Two locos one one decoder

Discussion in 'HO Scale Model Trains' started by jeffrey-wimberl, Aug 21, 2008.

  1. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    I'm getting ready to wire a Bachmann decoder to a pair of specially prepared P2K locos. The decoder will collect power from the wheels of both units and will drive the motors of both units. Obviously this means the units will be
    permanently tethered to each other. The units are a FA-1 with a Bachmann FT-A shell and a FB-1 with an Athearn F7-B shell. I've heard of this being done on a couple other forums. I'm about to put it to the test.
  2. Kevinkrey

    Kevinkrey Member

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    Take pics! I want to see. Make sure you also give us a good how to description, Id like to hear more!
  3. MasonJar

    MasonJar It's not rocket surgery

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    The only issue to be aware of is whether the two motors together exceed the decoder's rating. If you pull more amps than the decoder allows, you'll let the smoke out... ;)

    Let us know how it goes!

    Andrew
  4. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    According to the stall tests I performed each loco pulled under half an amp at full stall, so the combined stall amperage should be below one amp.
  5. Russ Bellinis

    Russ Bellinis Active Member

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    Jeffrey, one trick you could do to make sure you don't overload the decoder is to use a decoder designed for either S or O scale. Those decoders are probably rated for more load since the bigger size locomotives run more power. Make sure any decoder you use is designed for dc operation and not ac. If the decoders are larger physically than decoders designed for ho scale, you should still have enough room in the body of an f unit to fit them in.
  6. doctorwayne

    doctorwayne Active Member

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    Jeffrey, I'm curious as to why you'd want both locos on the same decoder. While you'll still have the various auxilliary functions, such as lights and sound, to be controlled by the decoder, you won't have the ability to programme each loco's running characteristics separately - in other words, controlling them will be similar to me running two locos together on my DC-powered layout. Not that I see that to be a problem, but I've read an awful lot of posts by people worried about getting their DCC-equipped locos starting at the same voltage and running at the same speed if they plan on using them together on the same train. Most of us Dinosaur Control types know that this isn't necessary, but, hey, if you've got a new toy, why not play with it?
    I can see the benefit of the 16 wheel pick-up, but you could have that with a couple of "mu" cables between the units, each with its own decoder.

    Wayne
  7. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    Wayne, I did this to prove to myself that it can be done. I'm one of the worlds biggest skeptics. Look up skeptic in a dictionary and you might find a picture of me.

    I made sure beforehand that both units run at the same speed. They're not exact but they're very, very close. Over a distance of thirty feet they separated by only one and a half inches. I would not have even thought of doing this units that weren't very close in speed.
  8. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    I've completed this weeks project. That was to install one decoder to run two locomotives. Here's an account (with photos) of how it was done.

    First, the item on which this is all centered. The decoder to be used.

    This is a standard Bachmann two function decoder. There's nothing special about it. Current capacity: 1 amp. Motor output: 1 amp. Function output: 100 mA.

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    Next are the chassis to be used. Twin Proto 2000 FA chassis. Since they're both identical we'll focus on one. Here the pickup wires have been linked with their identical twins on the other chassis. Now I know somebody out there is going to notice that a red pickup wire is connected to a gray pickup wire. The answer to that is simple. Life-Like used a red wire for the right rail pickup (hot frame). Now here's where it gets interesting. Life-Like, in it's infinite wisdom, used a red wire on the rear truck for left rail pickup and a gray wire on the front truck for left rail pickup.

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    Next, the wires for motor control have been added. Since the decoder will not be powering the headlight (that will be installed later and connected to track power so it's always on) I have elected to install it in the B unit. Here the wires in the A unit have been connected to the wires going to the B unit.

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    In the next photo we see that the wires have been passed through the door windows of the shells. I drilled the windows out a little bigger to insure that the wires can move freely.

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    For those who know that I have a past history of using masking tape here's a photo showing the wire connections wrapped in ELECTRICAL tape.

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    Here we see the decoder taped in place in the rear of the B unit and the red and black wires connected to the pickup wires of both units. This insures good power pickup as the joined units will be collecting power with 16 wheels. The orange and gray wires of the decoder have been connected to the wires linking the motors of both units.

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    Here the two chassis are coupled together as they will be in service. The decoder can be seen taped in place at the rear of the B unit chassis.

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    The shells have been put back on the chassis and the locos have already made several trips around the layout pulling an Athearn F7-A unit and 15 cars through the entire gambit of a crawling slow start at near full stall all the way up to top speed and the decoder didn't even get warm.

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    Here the wires can be seen passing between the two units. Being that they're close-coupled the gap is only a 1/4 of an inch.

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  9. CN_Fan

    CN_Fan New Member

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    Use diaphrams between them to hide the wires completly.
  10. jeffrey-wimberl

    jeffrey-wimberl Active Member

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    Already tried that. Didn't work. I have a S curve on my main line. When the locos go through it the diaphrams would move past each other and catch the wires in between, then the real fun would start as one loco would pull the other one up off the track on one side. That doesn't happen without the diaphrams.
  11. thedowneaster

    thedowneaster Brakeman

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    A little touch of black paint will help conseal the wiring a better. Or if you have slack you could even pull them out more to resemble a true MU cable. They also sell shrink wrap tubing at radio shack to make them appear to be a single black cable.

    I used to run 1-2 engines off of my Largescale decoder equipped engines. My CVP airwire900 decoders have a max output of 10 amps and cost around $150 each. It made more financial sense for me at the time to power 1-2 engines off of my decoder-equiped engines than it did to install in all 20 of them.

    The Engines also required batteries for power since my layout was too large for conventional track power to be used effectively.
  12. Russ Bellinis

    Russ Bellinis Active Member

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    I think some sort of flexible flat black paint on the visible portion of those wires would do a lot to make them disappear.