• Dynamic brake usage

  • General discussion about railroad operations, related facilities, maps, and other resources.
General discussion about railroad operations, related facilities, maps, and other resources.

Moderator: Robert Paniagua

  by U-Haul
 
If you have a lashup of four locomotives where the first one has dynamic brakes, the second one has no dynamic brakes, and the last two have dynamic brakes will this occur. Only the first unit will dynamic brake and not the last two including since they are separated by a unit lacking dynamic brakes?
http://www.railpictures.net/viewphoto.php?id=144006
STAR TREK 40TH ANNIVERSARY

  by emd_SD_60
 
Ask jg greenwood, he has plenty of experience in this field, working for the IC nonthless... :wink:

  by DutchRailnut
 
The rear two should still have dynamic brake, the signal to go to dynamic brake and rate go tru the 27 point jumper and those trainline all signals straight trough.

  by Jtgshu
 
Only on the BNSF would you see a relatively brand new loco coupled up to a 50 year old Geep on a mainline train! (I know its been rebuilt a few times, but still........)

It looks like that second unit has dynamic brakes though.........? Where they rebuilt without them?

  by roadster
 
Of late while operating CN power on Q621/620 on CSX's St.Lawrence sud. CN has mixed in their power with fomer IC power w/o dynamics (sd-40's)in the middle. The equiped loco's will still operate normally even with the non-dynamic equiped unit between. As Dutchrailnut said, the control is carried by the 27 point U cable between all operating units.

  by GOLDEN-ARM
 
Makes no difference, whether there is a non-equipped unit in the consist, or one is cut-out, due to defects, or axle/brake restrictions. Any unit online, capable of producing power, will also brake, if equipped. The only variation, is a unit isolated from "Select-A-Power", from the lead unit, won't load under power, but will produce dynamic braking, if equipped. Regards :wink:

  by BoilerBob
 
What are dynamic brakes anyway? I hear alot of people talking about them, but I don't know what they are. Are they on diesel locomotives only or do electrics have them too?

  by GOLDEN-ARM
 
Yes they can be on both. A means of using a turning motor, on a wheel/axle set, to retard the speed of the loco, through a process of generating electricity, in that motor, and sending it to a grid, or series of grids, that turn the juice into heat.(through resistance) This is like a toaster, and the current sent to the grids creates drag on the motor, as it generates more electricity. Some electrics send this electrity back into the wire, for use again when motoring. In the easist terms, like downshifting your car. The drag slows you down, without use of conventional brakes. Regards :-D

  by BR&P
 
In today's context the above posts are correct. One exception would be in an historical context - on early EMD's the circuitry for dynamic braking was a bit different, and actually had a second jumper cable (in addition to the normal MU cable). These were called "field loop" dynamic brakes and in that case, if the second unit was not DB equipped, there was no way to control the DBs on units farther back in the consist. Also, the DB equipped units were in series, so if one DB failed, ALL the units lost dynamic braking. Somewhere about 1955 they switched to "potential" type, using the regular MU jumper, and solved several problems in the process.

  by David Benton
 
Is the dynamic brake a straight on / off control , or can you vary the amount of dynamic braking ? Does it behave differently at different speeds ?

  by DutchRailnut
 
The dynamic brake can be regulated by engineer, and yes the lower the speed it will slowly fade away as motors don't spin fast enough anymore.
on AC locomotives techinicaly this does not happen and the dynamic brake will work till unit is stopped.

  by Jtgshu
 
There is also a "blended brake" system which AFAIK is mainly on passenger locomotives, where the dynamic brakes work in conjuction with the automatic brake (the train brake). There is no seperate dynamic brake handle on the control stand, its all integrated into the automatic brake. the amount of dynamic braking is dependant on how much of an automatic brake reduction is being made.

The system kicks on the dynamics automatically to help the AB (automatic brake), and is supposed to stop faster than wth just straight air (when working properly)

  by BoilerBob
 
Thanks everyone. These explanations really help.

  by slchub
 
Great replies. The only thing I did not see with the explanations is why we limit or cut-out the dynos. When we use the dynos, they create high buff forces, or alot of pressure on the couplers, especially on a grade, which can result in increase wear on the track as well as the potential for cars to jump the track or if you have an empty aluminum hopper near the front with loads behind it, crush the car. On the railroad I work for we limit the number of axles with dynos to 28 axles and 32 axles on unit trains.

  by jg greenwood
 
BoilerBob wrote:What are dynamic brakes anyway? I hear alot of people talking about them, but I don't know what they are. Are they on diesel locomotives only or do electrics have them too?
Straight from the book. (The Kansas City Southern Railway Company
Air Brake Systems and Train Handling Rules and Instructions)

Dynamic Brake: The system that electronically converts energy created by the momentum of a moving locomotive into an effective retarding brake.