How difficult is it to install dynamic breaks on units that were not built with the feature? I know back in the 60s and 70s, railroads wanting to save money opted to leave the dynamics off - but it seems that nowadays all locos have them as standard equipment. The Rock Island originally ordered 10 SD40-2s back in 73. These units went to ICG during the liquidation, and to EMD in 1989. They were built without dynamics, and they arrived at EMD that way. However, when 6 of these units ended up on the Wisconsin & Southern in 2003’ish, they had dynamic brakes. One would assume EMD added these while they were in their lease fleet. If anyone has any info about adding dynamic brakes to a non-dynamic equipped unit, I’d like to hear it. Thanks!
thats a pretty good question. I haven’t researched this at all but I’d be willing to bet once an old diesel like that goes into being leased dynamic breaks get added during rebuilding.
all you’d have to do is add the electrical gear, a bank of resistors, and a cooling fan or two…how hard could it be? even as a conductor i love dynamics…waaaay quieter in the cab than listening to the air exhaust of a 150-car train…dunno how engineers like 'em though. i’ve seen some that swear by dynos and some that hate it.
-and less chance of getting a knuckle with dynos…
You sound like my boss… “piece of cake !!!” NOT !!
Yeah, I like how he started the paragraph…“All you have to do…”
BTW, I absolutely love working with dynamics: a whole different way to handle a train; I feel almost lost without them. And every trainman I know likes them as well: far less sticky brakes to walk for…
Dynamic Braking, the turning of the Traction Motors into Generators. Effective at speeds above 25 mph.
With DC Traction Motors,:
Shutdown input voltage to the Traction Motor’s commutators. (close Throttle power)
Raise the voltage (strength) of the Motor Fields. (move Throttle to DB selected setting)
Traction Motors generate voltage.
The four quadrant SCR (solid state) drive directs the output back against a bank of resistors that changes the electrical current to heat. (Regeneration)
Fans cut in to cool the the resistors.
Need new control stand with DB settings, drive software to switch control from positive to negitive, resistor grids, cooling fans, and very heavy wiring connecting the system. Could be done but costly.
seems pretty simple to me…maybe i expect too much out of mechanics. oh wait, yeah i do. this is why i’m in train service…i don’t know how time consuming it would be. and i don’t care.
Of course you mean "not as effective at speeds above 25 MPH "? And you really meant to say current (Amps) instead of voltage?
In 1984 Santa Fe merged the TP&W Railway into its system. Part of TP&W’s assets included a GP30 and three GP35s all built without dynamic brakes. Santa Fe acquired a used Union Pacific GP30 and three used Union Pacific GP35s that year for “parts” for the rebuild process. When the rebuilt TP&W units appeared from the rebuild shop in San Bernardino they all sported dynamic brakes.
I would surmise that the Rock Island SD40-2s may have gone through a similar rebuild process with similar hoods and parts being taken from other units to get the dynamic brakes.
Thats why I love this forum. Info. Now keep in mind that I’m not going to state all this stuff word for word. But now I do have some understanding of how dynamics work. -not entirely but I know the traction motors are involved. And perhaps my speculation was somewhat correct. Things like that are added in rebuilds if a certain user needs them.
HAVE A HAPPY RAILROADIN’ DAY YA’LL!
CP’s New F Units CP 4106-07, were Equipped with Dynamic Brakes during their Recent Rebuild, NOT having them from the Factory when Built for CN as 6500s. ( CN’s Passenger CPA/B-16-5s did NOT have D/B Neither. )
Aside from Brake Shoe Wear and Heat Descending the Mountain Grades and Setting Retainers where Necessary, Complaints were being Received from Paying Passengers about Brake Shoe Smoke.
Good Morning SF Fan,
Here’s my laymans cut at how they work. Under normal pulling conditions, the diesel engine (aka prime mover) is turning a generator or alternator and is producing electricity. That electricity is fed to the traction motors which are mounted on the axles and which have a gear drive to turn the axles. So in short, feed juice to the traction motors and the train moves. However - and this is critical, if you recall, a motor can also act as a generator. Instead of feeding electricity “into the motor” you use some mechanical force to turn the motor and it produces electricity back out. In the case of dynamic braking, the momentum or gravity pushing downhill creates the mechanical force. That turns the axles and therefore turns the traction motors. When the dynamic brake lever is switched to the on position, some electicity is applied to the fields of the traction motors and by doing so, the windings are turning inside of an electrically created magnetic field. Voila - your traction motors just became electrical generators.
