I've worked through most of the issues I have with setting up the Atlas Signal System on my layout with the help of many on this forum, but I have one last issue that needs addressed. The Atlas signal system is designed to run on either AC or DC 6-22 volts (Atlas recommends DC). The NCE BD20 detector requires DC 6-12volts. Before switching to DCC, I planned on using the AC terminals on the back of my power pack, but with DCC, I have to use the BD20. I experimented and used a 9V 300ma Enercell DC power supply. It works fine, but I became concerned about the possibility of overloading the power supply. I contacted Atlas and they recommended that I use overcurrent protection; they also stated that each signal and signal board combined use about 20ma. They recommended a fuse on the line side of the power supply. I asked them exactly what type of fuse and they recommended a 1/2amp or 1amp fuse. Now, maybe I'm missing something, but a 1/2amp fuse is much higher than the 300ma rating of this transformer. In addition, I haven't been able to find anywhere a 300ma 9V fuse. I went to my local hardware store to talk to a guy who works there who can usually answer these questions, but he wasn't there. What should I do? I don't want to overload the transformer and create a fire. Even if I went with a transformer with a higher ma rating, it still wouldn't solve the problem of overcurrent protection.
Just go to radio shack and pick up an in-line fuse holder and 1/4 amp fuse. Simply wire it in series with one of the leads from the power supply and you'll be all set. Here's a link to the parts. The voltage rating doesn't matter in this case.
http://www.radioshack.com/product/index.jsp?productId=2102786
http://www.radioshack.com/product/index.jsp?productId=2103752
Springfield PA
o.k., I'll make sure and do that. Thanks.
Just for curiosity, what effect does voltage actually have on current? I understand that power companies increase voltage substantially so they don't have to send more amps and use extremely large wires, but for wire capacity and fuses/circuit breakers, what's the different between 12 amps at 10 volts vs 12 amps at 120 volts? I saw a wire chart once that basically said that 5 amps at 12V DCC is almost identical to 5 amps 120V AC in terms of the wire awg needed. In this case, so that I can avoid blowing the fuse by adding too many signals and detectors, about how much current could flow through the fuse at 9 volts instead of 250v before it blows?
The fuse will blow with over 5 amps whether 12 volts or 120 volts. It is a current device. Fuses for 120 volts are just fine and used by many people. They are very common. This all I and many others use.
There are twelve volt fuses for autos and electronics but I have used mostly 120 volt fuses. I keep only 120 volt fuses so I do not inadvertently put a 12 volt fuse into a 120 volt situation.
Many years ago when cars had glass fuses, we replaced a blown fuse with 120 volt ones.
Now maybe someone else has run into a problem doing this. No idea.
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.
Fuses work when current going through them heats up the element and melts it. The voltage doesn't affect the filament but is still rated more for safety based on the insulation. So when a fuse is rated at 1 amp it doesn't matter if it's 10 volt or 100 volt, it's still an amp of current flow that will blow the fuse.
nscsxcrrailfan Just for curiosity, what effect does voltage actually have on current?
Just for curiosity, what effect does voltage actually have on current?
More voltage across same load means proportionately more current flow.
nscsxcrrailfan what's the different between 12 amps at 10 volts vs 12 amps at 120 volts?
Same amount of electrons flowing. Same current. BUT more energy involved (think more power).
nscsxcrrailfanI saw a wire chart once that basically said that 5 amps at 12V DCC is almost identical to 5 amps 120V AC in terms of the wire awg needed.
That's undoubtedly an oversimplified chart. Wire size controls voltage "drop" (voltage that is not available to the load but is lost as heat across the wiring). A loss of 6 volts out 120volts is minimal (5%) but a loss of 6 volts out of 12 is catastrophic (50%). It's all relative as a wild haired wise man might have once said.
nscsxcrrailfanIn this case, so that I can avoid blowing the fuse by adding too many signals and detectors, about how much current could flow through the fuse at 9 volts instead of 250v before it blows?
The same as the current rating of the fuse of course. BTW: you can also buy 3/8 amp fuses (375mA).
Karl
The mind is like a parachute. It works better when it's open. www.stremy.net
That wall-wart power supply probably already has overcurrent protection in the form of a non-replaceable fusible link. SHort it out and poff - time to buy a new supply. So use a fuse rated UNDER 300ma so the replaceable fuse blows before the internal non-replaceable part.
Or check out an actual electronics place like Mouser ot Digi-Key and get a 1/4 amp circuit breaker. That way if somethign shorts the breaker will pop and you can simply reset it, like having an endless supply of spare fuses on hand.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
O.k., I'll look at those websites. Thanks for the replies everyone.
I would go with a fuse rather than a breaker, for a couple of reasons. First, the fuse is going to be a lot cheaper, and it's not something you should be replacing very often.
When you have a breaker pop, you tend to reset it and go on. If you are in a "load creep" situation, which is how many of us get this problem, the problem will persist. "Load creep" occurs as you gradually add more and more bulbs to a circuit. When you start out, you have only a few bulbs, and you're well within the limits of the supply. But, as your layout grows, you'll add another bulb here and there until you're up to the limit, and then things start popping. If you have a breaker, you'll just reset it. But, if you've got a fuse, you're more likely to analyze and correct the problem before you put in another fuse.
It takes an iron man to play with a toy iron horse.
Yeah, I'll probably go with a fuse because that's what RadioShack has. I do have another question: How do you know if a wall power supply is DC or AC? For example, the Enercell P.S. I have says that it takes in 120V 0.15A and converts it to 9V 300ma. But, it does not say if it's AC or DC. The only way I know is because the box it came in said it was AC to DC. Now, I know of a resell store in town that usually has several old wall power supplies from old appliances and electronic devices. I'll probably need a bigger one eventually, so how can I tell if they go from AC to AC or DC if they don't say?
I just found out something. Wall transformers are usually not regulated! I just read this on another site. If you don't pull the right load, you could end up with more voltage than you want. The one I have says it is regulated and filtered, which is very good for me. I'll probably just stick with buying the Radio Shack wall transformers that specifically state the voltage, current, and are regulated.
nscsxcrrailfan ...so how can I tell if they go from AC to AC or DC if they don't say?
Most of the ones I've seen do indicate AC or DC on the housing somewhere. It may not be obvious. If there is a diagram that shows the center lead is positive while the outside lead is negative, that would indicate DC. A picture of a sine wave on the output, on the other hand, would be AC.
If you're not sure, when you go to Radio $hack get yourself a cheap multimeter. Then you can measure voltages yourself and be sure.
Wall warts are usually clean enough for most applications so separate regulation isn't typically needed.
The supply will not always say DC or AC but may have a symbol. The symbol for DC is typically a dashed line over a solid line. AC is a sine wave.
O.k., Thanks.
I would not freak out over 'unregulated'. The voltage will be higher than the stated nominal value - when there is no or a light load. The voltage under a steady load won't vary up and down like some nut playing with the throttle knob on the power pack. Since the maximum range of the detectors goes up to 12 volts, 9 volts nominal should be just fine.