Tachometer Readings

Marx and many locos of that era run fast at relatively low voltage. Easily can run fast enough to fly off the rails.

So yeah- perfectly normal. In fact, typically running voltage starts off around 8 volts from many postwar transformers as your minimum speed.

You are right about that. This morning I was performing some time trials with a 999 locomotive - without any cars, and then with 5 cars.

Without any cars, the 999 wouldn't budge unless I applied at least 5.5 VAC to the track, and I couldn't apply anymore than 7 VAC - I was afraid it would derail.

With a tender, gondola, tank car, box car and caboose the range was even smaller. I needed at least 7 VAC to get the train moving, and at 8 VAC it was going so fast I was afraid it would derail.

The time trials I did yesterday with my Marx 999 locomotive produced some interesting results. First let me describe the test rig. I have a loop of 0-31 gauge tubular track, and the total center-rail length is 13.4434'. I have a 275 watt Lionel ZW transformer, and I have power applied in two separate equidistant points along the line. I have a digital multimeter to monitor the track voltage. I used a lock-on to connect the red and black probes. I have an inexpensive clamp-style amp meter to monitor the amperage from the hot wire between the transformer and the track. I also have a 10 turn loop in this hot wire to improve the accuracy of the amp readings. For the time trial, I used the stopwatch feature of my Android phone, and timed the train over 5 laps. I tested just the locomotive at 5.5 VAC, 6 VAC, 6.5 VAC, and 7 VAC. Outside of this narrow band, the locomotive either would not move or would move so fast I was afraid that I'd derail and damage the 80+ year old antique. I then connected a tender, three freight cars, and a caboose and repeated the time trials at 7 VAC, 7.5 VAC, and 8 VAC. This band is even narrower, and again the train would not move at less than 7 VAC, and would run too fast beyond 8 VAC. Below is the velocity calculations and amp draw:

Locomotive Only:

Locomotive pulling five cars:

The most interesting finding is at 7 VAC, the locomotive alone was running at 117.5 MPH (scale), drawing 1.86 amps, 13.02 watts. When I attached the cars to the locomotive and ran it at 7 VAC, it slowed down to 46.7 MPH (scale) drawing 2.1 amps and 14.7 watts. One thing I should point out is that my amp readings would usually spike when the train was on the curve sections, so my amp readings are sort of a composite. It seems as though the majority of the power was consumed just moving the locomotive. The locomotive weighs 1 lb and 12.1 ounces, and the mechanical efficiency of the gear train is typical - i.e. not so good.

The ratio of your Scale MPH to Speed MPH is 64. That is the correct ratio for S gauge and S scale. If you are  running on O-31, why aren't you using a factor of 48 to calculate the Scale MPH? I realize the model may be compressed to S scale dimensions but just thought I would ask.

MELGAR

MELGAR Thanks for showing an interest in this, and reviewing the numbers so thoroughly. The Marx train scales seem enigmatic to me. They are billed as "3/16th scale" - an architectural scale i.e. 3/16th of an inch is equal to one foot. This translates to 1/64th. However, these trains run on 0 gauge track. On paper it seems strange, but the old tinplate Marx trains have always seemed so nicely proportioned and attractive to me. So I used the 1/64th scale factor for my testing results. Later on, I am going to use the same test rig for some of my Lionel trains, and I will use the 1/48th scale factor for those. I have an old Pennsylvania GG-1 electric, a S-2 steam turbine loco, and a New York Central F-3 diesel.

As a follow-up, I bench tested the 999 Marx locomotive at 7 VAC and I am summarizing the performance as follows:

On the bench, with 7 VAC applied to the pickup, the motor's amp draw was 1.7A, and power was 11.9 watts.

On the track, without any cars, and with 7 VAC applied, the amp draw was 1.86A, and power was 13.02 watts.

On the track, with 5 cars, and with 7 VAC applied, the amp draw was 2.1A, and power was 14.7 watts.

Most of the power consumption seems to be attributable to the cumulative friction of the locomotive's drivetrain.

I did some bench testing and conducted some time trials with my Marx 333 Hudson-type 4-6-2 locomotive. The 333 is probably the finest locomotive that Marx produced. It weighs 2 lbs and 6.4 ounces.

