Dual Mode Decoders

[Yampa Bob]

Consider the following taken from the Atlas web site:

"Atlas offers a patented HO scale Dual-Mode Decoder which allows you to easily switch your locomotive from true analog to digital mode and back again. This is done by simply removing the jumper plug (shown in green on the decoder above) and replacing it in different holes. "

Now who would want to take the tender apart to change the jumper, just to be able to run on your friend's analog powered layout?  For that matter, just to run on your own DC layout?  Is Atlas that far behind in technology?

They claim (without naming brands) that other methods of dual mode creates a speed differential between analog and digital.  I run my Bachmann DCC locos on both DC and DCC, and have seen no difference in speeds, at least none that I can discern.  Not being a purist, I am not concerned with starting thresholds, speed steps, acceleration and deceleration curves or whatever.  I turn the throttle and the loco moves smoothly and realistically at varied speeds.  I close the throttle and it stops.  The loco will crawl very slowly with either DC or DCC.  I am happy.   

So far I only have DCC equipped locos, but am considering one that is DCC ready, which I usually take to mean that the motor wires have been "isolated".  I think Bachmann takes it a step further by having a DC compatible board installed. To get DCC in the model I want, I have to accept sound as well.  I would like to install a Bachmann plug in decoder, but the loco has a 9 pin plug which is irritating.  So I have to order a special  Digitrax decoder.

My question specifically is about the "DC compatible" issue.  What makes the Bachmann DC compatible?  I have always assumed it is the circuit board that allows this feature, not the decoder itself.  However someone told me that any dual mode decoder is DC compatible.  If that is true, then why does Bachmann bother installing the extra circuitry on the board.? 

Also, I have an extra DCC board from a Bachmann GE 70 ton.  As long as the new loco motor has the same stall current as the 70,  could not the board be installed and work ok?  According to Tonys Trains it will work, they even detail checking the stall current in their DCC handout.

Several have recommended removing the boards on my Connies and hard wiring the decoders.  One source says it will then not be DC compatible, another source says as long as the decoder is dual mode it will be.   When sound became a big issue, I was told that dual mode simply meant sound was included.  Dumb question: Is there a triple mode?...and why do some companies have an 8 pin and others 9 pin? What significant advantage is there to hard wiring the decoder other than personal preference?

I prefer "plug and play",  and don't particularly enjoy having to solder anything although that does not intimidate me.  I also don't like having to pay extra for sound I don't need or want just to get DCC.   Bottom line is, I want my locos DCC equipped but still be DC compatible.  I like having choices.

Bob

[Jim Banner]

I think that design dates back to the days when some decoders could not run on dc and ones that did took an awful lot of extra voltage.  The extra voltage was enough that you often could not double head a dc locomotive with a DCC locomotive set for analogue operation.  For example, I have some older MRC decoders that require an extra 6 volts to run forward.  So if I try to double head two locomotives, one with such a decoder and one without, I have to apply about 7 volts to the rails to get the decoder equipped one started but at that voltage, the one without a decoder is already spinning its wheels.

[Yampa Bob]

Thanks Jim.  I think you have the answers to all my other questions as well.  If I don't get other responses please weigh in on the rest.

Don't be modest, I know you can help and I was counting on your knowledge.

Bob

[Yampa Bob]

After visiting at least 50 more web sites, I may have found some answers.  If this is wrong then say so, and don't blame me.      

1.  Dual mode apparently means a DCC decoder that is DC compatible.
2.. Dual function means that sound is included on the decoder.

It was mentioned that Bachmann decoders by themselves are not dual mode, and require the circuit board to be DC compatible.  The only way to confirm that is to remove the board and hard wire a Bachmann decoder.  Anyone who has done this will know the answer.

I am inclined to agree as Bachmann DC ready and DCC equipped locos have extra circuitry on the board. I believe it is this circuitry that detects the presence of DC and bypasses the decoder. 

Bob

[Hunt]

Bob,
The two definitions you gave are good general working definitions. You can find where dual mode and dual function are incorrectly used as interchangeable. Heck, Atlas still refers to the NMRA 8-pin socket as a plug.

The Bachmann decoders I am familiar with are dual mode.

[mattallen37]

I have hard wired a dual mode decoder and it operates on dcc and dc. I hope this answers your question.

                                               Matt

[Yampa Bob]

Thanks Hunt.  I could only assume Bachmann decoders are dual mode though they don't specify them as such.  I have been told that not all decoders are dual mode, Athearn for one.  Pehaps Atlas should stick to what they do best, build track. LOL

Please follow through with me one step at a time. 

