PS-2 upgrade, can this be safely done?

I would guess that a relay would be best.

G or Stan would be best to answer. I know that you know more than I do about this stuff Chuck!

I've just been in contact enough to say that the board was near it's capacity with what was connected. I think that's a factor in the development of PS3. Again, I'm only guessing. I can't help but ponder over the answer!

My next question would be hooking the Suethe unit to the heater output. Off the top of your head, does anyone know the heater voltage output on L/M/H? I know I can check myself, but has someone already done this type of conversion?

Well if you're asking me.....?

 Someone told me that it's handled differently than you would expect. Just like measuring the lighting voltage. The power is applied in waves (cycles?) or something like that. Otherwise, it couldn't handle the amperage draws full on. Obviously, there is still a voltage spec somewhere.

 I really need to find my old notes from those guys! This stuff is over my head. I know just enough, to keep safe. Where's those darn engineers?

I suspect an MTH guy could tell you what the fan motor output can deliver for sure but consider these motors draw 30-50ma  with no load. Lionel uses a 100 ma regulator to drive them on some smoke units. I would measure the resistance of the smoke unit, then figure what 5V driving that resistance will draw. 

Pete

Don't try to use the motor output, the Seuthe unit requires several hundred MA at least, it'll load down the fan motor circuit!

The heater output varies during operation and according to the smoke level setting.  You won't have too much luck measuring it directly as it's a PWM signal and a normal voltmeter won't give an accurate reading.  Given that the smoke resistor pair in the smoke unit is 8 ohms, and the maximum power you'd likely want to see in the smoke unit is in the 7-8 watt range, I'd figure that the maximum effective voltage you should plan for is around 8 volts.  The Seuthe units are designed to run at 6 volts, so you may need a couple of series diodes to drop it a little to avoid burning out the smoke unit.

Yeah, ..... what they said!

Just leave the original CV inplace and switch for smoke on and off.  Trying to put it on the PS-2 will result in an over load of the 5V regulator which drives the processor power supply and other chips.  Not worth the risk especially if the element goes bad or shorts.  G

Putting it on the smoke heater output won't overload the 5V supply.

GGG posted:

Just leave the original CV inplace and switch for smoke on and off.  Trying to put it on the PS-2 will result in an over load of the 5V regulator which drives the processor power supply and other chips.  Not worth the risk especially if the element goes bad or shorts.  G

Now U show up!

Just kidding G. Thank you, again.

gunrunnerjohn posted:

Putting it on the smoke heater output won't overload the 5V supply.

Of course not, I was talking about if put on the 5V source.  I realize a desire to try to gain control of those units, but it would be better to just use a relay as previously stated or apply KISS and leave it alone.  They ain't great smokers to begin with.  G

To be truthful, I've never even considered trying to control the Seuthe unit from a PS/2 board, so I don't have any actual experience.   I did recently do a TMCC version where I kept the Seuthe unit, I fed the TMCC smoke output into a small switcher, set the output to 6V, and powered the smoke unit with that.  I will confess, if it's reasonably possible to offer command control of the smoke, I'll strive to do that.

I must be missing something.  If this is a steam engine wouldn't the fan motor voltage be pulsing on/off with each puff?  So even if the fan motor voltage drives a relay so as not to burden the 5V power supply I don't think this is the way to go.

I believe GRJ has a workable idea - connect it to the heater output compensating for any power mismatch.  I'd have to think about it but you may want to use a resistor (vs. diodes) to burn off any extra power.  The PS/2 heater circuit regulates power into a resistor - not voltage into a resistor. Hence it stands to reason that diodes (which drop voltage) might not be the way to go.   What is the Seuthe resistance?

The cold resistance of the 6V Seuthe smoke unit that's commonly used in Williams/Weaver/3rd Rail is 9 ohms, at least several of the ones in my parts box.  I still like the diode(s).

Are you thinking of a parallel resistor?

Series resistor.  A series resistor cuts power by the same percentage independent of the PS/2 heater bus voltage (so-called PV voltage).  A diode dropper cuts voltage by some fixed amount so the percentage of power diverted changes with bus voltage. 

So the Seuthe is nominally 4 Watts (6V x 6V / 9 ohms). 

I don't know the PS/2 smoke heat power levels for the engine in question but let's just say it's 8 Watts for simplicity.  If I put it a 9 ohm series resistor I know I will cut power in half all the time.  If the PS/2 drops heater power by, say, 25% to 6 Watts when the engine stops then the Seuthe will also see a 25% power drop to 3 Watts.

The key point is the PS/2 electronics controls the squared-voltage because Power = V x V / R.  So if you insert a diode drop which only reduces Voltage (not Voltage-squared) then you'll get an "exponentially" incorrect change in power when the PS/2 smoke controller changes power settings.  Of course I have no idea if the error is material or just mucking around in the noise.

I suspect that the PWM drive to the PS/2 heater is a fixed ratio that is based on the assumption that the heater is 8 ohms and not based on measured power consumption.

It would be nice of someone that actually knows how the innards of the heater algorithm works would comment.   One interesting fact is that there is special firmware to deal with the small single element MTH smoke unit that's found in stuff like the VO-1000.  It has a single 8 ohm resistor and obviously takes lower power as it's a pretty small unit.

They do have an algorithm that controls current which obviously effect the wattage.  It also measures Track voltage and compensates base on that, for conventional mode as example. 

If you want to run off PV go for it, your not going to hurt the PS-2 FET, but may lose the smoke unit.  G

stan2004 posted:

I must be missing something.  If this is a steam engine wouldn't the fan motor voltage be pulsing on/off with each puff?  So even if the fan motor voltage drives a relay so as not to burden the 5V power supply I don't think this is the way to go.

I believe GRJ has a workable idea - connect it to the heater output compensating for any power mismatch.  I'd have to think about it but you may want to use a resistor (vs. diodes) to burn off any extra power.  The PS/2 heater circuit regulates power into a resistor - not voltage into a resistor. Hence it stands to reason that diodes (which drop voltage) might not be the way to go.   What is the Seuthe resistance?

I was not recommending it, but what would it matter.  At low speed you would have pulsing to smoke unit.  At higher speeds there effectively is no pulsing.  I still think another 9 ohm load on the 5V regulator is not wise.  But your basically replacing the 12 ohm smoke fan motor.   G

GGG posted:

They do have an algorithm that controls current which obviously effect the wattage.  It also measures Track voltage and compensates base on that, for conventional mode as example.

I realize they control current, but they obviously also know that they have the smaller smoke unit and control the current at a lower value.  I'm just wondering are actually measuring the current, or just supplying the PWM signal based on track voltage and the smoke level they are trying to maintain.

I think it is just programming based on order speed and track voltage.  Based on steam versus diesel.  I do not think they specifically measure the current.  G

I may have to break out a Seuthe smoke unit and see if it works connected to the smoke heater output of a PS/2 board.