Two locos on one decoder

[jeffrey-wimberly]

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.

[Texas Zepher]

I use two brass draw bars separated by a similarly shaped piece of styrene for one pair of the "wire" connections between the locomotives.  Watch out for hot frames though!  Hot frames might require a second styrene insulator and plastic screws for the drawbars.  For the other pair, I use real wires that have the mini-connection plugs on them.  More often though I only connect the power and let each loco have its own decoder.

These connectors (used for track power in this case) can be seen at either end of the unit in the photo below.  The female plug is near where the front coupler should be.  One problem with this is the male/female of the plugs, the units always have to go into a consist the same way.  I've yet to find a plug with one male and one female plug on it (like sectional track), so they could be put in the consist in either direction.

[jeffrey-wimberly]

These locos have plastic shank couplers so hot frames shouldn't be a problem. Also, both locos are oriented in the same direction, nose to tail.

[bnonut]

 I use one decoder in 4 AB sets. You put the decoder in one unit. Solder the wires to another set. Run the longer ones throught the shells, I use the door windows.

Cheaper and they run nicely.

 Sincerely, Mark

[Phoebe Vet]

It's a lot easier and only slightly more expensive to use 2 decoders set to the same address.

That also makes it a lot simpler if you ever decide to separate the two engines.

[jeffrey-wimberly]

Yeah, but then I wouldn't have answered the question, 'Can I make this work?'

[Phoebe Vet]

Jeff:

I guess my answer to "can I make this work?" is:

Sure.  But why would you want to?

Not intended as a criticism.  It's your minature world, do it however you like.  I was just giving you an opinion.

[jeffrey-wimberly]

I've been wondering about this for some time so it has become a nagging question. I have to find out the answer and the best way to do that is through direct application. Besides, if it fails what have I lost? A Bachmann decoder.

[Mark R.]

As long as the maximum current draw of BOTH motors together does not exceed the amp rating of the decoder, there should be no problem. Todays high efficiency motors draw very little current and most decoders have a 1amp max rating, so it "should" work fine.

However, as another poster offered - I considered the same thing myself until I realized I would have to run two wires from the non-decodered engine (wheel pick up), then two wires back from the decodered engine (motor connection) and then two more wires for the headlight of the non-decodered unit !!!  Making a six wire connection between the two units did not appeal at all to me, especially considering I could easily drop another $15 decoder in the second unit and be done with it !

Just because it's feasable, doesn't necessarily make it the best option.

Mark.

[jeffrey-wimberly]

Since the second unit is a cabless B unit there will be only four wires and since I wire my lights directly to track power that makes the install that much easier.

[jeffrey-wimberly]

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.

[fredswain]

How do people deal with engines that don't run at the same speed as each other? I have 2 n-scale E-8's and if I try to run them at the same time, but not connected, one is noticably faster than the other. When hooked together you can tell if the faster one is the second engine as the couplers get pushed together. Both engines were bought new and have done this from day 1. Is there a way to get their speeds synchronized?

[jeffrey-wimberly]

If you convert them to DCC they can be speed matched through setting CV values. I got lucky and got two locos that run at very nearly the same speed out of the box.

[wjstix]

Ya that's the point I was going to bring up...if you have two engines and one decoder, you have no way to 'speed match' the two engines so they run at the same speed. If you're lucky as noted they might run close enough that it's not a problem, but I doubt they'll ever be as perfectly matched as they can be by setting the CV's on two decoders in two engines.

[jeffrey-wimberly]

They won't be perfectly matched, no. But then I'm not too worried about them being perfectly matched. The fact that it works is good enough for me.

[Phoebe Vet]

Shrink tubing works better than tape where wires are spliced.

Totally covering the decoder with electrical tape to hold it in place is begging for it to overheat.  It needs air flow for cooling.

[jeffrey-wimberly]

It's only taped on the edges. I don't have any shrink tubing. I do have electrical tape.

[mfm37]

Why one decoder?

I can understand the all wheel pickup. I used to run wires between DC engines to gain the same advantage. Install a decoder in each unit, use the linked pick ups to power each decoder. Best of both worlds and dissimilar units could still be speed matched.

Martin Myers 

[jeffrey-wimberly]

The point here wasn't to see if I could have the locos work on separate decoders with all the pickups linked. I already have two teams of locos set up that way, an Athearn F7 A-B set and an Athearn F7 & GP50 lashup. I have two more linked sets waiting on decoders.  A P2K E7-A/E6-B set and a Bachmann GP40/GP35 set. The goal of the project was to have two locomotives controlled by one decoder. I had heard that it was possible and had to find out for myself. I'm one of the worlds biggest skeptics. Look up skeptic in a dictionary and you might find a picture of me.

[topcopdoc]

Jeffrey,

I think you answered a question I have had for a long time. I have a Bowser T1 which has two motors in it. No one could tell me if I should use one decoder or two. 

Am I correct that both motors are running in parallel rather than series with the decoder hooked to one motor?

Doc

[jeffrey-wimberly]

Am I correct that both motors are running in parallel rather than series with the decoder hooked to one motor?

You are correct. The motors are connected in parallel so each motor is getting the full output of the decoder. If you're planning on doing this with your T1 I would suggest getting the biggest baddest decoder you can find. The Digitrax DH163D has a current rating of 1.5 amps. It peaks at 2 amps. It's listed on the Digitrax site for $29.99.

[Mark R.]

Unless you are planning to do this with some older equipment (open frame motors) a 1 amp decoder should be more than adequate to handle todays high efficient motors - most draw about 1/4 amp under load (not stall current). Unless to really abuse your equipment - over weighting / over pulling / over racing - I see no potential problems.

This is all based on the actual theory of logic, however, considering how inexpensive decoders are today, I wouldn't be bothered with all the excessive wiring. HOWEVER - in the case of the dual motored T-1, it's the perfect solution.

Mark.

[pastorbob]

I guess you proved your point, if that is the objective.  That sort of rigging would not be of interest to me in the least, starting with "I don't have any F or E units".  But in the photos I see the wires passing through, and that is a put off for me personally.

But if your happy, then we are all happy.

Bob 

 

[rustycoupler]

thats why for a novice like me with decoders it would be nice if manufactures would make dummy units and then just wire in the led headlights in n scale and call it a day.