I have purchased more than one loco with text stating with or without Dynamic Brakes as appropriate, what are they? What do they look like? Is there a diagram pointing out what they look like.
Please answer
On the EMD locos, the dynamic brake blister (actually the resistior grid and cooling fan) are at the top of the long hood, aprox in the center.
http://www.athearn.com/Products/Default.aspx?ProdID=ATH93572
Note the wide spot in the top of the hood and the first two fans (from the front) directly above the “C” part of the Conrail emblem. This is the dynamic brake blister, the main visible part of the system.
Note the same part of this loco is smooth. This is one without the dynamic brake.
http://www.athearn.com/Products/Default.aspx?ProdID=ATH93568
On the older models, this used to be a separate part of the body, so an undecorated one could be provided with or without dynamic brakes easily.
Dynamic brakes are basically a big electric toaster grid. Mechanical brakes apply pressure to the wheels to stop a locomotive, dynamic braking is when they use the traction motors as generators which puts drag on the axles and assists the mechanical brakes in slowing a train. Since they have no way to store the electricity generated they use the wire grid to eat up the current with big fans to dissipate the heat.
The dynamic brake section on EMD locomotives just behind the cab and in front of the diesel motor section. There is usually a wide grid at the top with a fan on the roof. Aft there are more fans but they are for cooling the radiator coolant that circulates in the diesel like most automobile cooling systems.
Dynamic brakes are used in mountainous territory to retard a train’s downhill speed without needing to apply the air brakes, provided the downhill grade is not too severe. The engineer can apply the dynamic brakes on the engines, which reverses the electrical polarity to the traction motors and turns them into generators.
Using the motors as generators causes a lot of drag on the wheels and slows the train down. In the process, a lot of heat is generated, which must be gotten rid of. A large resistor bank is mounted in the top of the engine, usually at the rear end, and large fans blow the heat away.
Engines with dynamic brakes usually have a protrusion from the sides that are the resistor banks.
Early locomotives with dynamic brakes had the resistor banks right behind the engineer’s cab, and there were grills near the top for air intake.
Can you hear it? That’s the sound of electrical engineers and technologists screaming at the phrase “reversing the polarity”. [}:)]
Try and imagine how painful the average action movie is, and pity us. [:o)]
Seriously though - aside from that one phrase, you hit the nail on the head.
While the technical explanation is helpful, you can experience the same thing in your car. It’s easier on a standard, but you can do it on an automatic. While going down a hill, downshift to a lower gear. You’ll immediately feel the drag on the car and it will begin to slow as you go down the hill. You won’t stop, just slow down a bit. Of course in your car you don’t want to drop it into too low of a gear… The basic effect of the dynamic braking is the same. Randy
When specifying options on a given diesel-electric locomotive railroads would specify dynamic brakes if the topography of their railroad justified the cost of this additional braking force. New York Central with its water level route would be less likely to order dynamic brakes than the Pennsylvania RR with its climb over the Allegheny Mountains(Horshoe Curve).
Jon
On truck-tractor/semi-trailer rigs, this is called a “Jake Brake”. It was named after a man named Jacobs who designed it. The best way to get this effect in your car with an automatic transmission would be to set the cruise control and take it out of overdrive.
Dick
Texas Chief
So, If I have a sound decoder with ‘Dynamic brakes’ as a sound function on an engine with the dynamic brake fans etc, I would only turn the function (sound) on while travelling down a grade correct? Or can it be used to stop on a flat/incline?
The description above reads like its used as an accelaration inhibitor (governor) versus a brake to slow the train from its current speed. Do they use them in conjuction with wheel brakes?
I can’t really answer the first paragraph, but I have seen pretty good descriptions. Google might be handy there.
As far as the second paragraph, that’s not quite it. The idea of slowing your car by going to a lower gear does use the engine to help you slow down, but it would be even more accurate if you turned the motor off (don’t try this at home, the steering wheel lock would be somewhat annoying). I’ll add a little more tech-speak to try to clarify. You know that a diesel-electric locomotive uses a diesel motor to run a generator to generate electricity to run electric motors to turn the wheels. The interesting thing about electric motors is that if you stop giving them power, but turn the shaft, they become generators. So, now you are turning the mechanical energy of the wheels turning back into electricity. But you’ve got no means of storing it (the nwe hybrid cars actually do this, but they do store the power generated back in the batteries, if I am not mistaken), so you put a big toaster in the locomotive with some fans to cool it to get rid of the heat. So dynamic brakes are indeed brakes. When you use them the generator is diconnected from the motors, which are hooked to the resistor grid (toaster) instead. Operationally, I beleive that there is an art to combining the dynamic and air brakes to get the best braking performance with the least wear on the mechanical and dynamic braking systems. I’ll look
The dynamic brake on a locomotive can be used with or without the main trainline air brake system. The dynamic brakes have more power at higher speeds, and drop off as the speed decreases. The current breed of new locomotive have an extended D/B capability that works down to very low speeds and give very fine control. Normally you hear the ‘howling’ of the D/B exhaust fans, and a sightly higher engine speed(reving the engine to provide excitation).
Jim
This is a good read, even better if you have a high speed connection and watch the videos!
I have 3 sound equiped locos, and all 3 you can turn the Dynamics on anytime. Its only a sound function. you can leave them all on the time but they won’t slow your train down
I hate when that happens…here is the link!
That link doesn’t work for me. It just comes up with “Page cannot be displayed”
I can’t figure why, it works for me. I’m not logged on to the site, so I don’t think that’s an issue. Did you try cutting and pasting it, too?
If it doesn’t work, go to http://www.trainboard.com , under around trainboard is forum index, look for Engineer Classes, make posts for the last year visible, and find Brake Class, this summer’s blockbuster:
http://www.trainboard.com/grapevine/showthread.php?t=78542
And another shot at the link, for good measure.
Dynamic brakes work by using the motor as a generator instead of a motor. This is done by simply cutting power to the rotating part of the motor, and increasing the power to the field coils. This obeys the rules Faraday laid down, and an electromotive force is created in the rotor. The connection to the rotor, instead of being to the power supply, is now made to a resistor bank, so current can flow through the circuit (and not result in destruction of the motor!). The resistors dissipate the power generated in the form of heat. Since it limits the amount of power that can be dissipated, a counter EMF is generated in the rotor’s windings, limiting how fast it can turn. By adjusting the power fed to the field windings, you can change the counter EMF, braking the rotor’s rotation. Basically what you have is a rotating magnet field that is trying to align itself with the stationary magnet field surrounding it. The torque developed while trying to align itself slows the train.
The dynamic brakes have a distinct sound to them when in use, and is usualy louder than the enguaged throttle under load. It’s kind of like a turbine engine sound. Prototypically, if you are using dynamic brakes on your layout, you would use it when decending a grade, or bringing a loaded train down to a slower speed, or to a stop.
To better understand this function in reality, take an electric motor with leads attached, and bring it up to speed with a 9v battery, then immediately cross the leads together. You will find that the motor will come to a screetching hault. If you have the motor leads crossed and try to spin it, you will find that it will only revolve maybe once or twice. This is the magnetic property of the motor coil (armature) resisting the natural magnetic field of the motor magnets. Resistance causes heat… like a rug burn.
Sorry if I reiterated some information from previous posts.