What is the preferred way to apply DCC to multiple unit locos?

Model Railroader Electronics and DCC
1

Hi!

Easy question (I hope) for you DCC folks…

I have 6 Stewart ATSF F unit ABBA consists - with all units powered on my DC layout. I am considering converting to DCC and would keep them whole (solid ABBA) or at most break them into separate AB units. I am “DCC challenged”, but suspect I would only need one decoder for each separate consist. That is to say, one decoder for an ABBA or AB unit if I choose to break them up.

Is that the preferred way, and if so, how do you wire the units together (so the single decoder will run the other unit(s)?

Thanks!

Mobilman44

2

Each powered unit should have it’s own decoder. If they will always run together - say you have a drawbar between two - you can give them both the same address. You can consist more to create larger loco consists which will then all operate under a single address. Since you can pretty much do anything you want with DCC, the option you chose is probably more up to either the way your protoype did it or the way you plan on operating. Given each unit an independent address is themost flexible, you can then build up consists in the terminal for whatever train requirements youhave - Single AB set, twin A’s, ABB, ABBA, whatever.

Regardless of how you address them, each powered unit should have it’s own decoder, not jumper wires between units with a single decoder running multiple motors. That way you have the flexibility in addresses as well as the ability to tune each unit so they run well together with no bucking or pushing.

–Randy

3

Decoders are really designed to be one-unit devices. Their power-handling capacity is limited, simply because they are small electronic devices, and the ones made for HO locomotives are sized to handle one HO locomotive. (Yes, some users will put a small N-scale decoder in a tight spot in a switcher, but these are special cases, and people have to recognize the limitations.) For reliability, a decoder is actually rated substantially higher than the “stall” current of a modern motor, but not orders of magnitude larger.

You can wire together multiple locomotives using the same decoder. I would certainly not go with more than 2 engines per decoder, and even then I would be careful to select a decoder with the largest possible current rating. For an AB pair, you would not need to run lighting wires, but you’d still want a pair of wires for track power, and another pair going back for motor power.

All of this means a lot of wiring inside each unit, plus the cabling between the units. Basic decoders, though, are so inexpensive that you’d might just as well give every unit its own decoder, and do it right the first time.

4

Another caution: The reason you would not want to use one decoder for more than one loco (even if it were possible) is that all your units will run at different speeds, start at different speeds, and brake at different speeds.

Therefore, after installing one decoder in each powered unit, you will have to spend some time “speed matching” them. (I am in the process of speed matching all 81 of my locos so each will have a companion to assist it on my steepest grade)

However, any powered AB or more unit will have to be speed matched whenever/wherever you want to use them together, and they won’t necessarity be interchangeable with other AB units. Why? Because even identical production models with identical decoders, and certainly B units compared to their As will run at different speeds.

More annoyingly, even if you speed match a pair in one direction, it is usually the case that the units will run at different speeds in reverse. One can only speed match in one direction whenever locos run at different speeds in reverse.

Of course, the more units you add to your consists, the longer will take the speed matching. Two units is acceptable to me in terms of time, I have speed matched 3 and 4 as well, but taking much longer.

One has to match speeds not only at the top end, but also set the CVs to ensure matching at starting, low and mid speeds as well.

Also, the units will only run at their proper matched speeds once warmed up to the same state they were in when you matched them. For the first few minutes, if you run them in a consist, the speeds can be quite different and you can tell one unit is pushing or pulling another.

However, don’t let me deter you. [:D] I just wrote all this because it is something with which I have been busy lately and it was on the top of my mi

5

You could configure them any way you want. I’ve got some sets with 1 decoder in an AB power set. But I did that way back when decoders cost $50 each and the dollar was worth a whole lot more than it is today. Stewart F units are one of the easiest DCC conversions that there is. I would recommend using 1 decoder per unit. I prefer the NCE DA-SR.

I do have Stewart sets where I’ve run power couplings between them. That way there are more than 8 wheels picking up power and sharing it to all units.

