Hi, first post:

I was wondering what kind of current older traction motors draw, with power applied to them to just get a locomotive crawling slowly? No cars to pull, just a slow crawl. For example, if you had a dead locomotive with good traction motors and properly lubed bearings, could you move it with a bank of batteries or some other low voltage high current source?

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Will

What you are speaking of is commonly called 'battery jog' or a jog circuit. The batteries used to start the engine can be used to jog, or move, the locomotive.

The customary motor arrangement is a pair of traction motors in series, where each motor sees the same current and half the voltage (keeps the motor speed down).

In order to make up the circuit on the HV side, it is necessary to add one or more contactors and some additional cables and/or bus bars. The controls are arranged so it is impossible to motor the circuit unless the diesel engine is dead.

Specifics depend upon the make and model in question.

DPK

I'll add a few other comments on battery jog circuits. Typically, pneumatic power contactors are used for connecting the batteries to the traction motors. This makes having air on a locomotive critical for not only closing those contactors, but also for brakes for stopping the movement! A battery jog circuit (low voltage side) might also be wired through the PCS switch for yet another fail safe protection - if your brake pipe is not charged, the PCS will not reset, and hence you will not be able to move the locomotive.

One comment, it is possible to battery jog a locomotive with the diesel engine running (I have witnessed this first hand) however the circuit is configured such that it is impossible to motor a locomotive by both batteries and main generator/alternator simultaneously.

CSX has a policy of not running locomotives in or out of a shop, and thus the battery jog feature is basically a necessity. I have seen one unit jogging through the house pushing five other units ahead of it, so battery jog is certainly a valuable tool!

I have seen battery switchers. In one case, at Enola, Conrail had turned a locomotive truck into a shop switcher by adding a stack of locomotive batteries and a requisite controller.

The WRM has a streetcar with two 1200V motors. It is wired in the conventional way for 600V motors, giving it a balance speed of around 30 mph. In series, each motor sees 1/4 of its design voltage, or 300V. It still moves along quite handily, hitting a balance speed of around 15 mph.

Now, correct me if I'm wrong, but balance speed at any particular voltage is going to be proportional to the voltage, right? I.E. if balance speed @ 600V is 60 mph, balance speed @ 60V will be 6 mph? Do traction motors have a functional minimum voltage, or will they develop torque with as little as 12VDC?

There are also the DC chopper controllers intended for homebrew electric vehicle (EV) conversions. Some are more than hefty enough to jog a locomotive at 2 mph.

Another comment:

The "poor man's wheel lathe" involves jacking up a locomotive, attaching the cutters to the truck frame at JUST the right spots, then attaching an arc welder to the disconnected traction motor leads to get the axle turning at a steady speed. I've seen/helped with this practice twice.

So, in a real pinch with dead batteries, there is theoretically this alternative......

Traction motor voltage is directly proportional to motor speed. Motor load current is inversely proportional to speed.

DPK

Thanks for the good info so far - I did not know about "jogging".

Anyway, I still am wonder about how much current is required. For example, if you had a dead GP-7, and you wanted to jog it at some slow speed, what sort of numbers are we talking about? Ballpark figures are fine.

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Will