# Smallest DCC decoder for large scale



## riderdan (Jan 2, 2014)

I looked around the forums, but wasn't able to find exactly what I'm searching for, so thought I'd ask here...

I have a very small speeder project. It's based on a Bachmann PCC trolley block which just barely fits in the body, so _really_ tiny. I've finished the body and have it pretty much looking how I want and running on DC. However, I want to add a decoder. I tried an ESU 53614 (I'm actually not sure where I picked that one up) but the 24v seems to have killed it. I have a couple large scale decoders (Zimo and NCE) but they're much too large to fit in the speeder.

So, I'm hoping someone out there has used a physically very small decoder, say about 1 amp, in a large scale project and can recommend it. I think a higher-end/good HO decoder would work... but was hoping someone with actual experience could comment on something that is known to actually work. I'm not particular as to brand and don't need sound. But it has to be really small.

Help!


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## Greg Elmassian (Jan 3, 2008)

Get a Zimo HO decoder, around 2.5 amp capability, sound, small, and will handle G scale voltages... MX645

all specs on this page: http://www.zimo.at/web2010/products/lokdecoder_EN.htm

Greg


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## Dan Pierce (Jan 2, 2008)

All present Zimo decoders will work at 30 volts and some are 35 volts and have a peak surge at 50 volts.
I used one smaller than a thumb nail (non sound) in the barrel of Gustav and set it to control motor, front/rear lights plus ditch lights. 

The MX645 (has Programmable sound) with wires is rated at 1.2 amps.
The MX645P22 has an adapter board with it and goes to 1.8 amps (2.5 amp surge).


Zimo MX621 specs:



 0.8A (1.5A peak) total output capacity
 4 output function (.8A combined limit)
 Size (inch): 15/32 x 21/64 x 3/32 | (mm): 12 x 8.5 x 2.2


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## John Gaarde (Oct 11, 2008)

I have used a Digitrax DH163D in an Accucraft RGS #1 Rail Inspection Car for years. It has worked well. It is 1.05" x .67" x .25" and rated at 1.5 amps, 2.5 amps peak. Digitrax doesn't make them any more, but they are still available for about $30. John


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## Paul Burch (Jan 2, 2008)

I don't know if this will help in your case or not.
http://forums.mylargescale.com/40-rc-battery-operations/27928-speeder-airwire.html


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## Greg Elmassian (Jan 3, 2008)

The decoder I mentioned is sound with a 3 watt amplifier. Much more fun.

Greg


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## riderdan (Jan 2, 2014)

Thanks all.

Greg, the MX645 looks good--but I don't even have room for a sugar-cube speaker. Once I get the decoder in it I'll post a picture. But essentially it's a plasticard shell over the Bachmann PW motor block without a millimeter to spare inside. I did go with a non-sound Zimo decoder--thanks to the reminder from you and Dan. I've bought a few Zimo 69x's and I love all the features, but they're way too big (and pricey) for this little guy.

I hope to get this put together this week and will post a pic.


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## Greg Elmassian (Jan 3, 2008)

Love to see a picture of your speeder. I'll say that you can do some amazing stuff with speakers nowadays, I model Z scale and we put speakers in them.

Greg


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## Dan Pierce (Jan 2, 2008)

The MX621 is under $30 from Trainli.


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## riderdan (Jan 2, 2014)

Here's a picture of it...










The wires you can see at the back are from the wiring of the block. There's a space at the rear where the body shell is just longer than the motor block--there's about 1 x 2.5 x .25 of space to fit a decoder. Not much room at all. In fact, in order to get it as low as I wanted, I had to remove the side brackets and file down the locating pin that was on the top of it as it shipped from B'mann.

Here's a front view, where you can tell just how rough the figure is. Also, it's clearer from this angle that I need to laser cut a narrower windscreen.










The LEDs aren't in the headlight housings yet, as I haven't got the decoder in hand. They're just styrene tubes. The housings will be forced round once the LEDs are in them--they're a little wonky at the moment.

This started as four or five laser-cut pieces drawn up in Corel. I measured the motor block to get the wheel openings right, and use styrene strip for the radiator grill. 

My original inspiration was this:









In fact, when I got started I drew it up pretty much exactly like the image. But I thought that it was a little boring, and since this was my first scratch-built project, I wanted it to be powered by an off-the-shelf block. So I changed it up

Once I get the decoder in it, I'll finish up by installing the headlights and an narrower windscreen, fixing the figure, and painting a stripe on the side.


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## Greg Elmassian (Jan 3, 2008)

Very cool!









