Marx Diesel E7 Locomotive Performance Testing

I recently acquired some Marx diesel E7 locomotives. I finished restoring them, and I did some performance testing. Overall, I am impressed with their pulling power, and stability at lower speeds. First up is a Marx 901 Western Pacific E7 unit in an ABA configuration with a "newer" motor that has aluminum sideplates, recessed drive-wheel gearing, and rubber traction wheels. Then I tested an older Marx 1095 Santa Fe E7 unit in an AA configuration, with the "older" style motor that does not have recessed drive wheel gearing and does not have rubber traction wheels.

Western Pacific 901

So, first let me describe some salient mechanical/electrical features of the locomotive. It weighs 1 lb 15.5 oz. It has very good traction due to the rubber drive-side wheels, so I could easily pull the B-unit, the dummy A unit and10 freight cars during my testing. The gear ratio is 6.933 to 1. I was able to determine this by counting the gear teeth, and doing the math.

I bench tested the locomotive at 13.5 VAC output from the transformer and measured the drive wheel rotational speed using a Cen Tech digital photo sensor tachometer. The drive wheel rpm was in the range of 1400 - 1450 rpm. So, for purposes of my calculations I used an average value of 1425 rpm. Since I don't have the ability to directly measure the rotational speed of the motor, and since my 901 has a gear ratio of 6.933 to 1, I calculated a motor rpm equal to 10,053. The amp draw on the bench was 1.9A, with a power consumption of 25.65 watts.

Now 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 have an inexpensive clamp-style amp meter to monitor the amperage from the hot wire between the transformer and the track. 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 discrete 1/2 volt increments from 5.5 to 8 volts AC. Outside of this band, the locomotive either would not move or would move so fast I was afraid that I'd derail and damage it. I then connected the consist and repeated the time trials at 8 through 10 VAC. Again, the train would not move at less than 8 VAC, and would run too fast beyond 10 VAC. Below is the velocity calculations and amp draw:

901 Locomotive only

901 Locomotive with with B unit, dummy A unit, and 10 cars

Note that at 8 VAC, the locomotive alone was running at 100.4 MPH (scale), drawing 2 amps, 16 watts. When I attached the consist to the locomotive and ran it at 8 VAC, it slowed down to 20.3 MPH (scale) drawing 2.45 amps and 19.6 watts. One thing I should point out is that my amp readings would usually spike when the locomotive was on the curve sections, so my amp readings are sort of a composite. I also bench tested the locomotive at 8 VAC, and it was drawing 1.8 amps and 14.4 watts. So, I prepared a pie chart showing the power profile at 8 VAC. As you can see, the majority of the power was consumed by mechanical/electrical inefficiencies and just moving the weight of the locomotive. Only a small fraction of the total power was consumed by pulling the cars.

Here is a short video clip of the Marx E7 Western Pacific 901 slowly pulling a B unit, dummy A unit, and 10 tinplate cars with an applied voltage of 8 VAC. The operation is very stable. The locomotive exhibited no discernable wheel slippage and effortlessly pulled the train around the track layout.

Santa Fe 1095

So, first let me describe some salient mechanical/electrical features of this locomotive. It weighs 1 lb 15.5 oz, same as the 901 locomotive. It does not have rubber drive-side traction wheels, but nonetheless,  I could easily pull the dummy A unit and10 freight cars during my testing.  However, occasionally, there would be some barely noticeable drive wheel slippage. The gear ratio is 8.6 to 1. I was able to determine this by counting the gear teeth, and doing the math.

I bench tested the locomotive at 13.5 VAC output from the transformer and measured the drive wheel rotational speed using a Cen Tech digital photo sensor tachometer. The drive wheel rpm was in the range of 925 - 975 rpm. So, for purposes of my calculations I used an average value of 950 rpm. Since I don't have the ability to directly measure the rotational speed of the motor, and since my 1095 has a gear ratio of 8.6 to 1, I calculated a motor rpm equal to 8,170. The amp draw on the bench was 2A, with a power consumption of 27 watts.

I used the same test rig as described above. I tested just the locomotive at discrete 1/2 volt increments from 5.5 to 8 volts AC. Outside of this band, the locomotive either would not move or would move so fast I was afraid that I'd derail and damage it. I then connected the consist and repeated the time trials at 7.5 through 9 VAC. Again, the train would not move at less than 7.5 VAC, and would run too fast beyond 9 VAC. Below is the velocity calculations and amp draw:

1095 Locomotive only

1095 Locomotive with dummy A unit and ten cars

Note that at 8 VAC, the locomotive alone was running at 87.2 MPH (scale), drawing 2 amps, 16 watts. When I attached the consist to the locomotive and ran it at 8 VAC, it slowed down to 25.3 MPH (scale) drawing 2.45 amps and 19.6 watts. One thing I should point out is that my amp readings would usually spike when the locomotive was on the curve sections, so my amp readings are sort of a composite. I also bench tested the locomotive at 8 VAC, and it was drawing 1.9 amps and 15.2 watts. So, I prepared a pie chart showing the power profile at 8 VAC. As you can see, the majority of the power was consumed by mechanical & electrical inefficiencies and just moving the weight of the locomotive. Only a small fraction of the total power was consumed by pulling the cars.

Here is a short video clip of the Marx diesel E7 Santa Fe 1095 locomotive slowly pulling a dummy A unit, and 10 tinplate cars with an applied voltage of 8 VAC. The operation is very stable. The traction was pretty good, but there was some slightly discernable wheel slippage. Otherwise, the locomotive effortlessly pulled the train around the track layout.

I have noticed a distinct lack of uniformity in the performance of the series-wound, universal motors used by Marx in my fleet of 999 locomotives. Some run much faster than the others. I haven't quantified this yet because I dont have any hard data, but my Crazy Train post has a video clip showing 5 Marx 999s in operation: https://ogrforum.com/...c/175427630523854700

I suspect that if I were to test some of my other E7s, I might find a similar lack of uniformity in the performance.