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Is is possible to control a PS2 slave board with a PS3 upgrade board?

I am adding PS3 to a B unit that will be sandwiched between two premier F7 A units, PS2 3V vintage (my friend didn't give me the model numbers). The current plan is to have a ten pin tether pass thru the B unit to the trailing A unit (which is the slave). I thought it would be cool to MU the B and trailing A in order to keep functionality of the rear coupler and lights.

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I initiated and was responding to this post using my cell phone and somehow deleted Vernon Barry's response. A copy was sent to my email, which I included below to help anybody who may have similar thoughts of tethering a PS2 slave unit to a unit with a PS3 diesel upgrade board (don't do it):

"The PS2 slave board is an analog board- think of it as a repeater. It's designed around incandescent lights and basically PS2 expected signals.

Yes, when using a PS3/2 stacker board, the wiring harness is retained and thus the signals and voltages/currents are all basically PS2.

However, if you ripped out the wiring harness and went true PS3 Diesel board, then I cannot speak on that being compatible."

My project involves adding motors and a control system to a dummy B unit, so no PS3/2 opportunity.

Thank you John and Vernon for you help and insight. 

Need to be clear here.  If doing an MTH Upgrade Kit PS-3 Diesel,(true PS-3 diesel board) you cannot drive a PS-2 slave board.  Only a PS-2 board and a PS-32 board which uses the daughter board top, can control a PS-2 slave board.

Mth does not make a PS-3 slave kit, and no longer makes ABA sets like that. 

Yes, even a PS-32 board (bottom is a PS-3 diesel) needs a resistor if you have a forward coupler, but no rear coupler.

If you just have a rear coupler you're ok.  G

@GGG posted:

Need to be clear here.  If doing an MTH Upgrade Kit PS-3 Diesel,(true PS-3 diesel board) you cannot drive a PS-2 slave board.  Only a PS-2 board and a PS-32 board which uses the daughter board top, can control a PS-2 slave board.

Mth does not make a PS-3 slave kit, and no longer makes ABA sets like that.

Yes, even a PS-32 board (bottom is a PS-3 diesel) needs a resistor if you have a forward coupler, but no rear coupler.

If you just have a rear coupler you're ok.  G

Thanks for chiming in, I didn't realize the PS32 board had the same issue with the couplers.  I was assuming the PS32 board, probably not a good assumption.

So the PS3 boards that are factory installed in steam engines already have the resistor for the front coupler installed since there is no front coupler in the steam engines?

No, because PS3 factory steam is a 2 board system (tender and boiler boards) and each board ONLY supports one coupler and is not subject to the same design limitation of the diesel PS3 board.

Again, in factory PS3 steam, a front coupler may or may not be used, the harness may not even have the wiring.

Again, let me see if I can try to clear some of this up. This is based on my understanding of the situation.

The PS3 diesel board, and that same board being the basis of the PS3/2 stacker set, uses a dual transistor in one package to control the couplers. Further, electrically, we are powering the coupler with DC and the coupler coil being an inductor- would kick back significant voltage when the current stops flowing. Most FETs (Field Effect Transistors) have a snubber diode built in to protect against just such an inductive load voltage spike being turned on and off. The problem is, when you further add wiring and board traces, you get additional capacitance and inductance and being a dual transistor in one package, there may be bleed, crosstalk and thermal considerations- energy has to go somewhere, shunting the spike does create heat. Again, this is specific to the diesel PS3 board, and then transfers also to the PS3/2 stacker because the base board is basically the same diesel PS3 board- same circuit, same components involved.

Again, my theory of what happens why we need a resistor is that if there is only one coupler, that inductive spike- even if shunted by a diode, causes a typical voltage spike "ring" in the circuit. especially since both coupler circuits share the same power return path (N channel MOSFETs switching DC negative-AKA board GND). If you don't have a coupler, connected to one of the paths, the circuit still has capacitance, still is very near and closely coupled electrically, so the firing of one coupler, without a second coupler installed cases a voltage spike in the traces and path, all causing the transistor to fail. Adding the resistor to the unused coupler port simply dampens any unwanted voltage ringing spikes, and prevents the failure.

