Dynamic braking

[ddechamp71]

Hi all, I've another question today:

When looking at videos, or watching real trains while railfanning in mountain areas I look at and listen carefully to downwards trains.
I have the feeling these trains' locomotives are not running idle when under dynamic braking. The locomotives' diesel engines make a sound as if they were under Run 2 or 3.

What's the explaination? Are the diesel engines actually above iddle? And if the reply is "yes", what is it for? Is it to energize an excitation alternator, or sthg like this?
Any answer appreciated!:shade:
Dom

[Charlie]

Hi all, I've another question today:
The locomotives' diesel engines make a sound as if they were under Run 2 or 3.[/SIZE]

What's the explaination? appreciated!:shade:
Dom

What you are hearing are the dynamic brake grid blower fans air-cooling the dynamic brake grids. It is a VERY loud noise.

Another neat sound to listen to(IMO) is on the METRA(Illinois)locos
which have "blended" brakes. This is a combination of dynamic and
automatic brake. It is computer sensed and operated. While in the cab
you can hear the whine of the dynamics and actually hear the system
as it pumps off the automatic. It is a graduated release and there is also a "quick release" feature built into the system. This is useful if
the train is braking too quickly or too "hard". The hogger can take a small(or large) release and then go back quickly to the ABV without having to worry much whether the brake pipe pressure has
equalized. It is still possible to "piss away" the brakes if you apply and
release too frequently but for the most part the dynamics are handling
the greater part of the braking effort. When a guy gets "good" at running the commuter trains he can knock off the air just at the point
where the independent will bring the train to its final stop.
I think most, if not all,the carriers want their engineers to rely on
dynamic braking as the desired method of stopping trains. This is fine,
but there are circumstances where an ABV reduction is actually a better
method.

I am digressing too much here.

You get the idea. I'll let some of the other hoggers add their opinion and
methods of braking. There are LOTS of both.

CT

[SteveM76]

The diesel engine is in idle during dynamic braking. It basically turns the traction motors into generators therefore producing a retarding effect. What you might be hearing is the diesel engine revving to pump air depending on what kind of loco it is. That would be the only time it is not at idle.

[SteveM76]

To elaborate on Charlie's post, fuel conservation is a major concern with railroads now. There are charts posted that show the difference of fuel comsumption in dynamic vs stretch braking. CSX has GPS on the newer locos that monitors everything I do and I hear about it from the road foreman if I stretch brake too much.. They want me to use dynamic all the time but for that to happen, the train needs to be made up properly. That means DO NOT PUT ALL OF MY LOADS ON THE REAR!!! I once had a train with 46 auto racks on the head end, followed by a big block of empties, and 28 covered hoppers loaded with cement on the REAR! It was 8600 feet and the worst handling train I've ever had.

[BnOEngrRick]

Earlier EMDs all rev up to about notch 5 when in dynamic. Later EMDs rev up when over 500 amps in dynamic. GEs have a step up range when in dynamic, the heavier the dynamic is applied, the higher the engine revs.

[ddechamp71]

Earlier EMDs all rev up to about notch 5 when in dynamic. Later EMDs rev up when over 500 amps in dynamic. GEs have a step up range when in dynamic, the heavier the dynamic is applied, the higher the engine revs.

My question came after I've watched "The Montana Rail Link" from Pentrex. This video has been taken in 1990 and locs are mostly SD40s and SD40-2s. And as far as I can hear, it appears clearly that diesel engines are not iddling when moving downgrade (but here I don't speak of the whine of the dynamic brake fans!)

BTW, when you speak of "rev up", does that mean the engineers changes his direction lever to "aft", and applies "opposite" current whose trend should be to move the loco aftwards if it wasn't going downgrade with an heavy load behind?

Dom

[ddechamp71]

The diesel engine is in idle during dynamic braking. It basically turns the traction motors into generators therefore producing a retarding effect. What you might be hearing is the diesel engine revving to pump air depending on what kind of loco it is. That would be the only time it is not at idle.

OK Steve, I'm seeing that you're a train engineer....So I guess your statement is true, and I consider my feeling of diesel engine above idle is false!:shade:

[Rule 281]

Earlier EMDs all rev up to about notch 5 when in dynamic. Later EMDs rev up when over 500 amps in dynamic. GEs have a step up range when in dynamic, the heavier the dynamic is applied, the higher the engine revs.

...and how! I dread catching those old units that rev up when in dynamic. Not only do you get the blowers screaming, you get the engine noise along with it. Never a moment of peace and quiet. Even some of the newer ones make waaaaay too much noise.

BTW, when you speak of "rev up", does that mean the engineers changes his direction lever to "aft", and applies "opposite" current whose trend should be to move the loco aftwards if it wasn't going downgrade with an heavy load behind?

That increase in RPM (rev) is to provide excitation and is automatic. It's not something the engineer can control and is one of the reasons there was (and still is in some quarters) a debate over the fuel savings in dynamic vs. power braking. As noted above...dynamic brakes turn the traction motors into generators to create resistance and the power generated is dumped overboard as heat through the brake grids. That's why they need the noisy high-speed fans to cool the big toasters in the roof...they'll melt into a puddle if that heat doesn't go away.
You're not applying current in the opposite direction (a measure of last resort known as 'plugging the motors' that most computer-controlled locomotives will not even allow because of the damage it can cause). The reverser is kept in the direction of travel but instead of the throttle, you use a separate dynamic brake control handle or on older units, you use a selector to switch the throttle handle to dynamic braking. Same effect, just a different way to get there.

[ddechamp71]

OK Rule 281, thanks a lot! This time I believe I've understood!:shade: And it confirms the diesel engine is above iddle when dynamic brake is in action.

(with your signature, are you a Blue Oÿster Cult fanatic?:lightbulb: )

Dom

[Rule 281]

(with your signature, are you a Blue Oÿster Cult fanatic?:lightbulb: )Dom

You're welcome Dom. And yes...Cult and I go back quite a ways. Railroading isn't the only 'Career of Evil'. ;)

[BnOEngrRick]

That increase in RPM (rev) is to provide excitation and is automatic. It's not something the engineer can control and is one of the reasons there was (and still is in some quarters) a debate over the fuel savings in dynamic vs. power braking.

There would still be considerable savings in fuel because the rev up is under very light load, the excitation load is minimal. Much less load than the same fuel requirements for operating under load with the same engine RPMs.

[Rule 281]

I agree. Noisy but not really doing much with the RPMs. I've heard the fuel use argument batted back and forth several times though, particularly among our neighbors to the north.
Since we get rule violations for power braking and running releases unless absolutely neccessary, it's kind of a moot point. Wear the earplugs and hope for a quiet cab next time.

[Charlie]

I once had a train with 46 auto racks on the head end, followed by a big block of empties, and 28 covered hoppers loaded with cement on the REAR! It was 8600 feet and the worst handling train I've ever had.

I winced when I read that!!!! OUCH!!!! One has to be(or have been)
an engineer to understand what Steve is talking about!

You're lucky you didn't "get" a knuckle on that one! I probably would have! LOL


CT

[Hytec]

Charlie, not only train drivers get a wakeup call from that unbalanced string. That's a problem for anybody who has driven a tractor with a string of hay wagons where the first few are empty. Talk about the hind end passing you while slowing down at the barn...WHEEE!