smoke unit voltage

@joe woods posted:

Can anyone tell me what voltage range the smoke unit motor and heating element operate in or need in an mth-railking proto2 steamer.

Catch22, depending on how you measure it, your meter may not show what you think it should.

Heater power in a PS2 is from PV (Positive Voltage) meaning it's unregulated and directly (more or less) the + side of the main bridge rectifier.

In a typical PS2 steam engine, this power is also passed between the board in the tender and the engine in a unique way over the yellow and white motor wires, and then picked off using 2 diodes from the motor wires to have PV in the engine. This is because in the motor drive circuit- one motor wire is always connected to PV. It's a way of getting PV to the engine without using another wire in the tether. Headlight is ALSO off the same PV.

The return or negative side of the smoke resistor and the headlight are individual wires through the tether back to the board and to transistors on the board to board ground, but PWM'd to limits the effective power.

The fan motor gets it's voltage from P5V (key there is the 5 meaning 5V)- a regulated voltage.  This is a separate wire over the tether for P5V, and I think the tachometer shares that needing a 5V source. The return for the smoke motor is again a dedicated wire through the tether back to the board in the tender for the smoke fan return or negative. It is pulsed for chuffing.

In some engines, those "PV" diodes might be under heatshrink beside the motor or they are in the PCB mounting of the tether connector.

I'll put it this way- sometimes for testing, I take the typical 6V MTH bulb used for all lights in a PS2, and plug that into the harness for smoke heat and motor to indicate when they are working. If the 6V bulb lights up and then pulses with chuff on the fan output- it's working.

Thanks Vernon for the quick reply and info.Can you also tell me how many milliamps the blower motor and heating element each draw?

@joe woods posted:

Thanks Vernon for the quick reply and info.Can you also tell me how many milliamps the blower motor and heating element each draw?

https://ogrforum.com/...oke-fan-what-voltage

@gunrunnerjohn posted:

The MTH fan motors are 5V motors, but I actually test them like Alan states.  If they won't run on 2 volts DC, then I consider them bad.  Also, they should not draw more than 40-45 milliamps at 5V DC.  Again, if they draw more current than that, I also consider them bad.

I do not have data on the smoke unit resistors. It's not a lot, less than 1A for sure. They are individually 16 Ohm resistors, but in parallel presenting an 8 Ohm load. The math says if you feed them 6V, that would be 0.75A, roughly 4.5Watt total at a cold start, but as they heat up, resistance increases, thus in theory decreasing current. Add into that mix the PWM the board is doing and being honest, I just don't have real world values or data on what the current might measure.

Thank you for your info.The reason for the questions are because I recently installed a Blunami 4408 decoder board in a MTH-RAILKING Hudson and spoke to a representative regarding the wiring of the smoke unit to the decoder board.He stated that the limit for the inputs on the board are 400 miliamps. So my question is do either the blower motor or the heating elements exceed the 400 miliamp limit?

Yes, the smoke resistor will certainly exceed that at times.  Also, it depends on the voltage applied to the smoke unit how much current is drawn, and also how much smoke (or flame if it's too much voltage) you see.  You need to balance the smoke heater voltage with the actual resistor value as well as it's power dissipation.

I certainly saw flame on a recent PS2 Mohawk I purchased. First, more smoke than I had ever seen from an O gauge engine. It was really awesome! Then flame after the resistors got hot enough to ignite the smoke oil vapor (everyone should see this at least once). The appearance was like a torch tip from the smoke stack and there was a roar because the fan was fueling the combustion. After I took off the shell I measured 24 Vdc with smoke "ON". That equates to (24)^2/8 = 72 watts. I find that a little hard to believe though. Could a single engine deliver a full 72 watts of power to the smoke unit without something else failing? I posted about it. Still working the problem. For example, what happens if I wire the two resistors in series.

