DCC concerns


Midnught Special

Midnught Special

Member
Ok I just got one of my cheap locos fitted with DCC, and before anyone says any thing about "spending more on the DCC then the locos are worth" please leave that out of the thread ;) anyways I got the Queen Elizabeth fitted with a DN163 (thats what the paper says) how ever when running it on my DC set up (least until I get my DC controler) it behaves a bit erraticially, when its set up with factory settings and values it runs fine, like a bat out of heck.

how ever when I try to adjust the speed curve to limit the unit to a specific speed cap it behaves a bit erraticially, mainly seems to be jerky. im trying to set the engine to cap at speed step 128 at 100 (im assumeing its scale MPH) for some what of a proto realistic top speed.



anyways what im trying to figure out is how can I do this, I am using JMRI so when I set the speed table up I use one of the graduating curves (I forget which button name it is but its like the first or second to the far left) and then write the values to the decoder, and then when testing on the layout it acts like it wants to die, also when I ran it flat out (with the configured speed steps to cap at a realistic top speed) it started real slow like I wanted then it just stopped tripped my DC circuit breaker then after it reset (the breaker) the engine was re tried at full it did the same except the second time it slowly started, stopped then two seconds later shot off like a bat out of heck again.


so I am wondering whats going on here, do I have a problematic decoder or is something else going on? the decoder that is being used is rated for the motor type in the engine so it should be working with out issues there, I have no lighting at all on this loco and I just needed basic control of the loco in question.


Thanks for the help!
 
Jim, I had a similar problem several years ago with a loco that was running great, then started doing exactly what you describe. This is how I fixed it in JMRI, after I found that a decoder reset didn't help.

In JMRI, under the motor tab, there are a series of speed compensator entries. The first is 128, the second is 48 and the last is 6. These are the default values. I set these to zero, thinking I could start raising them as needed. When I tested the loco after doing this, the loco ran perfect. They are still at zero.

Now this may not work on yours, but it did work on mine so I figure its worth a try. If it doesn't work, you can always reset the values back.
 
ok, I will give it a try, i am resetting all values to default as I know (and figured) out where the throttle limiter is located so I may try that, but that seems to be only good for when your using DCC and not DC mode, and I want to try and figure out a way to limit the speed in both DC and DCC opperations...
 
DCC works best with 'dither' entered, some BEMF, and otherwise 'torque compensation'. You must get into the manuals...no ifs, ands, or buts.

Speed tables take a long time to tailor manually, so many try JMRI and just slide the values. It's quick and JMRI saves the records.

Otherwise, your mid range voltage and top voltage are what matter for you. Set CV 6 for a value near halfway through the range of possible values the manual states that CV has, and set CV 5, for the highest voltage, near the top range for the value that CV can take according to the manual.

Next, you have to be able to figure out how quickly, in scale, the loco is moving at certan speed steps. Mark out a scale quarter mile and time the loco through it. Figure out from there how fast it is going in mph.
 
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