debugging a problem on a club layout.
a DCC Specialties circuit breaker has problems coming up without immediately shutting down.
while adding jumpers to measure current (~160 ma) we noticed that locos had power when one rail was disconnected from the circuit breaker (knife switch open, clip lead across on connection)
we then measured the voltage between each rail powered by that breaker and rails powered by a 2nd breaker with both wires from the 1st breaker disconnected with a knife switch.
we measured ~0 V on the one rail but ~7V on the other rail.
does this suggest the one rail connected to the multimeter is at ground? how would that be possible?
greg - Philadelphia & Reading / Reading
Greg.
The more I read your post the more confused I am getting.
You power up the layout and one breaker is tripped and will not recover. Correct? That would indicate a short in the district controlled by the breaker. Is this a newly installed breaker? Is the trip current set for the proper trip current?
What are the knife switches wired like? For disconnecting one rail before or after the breaker?
If you disconnect the track leads to the breaker and remove everything from the district. Can you Ohm the two rails to see if there is a short?
Most good multimeters can handle up to 10 amps going through them but I strongly recommend not doing that. I had a great Fluke meter and the contacts in the switch friedaand the fuse never popped. Better to de energize the layout and check resistance first.
Pete.
wrench567 The more I read your post the more confused I am getting
the installation has been in use for years and particular breakers have problems coming up when the layout is turned on. so i'm helping investigate
each breaker has a DP knife switch to disconnect it from both rails. the first thing we did was use an rrampMeter to measure ~160 ma without any locos on the track, presumably due to many(?) stationary decoders.
but when measuring with locos on the track, we noticed that the locos still had power with just one connection between the breaker and rail
so it appears there is an additional connection between one of the rails to one of the other breakers. locating that connection may be difficult. wondering what 7VAC instead of 14V means and if that's a clue
presumably we can disconnect all the breakers from the track and use an ohm meter to check for a path between the rails on different breakers.
A couple of reasons why there's 7V -
Mark P.
Website: http://www.thecbandqinwyoming.comVideos: https://www.youtube.com/user/mabrunton
The fact that there is voltage on the rails with the knife switch in the off position indicates that the is leakage between districts. Either a gap is closed, feeder connected to the wrong buss, or even a brass or metal rolling stock truck bridging a gap.
Good luck.
In electronics there are a thing called wiskers that pop up from time to time. They can cause anything from a dead short to slight leakage. Even on a new layout (mine) they can appear after a dead short where everything was perfect before (like leaving a caulk gun on the layout when powering up), these can be fun to try and track down at times.
all tracks appear to have correct power when all knife switches are closed and breakers come up properly
gregc all tracks appear to have correct power when all knife switches are closed and breakers come up properly
Even the one you posted about? Even though the other districts power up, there is leakage or even a short to the tracks giving you a problem. Have you tried to swap the suspect breaker with a known good one? If the problem migrates with the breaker than you know it's bad. If not then the track or wiring is the issue.
wrench567Have you tried to swap the suspect breaker with a known good one?
but then we found that the locos had power with just a single connection
Sounds a lot like either a gap closed somewhere (can happen) or that there is a connection "not known". (A jumper wire maybe? Screwdriver or other tool?)
Or, your "off" breaker isn't fully "off". (Could be a bad DP switch too.)
Either way, rule out the breaker first, then start ruling out other things.
As Sherlock Holmes said, whatever is left, no matter how impossible, must be the answer.
But the breaker is easiest to check and rule out quickly. So I would start there, then progress to more "it can't possibly be that, but what if we..." stuff.
Ricky W.
HO scale Proto-freelancer.
My Railroad rules:
1: It's my railroad, my rules.
2: It's for having fun and enjoyment.
3: Any objections, consult above rules.
One thing to note about the DCC specialties circuit breakers is they only disconnect one leg of the track to kill power. The other leg is just a pass thru. Depending on how the layout is wired you could have the pass thru leg on one breaker be rail A for example and then be Rail B on another breaker. This would allow power to still pass through a set of blocks ever if there is a a disconnect of one of the rails.
It does sound like you have a set of blocks where a gap has closed and its allowing pass thru to happen. Recommend using the quarter method to determine if multiple breakers trip if short out a single block. This should help you narrow down which blocks are connected together.
multiple breakers by Chuck Lee, on Flickr
As shown above, the inputs to be breakers are not consistent.
If the layout is wired like in this picture (not best practice) and one of the two gaps closes up, it can allow leakage across the breakers and still give power to both districts because only one leg of the breaker trips. The other is just a pass thru.
Below is what I would consider best practice where inputs and outputs are consistent across all breakers. Should a gap close up it makes it much easier to diagnose which block(s) have cross connections.
multiple breakers-BP by Chuck Lee, on Flickr
7 Volts generally indicates you are getting a half wave signal. When measuring DCC voltage, its generally good practice to measure rail to ground and rail B to ground and add the two voltages. In this case it seem you are only getting a single side of the voltage.
Hope this helps.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
Renegade1cOne thing to note about the DCC specialties circuit breakers is they only disconnect one leg of the track to kill power.
i see only 2 mosfet and 2 mosfets are needed to break a single path. most circuit breakers and auto-reversers have 4 mosfets (if not relays). thanks for pointing this out
a circuit breaker needs to not only prevent shorts between the rails of a particular track, but also between rails of different tracks. disconnecting just one rail wouldn't necessarily do this.
the breaker also needs to be able to detect a short in either path, as well as disconnect both paths.
Renegade1c7 Volts generally indicates you are getting a half wave signal.
Renegade1cWhen measuring DCC voltage, its generally good practice to measure rail to ground and rail B to ground and add the two voltages. In this case it seem you are only getting a single side of the voltage.
gregc Renegade1c When measuring DCC voltage, its generally good practice to measure rail to ground and rail B to ground and add the two voltages. In this case it seem you are only getting a single side of the voltage. why? how convenient is it to reach ground
Renegade1c
When measuring DCC voltage, its generally good practice to measure rail to ground and rail B to ground and add the two voltages. In this case it seem you are only getting a single side of the voltage.
why? how convenient is it to reach ground
Its not usually convenient to check against ground. Most Volt meters generally don't measure true RMS so even when measuring set to AC it will not usually be the most accurate.
By measuring to ground you get the most accurate representation of track voltage.
I don't generally do this but that could explain the 7 volts.
IF you look at the PSX-ar they do have numerous FETS to break and reverse both legs but the standard PSX do not.
i found out today that the knife switch is between the circuit breaker and booster, not the track
measurement accuracy is not the issue