miracle ACS-64 locomotive regen braking defies physics

[Jersey_Mike]

The ACS-86 and ALP-46 are both 100% regenerative as they lack the old style dynamic brake resistor grids. The breakthrough was the realization that one doesn't need fancy infrastructure to transfer power from one train into another, but that you always have the captive HEP load to dump the waste energy into and the AC inverter systems can work both ways. This is on the order of .7 to 1 Megawatt per 8-12 car train. NJT Arrow IIIs were retrofitted with this system during their 1990's rebuild and while they kept their grids power savings was still about 10%.

[schmod]

It's worth noting that it'd be pretty difficult to bring a train to a dead-stop using dynamic/regenerative braking. The braking power provided by the resistors/grid is proportional to the speed of the wheels.

It'd be about as effective as cutting the power, and waiting for the train to come to a stop. Not exactly practical.

[ACeInTheHole]

I think this one can be merged into the primary thread.

[Patrick Boylan]

what primary thread? I don't know that there's a primary regenerative braking thread.

[Tadman]

Schmod is exactly right. Rules around here state dynamics must be used down to 15 (10?) and then straight air below that to stop, except in case of emergency. You just don't have the physics to make dynamics worth using down to zero, although it could be done.

What the take away is that it save brake shoes by using dynamics above 10, and but it doesn't save enough below 10 to bother.

Quite a few operations now have a computerized blended setup or just a single control stick for brakes/throttle, rendering the decision to the computers only.

[DutchRailnut]

Passenger trains do not normally use Dynamic brake, they use Blended brake, a function where the locomotive uses Dynamic brake while cars use airbrakes at same time.
this function is automatic as part of the regular train brake system.

[Fan Railer]

Imagine using only regen brake to stop an 8 car regional train going at 125 mph though lol... that probably takes at least 8-10 miles

using the same traction motors, the 125-0 distance should equal the 0-125 distance

It should be just a bit less than the acceleration distance to the same speed, as it should be able to pull back the same horsepower it's taking during acceleration, plus friction, wind resistance (friction basically), electrical, and other losses. However, it's still not 100%, nothing's 100%, there's always friction losses, electrical conversion losses, etc, etc. I have no clue what the percentage efficiency would be for something like this, but I'd be shocked if it's any more than 80%, and I highly doubt it's that high. However, they may want to stop even faster than just a bit less than the acceleration distance, in which case, they would use regular brakes alongside regen braking.

The addition of large flux capacitors allows recovery of up to 105% of the stopping power.

Actually, not true for stopping distance. Braking effort is limited to 150 kN, so it would take longer to brake from 125-0 using only regen, verses 0-125 on max throttle.

[Tadman]

Dutch, I'm not sure how things work out east, but I once had an engineer on EMU's from these parts explain the dynamics and associated rules to me. At the time (20 years ago) there was a straight-dynamics-only control position and it was required use down to 15. Many of those cars have been rebuilt, not sure if the rebuilds have a blended capability. The new cars are blended only and there are still some existing old cars.

I figured, given the GE control equipment common to certain eastern MU's, that it might be the same out there.

[DutchRailnut]

we are not discussing EMU's here, we are discussing the ACS-64 and its regen features.
and on a 8 car amfleet train and 1 engine only one unit has the Dynamics feature (blended brake) while all 9 units brake equally.

[Patrick Boylan]

Dutch,
you may be discussing the ACS-64 and its regen features, but I am not. Again I apologize for mistakenly having put ACS-64 into the thread title. My intent was, as I mentioned above, to poke fun at the sloppy reporting which said "potentially returning ALL of the energy used to stop the train back to the overall power grid", something I know to be impossible based on things I learned in 3rd grade from Sister Europe Anasia. Or maybe it was her associate disciplinarian Attila the Nun.

For some unfathomable reason a moderator decided this general regenerative braking thread belonged in the Amtrak forum. If you want to limit the discussion to Amtrak, or the ACS-64 in particular, please make your own thread. I repeat, I, the original poster, want to discuss regenerative-dynamic braking in general, especially how efficient or inefficient it is, regardless of if it's MU's, locomotives, or water propelled funiculars.

And I'd like again to point out that you have contributed to thread creep, your first post talked about total energy to GET THE TRAIN MOVING, when my quibble was about the reporter's comment on energy to stop the train, so it's particularly unfair for you now to insist on limiting discussion to just ACS-64 locomotives.