Using stationary decoder to replace a DC transformer

[Kentuckian]

So the article in the Nov.-Dec. N Scale Railroading about computers, cell phones, etc. shows in Fig. 1 how to wire a mobile decoder as stationary so DC locomotives can be run by a DCC system.  After studying the article, I think I understand the concept, and want to try it on my HCD layout.  I have 30+ locomotives, and so far only four are DCC.

My question is since size doesn't matter, is there some advantage to using an HO scale decoder?  Would it put out too much amperage for N scale locomotives?

[peteski]

So the article in the Nov.-Dec. N Scale Railroading about computers, cell phones, etc. shows in Fig. 1 how to wire a mobile decoder as stationary so DC locomotives can be run by a DCC system.  After studying the article, I think I understand the concept, and want to try it on my HCD layout.  I have 30+ locomotives, and so far only four are DCC.

My question is since size doesn't matter, is there some advantage to using an HO scale decoder?  Would it put out too much amperage for N scale locomotives?

Too much amperage is not a problem.  Kind of like the circuit breaker panel in your house. You have 200 Amps at your disposal even the only think using energy in your house is a tiny 5 Watt night light (which uses only several milli-Amps).

The locomotives will draw only what they need.  If you are running 3 or 4 unit lashups, the HO size decoder will earn its keep (and N scale decoder would probably fail).

What you need to worry about is whether the decoder's motor output has a short-circuit protection.  If not (and the DCC booster supplies more current than the decoder motor output rating) then if you end up with a short at the rails the decoder will fry.

[Kentuckian]

Thanks, Peteski.  I do like seeing three or four geeps on the head end of a coal drag.  The magazine article does have a fuse or circuit breaker in the circuit.

[jagged ben]

The problem would be more likely to be not enough amperage.   An N scale decoder is designed to handle one locomotive.   If you want to put a multiple lashup of DC engines on it.

Another issue is that if you want to run DCC locomotives in analog mode you can't really do it this way.  this may or may not be considered a problem.

I'm actually very interested in this issue but don't have time at the moment to post a long comment.  Hopefully later.  We've talked about doing this at our club to replace some of our aging analog throttles.  There's a few potential complications we're a bit afraid of in our case.

[peteski]

Thanks, Peteski.  I do like seeing three or four geeps on the head end of a coal drag.  The magazine article does have a fuse or circuit breaker in the circuit.

I'm kind of leery of fuses protecting delicate output transistors of a decoder. Often, even the fast-blow fuse will not be fast enough to protect the transistors.  Plus then there is the constant replacing of the fuse (shorts on a layout usually happen more often than you realize).  Do you want to keep replacing fuses several times in an operating session?  It would be beneficial to find a decoder which has a good short circuit protection on the motor output. I'm not sure if they exist - I never looked specifically for that feature as this type of a short doesn't often occur on a locomotive-mounted decoder.

I also read Jagged Ben's reply and I wonder if his problem might be related to using multiple DCC decoder throttles to power multiple blocks on the layout (and what happens when a loco accidentally crosses the block boundary, shorting both decoder motor outputs together).

[cgw]

It does not make any sense to do what Wally Davis proposes.  There is no advantage in doing what he proposes.  You lose all the benefits in using DCC.  Layout control, engine control, lights etc.     I do not know how you layout is wired but each block will require a decoder programed to single number  so that the throttle can control the engine  transitioning from block to block. Look for a no frills decoder if you want to do this.  Ie cheap.   look for 1.5 amp output decoders.   and fuse the outputs with fast acting fuses.  If you want to go wireless then you have a lot of options.   buy a raspberry pi model B computer (about $40).  load jrmi  (free) and set it up as a wifi controller for the layout.  them you can use smart phones, tablets etc to control the layout.

[peteski]

The only benefit I see is the ability to run wireless throttles. But the overall cost will be quite high (for what you end up with).  I also don't think this is a good utilization of the DCC technology (the lighting effect and being able to run multiple engines on the same track without any blocks to deal with)

[C855B]

Wellllllllll... on my project list is to do exactly this idea on our club's N-Trak layout. The game plan at this point is to use a large-scale decoder for the capacity, pending confirmation that the max voltage output is limited by the command station.

