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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

Westinghouse Type SK Generator - use as motor to start engine?


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  #1  
Old 05-01-2019, 12:31:07 AM
Greg H Greg H is offline
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Default Westinghouse Type SK Generator - use as motor to start engine?

Can this 1920's Westinghouse Type SK DC Generator be used as a motor to start the 1920's 12 hp diesel engine it will be connected to? If so, does anyone have suggestions for how to do that? See the attached pictures of the generator and tag. Does anyone know where I could find any documentation for this type of generator?

I'm more concerned about displaying the engine and being able to start it reliably, and not as concerned about actually using the generator set to generate electricity. But ideally it would be nice if it was possible to supply 24V DC from two automotive batteries wired in series to use the generator as a motor to start the engine, then disconnect the batteries and flip a switch to use the generator to generate electricity.

The engine has a hand crank, but I'm concerned about being able to reliably start it that way. I'm expecting a lot of cranking time and troubleshooting, especially when I try to start it for the first time in over 50 years. Thanks in advance for any advice you can provide!
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Old 05-01-2019, 12:54:17 AM
Vanman Vanman is online now
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Default Re: Westinghouse Type SK Generator - use as motor to start engine?

Most likely, yes! You may have to help it over the first compression stroke if it is a single cylinder engine with no compression release. After that it ought to keep it spinning just fine until it fires. You may need more than 24 volts, but probably not. I would have an ammeter in the circuit. If the current while cranking does not exceed 60 amperes, it is safe to run it like that continuously.

For best results, performance, and lowest current while motoring, you would want to arrange your switching such that it is running as a cumulatively compounded motor.

It is a cumulatively compounded generator. That means that if you were to merely apply power to the generator terminals, it would be a differentially compounded motor. That's no good, don't do that.

The difficulty in achieving this switching will depend specifically on how it is currently physically wired. It may well be super easy!

Keith
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Old 10-05-2019, 05:15:51 PM
Greg H Greg H is offline
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Default Re: Westinghouse Type SK Generator - use as motor to start engine?

Thank you Keith. I've been focusing on the engine for the past few months, and now I'm back to thinking about using the generator as a starting motor for the engine. Can you explain more about the difference between cumulatively compounded and differentially compounded?

The generator has 6 wires that are labeled with metal tags: F1, F2, S1, S2, A1, A2. Looking at the pages from an Electrical Engineering handbook shown in the attached picture, here's what I'm thinking. Please confirm if this seems correct:

For use as a generator:
- F1 and A1 connected to output +
- F2 and S1 connected to output -
- A2 and S2 connected together

For use as a motor:
- F1 and A1 connected to battery +
- F2 and S2 connected to battery -
- A2 and S1 connected together
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Old 10-06-2019, 08:20:40 AM
Mark Dieckmann Mark Dieckmann is offline
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Default Re: Westinghouse Type SK Generator - use as motor to start engine?

Greg, that sure is a nice looking engine and generator. I see you are in Columbus, less than an hour from me. Will it be on display somewhere or at any shows? I would like to see it in person.
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Old 10-06-2019, 04:33:57 PM
Vanman Vanman is online now
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Default Re: Westinghouse Type SK Generator - use as motor to start engine?

Hi Greg, that sure is a beautiful restoration of a beautiful machine.

The diagrams and so forth appear to be appropriate for your machine. Yours does not appear to have interpoles, but the connections and their function are otherwise the same.

The field windings or “coils” serve to supply the magnetic flux or “field” in which the armature operates. The stronger the flux, the higher the voltage generated if speed is constant, or the lower the speed if voltage is constant. Also, the stronger the flux, the greater the torque per ampere of armature current.

Because field strength has great effect over the machine’s operating characteristics, various means of controlling it are employed. It can be seen that the shunt winding will provide a constant flux so long as the voltage is constant. On the other hand, the flux developed by the series winding will vary entirely with armature current. The two can be combined so as to aid one another (cumulatively compounded) or so as to buck one another (differentially compounded).

For a constant voltage generator, cumulative compounding is employed so as to keep the output voltage practically constant across the load range. This is “level compounded”. If the series winding is made stronger (more turns) the machine can be made to be “over compounded”, resulting in a rising output voltage as load increases. This would have been used to compensate for line losses when a generator is further from the load, for instance.

In the case of a motor, higher flux results in lower speed and higher torque. Exactly what you need for a motor being used to crank an engine. So in your case you want the strongest flux you can get, ie cumulatively compounded.

Since the current flow through the armature while motoring is reverse of that while generating, the series winding connections must be reversed in order for it to continue to aid the shunt winding while motoring.

In your case, my thought would be to arrange the connections to an appropriate knife switch such that one position connects the machine to the battery for starting, and the other position connects the load, while simultaneously reconnecting the series winding as appropriate.

Keith
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