Wiring a tender pickup roller to PS-3 board.

There are 2 pins side by side for RED 3rd rail pickup (one is not populated in the upgrade kit wiring harness

There are 2 pins for BLACK wires- outside rail or frame common- both are populated one is a ring terminal to attach to frame, the other is the wire going in the tether to the engine harness which has the pickup.

Because the PS3/2 stacker board emulates the original PS2 board pinout and wiring harness pattern you can easily see the PS2 diesel harness showing BOTH pairs of power input wires to the board.

All that said, a quick thought process note about safety and preventing future damage.

If you add a pickup roller to a tender like this and wire it in parallel to the engine pickups, if one derails, there can be short circuit currents across this wiring and connectors path finding the weak link and melting something.

So yes, the upper PS3/2 Stacker board connects 2 pins for 3rd rail and 2 pins for Common, but you would not want short circuit current between the 2 pins- that would possibly damage the board connector and/or trace. Again, you don't want the board and or connector carrying short circuit current.

If you splice into the PS3 steam upgrade harness- example the 3rd rail pickup wire(red) the pro is, a possible derailment short is never seen by the board, it's all in that wiring- but could melt the wire in the tether or cook the connector board at the engine side also connected to 3rd rail.

Recommend putting a fuse or self resetting breaker like a PTC in series with that tender pickup, so normal situation it provides the parallel power path no problem, but in short- the PTC would prevent a total meltdown of the tether.

Again, in that blue wire in the tender pickup setup you have built- put a PTC or fuse- something maybe 5A rated- maybe even less.

It's not if you derail- it's when it happens. Takes a bad day to a far worse day.

Thanks for the reply, Barry!

For the ground, looks like it's all good to go because it is already connected to the tender body. That's good to know.

For the 3rd rail, I guess I'm just a little confused as to why there would be a difference in a short occurring at the engine vs at the tender. They are always going to be on the same track, so I don't understand what the difference would be.

Here's a parts diagram of the engine (PS-1 version), with my crude drawing of the 3rd rail connection wires. Electrically, wouldn't it be the same with or without the new tender connection if a short were to occur?

For the 3rd rail, I guess I'm just a little confused as to why there would be a difference in a short occurring at the engine vs at the tender. They are always going to be on the same track, so I don't understand what the difference would be.

Because, the odds are one stays on the track and only one end (engine or tender) derails. This means one end is properly on the track- but the other end- if pickup roller shorts to outside rail= massive short circuit across this wiring and connectors and one of them is the weak link and goes up in smoke. Worse, because in the tether- there are high and low voltage wires side by side- if you melt one- you maybe short them all- an expensive accident.

If there was ever a common scenario that happens and causes damage- right there is it.

Heck, for the same reasons- this is how your typical unit trains like M10000 and Zephyrs burn up. PTC or Fuse or some form of current limit safety (fast breaker) can prevent cooking these typical tether and connector systems.

ptc-fuse-protection-for-more-than-2-rollers

https://ogrforum.com/topic/ptc...-more-than-2-rollers

PTC and TVS - Some Commonly Used Sizes and Part Numbers

https://ogrforum.com/topic/57038617467733545

OK, I think I understand now. Thanks for explaining!

So this can potentially happen on any engine with dual units, I suppose? I assume Steam engines with built-in tender rollers have this included? The only thing I don't get is why this can't happen on a regular diesel. If the front truck derails and the roller contacts the outside rail, while the rear truck stays on the track and it's roller remains in contact, wouldn't that be the same thing as the scenario with a steamer and tender?

Regardless, I will need to get a PTC. I see this one reccomended on the links you shared and also reccomended by other posts on this forum for connecting multiple units together.

https://www.digikey.com/en/pro...s-inc/MF-R110/259970

I guess I would just wire this PTC mid-line on that blue wire I've added from the new roller? Then continue with the splice into the red (kinda looks like pink in my included picture) 3rd rail feed to the board?

@VonFrank posted:

OK, I thunk I understand now. Thanks for explaining!

So this can potentially happen on any engine with dual units, I suppose? I assume Steam engines with built-in tender rollers have this included? The only thing I don't get is why this can't happen on a regular diesel. If the front truck derails and the roller contacts the outside rail, while the rear truck stays on the track and it's roller remains in contact, wouldn't that be the same thing as the scenario with a steamer and tender?

Yes it can happen with Diesel locomotives (and with lighted passenger cars).  But the consequences are usually not as severe.  A single isolated wire heats up until a weak point becomes a fuse.  It doesn't take down circuit boards or tethers with it.

Bob

@VonFrank posted:

https://www.digikey.com/en/pro...s-inc/MF-R110/259970

I guess I would just wire this PTC mid-line on that blue wire I've added from the new roller? Then continue with the splice into the red (kinda looks like pink in my included picture) 3rd rail feed to the board?

That's a reasonable choice for the protection PTC.  Remember, the link between the locomotive and tender pickups should only draw significant current for a moment in normal operation, so the idea here is to have the PTC trip fairly quickly if the current in that tender to locomotive wire spikes to amps for any length of time.  The time that that link can have extended high current is almost always from a derailment.