As I’m researching DCC systems, I can think of two reasons to choose a low amp (1.6-2.5) DCC system like the MRC Prodigy Express or Digitrax Zephyr …
With low amps you may be able to get away with using your existing DC wiring (20-22 gauge) … the voltage drop would be too high for a 3.5-5 amp system … which would require say 16 gauge wiring … is there any truth to this line of reasoning?
Lower amp systems are less likely to fry your decoders if something goes wrong. Is this true? You guys tell stories of frying lots of decoders.
So, how many amps does a loco (say a Bachmann HO Shay) running DCC without sound use? running with sound? idling with sound? Can you run 2 and idle 2 sound equiped loco with 1.6 or 2.5 amps?
Hopefully my questions aren’t too crazy. I have been learning a lot about DCC in the past week, even if it doesn’t seem so …
You should be able to run two non-sound DCC engines that are mechanically well engineered and in good running order with less than one amp,…but it depends on the load the motor must pull. Grades, tight curves, heavy cars, stiff and gummed up truck journals…they all add up.
As soon as you add a substantial load, and/or sound, you add another 0.4 amps, give or take, per decoder.
If you are a lone operator running two or three consisted non-sound diesels, your total amperage draw might be near 1.5+ amps if they are pulling 30-40 cars on level track. In the final analysis, only a rampmeter will tell you for sure, but this would be a good start for consideration of current needs and then what your future needs might be.
2x PCM T-1 (loksound decoders), BLI M1A (QSI sound), BLI GG1 (Qsi sound), 2x P2K GP-7 (DH163L0 motor only decoders), P2K S-1 (Digitrax motor decoder), and a Stewart DS4-4-1000 (TCS T1 motor only decoder).
That was all I could manage to fit on my 8x12 layout and not have them crash into each other. Low amps? People tend to grossly overestimate the power required for locos, particualrly sound ones. Pay attention to the stall current ratings in MR reviews, even some of the sound locos draw no more than half an amp with the wheels forcibly restrained fro moving. This is the absolutely maximum current the loco will draw, under most conditions it will be drawing less.
Hey, guys, although you sort of answered his how much current does an engine draw question, I think what really needs to be addressed are the two things he states above.
You are right maxman. Always the risk of asking more than one question in an e-mail or post. This is great information on loco current draw that I will use … but questions 1) & 2) are the main reason for the post.
Question #1. Yes and no. You may get away with the smaller wires but a quarter test is the only way to tell. If the system does not have short protection than troubles are the same as larger systems.
Question #2. You can still fry a decoder with 1 amp. You can stop a heart with less than 1 amp. I have had decoders go poof on the program track. A short on a layout for example running a thrown switch against you will cause a short and the reason for a super fast booster trip will limit the damage to a decoder. Some times they just get scrambled and need a reset.
Question #3. My Power Cab with less than 2 amps had 5 sound equipped and 6 silent HO scale locos running at the same time. There is a built in Amp meter on it and it read 1.5 amps on that load. The big draw you realize is the lighting of your Passenger cars. They can rob some power.
22 gauge wiring is not good on DC either! The only place you should use #22 is on the feeders from the ‘bus’ up to the track(usually about 6"). My DC layout used 6" #22 feeder drops to a #18 bus from the control panel. Most layouts are wired with too small wire(even DC).
The reason DCC layouts are wired with larger bus wiring from the start is due to ALL of the current flow is on the main bus, not just 1 or two engines worth of current like on a DC cab block.
A small home layout using something like a Digitrax Zephyr or a NCE Powercab should have at least #18 bus wire. You can then run #22 feeders from the bus to the track(one for every piece of flex track).
As far as a lower amp system is safer - A 10 amp system or a 1.6 amp system will ‘shut down’ when it detects a short. With smaller wire(higher resistance) - it may take a while to get to the short, and your decoder is ‘frying’ while that happens. Use larger wire. The ‘quarter test’ should force an immediate booster shutdown from any point on the layout.