I also went through my fleet and de-powered several of the units. When I realized an AB powered set could pull more than 65 cars flat and 55 up a 2% grade, I decided ABA, ABBA, and ABBB (Santa Fe style) powered sets were way overkill - even for the club layout. I added sound into the units that lost a motor.

6

Thanks Folks, I knew you would have the answer!

To have an individual decoder for every motorized unit makes sense. I just wish I had considered that over the last couple of years when I was buying up all those Stewart power chassis for the unpowered “B” units! Oh well, I can always resell them on Ebay if I find them too much of a challenge.

While I have you all here, what brand/type decoder would you recommend for Stewart F units? I have two F7 ABBA consists and one F3 ABBA consist all with Kato drives, and three FT ABBA consists with Stewart drives.

Thanks, I really appreciate your input (stuff like this helps make this hobby so good)!

Mobilman44

7

NCE DA-SR for all.

Just a few more sets and you’ll start having a real fleet there!

P.S. I haven’t done a conversion for quite some time, but I recall the FTs with their LED headlamps and marker lamps were the hardest. I replaced the factory LED for the headlight with a bright one.

8

Great! I know you will enjoy those units in DCC.

DECODERS: I do not use a great variety of decoders, but because I decided to do my whole fleet in the past year (90+ decoders) I went for the NCE D13SRs. They are a great decoder for the price ($13 ea.in bulk packs from LitchfieldStation.com) and certainly can be fit in a Stewart F7 (although I have put sound in two of my Stewart F sets)

They do not have back EMF but, as mentioned above, a Stewart F set will put very well and you don’t need to worry about needing that EMF compensation anyway.

Now this is ( [#offtopic] I know . But I have three Stewart & Steart/Kato sets on the layout. The only drawback with them compared to P2K is that they don’t come with diaphrams. Ihave just equipped all mine with American Limited Diaphrams and they units have to be coupled really really closely with a drawbar to be realistic (i.e. diaphrams mating) and then that impedes turning on even 18" radii in my experience. So I just let them have a little slack).

9

My Stewart F7’s were like most of their F units - sparsely detailed. Hence the various dress-up kits from DA, DW, and Walthers. Compared to P2K, they are as plain at Athearn Blue Box. However, the mechanisms and the superb Buhler motor mean they run better than any of the others. It’s not THAT hard to drill some holes and add the proper grabs and make it look really nice.

–Randy

10

Gerome,

All of my Stewarts have American Limited diaghprams (spell?) painted the proper color. I’ve also added the proper KD couplers on all but the FT A/B connections where I use a drawbar. They really look nice, and as all 4 units of the ABBA consist are powered, they can pull anything! Ha, thankfully I have two Controlmaster 20 units, so running out of amps is not a problem!

Also, its a shame you don’t live nearby, for your decoder installation experience would be invaluable!

ENJOY,

Mobilman44

11

I am sure there is a lot I could learn from you as well. I must say, in the two years since I took up this hobby, the conversion of locos to DCC & installing LEDs etc. is the most fun I have had. The bit of electronics learned, shop skills improved, and the notion of making a device work better is absolutely addictive.

If I had known about the invention of DCC I would have been doing this for the past 5-8 years at least.

12

Mobilman

TCS A4x and the A6x are excellent decoders. The Stewart/Kato drives should be pretty much speed matched right from the box. If you run an AB set regularly you can set them for the same address and then consist AB to BA or any way you want to. I regularly run a consist of RS3 and RS1 together that’s set to the same address so it acts like one loco instead of 6 separate locos. I wired the front unit and rear unit with only an LED headlight so no matter witch direction they go there’s only the lead units light on. It makes an impressive sight when pulling a long string of hoppers. My other consists are the normal way with separate addresses and consists with the throttle.