If the FET shorts, you can get a lot of power, normally PV for PS/2 is around 20-22 volts.  However, the 8 ohm load across it would drag it down a bunch, so I really doubt it had 72 watts, but more like half that.  Still enough for a real smoke and flame show.

I've seen a similar thing when the smoke regulator shorts on Lionel TMCC or early Legacy, it dumps 18 VAC into the 8 ohm resistor.  40 watts on a 2W resistor is impressive for 20-30 seconds and then nothing.  If it's a diesel with a plastic shell, it totally destroys the shell near the smoke unit.  Steam just stinks up the inside of the shell, I fixed one for a club member, and years later you can still smell the burnt fiberglass smell.

PV comes from the 8A rectifier direct or via motor lead and lower rated diodes for PS-2 3V steam.  All depends on if the board is in the engine or not.  If the ground side elements shorted to frame of smoke housing you have a short to AC ground and that will source high amps.  The smoke FET can handle higher amps then the normal lighting and coupler fets.  G

GGG and John, really glad you both weighed in. Doing something to get the smoke unit working without breathing fire is on my to-do list. Honestly I want to keep the incredible smoke output but reduce the resistor heat just enough to prevent "ignition". One thought is to somehow wire the resistors in series to go from 8 ohms to 32 and see what happens. I don't really care if I fry the smoke unit I have others lying around.

If it is a grounded element, that is easy fix to clear.  If FETs shorted you won't have control of Heat might want to consider a different method of powering the heating element and install an on/off switch too.  G

@gunrunnerjohn posted:

If the FET shorts, you can get a lot of power, normally PV for PS/2 is around 20-22 volts.  However, the 8 ohm load across it would drag it down a bunch, so I really doubt it had 72 watts, but more like half that.  Still enough for a real smoke and flame show.

I've seen a similar thing when the smoke regulator shorts on Lionel TMCC or early Legacy, it dumps 18 VAC into the 8 ohm resistor.  40 watts on a 2W resistor is impressive for 20-30 seconds and then nothing.  If it's a diesel with a plastic shell, it totally destroys the shell near the smoke unit.  Steam just stinks up the inside of the shell, I fixed one for a club member, and years later you can still smell the burnt fiberglass smell.

All this talk of flames reminds me when I was a kid and stuck a screw driver down the throat of a Lionel turbine ….flames and smoke than poof………I was was disciplined not to do that again. But it was cool to see….

@ThatGuy posted:

All this talk of flames reminds me when I was a kid and stuck a screw driver down the throat of a Lionel turbine ….flames and smoke than poof………I was was disciplined not to do that again. But it was cool to see….

If you really want to "tinker" with the smoke power for prodigious smoke and not cook expensive electronics, my thought would be to have a relay connected to the board smoke output and build your custom circuit for smoke power switched by the relay.  Then you can have any level of smoke power and not risk blowing the expensive board.

@gunrunnerjohn posted:

If you really want to "tinker" with the smoke power for prodigious smoke and not cook expensive electronics, my thought would be to have a relay connected to the board smoke output and build your custom circuit for smoke power switched by the relay.  Then you can have any level of smoke power and not risk blowing the expensive board.

True I was 10 and it was a Lionel Turbine………lmao

Years ago I also had  similar "fabulous smoke" shortly followed by a 6 inch "stack fire" on a brand new 1980's JLC locomotive. Now I know why!!!  Thankyou.

A very impressive and potentially dangerous (and hopefully once in a lifetime) "prototypical"/and pyrotechnical event, in O Gauge.

Needless to say, that loco, with its fire singed stack, went back to my LHS, Hodgsons (south of Buffalo).

GO BILLS ... next year!

When this little module croaks shorted on early Legacy locomotives or smart smoke equipped TMCC locomotives, you get roughly 5 to 6 times the power dumped into the little smoke unit.  The results are as you'd expect, fire and smoke!  I've personally seen it happen twice, and I've repaired probably at least a dozen locomotives that have had the failure.

@john in western pa posted:

GO BILLS ... next year!

Go Eagles ... next year!