Solves two problems. First is the wireless throttle capability, as mentioned. Second is the important one - we frequently operate dual-mode, where two tracks are on our DCC system and one remains DC. Problem is we then have to schlep both systems to shows, which are each built assuming they're running the whole layout. No conflicts, just more crap to have to pack/unpack/pack/unpack (you know the drill). Integrating a DCC-to-DC conversion system controlling a whole track would make our setup easier. The wireless benefits are even better, as our DC system only allows two control points, and that's only if we break the DC line into two blocks.

As to Ben's concern about running DCC-equipped locomotives on the converted DC line, I have not yet put a 'scope on the decoder output to see if that will be an issue, that the waveform is square enough at the right (i.e., wrong) frequency to make the loco-based decoders expect DCC. If it is, then that's easily enough solved with a filter network, either frequency-specific or even brute-force with big bipolar caps.

[peteski]

As to Ben's concern about running DCC-equipped locomotives on the converted DC line, I have not yet put a 'scope on the decoder output to see if that will be an issue, that the waveform is square enough at the right (i.e., wrong) frequency to make the loco-based decoders expect DCC. If it is, then that's easily enough solved with a filter network, either frequency-specific or even brute-force with big bipolar caps.

DCC decoder motor output is PWM square wave. I haven't compared it to DCC track signal but on most modern decoders I think it will be much higher frequency than the DCC pulses.  But it might be possible (at certain speed step) that it might fool the decoder into recognizing it as a DCC signal.

[jagged ben]

Okay, I'm back from my evening activity...
So let me explain my interest in the topic.

I'm a member of club with a large layout.  We have a common rail system with 6 mainline cabs, 5 DC and the sixth DCC.
Our DC cabs, which were never great to begin with, are dying (3 are operational now) and they are long discontinued and seemingly impossible to get support for.  We need replacement wireless DC cabs.   Wired cabs are not tenable for how large the layout is and how it's arranged.  And no, telling everyone they have to convert to DCC is not tenable either.

The only benefit I see is the ability to run wireless throttles.

You say 'only' benefit as if this is not perhaps the most valuable benefit that a DC throttle could have, especially on a large club layout.
And you should consider another aspect to this...
THERE IS NO SUCH PRODUCT AVAILABLE ON THE MARKET.  That is, a pure wireless DC throttle.
The Aristocraft Train Engineer has been discontinued.  Try finding something else available in the states.  I mean, seriously, if you know of something then I want to know about it, too.

But the overall cost will be quite high (for what you end up with).

Not necessarily.   The cost of a G scale decoder is not that significant, and as as club we already have the DCC system and throttles to run it.  We may need a new booster, etc.  Also more throttles may not even need to be purchased because guys just use their phones.

The Aristocraft product was, I believe, around $150 several years ago, so that seems possible to beat.

And besides, as alluded to above, anything that we try is going to be a DIY build.  Anything will be costly, at least in terms of time.

I also don't think this is a good utilization of the DCC technology (the lighting effect and being able to run multiple engines on the same track without any blocks to deal with)

As a club, we want to remain open to the members who have large DC legacy fleets that they don't want to convert or can't afford to.  So the question of whether it's superior to DCC is really moot.  For us the question is just whether we can come up with a solution to keep DC functional in our club or if we are effectively giving up on the DC members and the cool trains that many of them run.

I also read Jagged Ben's reply and I wonder if his problem might be related to using multiple DCC decoder throttles to power multiple blocks on the layout (and what happens when a loco accidentally crosses the block boundary, shorting both decoder motor outputs together).

Exactly.  This is where the idea breaks down, or at least needs serious scrutiny, for various reasons. 

