With the current issue of trains focusing on electrification, I have to ask a question. I remember back in the 1970’s when big time electrification was last discussed seriously. At that time I asked myself the question “why couldn’t electric locomotives be made from diesel locomotives?” It seems that it would be easy to remove the prime mover from a stored diesel, put the necessary electrical equipment in the space–and you have trucks with electric traction motors already–and put pantographs on the roof and there you have an electric locomotive. Obviously I was wrong since no one actually did that, but why didn’t it or wouldn’t it work? Can anyone explain?
Although todays locomotives are essentially an electric with a built in diesel powered generator, there are several things to consider:
Diesels change the amount of power generated by varying the speed of the engine. I know this is probably an oversimplified explanation, but they would need an entirely new control system.
The carbody structure is not designed to handle the weight or dynamics of a pantograph.
People that know the engineering of these in more detail can probably add a lot more differences.
You’re barking up the right tree. DE locos vary the excitation of the main generator along with varying the engine speed. Electric (ala E44s) have transformers with various secondary taps on them. The control system varies the voltage by connecting to the various taps. The output is rectified, then smoothed with an inductor before being fed to the traction motors.
You’d really only be saving the traction motors, trucks, frame, cab and couplers. Everything else would have to be new…and you’d wind up with a pretty wimpy locomotive compared to what you could do with a “clean sheet of paper” AC traction electric.
I suppose you could do just about anything but remodeling is always more expensive than new construction and the savings would be minimal. About all you are saving is the trucks, frame and carbody. I suspect the controls would need replacing also but it is all moot. No electrification will be done unless we start building huge numbers of fossil fueled power plants and the current demand levels decline neither of which is likely.
IINM, Milwaukee road looked into the possibility of converting SD40’s to stright electric back in the late 60’s when they were debating upgrading their Lines West electrification. There are some documents online (IIRC the site is called the "Milwaukee Road Archives)…
This thread may be a bit premature as realistically none of the Class 1’s have any truly concrete plans to electrify. The only medium term prospects I have read about are the Alameida Corridor in SoCal and NS’s discussions with the State of Virginia on High speed passenger projects using some of their ROW…
Tap-changing as a way of controlling electrical output from the transformer has been gone from electric locomotives for a number of years now (new builds, obviously there are still existing tap-changers out there), it disappeared with the advent of GTO Thyristors. Modern 3-phase AC Drive Diesel locomotives would be the easiest to convert. Pantograph mounting would be a consideration, the transformer should easily fit in the location of the fuel tank, so there should be plenty of space for the rest of the equipment. The biggest problem would be the control system and wiring, not the structural modifications.
While conversion from diesel-electric to straight electric may not be economically practicable, a diesel-electric design has been used as a starting point for a straight electric. Iron Ore Co. of Canada has about 7-10 straight electrics that are modified from an SW1200 design.
It’s already been done - for years.
Witness the NH FL-9’s and others of their ilk. The power pickup may have been third rail instead of catenary, but I believe they did operate as pure electrics “in the territory.”
They operated on third rail power from New Haven,Ct. South into Grand Central station. They have since been replaced by newer Dual Mode designs…
There have been other electrics built using standard Diesel Electric designs as a starting point, the GE E25Bs built for a utility owned coal hauler were built on U23B frames and trucks and BC Rail’s EMD built 6,000 HP GF6’s were built on SD40-2 frames and trucks. Both models wer new builds and not conversions…