I am looking at the circuit board in a Bachmann DCC ready tender.  It has 4 diodes, 2 chokes, 1 resistor and 2 capacitors,  apppears to be a standard AC to DC bridge rectifier circuit.  From a visual trace, it looks like the jumper plug bypasses the rectifier circuit for DC power, so for DC the board is not needed and could be eliminated completely.  So far so good.

Ok, now we plug in a Bachmann decoder.  If the decoder does not have a built in rectifier, then the board is needed to provide DC to the motor.  If the decoder does have a built in rectifier, then again the board is not needed.   Could it be that the board is a holdover from earlier technology?  If so, it's a waste of components but at least provides a handy socket for the decoder.

Matt:  Frankly it doesn't answer my question completely.  If the decoder was specified as dual mode, then it must be dc compatible.  But what brand was it?   Was it installed into a Bachmann, and if so, did you remove the board?

Unless someone can explain the purpose of the board in Bachmann locos, which I have been told is not used in other brands, the only way I can resolve this in my mind is to remove the board completely, then hardwire a Bachmann decoder and see what happens.

Several have told me they removed the board and hardwired a decoder in a Bachmann, they did not mention the decoder brand.  I have asked them if the loco was still DC compatible, and have not received an answer.  Is there an element of risk in trying to run DCC locos other than Bachmann on DC power?

I plan to order a Bachmann Mogul DC, and convert it to DCC by wiring in a Bachmann decoder.  Two scenarios:  If it runs on DC, then it will prove the decoder is indeed dual mode, but it also means that no extra circuitry (like the board above in question) is needed.  If it will not run on DC, then the decoder is not dual mode and I will have to obtain a decoder that is. 

Perhaps I am the only one in the world that wants all my DCC locos to be DC compatible.  Well, that's just me and I have my reasons.

Thanks everyone for your time. I have searched the net for weeks and can't find the information I seek.

Bob

[grumpy]

I have 4 Athern locos with dcc and sound .They are all also dc compatible  and therefore are dual mode and dual function. The Atherns also come with an rc transmitter to control the sound while in dc mode. I will not disassemble any of them so don't ask. They run just fine the way they are.
Don

[Jim Banner]

Thanks Hunt.  I could only assume Bachmann decoders are dual mode though they don't specify them as such.  I have been told that not all decoders are dual mode, Athearn for one.

The term "dual mode" can mean several things in decoders, and operation on both dc and DCC is certainly one of them.  Does Athearn use MRC decoders?  I still have a number of older MRC decoders that barely convert to dc in forward and not at all in reverse.

I am looking at the circuit board in a Bachmann DCC ready tender.  It has 4 diodes, 2 chokes, 1 resistor and 2 capacitors,  apppears to be a standard AC to DC bridge rectifier circuit.  From a visual trace, it looks like the jumper plug bypasses the rectifier circuit for DC power, so for DC the board is not needed and could be eliminated completely.  So far so good.

The chokes and capacitors are for suppression of electrical motor noise, as required in many countries in Europe.  The diodes are most likely for controlling the directional lighting on dc.

Ok, now we plug in a Bachmann decoder.  If the decoder does not have a built in rectifier, then the board is needed to provide DC to the motor.  If the decoder does have a built in rectifier, then again the board is not needed.   Could it be that the board is a holdover from earlier technology?  If so, it's a waste of components but at least provides a handy socket for the decoder.

All decoders include the necessary diodes to convert DCC (ac power) to dc power to operate the decoder and feed the motor.

Unless someone can explain the purpose of the board in Bachmann locos, which I have been told is not used in other brands, the only way I can resolve this in my mind is to remove the board completely, then hardwire a Bachmann decoder and see what happens.

The purpose of the board is threefold:
(1) to provide noise suppression so that Bachmann locomotives can be sold world wide.
(2) to allow directional lighting on dc.
(3) to provide a socket for plugging in a decoder or a dummy plug.
Not all manufacturers use this type of board because they are satisfied with only a limited market.  But most manufacturers have some kind of lighting board for directional lighting and it often includes a socket or is designed to be removed and replaced by a decoder with a similar or identical shape.

Several have told me they removed the board and hardwired a decoder in a Bachmann, they did not mention the decoder brand.  I have asked them if the loco was still DC compatible, and have not received an answer.  Is there an element of risk in trying to run DCC locos other than Bachmann on DC power?

