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jfugate wrote:Jeff:The reason I'm suspecting it could be less is the light bulbs act as a dynamic variable resistor and as you add locos, they start to kick in by glowing slightly to the DCC AC-like signal, which makes the resistance of the bulb change and the current limiting effect starts to kick in, which then causes the bulb to vary yet again ... and so it goes creating a very dynamic flow of current. I'm also not sure every bulb is completely identical, I've seen indications that there's some variance in manufacturing that affects how the bulbs behave for our purposes. All the manufacturers care about is that they burn bright on 12 volts DC and they last a decent length of time going "blink blink blink" over and over when you turn!
That's sort of what I was trying to say, they never really get to a full on state. What made me not like this line of reasoning was that as one increases resistance, the other should get more current, casuing it to increase, etc., etc. The DCC nature of things might have some impact, but it doesn't spend time at zero, and the transition is pretty fast, so I don't think it should cause what we are talking about. I'm sure they are not "identical", like you said, they just need to light up and last a while. And be produced as cheaply as possible.
Of course one could always try 3! I'm not going to worry about it any more, since in N scale 2 A is going to be plenty!
Jeff But it's a dry heat!
Joe Fugate Modeling the 1980s SP Siskiyou Line in southern Oregon
jfugate wrote:Putting two bulbs in parallel does increase the current limit somewhat beyond two amps -- in theory it should double the current limit, but because of other factors I suspect it's somewhat less, 3 amps or so maybe.I'd have to experiment with a DCC-savvy amp meter to be able to tell you for sure.
The results of that experiment would be interesting. I guess the eperiment could just be done with DC to see the difference, though the actual values might not be so accurate.
I've been using a few brain cells to try to figure why it sould be less, so far I can't see it, but the dynamic nature as the transition from a wire to a light bulb might cause the pair to get into some kind of equilibrium other than both dead on. Still can't make that work in my head, at least not with a dead short. But that won't stop me thinking about it! Or course, in N Scale, I am not going to have to worry about such a problem anyway!
MisterBeasley wrote: Joe - so the way this 1156 bulb thing works is that for normal loads like a locomotive and maybe a few passenger cars with lights, the bulb doesn't get enough voltage <-current to heat up, and therefore acts like a DC wire? And when you short the track, then the current goes up, the filament heats and glows, but now the voltage drop is across the lamp instead of the trains? Do you get the 2-amp limit as a by-product of the bulb? What happens if you're running a pair of sound-equipped engines, and they're pulling an amp apiece? Or is the bulb still just a wire in this case? Also, what special provisions do you have to make for reversers? Or does the bulb go between the reverser and the track?
Joe - so the way this 1156 bulb thing works is that for normal loads like a locomotive and maybe a few passenger cars with lights, the bulb doesn't get enough voltage <-current to heat up, and therefore acts like a DC wire? And when you short the track, then the current goes up, the filament heats and glows, but now the voltage drop is across the lamp instead of the trains?
Do you get the 2-amp limit as a by-product of the bulb? What happens if you're running a pair of sound-equipped engines, and they're pulling an amp apiece? Or is the bulb still just a wire in this case?
Also, what special provisions do you have to make for reversers? Or does the bulb go between the reverser and the track?
You've got the concept. If you are really going to draw 2 amps into one train block you are going to have to do somthing else, either a breaker or maybe a couple of bulbs in parallel (I'd have to think a bit of how that would work if the bulbs didn't act exactly the same way). I don't know the answer in the reverser question, since the reverser wants to see a short I guess the question would be does the reverser see it before the bulb eats it. Or, if the bulb was before the reverser maybe it all would work out. I think some reversers automatically protect as well, in which case it becomes a moot point. Someone with the relevant experience needs to save me here!
Joe - so the way this 1156 bulb thing works is that for normal loads like a locomotive and maybe a few passenger cars with lights, the bulb doesn't get enough voltage to heat up, and therefore acts like a DC wire? And when you short the track, then the current goes up, the filament heats and glows, but now the voltage drop is across the lamp instead of the trains?
It takes an iron man to play with a toy iron horse.
I suppose this is more a question of teminology than anything else:
What defines a "power district?" I had thought that each power district, by definition, had its own power booster. Subdividing things further than that, with a circuit breaker or reverser, for example, would not create a separate power district, but it would actually be more like an old Block.
By this definition, my layout has only one power district, because I've got only one booster. The turntable and yard areas, isolated electrically and run through reversers, are not separate "districts."
Even on my relatively small 5x12 foot layout, I do find having the breakers valuable when tracing shorts, by the way.
Alan_B wrote:The "easy" way to protect power districts is to use a 1156 tail light bulb for each district. The bulb will light up on a short and show which district has the problem. It will limit the current flowing to about 2 amps to "protect" your wiring and also will allow other power districts to continue to operate.
The "easy" way to protect power districts is to use a 1156 tail light bulb for each district. The bulb will light up on a short and show which district has the problem. It will limit the current flowing to about 2 amps to "protect" your wiring and also will allow other power districts to continue to operate.
The mind is like a parachute. It works better when it's open. www.stremy.net
I have a 10'x12' layout with 10 blocks being powered by two 5A and one 8A booster. Joe essentially hits the reasons why. I plan to add more sound locomotives and wanted smaller fault domains. I use Tony's power shields and reverse shields with no problems. Another advantage of having 10 blocks is that, if needed, I can always go to one booster per block. I highly recommend blocking and districts (if needed) at dedsign and wiring time. If you don't need them all day one, wire them in parallel until you do. Then split them out as needed. it is much easier this way than going back into a finished layout, cutting rails, fishing wire, soldering etc...
Here's the block breakouts for my layout. The thick red lines indicate gapped rails between blocks.
http://www.thebinks.com/trains/images/plan1v3_rev10_with_blocks.jpg
Engineer Jeff NS Nut Visit my layout at: http://www.thebinks.com/trains/
dadret wrote:I'm building my second layout and first DCC and have been doing a lot of homework on setting up the DCC but I am really wondering if I need to divide my relatively small layout into power districts. I probably won't run more than three locos at one time and my layout is approx 18' x 12'. I've purchased an MRC Prodigy Advance (which is probably more than I need but I got it for a great price). Do I really need additional power boosters, and , if so, do I have to use one by MRC or will any brand work. (I plan to control my switches with the DCC also as soon as I figure out how. I know I will need one or more stationary decoders).
I have a Prodigy Advance and can tell you that it will run at least four sound equipped engines with power left over for other use. You will not need any boosters.
You do need to divide your layout into several power districts. If you have a problem (derailment or short) in one district; the others will continue to operate. The other advantage of several districts is that you will know "about" where the problem is and not have to troubleshoot the entire layout.
I am using eight power districts on a 75" x 178" room sized layout that has 300' of track. I make each yard a district and have three climbing loops on one and a continuous run loop on another. I have had derailments in one district and enjoyed normal operation in all of the others.
I use Atlas snap switches and do not control them from the throttle. If you are running two or more engines; trying to access the switches from the throttle can get confusing (it may work well for you though).
Have a look at the post i started a little way down the page ref' DCC control of switch's.
On my old layout i skimped on any power boosters or indeed power districts but alot of lessons have been learnt since then. My old layout was 11'6x9'6 and if i got a short, it was a nightmare to find. I wouldnt go down that route again and plan to divide my new layout into seperate power districts. I did find that i didnt need any extra power boosters though and had no problems with loco's losing DCC signals or shooting off out of control. This may or may not be to do with the fact that i use the NCE Power Pro which gives a few more amps than some systems.
The mains transformer i use is a Lenz unit with the mandatory 14 volt output.
Hope that helps abit.