# Smoke units



## gc53dfgc (Apr 13, 2010)

This is more of a question for Sean/NIMT, but anyone that knows the answer or has electrical experience can answer and provide help. 

Alright, so I have a little 0-6-0 NYC steam engine that I plan to soon convert to DCC from DC. It is a Bachmann unit that has a smoke unit built into it, I already plan to keep the smoke unit but have it separate from the decoder and connected straight to the wheels (I also plan to have a small switch mounted to turn it on and off). 

My problem is that an analog (DC) layout is of course powered by DC current, whereas a Digital (DCC) layout is powered by AC current. So can this stock smoke unit that was made to run on a range of DC voltages be used on a DCC layout with the constant 18-25 volts or do I need to find a new one that works both ways or put a resistor in line?


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## gunrunnerjohn (Nov 10, 2010)

You could install a bridge rectifier between it and the track, problem solved. It'll run on AC or DC at that point.


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## gc53dfgc (Apr 13, 2010)

The only problem is those can be large, and in HO scale finding a hiding place could be hard.


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## gunrunnerjohn (Nov 10, 2010)

Actually, a 1A bridge can be pretty small, and I can't imagine you can't find room for a 6 pin mini-DIP package in there somewhere!


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## gc53dfgc (Apr 13, 2010)

I think it could all fit in the tender, the problem is there are no connections from engine to tender, and the tender has plastic trucks and wheels. I was hoping not to need a large amount of cables from engine to tender.


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## gunrunnerjohn (Nov 10, 2010)

I'm talking a package that is about 3/8" square and 3/16" thick with four leads that you can trim? Are you telling me you can't find a place for that?


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## NIMT (Jan 6, 2011)

gc53dfgc said:


> I already plan to keep the smoke unit but have it separate from the decoder and connected straight to the wheels (I also plan to have a small switch mounted to turn it on and off).


That would be a losing proposition as the smoke unit will burn out in nothing flat as it will be running a full capacity all the time!

The #1 best way to do it is put in a second decoder that will drive the smoke unit off or it's motor outputs, that way as the speed of the loco increases so does the smoke.
You will also need to be able to isolate both decoders at different times so you can program and set them up individually, they will get the same address but a different speed curve to allow the smoke unit to slightly run at 0 on the throttle. If you want to get tricky you can even control the second decoder with the first to make the second decoder turn on and off with a function control.

Yes you can run a smoke unit directly from the rails.

#2 Way to do it is to use a function to drive a relay or SCR to run the smoke unit, but again no control it's just full out all the time!

#3 It is also an option it to use the drivers and a cam unit to pulse the smoke unit on and off, that's very complicated to do but if you have a fan driven smoke unit it gives you an incredible look!!


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## gunrunnerjohn (Nov 10, 2010)

We do that in O-scale all the time, it's great to see the smoke synchronized with the chuff, very realistic.


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## NIMT (Jan 6, 2011)

Soundtraxx makes a very nice cable conection from the tender to the engine for just such installs!


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## gc53dfgc (Apr 13, 2010)

Well with the connection from Soundtraxx, and the bridge, I should be able to mount a switch in the tender and have a resistor in line to bring the constant voltage it receives down to a safe level. 
The second decoder idea is also a very good option. I suppose that the motor decoders 1A max is enough to power the smoke unit without to much draw correct?


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## gunrunnerjohn (Nov 10, 2010)

A resistor in series with the smoke unit doesn't seem to be that keen an idea, it'll be dissipating quite a bit of power, no?


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## gc53dfgc (Apr 13, 2010)

I figure the same type of resistor rated for like a 6 volt bulb, just at the proper amps pull.


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## gunrunnerjohn (Nov 10, 2010)

Think ohms law. Bulbs don't need nearly as much current as the smoke unit. Let's say you have 12 volts and you want 6V for the smoke unit. Assuming that it draws 1 amp, that's 6 watts you're dissipating in that resistor. So, you're going to need at least a 10 watt resistor, and the sucker will be getting mighty warm!


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## gc53dfgc (Apr 13, 2010)

hmm, it is looking like doing a dual DCC install is the only way to go.
Well thanks for all the help thus far. I will try to keep either this thread or the DCC one updated as I work on this project.

I guess I need to find out how many amps a smoke unit in one of the Bachmann 0-6-0 units uses.


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## gunrunnerjohn (Nov 10, 2010)

I have no idea what the smoke units in the HO stuff uses, but I'll bet Sean does.


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