I vaguely remember a post about a month ago and if I understood it right, the poster said there was a problem MUing a sound loco with a no-sound one. Something about the power draw being different but I don’t remember for sure. Can someone tell me if this is true and what the issue is with that. I have a BLI F7 AB set and both units have sound which seems kind of redundant. Should both units of an AB set, or any other MU arrangement, be configured the same way?
John,
That is correct. The sound decoder is more power hungry. So a “non-sound” unit will begin moving before the unit with the sound decoder in it. A way to remedy this is to either 1) run your A-B units with a dummy B, or 2) adjusting CVs with your DCC system, speed match the B-unit to the A-unit the best you can.
Tom
Thanks, Tom. I am considering buying a second set of NYC F7 AB, with different road numbers than the first set and I thought it would be cheaper to by two non sound units and just swap the A and B shells from the two sets to have sound for both pairs. I may still do that if there is a way to get the speeds to roughly match. I’d need to swap headlight as well.
John
John,
Another way to handle it is to just have the A-unit powered and all the sound (decoder, baffle, and speaker) in the dummy B-unit, where there’s plenty of room. Unless you really need the extra power for steep grades, a good strong A powered/B dummy unit (e.g. Stewart or Athearn) will probably more than suffice, be cheaper, and sound better because of the extra room in the B-unit. If you get a similar 2nd A-B combination, you’ll still need to speed match the two separate A-B units.
Tom
The remedies are true, but I don’t think the premise is accurate. With DCC full the power is available to the decoder at all times. The differences are going to de differences in the tuning of the decoder (factory or otherwise), and the mechanics of the locomotive, and these differences can be there in any pair of locomotives, reguardless of whether sound is involved or not. All of this breaks down if you are actually having voltage drops dur to inadequate wiring, or just plain system overload, of course.
EDIT:
I was just thinking, if this is using the sound locos in their DC mode there might be a slight difference in the starting voltages, but I’d have to think on that some.
JE, for what it’s worth: I have a 4 unit FT ABBA set with one of the B’s a dummy filled with sound. The power units have Digitrax decoders and the sound unit has Soundtraxx and 2 speakers. I program the power units with Acceleration/ Deceleration CV’s set at “10”. (the tail A unit is reverse operation) I program the sound unit with them set a “0”. This means that when I open the throttle a notch or two there is a slight lag between the sound revving up/or down, and the speed change. this really mimics the inertia of the real thing. A trick I found since the A and B sets are drawbarred together, I set an old credit card or piece of plastic under the wheels of the unit I don’t want to program change. That way just the unit being programmed is in contact with the rails, eh? jc5729
I’ve MU’d sound and non sound units and haven’t experienced any real problems. However, all units have had their CV’s adjusted so they start at step one and their top speed limited to close to prototypical speed. That does leave some small mechanical differences in the drive linkage which can cause some pushing or pulling on down grades.
Tilden
Logically, this is the key. As previously stated, the decoders must perforce, by design, get all they need for what they do, and that includes metering voltage out to the motor(s). How they meter the voltage is determined by their CV settings in 2,3,4 5, etc. (including the speed table CV’s). After you set CV Start (#2) for each loco on the same section of track, Randy will advise you to try setting low, mid, and high range CV’s first to see if that makes them work passably well when Mu’d. If not, you have a llllooooooonnnhhg row to hoe setting up the speed steps.
So, each decoder must individually have its CV’s tweaked so that it does the bare minimum for its mass and design characteristics with a given CV setting. Using that parameter, both locos should perform at the same time and the same way when you incrementally administer throttle.
If they are the same brand, just one with a sound decoder and one with a regular decoder,t hey will liekly run pretty much the same ON DCC. That whole ‘exptra voltage’ thing only applies in DC, where the loco won;t even move untilt hte throttle is well up since the sound board need the power first so it can play the stationary sounds, then you advance the throttle more and it finally starts to move. By this time a non-sound DC loco is rocketing around the layout. With DCC, this isn’t a problem, you more likely will experience slight variations from unit to unit, or possibly the sound unit uses a different motor and revised drive train to make room for the sound board and speakers. Or if it’s a good sound decoder ike a Tsunami or Loksound with very good Back-EMF for low speed operation and the non-sound unit uses a cheaper decoder without BEMF, The sound one will start and be able to maintain a slower speed than the one with the non-BEMF motor decoder.
Now if you have two completely different brands, like a BLI F unit and an Athearn Genesis F, all bets are off, and you will probably have to do a bunch of tweaking to speed match them. But really the presence of sound has nothign to do with it when running under DCC.
–Randy
If you do have to use speed tables to match units, I’d stongly recommend using DecoderPro. If your command station can be connected to a computer, all you’ll need is to get a connector (or possibly a USB-to-serial converter). The DecoderPro package is a freebie, from http://jmri.sourceforge.net/DecoderPro/
You can download it and experiment (see the screens, etc.) even without being connected to a command station. That same url has all the info on what you need for your command station and computer (Windoze, Mac, Linux).
It also lets you create a roster, with all your CV settings, in case you want to copy one, or have to do a decoder reset, then set all the CVs back to your saved settings.
Yes. on DCC, not DC…
Sound units in series with the motor uses voltage going to the motor, and the volage drop can be as much as 5 volts.DCC can offset this. This means on DC the non-sound can be up and running running when the sound equipped unit is just starting, or a DCC offset is programmed into its address.
In short, DCC can accomandate but DC cannot.
Answer is for DC users not to mix dissimilar engines, (or to use identical drives). My Stewart AB FTs and F3 ABs all run together, but not with each other. (The 3’s have Kato drives).
DCC changes this because each engine can be programmed to a different speed.
BLI (and others) state that “sound equipped engines cannot be mu’d with non-sound engines”. Exception: is removing the gears and motor from a sound unit - thereby creating a dummy with SOUND.
There is no ‘offset’ with DCC power tot he sound decoders, they ALWAYS have full power when the loco is on powered track. Assumign there was a way to somehow disconnect just the sound portion of a QSI decoder in one loco and put another identical one with everything operational next to it, they should out of the box run together, within manufacturing tolerances for the mechanisms. The problem comes inw ith different dcoders and different methods of drivig the motors. I wouldn;t expect two otherwise identical BLI locos to run together if one has the new upgrade QSI chip with BEMF and the RTC features and one was still ont he original chip with no BEMF.
–Randy
Unless the engineers were ninnies![:P] The only reason for it I can think of is if it is related to having DC only sound capability. But why the heck would you do anything to stop the decoder getting full track power. How could you without compromising the DCC signal, anyway? One would have thought all of the dual modeness would be after the rectifier, and the DCC decoder would be pretty much isolated from the sound system, except as it controlled it. I agree Randy, it just doesn’t make sense…