DCC runs slow???

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DaveF

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May 23, 2002
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Hi, building a DCC track for the first time, I finally got a section of track wired with a digitrax db150 and a 5.5amp powersupply built from a kit from loy's toys... I hooked it all up the first time, and havent gotten any decoders into my loco's yet, so I just put one on and ran it at address 00 to test my wiring... I've got no shorts, and the trains run smoothly, however they are slow... even with max throttle they run far slower than on my brothers track with non-dcc power.

I dont intend to race them of course :) but with how slow they run I now have to wonder, does DCC run slower just in general? or do I have some sort of wiring problem?

Thanks.
 
Hi Dave, Welcome to the Gauge. I am not familiar with the db150 but I do have the chief, so would expect similar performance. While there is some drop in speed, it shouldn't be all that noticeable. Is there anyone in your area who has another digitrax system you could run your loco on to compare? I'm in North Jersey and you would be welcome to come by if you are nearby.

While standard voltmeters will not give accurate readings of track power with dcc systems, they can be used to give ballpark numbers. Remove the loco from the track and measure track voltage with the throttle turned to 00 speed. Now measure with speed 100. Now change direction. The chief, when set for HO, puts about 14 to 15 volts on the track. I'm not sure, but I don't think this should change when you adjust your throttle setting. If it goes down it may indicate a problem with your unit.

The dcc signal is a square wave ac, when no throttle is set to address 00, the wave is even. When operating analog locos, one side or polarity of the wave is stretched and starts to look like dc to the analog motor. However, I do not think the actual voltage changes. The motor is actually going in one direction for the duration of one pulse, then in the other for a short pulse, therefore the speed is dependant on the length of the pulses, not voltage.

Install a decoder in one loco and see if its speed is about the same as it was analog, it should be. Good luck.


Gary
 
Dave

I noticed that you were running the loco without a decoder installed. Analog locomotives (one's w/o decoders) will run slower and noisier on an DCC layout. It has to do with the analog loco being run by phased AC voltage, if I understand DCC.
Install a decoder in your loco and you will see a definite improvement in how it runs.

Dan
 
thanks, I was thinking it might have to do with it not having a decoder yet, but couldnt find any documentation anywhere that mentioned that side affect...
 
Dave,
also have a look at the Digitrax website, technical FAQs

Since the DCC signal is symmetric around 0 volts (you have +12V and -12V at the same time, so to speak) the loco sees 0 Volt at first. To be exact: It tries to go forward, then reverse, forward again... So it just is sitting there - and it is humming and getting warm.:eek: Don't 'park' a non-decoder-loco on a live section of a DCC track, it could destroy the motor (notably the ironless mini-motors are vulnerable).

When you apply power, for instance the length of the positive waves (only the 0 bits, to be precise) is stretched. The negative wave stays the same. So the positive side 'wins' and your loco starts to run - as you surely have noted with notably more noise. And also the motor gets hotter than when running on pure DC.

Since there is always that negative, braking part of the wave which tries to run the motor in reverse, all the time the loco runs 'more' forward but also tries to run backward 'only a bit' at the same time. ---> This braking effect might be the cause that your engine runs so slowly.

I haven't made experiments myself, but perhaps my theory could be supported :D (or shredded :o) by some electronic Guru out there in Gaugeland???

Ron
 
I have installed my Digitrax Chief and have been running it for about 2 months now with 2 decodered locos and 5 non-decodered locos. I am having 4 decoders installed in other engines also. I haven't set the speed tables yet so I am just running them with the default settings. All of my non-decodered locos run well on address 00. Mostly 1 at a time but I have had 2 on the track at the same time. They do run a bit noisier than on straight DC and they give off a high pitched whine when sitting idle, which Ron identified above as something you should not do for a long period of time. Once they start to roll the whine becomes a hum and in a diesel engine sounds fine. None of my steam (2 Kato Mikes and 4 Bachmann 2-8-0's make any noise at all. I really have to look around the trackage to find them. I picked up a Soundtrax Decoder and speaker at the Greenburgs on Sunday and am going to try to convert one of the 2-8-0's for sound like the article in MR (Jan03).
 
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