[Branchliner]

I intend to fit a decoder to my HO gauge DD40AX, this loco was claimed to be the largest diesel ever built and was run by Union Pacific, it pushed out 6000 HP using two separate engines.

In common with the prototype the model also has two motors each driving its own 8 wheel truck. Has anyone ever fitted a single decoder to run two motors and if so are there any special considerations regarding the amperage required?

I would like to fit a sound decoder but there is not enough room unless I cut away the part of the die cast split chassis which occupies the fuel tank space.

Brian

 

[Branchliner]

Thanks to all for your inputs, the model is by Bachmann and no longer in production. The twin decoder solution had occured to me but I would prefer just one. Although the loco is a huge 380 mm in length, there is very little room internally due to the split chassis construction. There is a gap between the two facing flywheels of each motor which would take one larger decoder, possibly two smaller ones.

I shall check on the current draw and then find out if there is a suitable decoder. This project looks like being interesting as the motor contacts will need to be fully isolated from the chassis. I did this on another Bachmann diesel, the motor pick up insulation was relatively easy to achieve, hopefully this will be the same in principle but take twice as long.

At present both front and rear lighting is permanently on and a small internal circuit drives a flashing mars light on top, I'm not certain how this would react if I left the basic circuit in place and just powered it from 15 vac, I haven't done much with lighting and DCC yet.

Brian

 

[Branchliner]

Thanks Lisa,
Removing the circuit board will create more space between the top of the chassis and the plastic shell, maybe enough for a large chip. Lenz do a heavy duty chip (5 amps) but it does not support 128 step speeds. I could certainly get two small chips in the recovered space. I had the loco apart again today, I noticed that one of the contacts was on the outside of its wheel instead of inside, as the assembly comes apart easily it was quickly rectified but then I noticed that the two inner axles on that truck had stiff lateral movement, again rectified but I should not need to do this on a new product.

The good news is that the brass contacts on the motors are visible where they touch the two chassis side pieces, I reckon I could attach wires and isolate them without splitting the chassis.

Got to go now, we have a rare day here, sunshine and no wind. it's barby time.

Brian

 

[Branchliner]

Ozzie,
As I said earlier, the loco is a Bachmann product now out of production, it is one of their Spectrum series models but in my opinion is not up to the standard of their current Spectrum range. This one runs very smoothly on DC so should be OK for conversion. As far as I can see from the armatures without removing the motors they do not appear to be skew wound, pity, all the new ones are. I have a good local supplier who specializes in DCC conversions, he will probably have a suitable decoder, I can take the loco in and check for size.

Brian

 

[Branchliner]

Thanks Ozzie/Peter for that useful information, I have noted it down on the spares sheet for future reference. Setting up two decoders simultaneously? Thats an interesting problem, if there was a conflict of values for the same CV what would the feedback read if anything at all. One solution would be to isolate one decoder whilst setting up the other then reverse the process, every single CV would need to be identical on each decoder, you would have to pay attention to the polarity of the pick up and motor connections to avoid the trucks running in opposite directions, normally I don't bother which way round I connect the wires, if it runs the wrong way I just change the value of CV29 to correct it. I intend to start the installation next week, I shall keep you all posted, if nothing else it may help someone in the future.

I should not have bought this loco really,

it has just diverted me from the task of completing the loft layout and all that scrabbling about under the boards, another problem here, see my post on tracks etc.

Brian

 

[Branchliner]

Getting there slowly, I bought a Zimo MX64H decoder today from Digitrains, it has a 1.8 amp continuous rating which should do the biz for the DD40X. There is sufficient space to place the chip upright at the rear end of the chassis, a spin off is that it also gets some air from below.

I have done a quick installation to check it all out and the loco runs smoothly and quietly. Nevertheless I have decided to strip the chassis completely and carry out a better quality installation, this will require a bit of surgery to get full access to the brass connectors, there are no natural connections for the left and right pick ups, it might be an idea to drill and tap two connector screws directly into the chassis halves.

The Zimo decoder has 3rd and 4th function wires but I'm not sure whether I can use these to operate the flashing beacon.

Brian

 

[Branchliner]

OK so where are we now? It appears that twin decoders are not the answer to twin motor locos. A single decoder has to be able to handle the current draw. Due to variations in the motors they can still try to run at different speeds, depending how close the speed match is will result in a successfull or otherwise conversion. This is similar to the problem of multi headed consists, if one loco is significantly slower than another is it an asset or impedance to the overall pulling power? ie, will it tend to cause a drag on the stronger element of the consist and completely negate any expected advantage.

Back to my DD40X, eventually I had to completely dismantle the loco and cut away the flanges which make contact with the motor brass strips (do you think my warranty is now down the swanee

) I did not have a suitable thread tap so just drilled holes and used 2.5mm brass screws and nuts to pick up the power.

Current situation, the loco works but occasionally shorts out on the electrofrog points, I suspect the wheel sets are of poor standard but generally not a bad installation.

My loco is undecorated, does anyone know of a supplier of Union Pacific decals in HO?

Brian

 

[Branchliner]

Got the decals from microscale in the USA, excellent service, recommended.

Brian