to power back up then shutting down again?