DCC working on DC

QUOTE i thought that if i put the loco on my normal DC system it would sit there with comms because the chip would isolate the power. but the log started to move in both directions with no problem???? is this normal.

Yes. This is normal. I believe it is possible to change a CV in the decoder so that it doesn't run on DC but this is not how they are delivered from the factory. I don't know why this facility is available but I am sure someone else (cue Richard) does and can enlighten us.

QUOTE i can't understand if the DCC system is always live and the loco has to be told to move by the decoder why when i put it on my old DC sytem the loco moves

The DCC system is always live.
The loco has to be told to move by the decoder.

Here's the vital bit of info you need...
When you put the loco on DC, the decoder gets power and the software recognises that the signal on the rails is DC not DCC. The program in the decoder then runs the loco as if it were DC. So there it is. Although there is no DCC signal, on DC the decoder decides to drive the motor anyway. Clever little beasties are n't they?

QUOTE sorry if this is simple to explain but it well confusing to me
No apology is needed. It seems to me that you have a pretty good idea of what makes DCC work. It was just bit about the "autonomous " decoder that was foxing you.

David

David

thanks for the fast reply now i under stand. your explanation is first class.

Mark

QUOTE thanks for the fast reply

Beginner's luck! and welcome to the Forum too by the way

David

QUOTE (dwb @ 14 Jun 2008, 02:43) <{POST_SNAPBACK}>Yes. This is normal. I believe it is possible to change a CV in the decoder so that it doesn't run on DC but this is not how they are delivered from the factory. I don't know why this facility is available but I am sure someone else (cue Richard) does and can enlighten us.

David

***Good response David. Spot on. ALso - loco's with chips often run better on DC than they did before they were chipped - thats because the motor control is still via the chip which is mre clever at managing the motor than a DC controller.!

Re the ability to turn off running on DC, its done by looking at CV29 and taking away 4 from that numbe.

examples:

(1) a decoder set to short address have default CV29 set to 6 - if you change it to 2 then DC running will be turned off

(2) if it has been set to a long address, then CV29 will probably be 38, so setting it to 34 will turn DC running off

Why turn DC running off?

(a) If you turn DC running off, it will enable "brake on DC" function, which will allow a loco to automatically slow and stop at a signal etc if the layout has been specially wired to do this.

(b) sometimes some power supplies may be unstable, some brands of controllers and sometimes the wiring of the layout may be not good enough or at leaset way less than perfect and occasionally loco's will do strange things or suddenly start all by themselves. This is because the imperfect DCC signal is creating problems causing the loco to think it is on DC and it just takes off at full speed.
If you tirn off DC running then it will stop this happening (although its better to find the real cause of the problem and fix it properly)

Regards
Richard
DCCconcepts

QUOTE (Richard Johnson @ 14 Jun 2008, 05:40) <{POST_SNAPBACK}>***Good response David. Spot on. ALso - loco's with chips often run better on DC than they did before they were chipped - thats because the motor control is still via the chip which is mre clever at managing the motor than a DC controller.!

Re the ability to turn off running on DC, its done by looking at CV29 and taking away 4 from that numbe.

examples:

(1) a decoder set to short address have default CV29 set to 6 - if you change it to 2 then DC running will be turned off

(2) if it has been set to a long address, then CV29 will probably be 38, so setting it to 34 will turn DC running off

Why turn DC running off?

(a) If you turn DC running off, it will enable "brake on DC" function, which will allow a loco to automatically slow and stop at a signal etc if the layout has been specially wired to do this.

( sometimes some power supplies may be unstable, some brands of controllers and sometimes the wiring of the layout may be not good enough or at leaset way less than perfect and occasionally loco's will do strange things or suddenly start all by themselves. This is because the imperfect DCC signal is creating problems causing the loco to think it is on DC and it just takes off at full speed.
If you tirn off DC running then it will stop this happening (although its better to find the real cause of the problem and fix it properly)

Regards
Richard
DCCconcepts
Thanks for the information I've found out lots of new things regarding DCC