@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.
