PS1 to PS3 to TMCC Conversion Question

I converted a PS1 GP-9 to Blunami control this week.  I found no connection between the electrocoupler coils and the chassis or center rail.  So there should be no issue.

As for the diodes matter, I can't imagine what configuration would involve 3, rather than 1 or 4 rectifier diodes.  Unless a transformer internal to the locomotive is in use (impractical), the choices are half-wave (1) or full-wave (4).

@illinoiscentral posted:

bridge rectifier on the TMCC board (why would you put 4 diodes in a bridge if only three are needed)?

Because there are different parts of the circuit.

The DC can motor controller section uses the full wave bridge rectifier- which by what you said, I'm hoping you recognized DC negative is NOT = Frame AC (ground). However, ERR Cruise and AC/DC commanders in the AC section of the board- use a single ended diode for rectification making it common to AC frame ground. In other words- Lights, Electrocouplers, smoke output, even the serial data, are all referenced to frame AC ground.

Again, ERR commanders typically use TRIACs on the R4LC, which in and of itself is also single diode or half wave rectification for the 5V logic portion of the circuit, and then the TRIACS control AC outputs in reference to the common AC/DC ground.

Edit, and if you you are asking- how can they merge a DC full bridge circuit, and a single ended half wave rectified circuit since the ground reference is incompatible and different? Easy- that's why in the motor driver section- there are optical isolators.

So yes, on Lionel ERR upgrades- one side of the coupler would be in reference or connected to frame ground.

PS3 must use entirely different couplers, and uses DC FETs and the couplers are off of the DC+ bridge rectified PV voltage bus- so no light, output, or input can be in reference to AC frame, because the actual DC negative is not = frame.

And again, there is also a difference in the couplers since that is sort of the focus of this topic.

The original PS1 couplers can be used in an ERR upgrade as the impedance is correct and nearly the same as a Lionel coupler.

For PS2 and PS3 upgrades- you must use specific PS2/3 compatible couplers- included in the upgrade kit because of the different voltage that PS2 and PS3 applies to them compared to PS1.

PS1 coupler= Lionel ERR compatible, not compatible with PS2 or PS3

PS2/3 coupler= PS2 or PS3 compatible but do not use with Lionel ERR.

@illinoiscentral posted:

I see mention of a piece of plastic needed to keep the coupler isolated from the frame when converting to PS3.

Do I need that for TMCC conversion using a Cruise Commander as well?

I would say regardless it is best practice to use that plastic with the MTH style couplers. Why? Because unlike the typical Lionel coupler were the wires are soldered and connected under the tape or heatshrink over the coil- making them isolated but also a place that can need repair to reconnect a wire to coil- example.

VS

The MTH "way", where the coupler has nice handy external solder points to connect wiring to. The reason for the plastic is in some chassis, the exposed MTH style contacts could touch frame ground.

Well, even though one side of ERR/Lionel systems might be frame ground, the problem is you have no idea which side could short- so again as best practice, if reusing MTH exposed contact couplers, you would be wise to take precaution, use some plastic or other method to ensure those contacts cannot short to anything as this too could cause a problem even with ERR.

Thanks to @gunrunnerjohn

@gunrunnerjohn posted:

The PS/1 coupler is compatible with TMCC, the PS/2 coupler is NOT compatible with TMCC, it'll cook the coupler triacs.  It's easy to recognize the PS/2 couplers as they have a flat frame and a patent # on them, the PS/1 couplers don't have that flat frame.

Again, is those exposed solder contacts that sometimes in certain chassis and situations could possibly short to nearby frame or truck grounded metal.

This is the MTH part used ID0000123 https://www.mthpartsandsales.com/shop/search

Sorry gents, earlier today I was poking fun at our illustrious leader, Rich, who apparently converted a DCS engine to TMCC, because he didn't like DCS, or as my wife likes to say "its not my favorite". I then asked about the piece of plastic. Someone at OGR split the reply up for me, thanks. But there is no conversion to PS1 to PS3 to TMCC, its just PS1 to TMCC. I found out about the existence of the plastic shield while reading an MTH document on converting a PS1 engine to a PS3, and tried to keep my post from being War and Peace.

Thanks Vernon, John, that is exactly the info I will need.

Edit: Concerning the bridge rectifier. It amazes me that people that call themselves electrical engineers think that you can take a bridge rectifier and ground both sides and expect it to work. If you connect two nodes of the bridge rectifier to ground, you short out one of the diodes, and if it still worked with one of the diodes shorted, you wouldn't need that diode. So bridges would have three. I believe the Latin phrase is something like reducto ad absurdum, reduced to the absurd. If you can take two sides of an equation, manipulate both sides, and reduce the equation to something absurd, like 0 = 1, then the original statement is false.

The reason why you can have a the white wire of a AC power pack connected to ground, and the outer rail to connected to ground, is because of the transformer.

So if the TMCC board uses a bridge, and then the board ground is not chassis or outer rail.

That plastic insulator is only needed "usually" for steam conversions when the tender axle is directly under the exposed terminals of the coupler.  But as said it doesn't hurt to use it on any upgrade.  G

@illinoiscentral posted:

So if the TMCC board uses a bridge, and then the board ground is not chassis or outer rail.

Your analogy is certainly correct.  However, as it turns out, the basic TMCC electronics uses a frame ground DC reference.  That's not to say that shorting the coupler is a good idea, if it's the hot side it takes out the coupler triac on the R2LC.

@GGG posted:

That plastic insulator is only needed "usually" for steam conversions when the tender axle is directly under the exposed terminals of the coupler.  But as said it doesn't hurt to use it on any upgrade.  G

Correct, I install the insulator only when there's a possibility of the coupler terminals shorting to the axle on the truck.  If there's no possibility of a short to the anything with the full travel of the coupler, I don't bother.