Most of the newer HO engines will draw about .25 amps running. I have had 6 engines running off of a 2.5 amp Zephyr - and 3 were sound. Once a sound engfine powers up, it really does not use much more current that a non-sound engine. Idling really is not a lot of power drain. Our club had something like 32 engines parked in the engine terminal and finally that tripped the power district limiter(PM42).
My layout has a Digitrax Chief(5 amps) and a booster(5 amps) - real overkill for a home layout. I currently have 16 engines on the rails. About 1/2 are ‘sound’ engines(Spectrum/BLI steam & P2K sound diesels. Add a few more P2K and Atlas non-sound diesels. If I were to get the 2.5 amp
I don’t think this line of reasoning holds much water, the current only gets drawn when you need it. Actually, the small wire is going to work against you. You will get more voltage drop, turn the throttle up, and need to draw more current to get the same performance. So the capacity of your system to provide the current you need will be reached even sooner than it would otherwise.
More important is making sure your command station detects shorts and shuts down. Which mostly comes down to the wiring, again.
While those might be lower amp DCC systems, they are not low amp when compared to toy train power supplies. For years I had a heavy MRC DC throttle (the AMPACK) that had 2 full amps of output! Wow. Most are something like 12VA DC meaning they can’t quite muster a full amp at full throttle.
No, for years I ran a DCC system (a “high” amp system (Lenz set-01)) with the old existing DC wiring. What too small of wiring will get you is things melting down if the wires can’t carry enough current to trip the circuit breaker. If you short the track and the breaker doesn’t trip, heavier wire is needed.
Possibly but I doubt it. Usually a decoder gets fried when power is run into it backwards. The voltage is going to be the culprit not the current. The other way a decoder fries is to put too much of a load on it. In that case it is the current the motor is drawing which will be the same regardless of the supply. A motor is only going to draw its maximum current. So unless you plan on having a single locomotive draw more than 1.6 amps. No difference.
short answer is yes. Long answer is are they modern current manufacture run locomotive or are they old things with open frame motors and sound sy
No truth to it whatsoever. Ohms law still applies. E=IxR The voltage drop will not change no matter how many amps are available at the booster end. Voltage drop will be a factor of the resistance in the wiring and components. Smaller wire running long distance (bus wires) mean more resistance.
What will be affected is the system’s ability to detect a short circuit and cut power. Higher resistance will slow or completely fool your system’s breaker. Good news is the wire under the layout may melt before the rolling stock is damaged. Which brings us to #2
Who told you two amps won’t heat metal parts enough to cause damage? A tail light bulb uses two amps. I’ve seen those melt the plastic housings they are held in.
Not saying a low amp unit is not for you. Just saying these two reasons should not be part of the decision.
Lower amp draw will result in lower loss through otherwise identical wiring - a 2.5 amp load will show half the drop through identical wiring as a 5 amp load.
But the key word - LOAD. It doesn;t matter if you have a 2.5 amp DCC system or a 10 amp system, the LOAD in a given section of track will be whatever the current draw of the loco running there is. Just because the DCC system can supply up to 10 amps doesn’t mean it is PUSHING 10 amps intot he wires. It doesn’t work that way.
Still, #22 wire is definitely too small to use a bus wires. As short feeder drops in HO and smaller scales, it is fine. If you never expect to expand and run more trains at a time, then you might be able to get away with using somethign smaller than #12 as the bus wires (unless it’s a long run - here were are back at the size of the layout does not really determine the size of the DCC system - I could fill a 20x30 basement but if I never run more than a single loco at a time, I certainly do not need an 8 or 10 amp system. However, that’s a lot of wire in the bus runs and even with heavy wire at low loads there’s a significant voltage drop).
Bulbs get hot because they have to. An 1157 has low but measurable resistance, so when the appropriate current flows the filament gets hot enough to release photons (the light). That being said, the general point is well taken, 2.5 amps at 15 volts (power output of a Zephyr) is equivalent to a 35 watt soldering iron, and those get above 400F.
