DCC Specialties equipment


PSX-AR autoreverser

This is a new product (as of 2007) that is great for Large Scale.

First, it has the capability of much higher current trip points, i.e. the trip current is the point where the autoreverser decides that the load is not a train, but a short circuit (meaning that the unit should reverse the rail polarity).

Many autoreversers would trip at 4 or so amps. Running just a single USAT F unit, I set this system to 8 amps to eliminate false tripping. I'm still checking it out, but you can set the unit up to 19 amps!

It also has a detection system that can tell the difference between high inrush currents found in sound decoders, and a true short circuit.

The PSX comes in several flavors, with the base unit that just does autoreversing and short circuit detection, and units that can control stall and solenoid switch machines, have a photocell as an input detector, etc.

One thing that they list in the documentation is that you can fit this into a Radio Shack project box, #270-1805. Well that is true, but it sits in the top of the box where the lid would be. I milled the 4 supports inside and there are some small supporting ribs. I milled this flush with the box sides, about an inch into the box. The result is that the circuit board fits down nicely into the box.

I suggest labeling the input and output terminals so as not to hook it up backwards. Likewise, I made a label indicating the positions of J3, the programming jumper. Note: after programming, wait 1 minute until applying power again (Strange).

Manual link here: http://dccspecialties.com/products/pdf/man_psxar.pdf

Putting it in a box

Good idea! I bought the specified Radio Shack box, number 270-1805. The problem is that the board will just sit on top of the box, so you cannot put the top back on. You need to mill out the supports inside to let the board sit down in it. I took a 1/4" router bit and milled out the 4 corner posts, and all the little "ribs" on the sides to a depth of 1.15". You will probably have to get a Dremel tool with a sanding drum to smooth out the inside flush.

Now there is room for the 2 transformers underneath to clear, and plenty of room above the board for the heat sinks and a lid.

You will need to round off the corners of the board to a larger radius, and sand off the little "nubs" on the short edges of the board. It will now fit down inside nicely. Drill a hole in each end to get the input and output wires to the connectors. (This one is not mine, R.J. just had to show off and buy the unit with the switch machine controller built in, thus the extra screw terminals)


Alarm / buzzer

First, I bought the sonalert alarm "buzzer" they mention in the documentation just for the heck of it. The Digi-Key part number specified was good, but the minimum order is 500 pieces!. Well, I found them at Allied electronics. Manufacturer Motorola MSR320R, Allied number 854-0084, $4.62 each.

The board has no markings as to the polarity to connect it. The pads where it will solder are different shapes, one round, one square (viewed from the board top). The square pad is the plus, and the round pad the minus.

Heat sinks for high power operation

DCC Specialties states that you need heat sinks on the two rows of 4 output transistors if you run over 8 amps.

Well, I went over that setting the first day with just 2 USAT F3's. Seems the current spikes shut the unit down.

So they specify 2 Digikey #294-1085 heat sinks. I notices when ordering them that the heat sinks were for THREE TO-220 packages, but figured DCC Specialties knows what they are doing, maybe the transistors are closer together. WRONG. There are 2 rows of 4 transistors. These heat sinks will not span 4 in a row, and will not go from one row to the other. Call them and get their heat sinks, you use 4 of them, and each heat sink spans from one transistor in one row to the other transistor in the other row. They are still just barely long enough to span the transistors.

To attach the heat sinks to the transistors, you need a thermally conductive compound. You could use thermal epoxy.

DCC Specialites recommends getting Digikey #BER158-ND two sided .005" thick thermal tape. Well this comes on a 10" square sheet for $41 !!, and to top it off, is no longer stocked at Digi-Key.

I found an alternative at www.sidewindercomputers.com, it's Chomerics Thermattach T412. This is absolutely the best stuff around, albeit expensive. It was $19 for a a sheet about 5x7. You only need a fraction of this. You can find other thermal tape, but since my stuff is enclosed and not fan cooled, I went for the gusto. It's some pretty sophisticated stuff, an aluminum mesh with metal in the adhesive.

The picture below shows the unit in the box, with the sonalert buzzer and the heat sinks. Note I did some labeling so I don't screw up.


Using it:

I marked the input and output terminals with large labels so I did not get confused.

Just below the green input block you can see a small surface mount LED labeled D12. It is on when there is input power.

Just above right hand row of transistors, another surface mount LED labeled D7, indicating output

To the left of the programming jumper (blue plastic in this picture) is D6. This is the status LED:

  • off is normal
  • on is short
  • blinking is an indication that the output is reversed (this is fine).
  • this led also blinks about 4 times quickly when a cv or address is programmed`

 I found a reference to D10, and will have to look on the board for this.


Programming notes

Accessory address 2042 will turn the output on and off.

CV 49 sets the current trip point.

CV 53 enables/disables inrush boost. 0 disables, any other value enables.

CV63 controls address programming point, but also setting it to 42 sets the unit to factory defaults, default value is 0


Unanswered questions: ***need***

Which of these is D10? Is this number one above? (mentioned on page 6), most likely a mistake in the manual

In any case, a great product, there has not any autoreverser with these features, highly recommended.

Weather Underground PWS KCACARLS78