Purpose of Dynamic Brakes

[MP173]

I know dynamic braking is used in downgrade situations, but I am not completely sure how it works...and I am NOT electrically minded.

However, my main question is this...what purpose does dynamic braking have in relative level terrain?

Just heard an NS train report to the mechanical services that the dynamic brakes in a following unit went out and they tripped a relay.

What applications are dynamics used in level areas?

thanks,

ed

[ericsp]

Dynamic braking is basically making the traction motors in the trucks function as generators. It takes energy to turn a generator, so this slows down the wheels. The electricity from the traction motors is routed to resistors where it becomes heat (think of a light bulb or an electric heater). I would guess that some can be routed to the batteries if they are not fully charged, but I do not know. It can be used on level track.

[Modelcar]

...Dynamic braking can be used to suppliment train brakes or used by itself to help control train speed where ever it is....Used where ever braking or slowing a train is needed. As discribed above....An electric load is routed to the traction motors on an engine hence slowing the traction motors....and the motors are connected mechanically to the engine axles....When they slow, the engine slows....

[Modelcar]

....If you dig back in the archives of this forum on this subject..."Dynamic Brakes",....you will find pages of data discussed on this subject.

[Anonymous]

same reason you'd use them on a down grade, to help conserve the regular brakes or to augment them. if you're on level terrain and don't need to stop too quickly it makes it easier on equipment. try driving a semi-truck with an engine brake, it makes handling one quite a bit easier by not having to be on the brakes all the time. plus it sounds pretty cool.

my question about dynamic brakes is what if you're lead engine wasn't equipped with them but the following 3 units, for example, were. is the DB 'lever' or whatever still on the unit w/o DB?

[Anonymous]

And a resistance "grid" is installed to provide a load for the [motors functioning as generators], thus making the force necessary to turn them greater. These grids get hot from the current passing through them, just like an electric space heater for a cold room in the house. So fans are added to cool the grids.

Therefore the energy absorbed from the trains momentum is dissipated into the atmosphere as heat....

[wabash1]

QUOTE: Originally posted by farmer03

same reason you'd use them on a down grade, to help conserve the regular brakes or to augment them. if you're on level terrain and don't need to stop too quickly it makes it easier on equipment. try driving a semi-truck with an engine brake, it makes handling one quite a bit easier by not having to be on the brakes all the time. plus it sounds pretty cool.

my question about dynamic brakes is what if you're lead engine wasn't equipped with them but the following 3 units, for example, were. is the DB 'lever' or whatever still on the unit w/o DB?

if the lead unit has no dynamic brakes ( not equiped) there can be no dynamic for other units as there is no handle for the dynamic brakes. for the other units to work in dynamic you haft to be able to put on the dynamic from the lead unit.

[jchnhtfd]

They save a lot of wear and tear on the air brake equipment -- in fact, in 'level' territory, it's not uncommon for an entire run to be made using the dynamics only, setting the air only when you've stopped.

That said, however, a number of railroads with 'level' territory had units without dynamics, for a variety of reasons, and so did some lines which weren't level (the old CV -- now New England Central -- had several GP9s without them, for passenger service).

Further, the maximum speed of a train on hilly terrain is set assuming that the dyamics won't be available when you want them...

[MP173]

ok, i got it.

The description of the jake brakes on a semi helped...use the resistance of the generator to slow things down.

I can see how that would be an alternative method to using air.

ed