My test rig, instrumentation and methods are described above.

I first bench tested the locomotive at 7 VAC, and the motor's amp draw was 1.14A, 7.98 Watts. Bench testing like this allows me to get a good idea of how much power it takes just to overcome the combined friction loss of the drivetrain.

I ran the locomotive only on the track described above, and measured the elapsed time to cover 5 laps, while also measuring the amperage, at 5, 6, 7, and 8 VAC. I did not go outside this range because the locomotive wouldn't run consistently at voltages less than 5, and would run dangerously fast at voltages greater than 8. My results are:

Without tender or passenger cars

I then ran the locomotive with its diecast tender and three lighted passenger cars on the track described above, and measured the elapsed time to cover 5 laps, while also measuring the amperage, at 7, 8, 9, 10, 11, and 12 VAC. I did not go outside this range because the locomotive wouldn't run consistently at voltages less than 7, and would run dangerously fast at voltages greater than 12. My results are:

With tender a three passenger cars:

It is interesting to compare and contrast the results when the 333 locomotive was operated at 7 VAC. On the bench, the power requirement was 7.98 watts. On the track without anything in tow, the power requirement was 10.71 watts. On the track with a tender and three passenger cars in tow, the power requirement jumped up to 14.7 watts.

The 333 runs slower than the 999, it is more powerful, and operates within a wider range of voltages. The 333 however, does not run very well on 0-27 tracks because the turns are too tight and the drive wheels get hung up, loose adhesion, and start spinning. Other differences between the 333 and the 999 - the 333 has smaller diameter drive wheels, so at comparable rpms, the 333 will run slower than the 999. The 333 has a gear ratio of 9.74 to 1. while the 999 has a gear ratio of 5.4 to 1. The 999's motor runs at much higher rpms than the 333. See my tachometer readings above.

One other observation, it takes a good deal of power to pull the lighted passenger cars - because of the rolling resistance of the wheels, and because of the resistive friction of the lighting pickups. I did some interesting testing of the rolling resistance of my train cars and I produced some interesting data which I will provide in a follow-on posting.

One final note on my 333 - it does not have an e-unit ( I physically removed it) and the headlight is an E10, 24V cold-white LED screw-type bulb. So my locomotive is running a little more efficiently than a stock 333.

I did some bench testing and conducted some time trials with my Marx 21 Diesel F-3 locomotive. The Marx 21 is a large, good-looking, tinplate locomotive - closer in scale to 1/48th rather than most of the other Marx tinplate trains which are at 1/64th scale. It weighs 2 lbs and 10.6 ounces.

My test rig, instrumentation and methods are described above.

I first bench tested the locomotive at 9 VAC, and the motor's amp draw was 1.85A, 16.65 Watts. Bench testing like this allows me to get a good idea of how much power it takes just to overcome the combined friction loss of the drivetrain.

I ran the locomotive only on the track described above, and measured the elapsed time to cover 5 laps, while also measuring the amperage, at 7, 8, 9, and 10 VAC. I did not go outside this range because the locomotive wouldn't run consistently at voltages less than 7, and would run dangerously fast at voltages greater than 10. It's worth noting that the Marx 21 operates in a narrow band of voltages like to 999, but the band of voltages is higher. My results are:

Without a dummy A-unit or passenger cars

I then ran the locomotive with its dummy unit and three unlighted passenger cars on the track described above, and measured the elapsed time to cover 5 laps, while also measuring the amperage, at 8, 9, and 10 VAC. I did not go outside this range because the locomotive wouldn't run consistently at voltages less than 8, and would run dangerously fast at voltages greater than 10. My results are:

With dummy A-unit and three unlighted passenger cars:

It is interesting to compare and contrast the results when the 21 locomotive was operated at 9 VAC. On the bench, the power requirement was 16.65 watts. On the track without anything in tow, the power requirement was 21.15 watts. On the track with a dummy A-unit and three passenger cars in tow, the power requirement jumped up to 23.4 watts.

The operation of the Marx 21 is very fast. It's almost too fast, with a tendency to derail on curves at voltages above 10 VAC.