Pete

13

Pete, is this your experience or a guess? I ask in seriousness because I thought this should be true too! After working for several weeks on my whole collection, I was rather disappointed to find almost nothing, even identical out of the box, was close enough in speed. And I thought it should be. I think I had one AB set that was close.

Although, when you say Stewart/Kato you are speaking of something that is old stock/discontinued even if NIB. So perhaps just sitting on the shelf for seveal years can take its toll.

What gets me is that even several of my new Katos run at a different speed at the same throttle setting in reverse compared to forward.

Oh well, perhaps I just have not had good luck. Thanks for the info though.

14

Hmmmm, interesting in my entire fleet (very large fleet) of Stewart Kato & Buelher drives I’ve only had one that was significantly out of whack with the others out of the box. I don’t remember what I did to fix it…maybe just a lube job. BUT the point I am getting to is that I’ve never speed curved any of mine. Never had any problems with different speed issues. Oh the reason I prefer the DA-SR decoder over the others is because it is a drop in replacement for the existing circuit board. Solder 4 connectors to connect the existing track power feeds and solder the motor leads directly on - done other than lighting. The D13SR has wires and must be mounted somewhere.

15

As far as which decoder to use, I favor the Digitrax DZ125. It’s a Z Scale decoder for motor control and front and rear lights and is more than able to handle HO Scale equipment. They handle the big motors in my Athearn HO F7’s just fine and I also have a pair of them in an E7-A E6-B consist. I just recently wired one into an Athearn SD40 and did up a pair of Atlas GP40’s as well. Also, with their tiny size it’s easy to get them into small areas so there’s no having to squeeze them into the top of a locos body or removing weight to make room.

16

If you’re thinking about sound, now is the time to try it. Put a sound decoder in one of the B units, where I assume there will be more space. See if you end up running that unit more than the others. That’s a typical result of adding sound, according to many of us with partially-sound-equipped fleets.

17

I bought an F3 AB set at the same time from the same dealer. I installed identical Digitrax decoders and set them both to the same address.

To test them for speed match, I placed them on the track, about one foot apart, not connected.

I ran them in both directions at various speeds. They behaved as if they were connected by an invisible rod. They maintained the spacing almost perfectly.

I now run them together with no speed matching.

18

Mobilman

Yes that’s from experience. The RS units that run together are even a mix of manufactures. Atlas and Athearn. I have several sets of Stewart switchers that are run together very frequently and they are not speed matched by CVs. Perhaps a little maintenance is in order. Just an hour ago my PCM I1sa was pushing on a mixed freight pulled by 2 P2K SD9s with loksound. Again with no speed matching. The SD9s are advanced consisted and the helper I1sa is old consisted with them and they moved up the grade without a hitch or jump or spinning wheels.

Units dont have to be the exact speed together just close to it. The weaker or slower units will help on grades just like the real thing. You dont want to drag a unit and you dont want spinning wheels. Couple them together and watch them go and listen for any dragging or spinning wheels.

Pete

19

Thanks for the insight Pete, phoebevet and Texas Zephyr… Yes, I think I am forgetting what all the sets are like that I am working with. I do have 2 new sets of Stewart ABs, but most of my locos are pre-owned. No doubt I am forgetting what has been the case after working all month on 80 or so locos.

Indeed, I am also speed matching a variety of makes and models (but keeping early Geeps with others, and six axle units with other six axle units etc.)

I am also quite critical in the matching speed. Perhaps I don’t need to worry about a few inches of creep over 5 or 6 laps of the matching circuit or a few 10ths of seconds in the timed zone.

20

Speed matching with the Stewart F’s shouldn’t be hard. I’ve done it with just using CV 2, 5 & 6. Once you have one A-B set speed matched, speed match your other engines one at a time to match that pair. Then ALL of them will be able to run together in any combination.

BTW as long as you’re doing DCC conversions, why not slap in a sound decoder in the B units?? Lots of room in the B unit (no cab) for a 1" speaker and enclosure. Soundtraxx LC decoders work well and are fairly cheap.