When reading the description on the different engines found in the "O" scale catalogs, dynamic brakes are mentioned as part of the realism of the model. What exactly are dynamic brakes, where are they located on an engine and how would I spot them and what makes them different/special from other types of brakes? I thank all of you in advance for your for replies.
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Dynamic brakes are brakes that slow down the train when going down a hill. It converts the traction motors into resistors that take the energy of the forward movement into heat that escapes through the exhaust fans in the top.
Hi, Paul.
An electric motor can also be a generator. Feeding electricity to it makes it a motor. If you can turn the motor shaft the manually, it will create a current as it does in your car's alternator (earlier generator). If you apply a load across the leads from the motor it will be more difficult to turn. In a locomotive with dynamic brakes the output from the motors is routed to a grid of resistors. Because this generates a lot of heat (E=mc²
the resistor grid(s) are located on top of the car body with exhaust fans. The shape an size of these grids varies from locomotive to locomotive.
Attached is a photo of EMD demonstrator FT103 without dynamic brakes and Reading FT 251 with dynamic brakes. The gird is the rectangular box on the roof.
Hope this helps,
I see that Amtrak's new locomotives are going to send the generated energy from the dynamic brakes back to the power grid, probably makes sense...
John, wouldn't that apply to electric locomotives? With a diesel-electric you would have to plug into the nearest outlet with a long extension cord ;-)
It would be rather interesting if they came up with a battery car to capture that energy, instead of wasting it as heat. Most useful on mountain running. It would probably get you half way up the next hill.
It would be rather interesting if they came up with a battery car to capture that energy, instead of wasting it as heat. Most useful on mountain running. It would probably get you half way up the next hill.
That's the concept of GE's hybrid GEVO unit.
Stuart
It would be rather interesting if they came up with a battery car to capture that energy, instead of wasting it as heat. Most useful on mountain running. It would probably get you half way up the next hill.
Elliot,
I would like to know if they do that on the hybrid or battery locomotives being tested by some railroads. That technology is being used in the all electric cars (battery)being developed by the German big three. It seriously increases the mileage per charge by returning a charge created from braking back to the batteries.
Dynamic brakes are brakes that slow down the train when going down a hill. It converts the traction motors into resistors that take the energy of the forward movement into heat that escapes through the exhaust fans in the top.
Sorry, but your description is completely incorrect.
Thanks Stuart. I guess I never really paid attention to what was inside the GEVO units.
My guess is that if Amtrak regenerates into the overhead, all the power will be used by other trains. None of it will ever get to a commercial power grid. The cost of installing equipment to convert the two phase, 25 cycle, 11000 volt power to anything that can be used commercially is not justified.
Dynamic brakes are brakes that slow down the train when going down a hill. It converts the traction motors into resistors that take the energy of the forward movement into heat that escapes through the exhaust fans in the top.
Sorry, but your description is completely incorrect.
Actually, according to how the physics of dynamic brakes work, he's pretty close. Kinetic energy transformed into heat is how they work. However, saying the traction motors become resistors is incorrect- the traction motors are connected to resistors. Simplifying it a bit, but that's the gist of it.
John, wouldn't that apply to electric locomotives? With a diesel-electric you would have to plug into the nearest outlet with a long extension cord ;-)
The ultimate "lash-up"!
It would be rather interesting if they came up with a battery car to capture that energy, instead of wasting it as heat. Most useful on mountain running. It would probably get you half way up the next hill.
Elliot,
I would like to know if they do that on the hybrid or battery locomotives being tested by some railroads. That technology is being used in the all electric cars (battery)being developed by the German big three. It seriously increases the mileage per charge by returning a charge created from braking back to the batteries.
But in terms of price per hp, I don't think pure or hybrid electric cars have gotten close to conventional gas/diesel transmissions.
Dynamic brakes are brakes that slow down the train when going down a hill. It converts the traction motors into resistors that take the energy of the forward movement into heat that escapes through the exhaust fans in the top.
Converts the traction motors to "generators" and the electricity generated is dissipated in a resistance bank that generates pleanty of heat.
MilwRdPaul,to describe it I think a little easier,the electricity that's being generated in the traction motors is routed to grids when the Engineer takes the engine out of power,and sets-up the dynamic braking with a separate dynamic brake handle .
The electricity is then cooled by fans, that are the loud whining noise you hear when a locomotive is slowing down using dynamic brakes.
The drag created on the traction motors by pulling the electricity from the them, slows the wheel speed down resulting in the train slowing down.
But remember the dynamic brakes have nothing to do with the brakes on the cars ,those are air or electric brakes that are on each car that's applied by a separate brake handle on the Engineer control stand .
Now of course there's much more going on than that,but I hope that helps.
The Prius hybrid does convert braking energy to electrical energy to be stored in the battery. There is a limit to how much energy the Prius battery will hold. I recently had a state inspection done on my Prius, at 40,000 miles there was still 60% of the mechanical braking pads left.
Collin,
Did you ever get a set of light units up to about 50mph, then ease the DB into full and listen as the unit seems to downshift through the gears, even chirping the wheels, as the banks of resistors change?
Dynamic brakes are brakes that slow down the train when going down a hill. It converts the traction motors into resistors that take the energy of the forward movement into heat that escapes through the exhaust fans in the top.
Sorry, but your description is completely incorrect.
And that would be completely destructive to the traction motors.
LLKJR wins the Kewpie doll for the concise and correct answer. 
Converts the traction motors to "generators" and the electricity generated is dissipated in a resistance bank that generates pleanty of heat.
To get back to Paul's question:
When reading the description on the different engines found in the "O" scale catalogs, dynamic brakes are mentioned as part of the realism of the model. What exactly are dynamic brakes, where are they located on an engine and how would I spot them and what makes them different/special from other types of brakes?
The dynamic brake resistor grids on EMD road switchers from the GP7 and SD7 up to the GP60 and SD60 were housed in blisters near the middle of the long hood with their cooling fans mounted directly above them.
The dynamic brakes and their twin fans are located just aft of the road number and above the MILW on this SD40-2 model.
The Soo did not specify dynamic brakes on their SD40-2 so they lack the blisters and fans.
Dynamic brake blister on a GP-7 model. This Atlas model can be done either with or with out the blister. Note that the dynamic brake unit has it's own cooling fan. Middle top hood area. Straight engine compartment top, (no dynamic brake) is lower, right, front in this picture.
Cooling fans installed.
The Prius Hybrid has a gear selection marked (B), which does dynamic braking without touching the foot peddle. Watching the charging bar graph on the Pruis operational display allows for foot peddle dynamic braking without the use of friction pad braking. An interesting concept, IMO
Ok, silly me. The use of dynamic braking as a power source has been around for sometime. (2004). The Railpower GG20B is a "genset" hybrid engine that uses the energy generated from dynamic braking to charge the batteries. (regenerative braking). Too much energy to waste these days.
I also have the EMD GP38-2 operators manual as I have those Alaska engines. I read the operation and checks for the dynamic brake system and found it very interesting.
Thanks, MilwRdPaul for an interesting topic for non-train savvy hobbyists.
BigJim, thanks for the insight to the sounds and feel of actually using dynamic brakes.
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