Hi Tony's, I am building a layout and installing a mixture of Tortoise & Cobalt Digital IP switch machines.  The problem is that the PSXXs raise a short circuit every time I attempt to throw a switch Using the Cobalt IP.  After some debugging I found that if I lifted the trip current of the PSXX to 7 amps, one Cobalt could (most, but not all times) be thrown without raising a short.  Switching two Cobalts simultaneously necessitated lifting the trip current to 8 amps.  I can only guess that attempting to set a route of multiple switches, or when multiple operators happen to throw switches simultaneously could potentially cause a short even if the current limit was set to max.

As an aside, my Booster is only rated for 5 amps so having one of its districts set to limit current to a value exceeding the Booster seems a wasted resource. The Booster never tripped in these tests.

To attempt to isolate the problem, I bench tested all 6 of my PSXXs with a total of 5 different Cobalt digital IP switch machines – all brand new – and the same experience was had in every case.

The actual sequence of events is that :

  1. With factory default 2amp trip – The Cobalt Digital IP switch machine would just commence to move (ie barely)
  2. A hard short would be detected and power cut.  You were not able to throw the switch at all.
  3. With an overly high trip current – ie 7 amps – the PSXX’s Current Limit blue led would typically momentarily flash
  4. The switch motor would complete its cycle and
  5. The blue led would flash again at the end of the throw.  Sometimes this would then be followed by a hard short.

Without being an electronics expert, it would seem that a very brief high current load is being recognized causing the PSXX to trip.

If its not the problem, what is the recommended solution ?

Thankyou & Kind Regards........................Kym H.

Kym: Unfortunately, you have discovered that the Cobalt machines are not well designed. In the instance where you set the PSXX to 8 amperes, ran a Cobalt, and saw the blue LED flash, the Cobalt was drawing 8 amperes for more than 40 ms. This is a Cobalt problem, not a problem with the PSXX.

The PSXX is doing exactly what it is designed to do: protecting the layout from shorts (8 amps on a 5 amp booster is by definition a short - and yes, the 5 amp booster can output 8 amperes for a small length of time - that is why the PSXX trips). If the Cobalt is pulling 8 ampere spikes, that means that every time you move a turnout, the DCC track voltage is getting pulsed by the current draw. This is not good for your decoders, and can result in damage or inadvertent re-programming.

Here is our best advice: Best case only use Tortoise turnout motors. They have a maximum current draw of about 20mA, and even less while running. Given that you have Cobalt machines, you should run a separate DCC bus to these units that operates on its own booster and is isolated from any track bus so the current spikes cannot affect your engine decoders. At your option, you may or may not choose to use a circuit breaker on the Cobalt bus, and if you run enough at one time, it may trip the booster. However, your track bus will be unaffected and your decoders will be safe. Use the PSXX on your track bus(es) to prevent damage from any normal short circuit.

As an aside, we get a lot of complaints about the Cobalt machine. In comparison, the Tortoise uses about 20-25ma [0.025amps] under maximum load when stalled. Over the past 35 years we've sold tens of thousands of Tortoise with only a handful of failures. This incredibly high success rate is a testament to Circuiton's rock solid design, use of materials and testing.