# A+B units: one decoder or two decoders?



## rva1945 (Feb 11, 2016)

Hi:

I have a FT-A already running on DCC and just received the analog FT-B. My plan is to take a couple of wires from the A's motor and connect the B in parallel, so the decoder will drive both, providing they are an electrical and mechanical match.

Now the BEMF topic. Should I turn it off?

And in the long run: will their performances deviate? Will I need a second decoder for the B unit? Can both decoders have the same address so they will respod to the same DCC command?

Thanks


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## DonR (Oct 18, 2012)

Connecting two motors on the output of
your decoder could burn it out. Many decoders
today are rated at 1.5 amps. One of those
may be suitable for your project. I don't know
the rating of the existing Bachmann decoder
but until recently most decoders had a 1.0 amp
rating.

IMHO you would do much better installing a
decoder in the new loco.

Don


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## mopac (Feb 24, 2011)

I agree, 2 motors on one decoder could be too much and lead to decoder failure.
Add another decoder to other unit.

Can one DCC command operate both units? Yes.
Its called "consisting". It is putting 2 or more units into a group and all units in the
group will respond to a single DCC command. Pretty cool. You don't change each
unit address. The group or a consist will have an address. Your DCC system instructions
will tell you how to make a consist.


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## santafealltheway (Nov 27, 2012)

Yup. Get another decoder.

You can get a digitrax one for about 17$ off ebay. Worth it.


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## irishthump (Jul 1, 2013)

Depending on what make the locos are I'd depower the B unit rather than installing a 
2nd decoder and going through the process of speed matching.
I recently installed DCC and sound into a Proto F3 A+B set. I removed the motor and drive train to use in another project and ran a second speaker into the B unit.
It has more thaan enough pulling power and even if did'nt it's a perect excuse to add another A/B set to the consist... which I did!


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## CTValleyRR (Jul 26, 2014)

irishthump said:


> Depending on what make the locos are I'd depower the B unit rather than installing a
> 2nd decoder and going through the process of speed matching.
> I recently installed DCC and sound into a Proto F3 A+B set. I removed the motor and drive train to use in another project and ran a second speaker into the B unit.
> It has more thaan enough pulling power and even if did'nt it's a perect excuse to add another A/B set to the consist... which I did!


Depowering is different than trying to run 2 different motors off the same decoder, which is what the OP is asking.

Most of the time, a single loco is going to have enough power to drag a dummy unit around as part of its consist. But as we've discussed elsewhere, 2 powered locos pulling that same consist will allow you to include many more cars than if the second loco is a dummy. And the ability to pull a longer train is exactly why real railroads add additional power.

Given how easy it is to consist two locos using most DCC systems -- and unless the two locos are grossly mismatched in their speed at a given throttle setting, you don't have speed match them to consist them -- I would say that removing the motor and drive train requires a heck of a lot more work than just adding a decoder to the B unit. Given the cost of inexpensive decoders, it's not much of a cost savings, either.


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## Lemonhawk (Sep 24, 2013)

I agree with CT. I think you would be disappointing in the results of making a power unit a dummy as opposed to putting in a decoder and consisting. As long as your 
DCC system supports consisting that would be my preference.


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## irishthump (Jul 1, 2013)

CTValleyRR said:


> Depowering is different than trying to run 2 different motors off the same decoder, which is what the OP is asking.
> 
> Most of the time, a single loco is going to have enough power to drag a dummy unit around as part of its consist. But as we've discussed elsewhere, 2 powered locos pulling that same consist will allow you to include many more cars than if the second loco is a dummy. And the ability to pull a longer train is exactly why real railroads add additional power.
> 
> Given how easy it is to consist two locos using most DCC systems -- and unless the two locos are grossly mismatched in their speed at a given throttle setting, you don't have speed match them to consist them -- I would say that removing the motor and drive train requires a heck of a lot more work than just adding a decoder to the B unit. Given the cost of inexpensive decoders, it's not much of a cost savings, either.


Sorry CT, I was just trying to offer the op an alternative to adding a decoder.

Just to explain my perspective on this:

I was thinking of the cost of installing a sound decoder in each unit, simply installing a speaker in the loco saved me around $100! 

Also, my Proto F3's were not DCC ready, so removing the drive train and motor took a fraction of the time that hardwiring a decoder would.

My layout is not large, so the longest train I run is usually 10-12 cars max. One powerd F3 is more than enough to haul that train length as well as the dummy B unit.

On a side note I recently read an article by the late Andy Sperandeo where he mentions depowering his B units in his FT lash-ups so that he would have to add extra power to a consist to haul a long train! Prototypicality taken to the extreme perhaps, but a neat idea all the same.


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## irishthump (Jul 1, 2013)

rva1945 said:


> Can both decoders have the same address so they will respond to the same DCC command?
> 
> Thanks


If they are always going to be ran in a lash-up together I would give both decoders the same address.

Did the same with my Bachmann F7 A/B set.


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## DonR (Oct 18, 2012)

I have 3 consists. 2 FTs, 2 GP40s, and 2 70 ton Switchers.
The locos in each consist have the same address.
All of them are Bachmann DCC.

Don


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## CTValleyRR (Jul 26, 2014)

irishthump said:


> Sorry CT, I was just trying to offer the op an alternative to adding a decoder.
> 
> Just to explain my perspective on this:
> 
> ...


Why would you be sorry? There is nothing wrong with presenting an alternative opinion. Just as there is nothing wrong with disagreeing with that alternative opinion. As long as it's done politely.

Discussion is good -- it helps people to see a problem from many different angles / perspectives.


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## irishthump (Jul 1, 2013)

CTValleyRR said:


> Why would you be sorry? There is nothing wrong with presenting an alternative opinion. Just as there is nothing wrong with disagreeing with that alternative opinion. As long as it's done politely.
> 
> Discussion is good -- it helps people to see a problem from many different angles / perspectives.


Haha! I guess I was apologizing as I did'nt really offer any solution to the OP's original question!

My main point is that a single, good quality A unit should be well able to pull a train of equivalent size to the prototype A+B set.


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## CTValleyRR (Jul 26, 2014)

irishthump said:


> Haha! I guess I was apologizing as I did'nt really offer any solution to the OP's original question!
> 
> My main point is that a single, good quality A unit should be well able to pull a train of equivalent size to the prototype A+B set.


If I had a dollar for every time I misunderstood a question, I would have retired in luxury long ago!


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