However, it takes energy to continue to turn those windings inside of that magnetic field which is creating some measure of magnetic resistance to turning. That energy that is required to keep turning the motors is the “drag” that slows down the train. Think about the power it takes from the diesel engine to turn the main generator - it takes a lot of horsepower to turn the generator. Likewise, turning the 4 or 6 tract
Just a few more lines. DC motor speed is a product of armature voltage and motor field strengh.
The higher the armature voltage the higher the RPM, the weaker the motor field the higher the RPM. The stronger the Motor Field the more Torque but at less RPM.
You would start moving a load with a strong Motor Field (max torque) and enough armature voltage to get moving. As you gather speed by increasing amature voltage, the control system should, at about 50% speed, start to reduce the Motor Field strengh, maybe down to as low as 50% of Full Field value. You now have enough Torque to maintain speed at a much lower Armature voltage than would be required if you were at Full Field.
When you go to slow down, the traction motor go to Full Field while reducing the armature voltage back to a low value. Under this condition the Motor thinks it should be running at a low RPM but is being pushed at a high RPM by the load. It become a generator, with a " short curcuit" across the armature in the form of the DB Resistors. The motor is heavily loaded and its RPM is draged down while developing a great deal of heat. This limits the time that Dynamic Braking can be applied.
This, besides locomotives, is how we control the electric Elevators in your High Rise buildings. And yes, we do “regenerate” the power back into the local power company and only use the DB Resistors for Emergency Stops.
WOW, thankyou Doublestack and DMUinCT. Very interesting! I’m goning to copy this to a personal file so I have this to refer to. One more question, does this put more wear and tear on traction motors? and what the heck one more; Is there a difference in Dynamic Braking between AC and DC traction?
I should let the electo-wizards explain this because it involves Ohms Law, but there is more than one bank of resistors. As the speed keeps dropping to certain levels, the resistor banks start dropping out in a similar manner as when in power there are transition changes.
Normally you don’t pay a lot of attention to it, except when there is a 10mph slow order going downhill and the D/B banks keep wanting to change causing big fluxuations in amperage when it isn’t wanted. You wind up either going 9mph or 11mph.
D/B in an AC unit is great. It holds down to a much slower speed and the best thing is if a traction motor burns out the D/B will still work! Not so in a DC unit.
The reason that dynamic braking grids on D.C. have sections that drop out as speed decreases is that. The current in a D.C. motor (or generator in this case) is proportional to the current, while at the same time the voltage is proportional to the speed. The current though the dynamic braking resistor grids is (as per ohm’s law) the voltage divided by the resistance. Hence the motor torque, and therefore braking effort in dynamics is proportion to the locomtive speed divided by the grid resistance. So as speed decreases, it is nessessary to decrese braking grid resisitance to maintain braking effort. This is done by having contactors that short out sections of the dynamic braking grids.
Thanks Joe.
See folks, I told you it was about Ohm’s Law…among other things.[;)]
You ought to be on a set of lite GE’s at speed and move the D/B to #8. You’d swear Dan Gurney was downshifting for a hairpin. Listen close and you can hear the tires chirpping with each downshift.[:-^]
[quote user=“Doublestack”]
Good Morning SF Fan,
Here’s my laymans cut at how they work. Under normal pulling conditions, the diesel engine (aka prime mover) is turning a generator or alternator and is producing electricity. That electricity is fed to the traction motors which are mounted on the axles and which have a gear drive to turn the axles. So in short, feed juice to the traction motors and the train moves. However - and this is critical, if you recall, a motor can also act as a generator. Instead of feeding electricity “into the motor” you use some mechanical force to turn the motor and it produces electricity back out. In the case of dynamic braking, the momentum or gravity pushing downhill creates the mechanical force. That turns the axles and therefore turns the traction motors. When the dynamic brake lever is switched to the on position, some electicity is applied to the fields of the traction motors and by doing so, the windings are turning inside of an electrically created magnetic field. Voila - your traction motors just became electrical generators.
However, it takes energy to continue to turn those windings inside of that magnetic field which is creating some measure of magnetic resistance to turning. That energy that is required to keep turning the motors is the “drag” that slows down the train. Think about the power it takes from the diesel engine to turn the main generator - it takes a lot of horsepower to turn the generator. Likewis