Posted By jimtyp on 10/16/2008 9:38 AM
The following is a quote from the document below "NMRA recommends 12V for N-scale, 14.25V for TT, HO, S, O-scale & 18V for G-scale"
Source:
Wiring
Hi Jimtyp -
I was going to ask you for a link to this wiring source since I couldn't find it in the NMRA standards and RP's, but when I used the 'quote' feature in this forum it turns out that the word wiring was the link already.
When that text is quoted, 'Wiring' is underlined to show it's a link - in the original post it's not underlined. If I look real close, in the original post, I can see now that the word 'Wiring' is in dark blue (which I assume indicated a link), but that colour is so close to the black of the rest of the text that it's not noticeable.
I really wish mls wouldn't be using alpha software to run this forum - it just wastes so much time and the bottom line is that people just don't post.
As to the presentation you linked to - it desperately needs an update. It's more than five years old and a lot of things have happened in DCC. Not only are there things missing in the presentation but some items are no longer correct.
As to this NMRA recommendation - I still don't know where it is in the current NMRA specs, but I do remember the 14.25 volt number for H0.
That is based on the maximum specified voltage of 12 volts DC for H0 plus the expexted drop through the DCC decoder.
What you want to achieve with DCC is the same maximum voltage at the motor leads of the engine as you would have if you were running DC. So for H0 that makes sense.
I'm not sure where the 18 volts for G-scale comes from. For the last ten years at least, G-scale DC power packs had a maximum voltage of typically 24 volts with the odd one at 22 volts, so the DCC voltage for G-scale should have been defined at 26 volts to get 24 volts to the motor.
For some reason which nobody has ever been able to explain to me, NMRA specifies the maximum DCC voltage to the track at 22 volts which in turn only allows up to 20 volts to the motor which is not enough for some engines.