What you describe is called "plugging", an electric
motor. It is very destructive as, in theory, the
plugging current, (measured in amps) is TWICE the
running current. Some electrical motor control
circuits (mostly for dc motors) have "anti-plugging"
relays to prevent this practice. The name comes from
the old steam engine procedure of stopping by
"horseing over" the reverse lever. That didn't hurt
the steam engine one bit.
John
--- zephyr9903 <zephyr9903@iowatelecom.net> wrote:
> On Sun, 26 Oct 2003 15:19:44 -0800 (PST), George
> William \(Bill\) Newport
> wrote
> > No,
> > but the diesel is still needed to make air for the
> brake system and
> > heat for the crew and to keep the batteries
> charged up and to
> > operate the relays that make everything work, the
> magnets you speak
> > of is the magnetic field of the electrical system
> which either
> > generates power or makes resistance without any of
> the parts
> > actually touching each other, and dynamics cannot
> stop the train
> > like the air brakes can and you still have to use
> the air brakes,
> > you just add dynamics to it as an assist, the
> Seaboard did not buy
> > much dynamics if they had any at all, early
> Seaboard engineers used
> > what some people call Seaboard dynamics, they set
> the reversers in
> > the opposite direction of travel and used a little
> throttle to send
> > reverse current through the traction motors to
> slow them down, they
> > also burned up a few traction motors as the system
> is not designed
> > for that, but leave it up to a bunch of ex steam
> engineers to find
> > something to tear up them diesels that took away
> their favored steam
> > engines G
> >
> > wollffee <wolfee@onebox.com> wrote:
> > OK, thanks, I think I understand. This means that
> the diesel is not
> > used then, right? When the wheels turn, instead of
> getting pushed by
> > the magnets in the electric motors, they get the
> opposite force and
> > the magnets push AGAINST the direction they are
> turning, right?
> >
> Let me see if I can simplify this:
>
> If you take a system that applies power to work, but
> reverse the input, you
> reverdse the effect.
>
> Take a windmill, where the moving air turns a shaft.
> Put a motor on the
> haft, and you have a fan producing wind. Take a
> water wheel, which uses the
> weight of falling water to turn a shaft. Apply
> power to the shaft, and you
> have a pump which lifts water.
>
> Take an electric motor which uses electricity to
> turn, and let the weight of
> the moving train turn the "motor". It now generates
> electricity.
>
> The key to dynamic braking is the bank of resistors,
> which turns the
> generated electricity into heat, exhausted by the DB
> fan (of whatever
> configuration). The same effect could have been
> achieved by mounting
> (remember, this happened during World War II)
> air-raid seachlights on the
> front of the unit and using the generated current to
> blind approaching
> motorists (which would have raised liabulity
> insurance rates) - far more
> seriously, you need to impose a load on a generator
> to make it "drag", and
> the resistor banks in a GP blister or an F hatch
> "uses" the electric current
> to generate discardable heat, and that spent
> electricity, generated by the
> turning traction motors/generators slows the unit(s)
> . . . see the "Second
> Law of Thermodynamics" whence comes the name,
> "Dynamic Brake".
>
> Marshall Thayer
>
> PS: CB&Q was the third buyer of EMD's FT units -
> which were the first
> diesels to offer DBs . . . the Santa Fe & Q eook
> them . . . the Southern
> (with the notorious Salida grade, passed!
>
>
>
> --
> Iowa Telecom WebMail (http://www.iowatelecom.net)
>
>
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