DCC Volt loss Maximum

[RF&Prr]

 Using a 5A NCE DCC system for HO, and assuming a full load of 5A (multiple- 5 or 6 sound equiped engines MU'd) at the farthest point?   I don't want to just rely on the quarter test after having purchased the wire for the layout.  My feeder runs off the main bus will be a maximum of 20" or less and the longest main bus run is 48 ft from the midpoint of the layout where the DCC system will be located.

 I am looking for the maximum voltage loss acceptable to the DCC system and still trip the breaker on a short.  

Thanks,

RF&PRR

[rrinker]

#12 wire with a 48 foot bus run (96 total feet of wire) will have a drop of .9 volts at 5 amps. 5 or 6 sound locos probably won't draw 5 amps unless you grab the wheels of all of them so they can't turn, so the actual drop will be less. And unless you have all 5 or 6 on the smae train they probably won't all be at the same spot at the same time.

 Assume a more realistic 3 amp load, the drop will be slightly over .5 volt.

                          --Randy

 

[fwright]

Some of the more sensitive (not in the good sense) decoders, such as earlier MRC, would lose the DCC control signal at around 5% voltage drop, or 0.7 volts for 14 volt on the rails.  Most decoders will tolerate double that voltage drop.

As Randy's calcs show, you should be in good shape.  The allowable voltage drop (there is no spec for voltage drop in the NMRA DCC RPs) is based on 2 things - making sure your circuit breaker trips on a short circuit on the track, and keeping the signal robust enough for decoders to track.  If you meet one criteria, the second almost always follows.

I'm not a big fan of beefing everything up for 5 amp loads/capacity unless absolutely necessary.  When shorts do happen, 5 amps starts creating real sparks and pits before circuit breakers pop.  It's much better IMHO to limit the current in a given power district to the 2-3 amp level with light bulbs or adjustable circuit breakers/current limiters.

my thoughts, your choices

Fred W