1)  We have to plan for the fact that accidental block boundary crossing will unfortunately happen.  Accidental crossing into a DCC controlled block is the equivalent of touching decoder motor leads to the rail, which may not destroy the decoder the first time but definitely needs some kind of protection.
2) Accidental crossing into a block controlled by a different decoder
3) We have a common rail system and the possibility of interference between the DCC controlled blocks and decoder controlled blocks would have to be considered.

Really what I would like is a simple way to control a quality variable DC power source with JMRI.  Something where the source could have a non-DCC power supply, but be controlled by a DCC throttle.

[C855B]

I think the common-rail design is going to be your major "oops" point. Personally, I abandoned common-rail 40 years ago as false economy, but to each their own.

Fortunately, our club's needs are for but a single decoder(ed) DC line, and I am going out on a limb here to say that crossing (in our case it would be accidental) from a DCC line to a converted DC line (and vice versa) is likely to have little consequence to the decoders, either the big one driving the DC block or the little one in the offending loco. Things may act strange and there may be a runaway, but I doubt that any magic smoke will be released.

[peteski]

But the overall cost will be quite high (for what you end up with).

Not necessarily.   The cost of a G scale decoder is not that significant, and as as club we already have the DCC system and throttles to run it.  We may need a new booster, etc.  Also more throttles may not even need to be purchased because guys just use their phones.

The Aristocraft product was, I believe, around $150 several years ago, so that seems possible to beat.

And besides, as alluded to above, anything that we try is going to be a DIY build.  Anything will be costly, at least in terms of time.

I was responding to the OP - not to your specific situation (which I didn't even know at the time I replied). I just didn't see buying a complete DCC system (wireless DCC throttle, command station, booster, power supply and a high-current decoder) just to make it into a wireless DC throttle.  The OP didn't mention anything that he already had most of the components needed.

[peteski]

Things may act strange and there may be a runaway, but I doubt that any magic smoke will be released.

One way to find out .... 

[jagged ben]

I think the common-rail design is going to be your major "oops" point. Personally, I abandoned common-rail 40 years ago as false economy, but to each their own.

It may be a problem for the DCC decoder as DC supply idea; I don't actually know.   It would not be a problem for any other kind of DC supply.  The layout does work fine with both DCC and DC on common rail.  The DCC boosters have to have optical isolation for the Loconet connections but that issue is already solved.

I was hoping this thread would actually generate a discussion of various ideas on how to achieve a DC track supply that can be controlled by a DCC system.   There seem to be plenty of cheap 12V motor controllers on eBay, some of which are apparently designed to work with Arduino boards.  How difficult would it be to get an Arduino board to interpret DCC throttle commands?  Or are there other approaches to consider?    I am not a coder so I'm not gonna figure this out all on my own. 

And then there's circuit breaker protection.  I'm intrigued by this other thread but can't really follow the electronics.

[PennsyPride]

Wellllllllll... on my project list is to do exactly this idea on our club's N-Trak layout. The game plan at this point is to use a large-scale decoder for the capacity, pending confirmation that the max voltage output is limited by the command station.

Solves two problems. First is the wireless throttle capability, as mentioned. Second is the important one - we frequently operate dual-mode, where two tracks are on our DCC system and one remains DC. Problem is we then have to schlep both systems to shows, which are each built assuming they're running the whole layout. No conflicts, just more crap to have to pack/unpack/pack/unpack (you know the drill). Integrating a DCC-to-DC conversion system controlling a whole track would make our setup easier. The wireless benefits are even better, as our DC system only allows two control points, and that's only if we break the DC line into two blocks.

The Capital PenNscalers Ntrak embarked on this endeavor a few years ago.  We started by testing the concept on the blue line. It has been successful in use for going on three years. Additionally the red and yellow lines were converted to this method early this year. We now use the digtrax command stations and throttles to control the layout whether the track power is DC or DCC.  Initially we keep the Arito units as back-ups but now the Aristo Throttles have been completely removed and retired. In a matter of seconds the any of the lines can be switched to either DC or DCC track power.  No longer need to keep both 9volt and AA batteries. Operators only need to learn one type of throttle.  Go for it. You wont regret it.