I am really confused, which doesn't take much. I have switched back to DC to test my track after adding an extension. Everything has been working just fine, until it just stopped. I turned everything off, came back a little later and things were working again. After a few minutes, stopped again. Tried a different locomotive, things worked. Few minutes later, stopped. Removed the locomotive and hooked up the meter to the rails. Meter shows the voltage changing with the throttle; so far, so good. Put the second locomotive on the track, voltage drops to about .1V (from about 6V). Put the first locomotive back on, everything works. A few minutes later, it stops--meter showing .1V. Remove the locomotive and it jumps back up to 6V. Put the second locomotive on, everything works then fails. Same symptoms. Eventually nothing works. I even tried a brand new locomotive and it caused the voltage to drop to near zero. It almost seems like anything that draws current is causing the voltage to drop. Any suggestions? (Be gentle--I am still a relative novice to all of this electricity stuff.)
Richard
Check it with another power pack if you have one as it sounds as though it may be a faulty power pack. Or disconnect the pack and remove all angines and measure the resistance between the rails. You may have something creating a short. Not a direct short but drawing enough current to trip the overload in the power pack.
Hope this helps,
Mark
I removed all locomotives, disconnected the power supply, hooked up the meter and it does not appear to show a short. As for an alternative power supply, the power supply I have is the dual throttle MRC Tech 7 780. The question is, are there two, independent power supplies in the unit, or do two throttles share a single power supply? The reason I ask is that I tried hooking up the second throttle on the Tech 7 and had the same failure.
RideOnRoad I have switched back to DC to test my track after adding an extension.
Assuming the problem is with the new extension and not the throttle, try disconnecting the new extension to isolate the problem.
If it's in the extension, you can try measuring the current thru the extension without any locomotives on the track to see if there is any type of short drawing current,
If there is, try further electrically dividing the extension to further isolate the problem.
greg - Philadelphia & Reading / Reading
gregcAssuming the problem is with the new extension and not the throttle, try disconnecting the new extension to isolate the problem.
Unforunately, the extension is part of the main line loop. It is integral to the layout and cannot be easily disconnected. Also, it has been working fine for a week or so. The intermittent, then complete failure, just happened today. My gut is telling me it is the power supply failing...
It really sounds like you have a faulty power pack. Yes the dual pack has only one internal power supply that is shared by both throttles. So failure of the supply would mean both throttles would exibit the same behavior.
You mentioned switching back to DC from DCC. If still available, connect your DCC system after disconnecting DC and give it a try. If power stays constant as it should with DCC, your problem is the DC power pack. If there is a short trouble is on the track and wiring. DCC will show a short much faster than most DC packs.
Martin Myers
You don't have something DCC related still connected to your track, do you?
maxman You don't have something DCC related still connected to your track, do you?
I can swap the DCC power supply back in fairly easily. I have DCC-enabled locomotives that I can use to test. I will give it a shot tomorrow and see what happens.
The MRC Tech 7 780 has two independent power supplies, meaning
separate transformers. It was designed for cab control with common rail wiring, so it must have two transformer's in order to do that.
http://www.modelrectifier.com/search/product-view.asp?ID=13444
Take Care!
Frank
Frank: That's what I thought, which tends to discredit the transformer failure.
Before I switch back to DCC, I am going to try the transformer on a piece of test track. Isolate your variables--problem determination 101.
Here's the update.
I hooked up a section of test track to the first transformer and everything works like a charm. I hooked up the second imbedded transformer to real track and it failed. I placed a locomotive onto a completely insulated (but not isolated, in that they share the same power bus) and it fails with a locomotive on that track. All indicator now point to a problem with the track.
This is where I am at a loss. In my mind, a short is a binary thing--either there is a short and you see the drop in voltage regardless, or there isn't and everything works. This seems to only short out if there is current draw on the line. I know the locomotives aren't shorting, in that they work just fine on the test track. I don't know where to start to determine the cause.
not long ago, someone had a problem where combinations of things had a problem. Eventually it was realized that the current limit on the supply was exceded and protection circuits shut it down. There were several locomotives with sound on the track. Each drew a decent amount of current just sitting still. One more loco broke the camels back.
Have you tried putting an amp-meter between the trottle and the track to measure the current without a locomotive on the track (should be zero) and with it on the track (something about zero).
You can also use probes to connect the throttle directly to the wheels of the locomotive to measure the current to the locomotive.
as you said, try to isolate where the problem is as well as were is isn't.
I asked my local electrical expert (my retired father) for advice. His comment was it sounds like a "cold solder problem." He told me to check all of the connection points to determine if there is a marginal connection anywhere that could be creating significant resistance when the circuit is closed with the introduction of the locomotive. This is going to take some time...
wouldn't a poor solder joint result in a loss of power not a short or partial short?
my crystal ball is pretty cloudy, so i avoid guessing and try to methodically solve problems ... did i mention isolate ?
Here is the update. I spent the day isolating and diagnosing. I started with the back loop and worked my way back. I did find a couple of loose feeder wires that I resoldered. Bottom line, after disconnecting and reconnecting, everything seems to work--for now. We shall see...
Richard,
Your loose feeder wires were creating a high resistance in the circuit and the supply was seeing it as a short and shutting down, hence Your thread title, ''Odd Short-Like Behavior".
zstripeYour loose feeder wires were creating a high resistance in the circuit and the supply was seeing it as a short and shutting down
how is high-resistance a short? ?
I think people get confused easily about this.
If you have insufficient feeders, and you have a short, such as a loco derails and sits diagonally across the tracks - the resistence of the poor feeders means that instead of a short, you actually have a resistive load - rail ro rail through the derailed loco, back to the power supply through not nice clean heavy wire connections with almost no resistence, but instead poorly attached undersized feeders which do have significant resistence. If this resistence is sufficient such that the current flowing through this "short" circuit is under the trip point of the power source's fuse or circuit breaker, it will never trip. In the case of say a 5 amp DCC booster - if 4 amps is flowing, the breaker will never trip, it's good for 5 amps. But you have 4 amps flowing through the frame of the loco. At 15 volts, that's 60 watts. Ever touch a 60 watt light bulb that's been turned on?
In the case of insufficient feeders but otherwise everything is OK, no derailment, no Kadee coupler gauge across the rails, etc., that extra resistence manifests as a slowing down of the loco, not as a power supply short. The available power to the loco is reduced, but there's nothing happening that would cause the power suppyl breaker to trip in this situation. If the loco in this case is drawing 1 amp, then 1 amp is flowing at all points of the circuit. Loose joiners or poorly attached feeders may get warm, but the bad joint does not increase the current being drawn by the overall system of loco and feeders.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.