Wiring a smoke generator to a dcc decoder?

[Tylerf]

Hi everyone
I'm trying to install a 8volt smoke generator to a digitrax dh123, but I'm not sure which way is best to connect it or if there's any kind of resistors needed? If anyone knows a bit about this I would greatly appreciate the help. Thanks

[Hunt]

DCC works best with clean track railheads and clean equipment electrical pickups/wheels.

I suggest you not use smoke generator but it is your railroad and your time to keep things working.

Check the current draw of the smoke generator you want to use. It may exceed the Amp rating of the function output of the decoder.

[Tylerf]

Thanks that should help.

[lmackattack]

if you want to turn the smoke on and off I would wire it to the function 5 or 6  wire output. Then if you want you can link the smoke function with other functions on the decoder. you can simply press the F5 or F6 button to turn on/off... or if linked with another function such as the bell your smoke only will turn on and off with the bell buy useing the F1 Key

If the max power is 8 volts I think you will need resistors to bring down the voltage to the smoke machine.

The down side with smoke is that it oils up the track and will leave a film.

[Tylerf]

Ok great that's what I was hopeing to do. So I'll just have to do some voltage and draw test and I'll be good. As for the film I don't care because my layout is situated in my half done garage so constant track cleaning is all ready required.

[Len]

You don't say whose smoke generator your using, and some of them can pull a hefty current load, regardless of operating voltage.

You might want to consider using the function output of the decoder to trigger a relay on/off that actually controls the power to the smoke unit, rather that connecting it directly to the decoder.

Len

[Tylerf]

Oops ya it's a lifelike generator, and I also didn't mention it's being installed in an atlas dash 8-40cw. The loco has a perfect empty space under the exaust stack. I can't find any function leads that have 8-9volts running through them so I think I may bypass the decoder and just run the generator in paralell with the track leads and add a micro switch hidden in the radiator.

[Len]

Then like I said, there should be room for a low control voltage solid state or micro-sized relay rated to control 12VDC to handle the track power to the smoke unit. Then you can use the decoder function output to trigger the control side of the relay.

I've done this with some old American Flyer locos that I converted to DC can motors and DCC control. The decoder only has to supply a volt or two to trigger the relay. The main relay contacts actually handle the track voltage to the smoke unit.

Len

[Tylerf]

Thanks for the help.

[Jim Banner]

If you use a relay, be sure to connect a snubber diode across the coil.  Otherwise the inductive kick when you turn the relay off is likely to damage the accessory output of your decoder.  A snubber diode is an ordinary diode (e.g. an 1N4401) with the cathode end (white bar) connected to the end of the relay coil that connects to the positive (blue) decoder lead.  Be sure to install the snubber diode right way around or it will damage the decoder output.

I assume you know the difference between connecting one item across or in parallel with another item as opposed to connecting them in series, and that you can calculate the resistance and wattage of the required resistor, once you have measured the smoke unit's current draw.  If not, don't hesitate to ask.

It seems with relays that the smaller unit the larger the price.  If you balk at the price of a really small relay, consider using a transistor.  One small transistor and two resistors can easily multiply the current output of a decoder by a factor of 10.  Circuit diagram on request.

[Tylerf]

Alright, thanks I think I have all the required information for the project and I'm really exited. Now if only I could get the quality of smoke in ho as in say g scale locomotives:) it's quite impressive the thickness and realism of smoke in those diesels.

[Hunt]

Best smoke generator I have seen in a HO scale locomotive is used in MTH smoke equipped steam locomotives. They are synchronized puffing smoke timed to drive wheel revolutions. One will test the home smoke detector. 

[Len]

Jim,

I went and looked in one of he AF locos I converted a while back, and your correct about the diode. I did them long enough ago I forgot about it. Thanks for the reminder.

Len