Being me, I'd still try to find a speaker, like the sugar cubes we use in Z, but very cool speeder nonetheless.

Greg


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## Dan Pierce (Jan 2, 2008)

If you make a single axle trailer for this unit you would have a lot of space for a speaker and sound decoder!!

I still run the single axle boat trailer from the Mystic 2004 convention behind the Mystic LGB porter.


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## riderdan (Jan 2, 2014)

Greg Elmassian said:


> Very cool!
> 
> 
> 
> ...


Thanks Greg.



Dan Pierce said:


> If you make a single axle trailer for this unit you would have a lot of space for a speaker and sound decoder!!
> 
> I still run the single axle boat trailer from the Mystic 2004 convention behind the Mystic LGB porter.


I thought about that, but part of it's charm (I think) is it's diminutive size, which is sort of spoiled by pulling a trailer. I did consider a toolbox/crate on the back behind the driver, but even that would be too small for all but the tiniest decoders.

I thought the ESU HO decoder I had was perfect, but apparently it couldn't handle the voltage, as I let out the magic smoke  Once my Zimo decoder gets here, I'll finish up and post another picture (unless that "Squirrel!" thing happens again)


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## Greg Elmassian (Jan 3, 2008)

The only HO decoders I have found to easily handle our voltages are the Zimo, I have had ESU and Sountraxx not work at all.

Greg


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## riderdan (Jan 2, 2014)

Just to close this off...

Size comparision to a Hartland Mac


















I still have a bit of cleanup to do on the windshield. And I need to add lenses for the headlights, since the LEDs weren't quite big enough to force the openings to round.

But mostly I'm happy with it.

Videos below


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## riderdan (Jan 2, 2014)




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## riderdan (Jan 2, 2014)

One more to show how tight it was getting the decoder in (a little fuzzy, because phone cameras are like that  )[


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## Greg Elmassian (Jan 3, 2008)

Time to get a new phone, my phone is 16 megapixel, often better than most "real" cameras.

Greg

p.s. love the speeder!!!


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## rdamurphy (Jan 3, 2008)

With something that small, do you really need a motor block that big? I mean, you could use an N or HO scale drive, and simply extend the axles out. Then you'd have enough room for a Z scale layout in the trunk...

Robert


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## Dan Pierce (Jan 2, 2008)

HO motors may not last. My guess is that any motor would need to be 24 volt rating in order to not over heat from the 24 volt pulses (motors are pulse controlled) in large scale. LGB does have some small motors as in the Gustav and Chloe engines and these are 24 volt motors.


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## riderdan (Jan 2, 2014)

rdamurphy said:


> With something that small, do you really need a motor block that big? I mean, you could use an N or HO scale drive, and simply extend the axles out. Then you'd have enough room for a Z scale layout in the trunk...
> 
> Robert


Good point, Robert,

I thought about using a different "scale" motor, but as Dan mentioned, I was uncertain if it would stand up to the 24v I have on the track. I think you can limit the output voltage by setting CVs 5 and 6, but I'm pretty sure that's actually dependent on the output of your command station. In other words, if I do the math and set the max to 1/4 of my 24v command station output, then put it on another layout, it's going to be getting a different voltage. (Probably lower--but...) Also, if the decoder is reset and you forget to re-write these CV values, you'll let out the magic smoke.


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## Greg Elmassian (Jan 3, 2008)

No, you cannot limit the voltage, the FET transistors turn FULL track voltage on and off in pulses, this is how PWM works.

The motor basically "averages" the pulses, but it makes heat. A 12v motor on 24v PWM is not great. You would do best to put a voltage dropper in line with the motor to reduce the voltage:

On this page: http://www.elmassian.com/index.php?...ctronics&catid=19:trainelectronics&Itemid=353

You should be able to use a 1 to 1.5 amp FW bridge and a few diodes to do it.

Greg


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## Dan Pierce (Jan 2, 2008)

And there are diodes that drop .7 volts (silicon) vs. the .3 volt drop (shottky) of others.
For a large motor use 3 amp diodes, small ho motors a 1 amp would work.


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## Greg Elmassian (Jan 3, 2008)

yes, but a full wave bridge is even more compact than separate diodes, and the circuit I showed will be the smallest physically, or at least what a normal human can solder up.

The circuit I showed was the fewest components for the most voltage drop, and remember you need a "bipolar" dropper, it needs to work with both polarities.

Greg


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## rdamurphy (Jan 3, 2008)

You might be able to put a speaker inside the driver, if you hollowed him out, you could probably realistically add a "pot-belly" to him if you needed the extra room.

Robert


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