I am pulling 45 cars on my N scale DC layout. I used three 6-axle engines to pull the train. How many 4-axle engines will it take to pull the same train? (Ans: three.) Rather than answer that question, here are the facts for the three different power consists. Three, 6-axle engines: two Kato SD40; one Atlas SD50 5.0 volts .55 amps 18 total axles weight: 11.1 ounces (314 grams) Four, 4-axle engines: four Atlas GP40s 5.0 volts 16 total axles .55 amps weight: 11.7 ounces (333 grams) But, the 6-axle units were much slower at five volts than the 4-axle engines. I had to go to 7.3 volts with the 6-axle engines to get the same speed of the 4-axle engines at five volts. The 6-axle engines still pulled .55 amps at 7.3 volts. To my surprise, three 4-axle engines easily pulled the train. Three, 4-axle engines: three Atlas GP40s 5.0 volts 12 total axles .50 amps weight: 8.7 ounces (248 grams) Two 4-axle engines (5.7 ounces; 163 grams) would not pull the train up some very slight (less than one percent) grades and 24 inch radius curves. I am still thinking about it. I believe it is what you would expect. Same load (45 cars), same amps. About the same number of axles and weight for three 6-axle and four 4-axle lashups. I'm still surprised at the three 4-axle engine performance.
My guess as to why the 4 axle loco's perform just about as well as 6 axle models would be because the axles are not spring loaded. When each axle is not spring loaded, on a three axle truck, it is quite possible that when the track is not perfectly flat, as on an incline, the center axle does not touch the rail hard enough to add to the traction. Therefore, if the 6 axle loco does not weight significantly more than the 4 axle loco it does not have all that much more draw bar force.
The traction available is a factor of weight x coefficient of friction between rail and wheel. The number of wheels doesn't really enter into it. In theory. In practice there are some subtle effects that are noticeable at 12":1ft, but on a small model they are probably not measurable. On the prototype the number of axles is usually to do with wheel/axle loading and the power each traction motor can handle. SDs were originally built for light track (Special Duty), but even on a modern main there are real limits to how much weight can go on each wheel without damaging the rail surface, even if the substructure can stand it. Traction motors are generally maxed at about 900 amps IIRC (though I think some modern AC units can go to 1000+). Current draw on models is determined more by the motor design and quality, and friction in the drive train than by load. Likewise the speed/volts ratio will depend on the motor characteristic and the gearing. Some units even take little more current stalled than running normally. So your results seem quite reasonable and, like the prototype, adding units beyond the number needed to get the train over the road comfortably doesn't generally add much value ... except for looking cool which is the most important thing for us
I run DC (like Flash, IIRC) and I have a question: when I run 5 or 6 6-axle Katos with a 80-cars coal train or 80-well intermodal train, will the current draw exceed 1 amp?
William: I don't think so. I have an open house here later tonight, so I will try to get six Katos on there (without a train) to take a look. I usually think of 0.1 amp per engine and that is a little too much. So, maybe 0.5 amp for six Katos. But the load will make that creep up. Grades and curves and wheels not slipping will increase the amps, but I don't think it will go over one amp and then, probably not much. I'm sure we have some long train guys here that can be more specific. [edit] I have five SD40s and one U30C pulling one amp with no cars at 4-5 volts. That's more than I would have thought it would be.
Good recall, Robbman! SD40/45, C30-7, U30C all quoted at 0.32A, GP38(-2) at 0.36A. All a bit overrated ampage-wise, in my opinion. I've measured the six-axle power at less than 200mA (0.2A) in the past.
Guys, this is a good thread. I run DC as well. I have a question: Following are nine Kato locomotives (two Kato U23Cs, 1 Kato original SD40, rest are Atlas/Kato GP30s/GP35s) running on my layout. They run fine around my layout, running light. I have a MRC 200 powerpack. Given the number of amps that 9 locos might pull out of the MRC 200 powerpack, am I in danger of blowing up something if I run a lashup like this? Does it make any difference if I'm pulling a long train or not? Would I endanger someone else's layout / wiring / etc. if I ran this lashup? Not being an electrically-trained individual, just wanting to make sure I'm not in danger of something, not wanting to endanger someone else's layout wiring .... Thx for any comments.
I think that MRC has a circuit breaker so it won't hurt itself if you load it up. With nine engines, I expect they will run a while and then the CB will pop. With nine engines, I would expect 1.5-2.0 mA. That's a lot, to me. The amps should increase with a long train or increase load on the engines. BTW, having an ammeter and a volt meter on your layout is a good idea. They are easy to build.
Unlike the prototype, which has a separate traction motor and gearing for each axle, our models have only a single motor with associated drive train. Considering that the motors are the same, and that there is likely greater drive train resistance in the 6 axle (more gears), and rougly equivalent weight, and allowing for slightly greater adhesion for 12 wheels vs. 8, I would expect the results to be roughly the same. The amperage draw figures above would tend to bear this out. 9 locos does look way cool, however!
I run DCC, and rarely see above 100 mA (0.1 amps) per loco, up a 2.5% grade, pulling 60 cars. I've seen a maximum of 440 mA a few times on an ABBA. It's usually much lower. With two ABBA consists running, I might see 600 mA for the eight engines.
Here is a cheap and easy method to monitor volts at various locations on a layout. If you have multiple blocks on your layout permanently wire a $4.00 digital volt meter into each block. I bought 6 such meters at Harbor Freight for $4.00 each. I removed the 9 volt battery and have all 6 meters wired to a 9VDC wall wart. You can easily mount each meter in the fascia or anywhere convenient.
But remember that for DCC these readings might be proportional to the actual reading, but there are not accurate. Jeff
