me too
thanks selector ,would the " sub " mean "sub buss " as in forming a power district off the main buss,and if so (1) light per sub buss or district ?
and what was the number of the tail light bulb used ? I want to say 54somthing
Jerry
This should possibily be in the DCC, electrical forum.
Light bulb info in the below link.
http://members.optusnet.com.au/nswmn/1156.htm
Store the link in Favorites. There is a lot more to this subject that the link pretty much covers.
Some use this method. Some prefer circuit breakers. A lot can depend on the size and complexity of the layout.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Remember that the commonly-recommended 1156 bulb is rated at 2.1 amps at 12.8 volts, which works out to 26.9 watts.
By putting that bulb in the circuit, you're allowing 27 watts of current to flow through the short circuit.
That's almost double the wattage of the soldering pencil I use to install decoders, and it's certainly more than enough to melt a plastic truck sideframe, or possibly even start a fire.
Personally, I'll leave the auto tail light bulbs in the circuits they were designed for, and put a circuit breaker in the circuit that it was designed for.
Jerr, the bulb has been mentioned, and yes, the 'sub' means a sub bus. I have found the bulb to illuminate rather nicely, as it is intended to do, and it has performed well at protecting my decoders from amperage they were not intended to receive. The main advantage is that, when they are limited to a defined range of track, they limit the short current to that section. The other sections, with other operators or other engines, will continue to function because the circuit that detects shorts in the base module won't notice the short.
I have never had wheels or sideframes glow like a tungsten filament, nor get hot to the touch.
Crandell
Stevert Remember that the commonly-recommended 1156 bulb is rated at 2.1 amps at 12.8 volts, which works out to 26.9 watts. By putting that bulb in the circuit, you're allowing 27 watts of current to flow through the short circuit. That's almost double the wattage of the soldering pencil I use to install decoders, and it's certainly more than enough to melt a plastic truck sideframe, or possibly even start a fire. Personally, I'll leave the auto tail light bulbs in the circuits they were designed for, and put a circuit breaker in the circuit that it was designed for.
The bulbs will not act instantly; but will limit the current in the power district. Here is a 'table' of various auto lamps and their limit rating:
1152 - 1.4 amps
1142 - 1.5 amps
1156 - 2.1 amps
1157 - 2.5 amps
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
There is a bit of a flaw in your logic....
The 25W (Watts is power, not current) is being disappated at the bulb, as light and heat. The resistance of the bulb at about 2A (that's the current) goes up from near zero to sixish Ohms, which means that most of the power in the circuit goes from being disappated by the layout, to be diassapated by the bulb. So, yes, there is about 2 Amps in the circuit, but very little voltage left after the 12V dropped over the bulb. So, the power that can be turned into heat at the layout actually becomes pretty small. That's not to say it is impossible that something could burn, but it isn't quite what you are picturing. The biggest risk is in a "almost" short situation, where the bulb hasn't made it's non linear jump, whcih could cause cansiderable heat at the near short. A 12 Ohm "short" situation would draw about about an Amp, not enough to light the light, but about a 12W load. Then something could well get hot. Of course, a breaker isn't going to catch that either.
Jeff But it's a dry heat!
Nope. Devices in series, the current flow through them is the same. So if 2A is goign through teh bulb, 2A is going through the rest of the circuit. There is no 'subtracting'. VOLTAGES in series add.
It's the same as figuring a resistor value for an LED. The current flow through the resistor is the same as the current flow through the LED.
In the case of a 'perfect' short, then there is indeed 0 volts through the short, it's a piece of wire. But unless the derailed loco is jammed into the rails, the odds of it being near zero ohms are quite small.
A better light bulb solution is shown on Dick Bronson's RR-CirKits web site. For a few cents more than just the proce of the bulb, Dick's circuit uses a dual filament bulb and a PTC resistor to switch between oen filament and the enxt, the one limiting current to under 1 amp, the alrger one beign around 2 amps. So uyou have the initial surge handling of 2 amps, but on a sustained short the PTC resistor causes the short to change to the higher resistence lower current second filament in the bulb, cutting the long term sustained current int he short.
I still do not consider this a true short circuit protection system. It does not compeltely cut power int he event of a fault. You really want the power completely cut. Not sure where allt eh problems are, but I used a Digitrax PM42 and even with Tsunami and other sound dcoders all in the saem section (I have 4 sound locos), it resets just fine after a short WITHOUT havign to tip the locos off. Other have said they have problems with even just ONE sound loco on the track.
