PS/2 3V board powering four smoke units

I thought I had heard in the past that there was a way, but I'm not sure if the slave board actually has circuitry to control the slave smoke units or they just get connected through to the master.

I've used two smoke units before, but never four.

I cant remember if it is run through the slave but then again there are only 2 smoke units on a coal turbine

It goes through the slave board, but it's hard to see if they actually buffer the signal.

Theoretically you could use a relay for the heaters.  NO idea how to handle the fan motors.

Not really since the smoke unit outputs are PWM.

If you have a slave board in your hand look at the upper right hand corner as per this photo taken from another thread.

https://ogrforum.ogaugerr.com/t...or-mth-proto-diesels

It appears there's a SOT-223 FET (I can't make out the part number from the photo though) driving the heater pin of the 4-pin smoke connector.  But I don't see a smoke motor fan FET on the board.  Of course the fan drive on MTH is a trickier circuit since it uses a 2nd FET to dynamic brake the motor to create puffing...so additional study needed to determine if the slave tether carries the extra control signals.  Otherwise, if fan drive tied directly to master, can master fan circuit can safely drive 4 (or however many) motors.  Of course since a diesel smoke fan does not start/stop like a steamer, I suppose you could cobble together a simple FET buffer to drive to fan motors in the slave.

The relay isn't going to get it, Matt's right.  I suspect that maybe the TO-220 FET on the slave board is for the extra smoke units, but I'm not 100% positive.

Stan, you may be right, I just looked again.  That does go to the fan connection, so I think they probably use that.  The fan motor isn't much of an issue, the current there shouldn't tax the FET on the master, even if they are tied together.

No Only 2.  2 units drive the effective resistance down to 4 ohms.  So units with 3 or 4 smoke units use the slave board for the other 2 units.

Trying to parallel 4 smoke units off one board would be 1 ohm effective and surely damage trace or fet.  Stan does show the heater FET in his picture.

Look at your ASC notes on Diesel slave units and it will show you the signal wires going to the slave unit.  They are used to trigger the slave components.

I would be careful loading up the 5V side.  Not necessarily the FET, but think of the load on the 1 amp 5V power supply, that is meant to run the micro chips and power the Processor Power Supply.  That is why a bad fan motor can cause a PS-2 board to miss behave.  G

I'm talking about the slave board, it does appear it drives the smoke units with it's own drivers.

I've never done PS/2 in the Centipedes, but I'm assuming that it's possible to drive all the smoke units with the master slave, they somehow do it in production.

Wouldn't 4 parallel be 2 ohms?  In any event with say 20V PV driving 2 ohms that would be 10 Amp pulses which does seem a bit aggressive.

The question is whether the slave board has its own 5V DC supply that powers the "high side" voltage to the slave's fan motor(s).  It looks like a relatively un-cluttered board from a layout perspective so it should be easy to visually trace the fan power source from the 4-pin smoke connector.  If it goes to a local 5V supply (instead of coming from the tether) then it should not load the master's 5V supply.  Then the issue is whether the master's fan FET is capable of driving 4 motors...in my opinion of course.

Stan, My mistake, I did 2 x 3 (using 4 ohms vice 2 x 2 with 4 ohms.  Should of stuck with 8ohms 4 times.  So 2ohms it is.

The FET Stan shows is the heater fet, not a smoke fan fet.

John, Your original post was can a PS-2 3V board handle 4 smoke units.  You should already know that answer.  Not sure when it switched to only the slave board.

The slave does produce it's own 5V DC source to supply the fan, but the fan motor return is not buffered other than a diode and returns via the 10 pin harness to the Master PS-2 3V board.  So the PS-2 3V or 5V fan motor FETs have to handle the current.

Production units with more than 2 smoke fans in the same unit that I have seen usually have 4 truck motors also.  They use the PS-2 with Slave board inside the unit.  Veranda Turbine as example.  If that engine only has 2 smoke units they run them off the PS-2 board.  Probably to save harness wires.   G

John, Your original post was can a PS-2 3V board handle 4 smoke units.  You should already know that answer.  Not sure when it switched to only the slave board.

Actually, that's not really true.  This is my original query.

Is the PS/2 3V board capable of powering four smoke units?  I have a Centipede set that I want to upgrade, does the slave board have it's own power for smoke units in the slave, or is the connection just passed through from the master?

I thought that was pretty clear that I wasn't sure the slave provided the power or it would all have to come from the master.  I think I have my answer, the slave will indeed provide the drive for the extra smoke units and the 5VDC.  The exception is switching the smoke motors.  Hopefully, the FET on the master is up to the task of switching 200-300ma for all four motors.

Does that sound correct?

Correct.  Is there a unit with 4 smoke units?  I have only seen one with 3.

It is funny since MTH recommends only 2-3 bulbs on the fet and bulbs are 60ma ea. 

4 fan motors you would think would draw more current then 3 bulbs, let alone any startup current surge.   G

Well I've converted many a smoke units to use 4 heaters and that's usually around a 4 ohm load. So maybe 2 heaters per each smoke unit then series 2 smoke units then run 2 pair parallel?? I never tried that. The smoke unit Fet is rated at 3.8 amps but I never thought about the fan motor current draw...hmm!

Can always use a mix of different ohm heaters to get the load right.

On some really bizarre conversions with smoke units I've stuffed up to 16 heaters in a smoke unit by soldering 4 in series to form a W then install...4 rows of those all paralled then powered via track power yields some spectacular results! The MTH one gauge Big Boy smoke units have room to do this...could even shove more heaters into those things. If I need say 12 heaters then just make a N and use 4 rows.

To power those via track power I use a Crydom Solid State Relay that's activated by the PS2 heater circuit...those little relays cost $25 each these days

  http://www.digikey.com/product...p;keywords=CC1061-ND

If the smoke heater circuit can power that little relay then I don't see why the fan circuit couldn't??

The A-A Centipede has four smoke units, two in each unit.  That's the one I'm converting.

That is a pretty cool idea!

One issue with using the solid state relay is you can't change the smoke intensity like you can with the native control.

Got it.  Normally that is 2 on the PS-2 board and 2 on the slave.   G

Can you guys talk slower so I can keep up?  

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