Wouldn’t that be, “a lot of measurable resistance?” The whole point of the filament is to provide so much resistance, but in a temperature capable metal, such that its temperature rises to the point of releasing much of its ‘gray’ body radiation in the visible spectrum, with the rest in IR.
The beauty of the light bulbs as current limiting devices is that at low currents they have very low resistance. Hence the voltage drop, and hence the power, is used by the decoders. Conveniently, as the current gets above two Amps or so (I don’t remember the exact number), the light come on, and the resistance goes up, so that the voltage is mostly dropped through the bulb rather than through whatever caused the short. Figuring 15V, and 2A, the resistance of the bulb is in the neighborhood of 7.5 Ohms when it is lit and hot.
UPDATE: Well, I bought a Digitrax Super Chief xtra 5 amp system. I tested it on my coffee table with a piece of flex track on a DC and DCC locomotive. Worked great. Then replaced one of my 3 DC powerpacks and slid all of the DC switches to let the DCC system power everything. Worked fine everywhere on the layout. I did the quarter test for shorts and that worked everywhere except at part of one long block. I added an extra feeder to the other end of the block and the quarter test now works everywhere on the layout. I had previously installed a pair of bus wires around the layout (small, but 2-level), but I am currently not using them.
Do you agree that if the quarter test works everywhere and operation is normal, that I do not need to wire to the bus?
I currently am using the existing DC reversing switch (DPDT from an Atlas Controller) for my single wye section. It works, but does short out the layout if you don’t guess right in setting the directions. I have a Digitrax AR1 auto reversing unit that I will probably install after I get the majority of my locomotives converted to DCC.
Welcome to the DCC world. If the layout wiring passes the quarter test than I see no reason to rewire the layout. Probably a good idea to test every now and then down the road. It would be wise to disconnect the rest of the DC power packs from the track wiring. If you accidentally flip a switch and put DC on the rails it would turn your Super Chief to a super smoking chief. If you really need to keep the DC installed at least make it very hard to switch between DC and DCC. Even if the Chief is powered down I don’t know what would happen if DC is back fed to the booster/command station. I would not want to find out.
With low amps you may be able to get away with using your existing DC wiring (20-22 gauge) … the voltage drop would be too high for a 3.5-5 amp system … which would require say 16 gauge wiring … is there any truth to this line of reasoning? 2) Lower amp systems are less likely to fry your decoders if something goes wrong. Is this true? You guys tell stories of frying lots of decoders.
Marty -
rrinker is right on. Electrical current (amperes) is not the driving number; current will be drawn as required by the load (resistance, motor, lamp) at the driving voltage. The amperage rating is just the upper limit on the current that the system can supply and still maintain the rated voltage. Low current available, fewer engines can be driven.
A Zephyr is good for small applications only - like a 4x8 with one or two engines. Sure the ads say it can do more, mine gets confused and overloaded pretty easily. If that’s the kind of layout you have, a Zeph will work for you. If you have several engines, you really need something huskier.
Decoders do not fry because of ‘high-amp’ systems - they fry because they have been hooked up incorrectly, or the track layout brings them into a dc-dcc bridge, or something like that. A Zeph will fry a decoder just as fast as any.
And yes, #22 wire is too small for much more than short runs (a few feet at most) - whether dc or dcc.
Dunno what you’re running on your Zephyr - but I’ve had 8 HO locos running at once with no problems. 4 had sound decoders, 4 did not. I wanted to try more but it was getting tough to keep them going without hitting each other. I even tried shorting the track to see if it would recover and indeed it did. Even if I have 2 other operators besides myself, I wouldn’t need a more powerful system.
ANd I’m not the only one who has managed more than 4-5 locos with a Zephyr. If things start slowing down or getting wierd I suspect you don’t have suffcient wiring, eithe rnot enough feeders or too thin a wire used for the bus.
