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Comment by zeusk | Hacker News Reader

AFAIK, most "diesel locos" are really diesel electric, with the diesel engine feeding a generator. Hybridization of locomotives seems like a no brainer since they can recover so much more energy with regenerative braking and can plan for braking to be recovery efficient.

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As I understand, braking occurs across the entire train, not just via the drive axles, so the hybrid regeneration method would be a considerable departure from normal operations.

Yes, but diesel-electric locomotives have a brake mode where the "regenerative" current is shunted through big air-cooled resistors and exhausted as heat. Often used on downgrades to control speed without burning up the brake shoes. Recovering this into battery charge would be an easy win, though you might still need the resistors after the batteries are fully charged or if they can't absorb the charge fast enough.

This is where overhead electric is great, and why the Pennsylvania railroad ran full electric over the mountains back in the steam era. A coal train going down the mountain could mostly power the one going up.

I have the impression that engaging the airbrakes is a little bit all-or-nothing.

They're great for stopping (relatively) quickly on level ground. But not so grest for controlling your speed.

Big diesel-electric locomotives have large, actively cooled resistor banks, usually on top of the engine. When rolling down hill they run the electric motors as generators, and dumping the energy into the resistor banks.

The mechanical brakes can't absorb that much energy - they'd wear out after a few minutes.

resistors or capacitor banks?

It seams like a resistor on a generator would just be a breaking load, and not actually capture any power.

The end result is waste heat. Capturing it would be great, but a battery is needed for that. Capacitors are still not up to the task for that amount of energy.

I'm not aware of any locomotives that captures power from braking.

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