Don;t get a PM42 unless you have a Digitrax system, you can't program them without a Digitrax throttle (at least not easily). But if you do have Digitrax, they work great - and do things the otehrs don't - liek feed back the staus of each section on Loconet and allow manual on/off of each section, again via Loconet. So I can actually shut down sections of my layout with controls on a JMRI panel. Or as I saw mentioed before, someone wanted a loud horn to go off when there was a short - a PM42 and JMRI can do this, if your computer runnign JMRI has speakers, and you can play any sound you want. Different sounds for different sections if you so desire. There is value in teh feedback. Others say they offer feedback, but only if you buy some additional input deivce, it's not build in to the breaker.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I may have fumbled my words... the current is the same, but the voltage left to drop over the short is small, so the power will be small. The bulb is limiting the current to about 2 Amps, which should go a long way towards protecting things from major disaster.
I think the most dangerous short is the near short that isn't enough to be detected, whether by the bulb or a breaker, Then you can have something getting hot, and for a "long" time, and there isn't a great way to protect it. The idea of the bulbs (at least in my mind) is that you could have more of them per breaker, and thence break things into smaller sections to help in isolating any faults.
Ask Cuda Ken about that one - 8 amp booster into insufficient feeders, and how many decoders he fried.
Good place for a reminder about the quarter test. Set a quarter (or similar size currency from whatever country you're in) on the rails. Do NOT push it down, just set it there. At various places around the layout. If your circuit protection does not trip, you have too much resistence in the circuit, usualy not enough feeders, or relying on rail joiners, or the bus wires being too small for the length of run involved. Even if your trains seem to run fine - if the breaker does not trip with the coin on the tracks, you just have a tickign time bomb. Sooner or later you will have a derailment, and it won;t trip the breaker, and you won't notice - until the unmistakable odor of eaue de electronica permeates the air.
Why defeat the protection circuits the manufacturer built into his booster?
At the point of the short it is possible to have a tremendous amount of energy present, at the energy is equal to the resistance times the current squared. Twenty, 30, or 40 W can be dissipated at that point, which is enough to melt or destroy something.
Adding additional resistance to the DCC loop is not a good idea. It doesn't cut the current when something goes wrong, and prevents the protection circuits from operating properly.
betamax Why defeat the protection circuits the manufacturer built into his booster? At the point of the short it is possible to have a tremendous amount of energy present, at the energy is equal to the resistance times the current squared. Twenty, 30, or 40 W can be dissipated at that point, which is enough to melt or destroy something. Adding additional resistance to the DCC loop is not a good idea. It doesn't cut the current when something goes wrong, and prevents the protection circuits from operating properly.
In the application that I witnessed (Joe Fugate's layout, specifically) the idea was that the power district (area powered by the booster), was split into smaller subdistricts, each protected (or perhaps we should say monitored) by a bulb. That way if there was a short in a subdistrict the current in that subdistrict was limited, but the booster continued to operate, so that trains not in that subdistrict kept running. The problem was well isolated, and easy to track down, in general. I saw it work, and it seemed to work just as he wanted it to. I can see the argument that breakers might be a "better" solution, though in Joe's case they could well have been cost prohibitive, at least if he used as many as he did bulbs.
The bulb does limit the current, though there is no question that 2A can still cause trouble. Though I think that the type of near short that is most likely to be the biggest problem is going to be a problem no matter what protection is in place.
There's no question that there are scenarios that won't be ideal, that 's the case no matter how you try to protect it.
I think the real question here is: Do you need this particular modification?
Joe installed this modification on his layout to solve a very specific problem: operator caused shorts bringing down the whole power district during operating sessions.. I don't see how most layouts would need this type of short protection. A properly installed booster with appropriate wiring practices/gauges already provides short protection. Few layouts have the number of operators that Joe has on his layout.
Among the layouts that I regularly operate on, some with 8-10 operators, no one is using this system. In fact only one of these RR's has more than one power district. If some one shorts, it is not rocket science to figure out where the short is and the operator causing the short has drawn the attention of the whole crowd. This leads to pressure to be more careful (did those points move???) and good natured ribbing that is common at these events.
As for the modification itself, it is A LOT of extra wiring, especially if you look at how Joe has applied it. He basically cut his layout wiring up into lots of little blocks. To create these mini-districts, the wiring for the section must be isolated from the buss and the track has to be gapped. When the layout is large, this task becomes a large time expenditure.
In sum, I see it as lots of extra work for marginal improvement in layout performance. Certainly not necessary on non-OPs based layouts and not very common even on operating layouts..
Of course your mileage may vary,
Guy
see stuff at: the Willoughby Line Site
This is a DC solution to a DCC problem. It belongs in the DC age, not today's DCC.
DC systems do not deliver a lot of current to begin with. DCC delivers a lot of current with constant voltage, and it is not a DC or AC waveform either, so it's effect on a lamp will be different.
DCC systems are built with sophisticated current protection systems that detect an abnormal condition and shut down. You don't need 5A to cause the breaker to open.Yes, it can be expensive to install proper circuit protection systems, but which costs more, circuit breakers or a Tsunami? Four power districts can serve a large area to begin with.