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Have USA G Switcher hook up smoke generators

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JRad:
There are no transistors in the USA Trains smoke circuit. The square item on the board is a bridge rectifier and the three legged device is a voltage regulator.

The LM-3S-G outputs are all switched grounds.  Source voltage is EITHER the +5 terminal or the V+ terminal. V+ will output a volt or two under the battery voltage due to circuit losses.

I agree that you need a relay or a power transistor circuit for the smoke. Trying to pull that much current through the LM will either shut it down, or burn it up.  You could use either a 5 volt or 18 volt relay with one side of the coil attached to an output (ground) and the other side to either +5 or V+ depending on coil voltage.

Many of us that run battery power just eliminate smoke units because they use too much power reducing run time.

Alan:
So, it is a LM7805 regulator in the picture? Interesting that it doesn't have a stabilization capacitor. Out of curiosity, what is the 5V supply used for on G locos? Bulbs and LEDs maybe?

What is the small transistor used for?

Joel W:
Check your chip - the separate 3 wire device that is attached to the weight.  On both my NW2s it is a single TIP 122 Darlington transistor and only used for the smoke - the light bulbs are high voltage bulbs, On most of my other USA Trains engines there are two transistors - both voltage regulators - and the bulbs/LEDs are low voltage.

As others have mentioned, be sure to put a diode (like a 4001) across the relay coil leads to block the backwards voltage spike that will occur when the relay turns off.

Alan:

--- Quote from: Joel W on January 18, 2021, 08:19:29 AM ---Check your chip - the separate 3 wire device that is attached to the weight.  On both my NW2s it is a single TIP 122 Darlington transistor and only used for the smoke.

--- End quote ---

That makes a ton of sense. Exactly what is expected. Now we also know why the package isn't mounted to the board. I imagine the weight makes an excellent heat sink which will certainly be needed in this application.

Still curious why the little transistor...

MichaelK:

--- Quote from: JRad on January 17, 2021, 06:33:49 PM ---Many of us that run battery power just eliminate smoke units because they use too much power reducing run time.
--- End quote ---

Yep! There's the best answer right there. USA Trains - I have four GP-9's, one F-3A/B combo, and one NW2. Drains the batteries like there's no tomorrow, so I took all of the smokers out of 'em.

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