I am one that has, on occasion, removed a board and hardwired a decoder into a Bachmann tender.  There can be several reasons for this - the decoder on hand does not have a plug; the owner wants the decoder in the locomotive and a sound system in the tender; the adapter board is faulty on DCC (but might still be okay on dc); the tender wiring is damaged or does not correspond to the locomotive (tender swap) and probably other reasons.  The locomotive is still dc compatible, as long as the decoder supports analogue converion (and most of them do.)  There is no danger in trying to run DCC locomotive, Bachmann or otherwise, on dc, even if the decoders in them do not support analogue conversion.  "Analogue conversion" is just a fancy term for "automatically switches over to dc operation if no DCC is present and you want it to automatically switch over."  In all decoders that use analogue conversion, it can be turned on and off by programming with a suitable command station.  And most if not all modern decoders do support analogue conversion.  If you want a brand name, I use Digitrax decoders almost exclusively because I have a good supply line, but there are many other good decoders out there.  Bachmann decoders are the easiest to install and use in Bachmann locomotives because their design includes allowances for the motor noise suppression that Bachmann uses.  With other brands, you either have to remove the capacitors from the adapter boards or from across the motors.  With some decoders, including Digitrax, you have an extra option of reprogramming the decoder to deal with the noise suppression circuitry, but again you need a suitable command station to do so.

I plan to order a Bachmann Mogul DC, and convert it to DCC by wiring in a Bachmann decoder.  Two scenarios:  If it runs on DC, then it will prove the decoder is indeed dual mode, but it also means that no extra circuitry (like the board above in question) is needed.  If it will not run on DC, then the decoder is not dual mode and I will have to obtain a decoder that is.

Hard wiring a decoder in your Mogul will indeed prove that you can have great operation on both DCC and dc even with the adpter board removed, with only one exception.   That exception would be double heading with a similar locomotive not fitted with a decoder.   I have gone into that on the posting on the 2-8-0 problems.  By the way, with the proper decoder installed, the lights will even work properly on dc as long as you make sure they are left turned on when you take the locomotive off the DCC track.

Perhaps I am the only one in the world that wants all my DCC locos to be DC compatible.  Well, that's just me and I have my reasons.

Thanks everyone for your time. I have searched the net for weeks and can't find the information I seek.

Bob

You are not alone in wanting your DCC locomotives to all be dc compatible as well.  Your reasons may be unique, but not your desire.

I hope this rather long posting has given you the information you have been looking for.  If not, keep on asking. 

[Yampa Bob]

Jim
I knew you would come through for me. 

I did remember that capacitors were used for noise suppression, but I had momentarily forgotten about the diodes required for directional lighting on DC.  My only defense is  "DUH"... The board does provide for a convenient socket. 

Ok, then to sum it all up:
1. Since the decoder has built in rectification and provides directional lighting, the board is not needed for DCC, except for the suppression issue, and Bachmann decoders will work fine with the capacitors intact.

2.  I do not plan to double head a dc loco with a dcc loco, so there is no issue there.

3.  This is an assumption, please correct me if wrong.  I assume Bachmann DC locos (non DCC ready)  have the suppression capacitors on the motor  If not, what is the best way to achieve suppression once I hard wire the decoder into the Mogul ?  Would connecting capacitors from the Orange and Gray motor wires to a common wire connected to the motor case do the job?  For that matter, is suppression even necessary? 

One final question, relating to some extra DCC boards I have from GE 70s, as mentioned in my first post.  They have solderless terminals and might work ok in a Mogul. providing the stall current is correct.  Any comments on that?

On behalf of myself and other modelers venturing into DCC, thank you very much for your kind input.

Bob

[Jim Banner]

Motor noise suppression is not required in North America - the FCC will not come knocking on your door if you leave the suppression components out.

As for the board, if Tony's says it will work, that it good enough for me.

[Yampa Bob]

I'm not concerned about the FCC, only about possible interference to our own TV.  I once had an old loco and controller that caused some specks on the TV, which my wife didn't appreciate.  Anything that plugs into the house circuit has a potential for interference.  Good old Part 15.

Bob

[Jim Banner]

Bob, I suspect that the specs on your wife's tv were back in the days of rabbit ears.  With cable, or even an antenna in the attic, this should not happen.

Remember the "good old days" when airplane flutter and ignition noise were common problems?  I had a friend who claimed he could tell whether it was a straight 6 or a V-8 going down the street, just by looking at the specs it caused on his tv.  Needless to say, none of us was willing to stop the cars in question and ask the drivers what they had under the hood, so we never knew if he really could tell or was just pulling our legs.

Come to think of it, I don't remember seeing either of these problems in recent years, even on a portable tv with one rabbit ear.  Maybe improvements in tv sets have made these types of interference a thing of the past.  And maybe interference from model train motors is a thing of the past too.

[r.cprmier]

Jim;
Wouldn't it make sense that there are more ignitions per second with an eight than a six?  Therefore, the frequency of occurrance would then be greater.  I have a twelve-cyl Jaguar XJS.  I bet that would raise holy merry hell too...

[Jim Banner]

Rich, you are undoubtedly correct.  Mystery solved.