I have an early Digitraxx Empire Builder system that has worked well for many years. The DCS100 has been set on the "N" scale voltage all this time. Now, I'm starting to run some sound decoder equipped engines, and have heard that a higher voltage ("HO" setting) would be better. When I throw the switch to "HO" I see shorts being detected on my two PM-4. I have two reverse loops, a turntable, and six layout sections controlled through the PM-4's. Power is supplied to the rails by 18 ga feeders off of a 12 ga bus. Is there any good reason for the shorting to occur only at the higher voltage?
GNR8055 I have an early Digitraxx Empire Builder system that has worked well for many years. The DCS100 has been set on the "N" scale voltage all this time. Now, I'm starting to run some sound decoder equipped engines, and have heard that a higher voltage ("HO" setting) would be better. When I throw the switch to "HO" I see shorts being detected on my two PM-4. I have two reverse loops, a turntable, and six layout sections controlled through the PM-4's. Power is supplied to the rails by 18 ga feeders off of a 12 ga bus. Is there any good reason for the shorting to occur only at the higher voltage?
Are you seeing shorts on all sections of the PM4s or just certain sections ? If it is just certain sections, have you tried removing everything from the track and then powering up to see if this resolves the issue ? If so, it may be related to the current limit setting on the PM4s and the higher current being drawn caused by the increased voltage. Are these still PM4s or have they been upgraded to PM ? Is your layout N scale or HO scale ?
Engineer Jeff NS Nut Visit my layout at: http://www.thebinks.com/trains/
Great questions. First, it is an HO scale layout with original PM-4's that have not been upgraded. It's been awhile, but I believe the PM-4's are set on the lowest trip current. I have the ability to turn off each section, so I will try to isolate the shorting problem that way. Am I correct in using the higher voltage with sound decoders or does it really matter? Is there any downside to the higher voltage? Years ago (about 10) when I installed the system the recommendation was to run the lower voltage. Thanks.
Well in DC sound equipped engines eat up a lot more voltage than a standard DC engine. In DCC the rule of thumb I've heard is to assume a sound-equipped engine would count as two regular DCC engines...although I don't know if the issue there is volts or amps?? Anyway, in HO DCC normally runs about 14V AC on the track, I'd maybe try measuring the output of your system in both N and HO settings. Could be since it's older the power output isn't the same as it would be on a new system built today??
Voltage shouldn't matter. I ran sound locos just fine with a Zephyr which has a fixed track voltage near the N scale setting. Most models still run too fast at full throttle, either faster than the actual prototype or too fast for the size of most layouts (even 30 scale mph is too fast for 24" radius curves and #6 turnouts but we won't go that far), so using the N scale setting should be just fine, even with sound locos. The sound system doesn't affect the DCC speed - it does when they run on DC because they are set up so that the sounds come on before the loco starts to move - so with a DC power pack you end up cranking it up half way before the engine even moves. When running on DCC, at full throttle approximately the same voltage is applied to the sound unit's motor as that supplied to the motor of any other unit with a decoder in it.
CHanging the voltage with nothing sitting on the tracks should not cause the PM4 to trip. Nothing on the track, nothing conencted to it, no current being drawn regardless of the voltage. With a fixed load, the higher voltage will yield higher current, but the difference should be miniscule - if the PM4 was running that close to tripping on the N scale setting simply holding back a loco would have been the same or greater increase in current as changing the voltage to the HO setting.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
randy, you said......With a fixed load, the higher voltage will yield higher current, but the difference should be miniscule.
i know im new to this dcc stuff but according to ohms law,with a fixed load shouldent the current acculy be lower when the voltage is raised....or is dcc different. sorry just wondering
To get the same work out it would be less amps - which is why you see dual ratings on things that can work on 120V and 250V, and it's usually half the current.
However - if you have a fixed load across the tracks, say 1K ohms, the current flowing through it at 12 volts would be 12/1000 = .012 amps. At 15 volts it would be 15/1000 = .015 amps. On the other hand, a locomotive motor should be able to pull the same load with less amps at the higher voltage. The resistance is not fixed for a motor, it varies with rotation speed and strength of the magnetic field. E (votls) goes up and R goes up, so I goes down in that case.
A fixed load would be something like resistor wheelsets for block detection.
yes i see what u mean now thanks forr clearing me up on that........
i wasent thinking of it in that terms.
thanks
You shouldn't need to upgrade that PM4. The upgrade came about due to a specific set of circumstances. One advantage to purchasing the upgrade chip is the additional current settings. Original PM4 had trip current settings 3 amps apart.
With a 5amp booster, the default 3amp setting is the only choice that will work. With the PM42 upgrade chip, you get 1.5 volt increments which allows setting the trip current to 4.5 amps.
Martin Myers