dynamic brakes

[Anonymous]

What part does the diesel engine play when in dynamic brake mode. I know the traction motors are then generators loaded by a heat disipation grid using fans to cool the grid and distribute the heat. The engineer, once switched to dynamic brakes, can increase and decrease the brakeing force of the dynamic brakes using the throttle. How is this accomplished? What part does this power play and how does it do it?[:)] Thanks. Robert Graves.

[BentnoseWillie]

None, aside from providing enough electricity to set up the magnetic fields in the motors so they can generate electricity, and to power the cooling fans and other normal onboard electrical loads.

When in DB, the throttle controls the amount of braking force.

[jchnhtfd]

When the traction motors are switched to dynamic braking, they are acting as generators -- as you say. An generator, though, requires a small current in the field windings, called excitation. This current, in the case of dynamic braking, is supplied by the main generator, and is controlled by the engineer from the throttle. More field current (excitation), more current generated in the armature -- and it is the armature current which is fed to the grids. It is the generation of the armature current which absorbs mechanical energy from the wheels, thus slowing the train.

[oltmannd]

The diesel engine provides the following in dynamic braking:

1. excitation to the traction motor field coils from the main generator (or alternator)
2. cooling air for the DB grids (GE U series and older -7s)
3. cooling air for traction motors

The dynamic braking force is regulated by controlling the excitation of the field coils in the traction motors. The engineer doesn't work the throttle to do this, but the dynamic brake lever which is really just a big rheostat (on some older locomotive, the throttle lever did double duty)

On rising current to the grids, the diesel engine will increase speed in order to supply enough excitation voltage and cooling air. The diesel engine is making very little horsepower when in DB. It only revs up to spin the traction motor blower fast enough to provide enough cooling air and the main generator fast enough to provide enough voltage to the TM field coils.

[wabash1]

QUOTE: Originally posted by oltmannd

The diesel engine provides the following in dynamic braking:

1. excitation to the traction motor field coils from the main generator (or alternator)
2. cooling air for the DB grids (GE U series and older -7s)
3. cooling air for traction motors

The dynamic braking force is regulated by controlling the excitation of the field coils in the traction motors. The engineer doesn't work the throttle to do this, but the dynamic brake lever which is really just a big rheostat (on some older locomotive, the throttle lever did double duty)

On rising current to the grids, the diesel engine will increase speed in order to supply enough excitation voltage and cooling air. The diesel engine is making very little horsepower when in DB. It only revs up to spin the traction motor blower fast enough to provide enough cooling air and the main generator fast enough to provide enough voltage to the TM field coils.

I agree with you. if i was using the throttle why would i be slowing down?? the non aar controll stand used the same handle for power and dynamic. and now they do it again on the desk top junk. and these handles are wearing out quick on some units the slop in some ( mostly the ge engines) are terrible.

[BentnoseWillie]

QUOTE: Originally posted by wabash1I agree with you. if i was using the throttle why would i be slowing down??

Because on some units engine speed and DB excitation are both controlled by the throttle lever, dependent upon another selector. I didn't get into different DB controls because (a) the question was about the role of the prime mover, not how the controls worked; and (b) I'm more of an "engine compartment and electrical cabinet guy" than a "control-stand guy". [;)]

Incidentally, VIA's F40PH's and many other passenger units control DB and air together, proportioned according to train speed and control setting ("blended" braking). In these units there is still an independent control for the engine brakes.

[Anonymous]

Thanks all. I now feel I understand Dynamic Brakes. Trainmang

[wabash1]

QUOTE: Originally posted by BentnoseWillie

QUOTE: Originally posted by wabash1I agree with you. if i was using the throttle why would i be slowing down??

Because on some units engine speed and DB excitation are both controlled by the throttle lever, dependent upon another selector. I didn't get into different DB controls because (a) the question was about the role of the prime mover, not how the controls worked; and (b) I'm more of an "engine compartment and electrical cabinet guy" than a "control-stand guy". [;)]

Incidentally, VIA's F40PH's and many other passenger units control DB and air together, proportioned according to train speed and control setting ("blended" braking). In these units there is still an independent control for the engine brakes.

Just yanking your chain a little. no harm was ment. and i understood what you was getting at. and I would love to be on a amtrak train to see the dynamic brake and air ( for lack of better wording) use for a stop. I have heard of this but in freight we dont have the need to amtrak in to a stop.

[BentnoseWillie]

Just yankin' ya back. [:o)] Like I said, I'm not conversant with all types of control stands, having only seen a few and never for long.

I don't know whether the Amtrak F40's had blended braking or not - I assume that the newer units do.

[Anonymous]

Do all new Locomotives have Dymanic Breaks

DOGGY

[mudchicken]

no

[csxengineer98]

dynamic brake is an opption... just like windsheild washers....desktop or AAR style controll stands... it comes down to what the rail roads want on thier power..and how much they want to spend on it...
no differnt to when you go to a car lot and buy a car... some cars of the same model have more opptions then others... you buy what best suits you...and what is in your price range
csx engineer

[M636C]

Guys,

At the risk of confusing people, in the Montreal-built M630 and M636, the dynamic brake grids were cooled by air from the traction motor blower, and the brake grids were located just above the blower. To acheive this, the engine had to run in notch 8 whenever the dynamic brakes were engaged, although it was not producing much more than idle power.

In most locomotives, including Alco designed C-630 and C-636, the dynamic brakes are cooled by DC electric fans driven by the brake current from the motors.

The GE U series had dynamic brake grids mounted in the radiator air intakes, cooled by the (engine driven) radiator fans, and this may have required the engine to run at a speed higher than idle as well. It was the change to motor driven fans in the later Dash 7 locomotives that introduced the "hump" behind the cab on these units, which carried on to the early Dash 8s.

I don't think any SD70, SD80 or SD90, Dash 9 or AC 4400 or AC6000 has been built without dynamic brakes! However, none of the more than 400 JT42CWR ("Class 66") built for use in England and Europe have dynamic brakes, because the big muffler to meet sound regulations takes up all of the space needed for dynamic brakes.

Peter

[UPTRAIN]

Instead of puting the power to the traction motors, your putting it through a grid of resistors and relesing it as heat causing drag, kinda like your toaster.

[kenneo]

For a bit of completeness, here, first generation units (straight DC generation without an alternator) had a main generator, an exiter (for the main generator) and an auxillary generator for such things as battery charging, lights, traction motor cooling fans and so on. The Aux Gen could be set up to exite the traction motors for Dynamic Braking. The Main Gen exiter could also be used. But the Main Generator, was as far as I know, not used to excite the traction motors.

Locomotives with Alternators, however, are a different story. For starters, they don't have Auxillary Generators nor exiters. They don't need them.

[UPTRAIN]

Yes that's alittle more indepth...I was getting at the basics!!![:p]