This is probably one of the better tutorials I have known about this when learning electronics and electromechanics

Again, the point being why you need it is specifically for PS3 diesel kits- when only one coupler is used.

You may need or want it when using a stacker in diesel retrofit, where only one coupler is used.

The exception to the rule is a PS3 steam upgrade kit, or typically a PS2 5V upgrade where a stacker was used, to my knowledge, even though we are using a stacker board set, the wiring harness likely doesn't even have the provision for the resistor to plug into. Analysis- Is it because the stacker board being more wiring path with some capacitance and resistance changes the nature of the potential for ringing? Is it because only the rear coupler is used and somehow, someway, the minor difference between front and rear coupler wiring is enough it doesn't ring? Again, the PS3 Steam upgrade kit wiring doesn't have the provision for front coupler even in the harness.

Last, we don't even worry about this on PS3 factory steam because the 2 board system (boiler and tender boards) are designed around only one coupler per board, and that circuit doesn't appear to be subject to the same problem at the PS3 dual coupler diesel board situation.

It is a simple truth table for PS-3 Diesel boards which means PS-32 also.  Front coupler and no rear coupler (think F and E units) place a resistor in the rear coupler plug.  OR run it with a trailing A that has a coupler tethered to the lead A rear coupler.  As in PS-1 upgrades with dummys.  Since PS-32 can replace PS-2 boards in ABA that had a slave, the slave just passed through the rear coupler function to the trail A.

This means the Lead PS-32 sees and has connected a rear coupler as long as the trail A connected.  Running A only, or AB no rear coupler, just don't fire the forward coupler.

Any combination of PS-3 diesel or PS-32 with rear coupler only is fine.  G

This thread makes me think of something I have been thinking about for some time. I have several 4 motor locos which I intend to convert to DCS or TMCC. My solution for TMCC is to use old TAS boards for which is easy to swap the 8A triacs for 15A .However I have used my last Engineer On Board TAS board  thus no cruise unless I install PS2 or 3 boards then I feel like I need to install a PS board in each powered unit which really runs the cost up. I have read on the forum someone say they are driving 4  385 motors in an AA diesel with one PS board. I have a light hand on the throttle and could probably make do without frying a PS board. I don't have a layout at my house and many of my trains are at my brothers house. I don't feel right telling him not to run my latest upgrade and he tends to drive trains as fast as they will stay on the track and I just don't think PS 2 or 3 boards stand a chance driving 4 motors with Tommy's hand on the throttle. What would be my dream solution would be a slave H-bridge driver board which would connect directly to the motor outputs on a TMCC or Protosound board. A slave driver which took it's commands directly from the motor outputs on the command loco.  Sounds like something you might find on "Gunrunner" alley,           j

MTH always said NO to four.  Folks use ERR CC to drive AA units, and I did a few back in the day.  Customer clearly wanted it done that way.

Slave board input is simple and techs have the wiring diagram.  Motor feeds, RL, IL, MARS, R Coupler, smoke control inputs, PV and PCB ground. 

But you have 4 logic chips used to decipher what the PS-2 board is telling it to do and control the PW to the Motor FETs.  This not just a isolating an input and turning a transistor on.  There is no tach in PS-2 slave it is synchronized to the PS-2 boards motor driver section and they are similar devices.

Don't know how your going to match that to TMCC and how your going to create PV and PCB ground since TMCC doesn't use it.  G

You can drive four motors using the ERR boards, you just have to tether the bridge rectifier to heatsink it for power dissipation.

Some time back, I also designed a little board that buffered the PWM and serial data to allow me to use a separate CC-M in the slave.  The PWM outputs won't drive two boards without a little help, and the serial data gets bogged down with multiple boards as well.

TMCC Motor Driver Buffer 1.2


Images (3)
  • TMCC Motor Driver Buffer 1.2
  • mceclip0
  • mceclip1

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