PS2/3 smoke unit input voltage

So here is the problem. You bought a PS2 smoke unit meant to be driven by smoke outputs on a PS2 or PS3 board. And while yes, PS2 might use roughly 6V and you can test a PS2 board smoke output by plugging in a 6V lamp, it's not the same thing.

The fact is, PV is a (the voltage that drives a PS2 headlight and smoke resistor- the board controlled transistors are PWM/Duty cycle controlled to approximate that correct average power. Again, this is a track voltage rectified source, however the return path (negative) to the control board PWMs/Duty cycles so it's NOT track power either.

@Darrell posted:

I bought from MTH a PS2/3 smoke unit to upgrade my Williams GS-4. The loco has a regulated 6v power board in it that ran the original smoke unit and lights. When I hooked up the MTH unit to it the smoke was ok but nothing like what MTH smokes units can do.

Do I need to hook this up straight to track power? I will be running 18v DCC to the track, would it have to be rectified first? That should give me ~16.5vdc to the smoke unit, is it enough? NO, do not connect that unit directly to track power.

This is the unit I got:

SMOKE UNIT / PS 2 & 3 / 7.5mm POST HEIGHT / 25mm W x 36mm L / BRASS CUP 4.6mm H
Item# AA0000057

You slammed 8 ohms worth of resistance (2 16 Ohm resistors in parallel) and the DC fan, on a 6V DC output.

That equates to roughly 750mA cold for the heater which will reduce as it heats up. Then pushing 6V to the fan is on the high side of voltage, probably screaming away at top RPM.

And you may be pushing that 6V regulator near it's limit thermally and/or seeing sag on the DC.

The correct unit would be use a PS1 style for direct track power that is meant for variable track voltage.

Found on the upgrade page. https://www.mthpartsandsales.c...ts/240?type=products

This topic is also related to somewhat a similar situation. Good read https://ogrforum.com/...79#47889442589426979

Thank you, I will be using fix voltage on the track. This will be a command controlled loco. The smoke fan will be ran by  a JWA super chuffer 2 board, not the 6v board that is already in the loco. I'm just trying to find the best way to power the smoke heating element(s).

I looked up the regulator on the 6v board, it's rated at 1 amp.

@Darrell posted:

I looked up the regulator on the 6v board, it's rated at 1 amp.

Right, but it's a linear regulator. That means it wastes a TON of heat proportional to the load. Example, 18V DC, 6V regulator, it's dropping 18-6=12V. More appropriate wording is converting 12V and proportional load current to HEAT.

Example Williams regulator from the Baldwin. 780X series with 1A diodes as the rectifier

Using an online linear regulator heat/power calculator:

18V source

6V linear regulator

750mA load current

= 9 Watts of heat from the regulator (12V times 750mA)

Meanwhile, the smoke resistor only sees 6V times 750mA= 4.5 Watts

I don't have to use that power board, I can use a more efficient buck converter with a bridge rectifier if that will work. I just need to know what the proper input voltage to the heating element is. Would like to keep it under 2 amps as well, I have a pair of PS/2 F3's that pull less than 2 amps with all 4 motors and both smoke units running, I should be able to get this to work. Something like this.

I found my answer. This unit will work perfectly for me. Digging around the MTH parts site yielded the information that they use 2W resisitors, 5 volts across 16 ohms is ~ 1.5 watts - Bingo! 5 volt power is what I need! Thanks for the informative discussion!

Truthfully, for TMCC applications of the MTH smoke unit I replace the two 16 ohm resistors with one 20 ohm resistor and run it from the smoke output of the R2LC.  This gives be excellent smoke and I don't need any aux power supply.

My DCC decoder won't do smoke output, so I have to build something to power it and turn it on and off by the remote. Think I have it all figured out now. I do believe working on radars was easier!

@Vernon Barry, you are correct as you always seem to be. I should have bought the PS/1 unit.