DCC and DC smoke generator

[Will1707822018]

Hi Im converting all my dc to dcc and sofar have managed to do 12 engines sofar with 20 togo and a turntable my question is I am now onto my bigger locos like Britania class which have smoke generators Now i have got it fitted with the dcc chip and running but am undecided where to connect the generator wire . Any help is greatfully received.

Thanks

Will

[Chrissaf]

Which brand / model of DCC decoder are you using.

In principle, smoke units can draw more current than some DCC decoders can handle. Therefore you have to match the spec of the smoke unit to the spec of the decoder.

Hornby decoder function outputs are limited to 100mA and some smoke units can draw significantly more than that.

Even if you have a decoder with sufficient current capacity, then there is the issue of how the smoke unit was powered in the DC model. Many smoke units have a single wire on them and use the loco chassis as the return path to the track. To successfully power a smoke unit via a decoder you need to electrically isolate these single wire smoke units from the chassis so that you can use two wires from the decoder to power them. The blue decoder wire is the permanently positive voltage and then either the green OR the purple decoder wire provides the switched negative supply - controlled 'on & off' by a decoder function command.

If you do not electrically isolate the smoke unit from the chassis, then the decoder WILL be damaged when you power it up.

[96RAF]

To get the required amperage to run a smoke generator you may have to gang two functions together as most decoder’s function outputs are limited to 100mA.

The blue wire is a common positive but you could use green and purple switched negative function outputs together, although how you switch both at once is down to the capability of the decoder. Some can be mapped to turn on X when Y is selected, but many decoders can’t do this.

The other alternative is to use the function output to switch a relay that can handle the current required.

Some modern smoke generators are low current drain devices.

Edit: Chris was typing at the same time I was posting.

[ColinB]

The easiest solution is to use a Zimo decoder these have higher function current capability. I successfully used these in my early 80's locos with smoke units. To be quite honest if your loco is relatively old they are a better bet as their max output current is 0.8 amps compared to 0.5 for a Hornby one, with better function capability. Some ringfield motors can draw more than 0.5 amps. Zimo decoders are virtually the same price as a Hornby one at full price. Sadly paralleling up two function outputs is not a good idea as you cannot guarantee that the two functions will split the current equally. I did find that my Hornby smoke units drew less than 100 milliamps, but with tolerance spread it could be more with a different unit. Anyway using a higher spec decoder makes wiring easier.