Dynamic Brakes

[Cody J]

I have been shopping for a new locomotive and in the "features" section of some locomotives it says that some locos are equipped with dynamic brakes. How do dynamic brakes work on model trains?

Thanks,
Cody

[rustyrails]

Hey, Cody,
They don't really work on the models.  The "feature" is the inclusion of the dynamic brake spotting features on the model.
Rusty

[Tylerf]

Ooo that would be neat. I have seen some O scale brass steam locos with a dynamic brake system that can be applied but that's because they have no worm gears so they can coast until you hit a down hill grade so this braking system is the solution. In this case I doubt they've created working dynamics so I they probably just mean dynamic brakes on the model, not actually working braking. I assume it said on the label W/dynamic brakes which does just mean the model has dynamics.

[Yampa Bob]

http://en.wikipedia.org/wiki/Dynamic_braking

Note the dyamic braking grids on the locomotive pictured, circled in red.

http://en.wikipedia.org/wiki/File:TVS2018_2.jpg

[Guilford Guy]

Different Railroads had different views on dynamics. Mountainous railroads frequently ordered locomotives with dynamics, and prairie railroads ordered those without. In order to accurately model locomotives, molds are created to produce both dynamic equipped, and non dynamic equipped locomotives.

[rogertra]

It's not a case of "Dynamic brakes don't really work on model locos" it's a case of "They don't work at all."

The blisters and or grids on the model are there because they are on the real loco.  On a model they are there for aesthetic reasons only.

[Yampa Bob]

Actually, "dynamic" braking can be achieved easily, just remove power from the motor, then short the motor terminals together. This shorts out the motor back EMF, causing a current flow in the opposite direction.

I notice the Digitrax Zephyr has a "brake" position on the direction control.   

http://www.girr.org/girr/tips/tips5/motor_tips.html

In a real diesel loco, the braking can be rheostatic if the generated electrical power is dissipated as heat in brake grid resistors or regenerative if the power is returned to the supply line, or a combination of both.

[WGL]

 Bob, I like the brake feature on the Zephyr.  It stops a locomotive gradually, in contrast to the Stop button on the EZ Command.  Releasing the Stop button causes uncouplings with my trains, because they rush back to the speeds at which they were running.  However, the Zephyr's brake stops only the locomotive currently addressed, but EZ Command's Stop stops all locos.  To stop all locos with the Zephyr, one presses the Power button.

[Yampa Bob]

Thanks WGL, that is a nice feature. If you "brake" an addressed loco to a full stop without turning the throttle down, then turn the control to forward, I assume the loco resumes its original speed.

I understand you can have a loco moving forward full throttle, then throw the control to reverse. The loco will slow to a stop, then move in reverse gradually to full speed.  Any comment?

I sometimes run two short trains on the single main at one time, at "half loop" intervals.  To slow both trains down and maintain the interval is a waltz, access one loco, gradually turn the throttle down, then access the other, turn the knob quickly back up to match the speed, then turn the knob down again to the pace.

If I pause a few seconds between accesses, the second loco will automatically slow (abruptly) to the lower speed setting, but sometimes not quick enough to avoid a rear ender.  It takes a bit of practice to do it smoothly.

Try it sometime with your Zephyr. I don't think you can push address buttons fast enough to prevent a crash, especially using 4 digit addresses.   

[rustyrails]

My personal philosophy has always been: "One loco, one throttle."  So I would simply plug my utility throttle into a loconet port (there are two on the back of the Zephyr), acquire the 2nd engine, and manage them both a lot more smoothly than the EZCmd.  Just a thought.
Rusty
PS:  I notice that EZCmd allows the use of a DC power pack to turn address 10 into a 10th DCC address, sort of like a jump port on the Zephyr, giving you a second throttle which would smooth out your waltz a whole lot.    

[jward]

my observations regarding dynamic braking

dynamic braking is one of the great advantages of diesel over steam. it has not only cut down on the wear and tear of the brake shoes, but has also immeasurably speeded up operations in mountainous areas.

trains without dynamic brakes had to stop at the top of the grade, and somebody had to walk the train turning up the retainer valves on each car. once under way, the engineer had to be very careful not to use too much air or he'd use it all up. the train could possibly get out of control while he recharged the brake line. runaways were common. at the bottom of the grade, somebody had to walk the train again, turning the retainer valves back to their normal positions. if for any reason the train had to stop on the downgrade, hand brakes had top be set on enough cars to hold the train while the engineer recharged the brake line....another problem was the fact that most grades are compensated, that is, the grade lessens in the curves so a locomotive pulling uphill feels no change in the resistance of the train. downhill, it is possible to stall the train in these curves if you have too much air set. often the engineer had to apply power even though the brakes were on, to pull the train through the curve.....

with dynamic brakes, the engineer can use a minimal amount of air, and let the dynamics do most of the work. come to a curve, back off on the dynamic, and coast through. the use of retainers is greatly reduced of eliminated.....

over the years, dynamic brakes have gotten much stronger. on today's locomotives, there may be restrictions on how much dynamic can be used, at full dynamic, enough force is exerted to turn a rail over under certain conditions. for example, the sd80macs i worked with were restricted to 6 notches of dynamic, out of a possible 8, for that reason.....

not all mountain railroads used dynamic brakes on all locomotives. switchers were almost never equipped with dynamic brakes. often the first few orders of road locomotives on a railroad lacked them as well, as they were optional equipment and railroad managements in that era were unfamiliar with them. as their benefits became known, most railroads in mountainous territory quickly adopted them as standard. a few, such as the l&n and cn, were too cheap to order them until the 1960s or later...
and, as has been mentioned elsewhere in this thread, railroads running in flat territory often did not order them at all.

i don't believe EMD or GE build locomotives without dynamic brakes anymore.....

with

[Yampa Bob]

I should expand my philosophy a bit: "One engineer, one throttle, one train. I only run two trains for practice, to hone my dexterity skills with EZ Command. Normally when we run two trains, I use the EZC from Craig station, my wife runs the  EZ Companion throttle on the Phippsburg side.

Having two engineers is twice the fun.