Not always true, We have a spot where the speed drops from 60 to 50. Its much easier to squeeze off 10lbs, let the speed drop about 5mph, kick off the brakes and keep right on plugging away. All this in about mile. Now to do it by the book (which I always do*) You have to stair-step your throttle down to idle, wait 10 seconds, move the dynamic brake lever to set-up, pause and now move it into braking. But not too much. Only about 200-300 amps first, gather up the slack then full dynamic. After you get the train down to the desired speed, shut off the dynamic brake, go back to power, stretch out the slack then start pulling on them again. The newer locos have excellent dynamic brakes but horrible response when you go back into power. They seem to take forever to start to load up. And when they final do, your another mile down the track and your speed has dropped another 5mph.
*just in case anyone with any authority is reading. Hello Roadforeman!
I don’t think even a road foreman would be dumb enough to expect one to do a dynamic speed reduction in the situation you describe; at least I would hope not, unless the train is less than maybe 50 cars long.
Of course, if you’re just drifting along in the 3rd or 4th notch, power braking might not be the best idea. And one must also consider the load/empty distribution, as well as the grade, and the speed requirements 5-10 miles further down the line, etc.
There are some spots where I railfan around Atlanta that look flat to the naked eye, although when you zoom in on sections of this track you can clearly see the very slight grades. And when the trains are coming “down”, you can clearly hear the whine of the dynamics. In fact, its sometimes eery to me for some reason to hear that sound when I expect to hear the “regular” roar of diesels instead.
The runaway at Watertown, NY involved an elevation drop of around 200’ over better than six miles. If my math is correct, that’s around .6% aggregrate grade. About a quarter of that 200’ is in the first mile or so.
The two cars managed to acheive speeds as high as 60 mph. I know CSX sometimes uses dynamics for at least a part of that route.
dynamic brakes have changed and most on here are talking old school. Engines have 2 differant kinds of dynamic brakes, flat and tapered. let me start with tapered this starts as when moving dynamic brakes into set up wait for a few seconds for the relays to set up then move nto dynamic brake get about 300-400 amps and let the train come against the engine once the train is up against the engine then increase the amprage to controll your speed. now this is tapered so you really haft to apply to get the amps up. in some ( older engines sd-40s) they go to 700-750 amps total. as your speed comes down the amps come down. now lets talk about flat. these engine will load all the dynamic avalible by notch 4. they are cheaper to build and maintain that is why the carrier goes this route. it still has 8 notches but you have all by notch 4. now i hear you say why have 8 notches if you have all of it by notch 4? because you just might have units behind you that are tapered and not flat so you still need 8. the nest questions is do you feel a differance in braking or reaction. the units that comes on quicker ( flat) does all the work you wont feel the differance until you get all 8 notches making the other units work. there is also extended range and high adhishion unit. most carrier wont mix power they want power to be the same for better train handling, back in the day we ran trains with what they gave us and some were nightmares of power lashups. what wears out fastest dynamic seams to keep going and going, mostly the grids need replacing when they blow thats real pretty blue /white flash of light followed by a loud boom. ( sorta like lightning) then silence. the dynamic is not like in trucking we can very the braking forces easy over a broad area .
One reason why the RR’s you mentioned did purchased dynamic brakes was they were first marketed by the builders as mountain RR equipment and the dynamics quit at 20 MPH.
Their engineers were mostly still steam era and they were used to using the automatic train brake as their primary.
As the dynamics improved in performance with extended range and RR’s got into serious operational cost cutting and also when certain modern cars seemed to have problematic train brake(TTX cars had a reputation of going into emergency when given a low to moderate brakepipe reduction). Not to mention the modern practice of run through power .Then Dynamics became the rigeur for all road locomotive purchases.
There were of course the serious holdouts. The MoPac purchased a few DB equipped SD40-2’s only because they had interline those uints on unit coal trains.
Because the railroads were too cheap regarding both the original purchase price as well as the cost of extra maintenance. After all, it’s how the C&NW got it’s nickname. Cheap
& Nothing Works
That chart is very accurate Wabash, that is the same chart that was given to me when I went through locomotive engineer training program, look at the speed less than 20mph that is when the dynamic realy works its best.
When the TMs are in dynamic the energy is fed to the resistance grids (and a portion to the fan). As the speed of the TMs increases more energy is sent to the grid and more resistance to the TM rotation is offered, and thus more brakeing effort. this is a linear increase up to the limit of the grid (about 750 amps). At this point (24 mph, or 12 mph with extended range, give or take a bit) the brakeing force is at its max. As the speed increases beyond this point the energy to the grid is chopped so that the average current does not exceede the max. As the speed continues to increase the brakeing has less and less effect because less and less of a portion of energy can be dissipated.
Is the training on the use of dynamic brakes the same thoughout the company? For example, would a future engineer learn it the same, if his school(?) was in the flatlands, than if it was in the mountains? Do different railroads teach, and use dynamic brake useage differently?
You mainly learn how to use the dynamic brakes is when you are in the seat running (i.e.) it is all feel on how the train reacts, the trick is to get the train bunched up then slowly more dynamic. The first few times I got the s kicked out out me then more seat time it got better.
I dont agree with the post because it shows using standard dynamic but keeps refering to extended range. the extended range numbers you need to remeber is 24-18-12-6. this is when the grids drop out to offer more resistance. and in moderern engines the dynamic is at 900-950 amps not 750 as standard amp ( sd-40) dynamic,
I’m looking at the possibility of some seat time this fall on our line. As it stands, our primary locomotive will be our RS-3 (no dynamics, No. 6 brakestand), but our backup may well have dynamics (one of our two Century series ALCO’s). Decent overall trainhandling notwithstanding, this is the real challenge:
You’re looking south, from about a .5% grade toward a ~1% grade on the other side of the “Camel’s Hump.” It’s fun - from heavy throttle to a brake application in the length of the train. With regular braking, the train stays stretched (make an initial set and bail off the independent). The fun will be in gracefully going from stretch to bunched as the dynamics come into play.
