Dynamic Brakes

I got into a discussion with someone about dynamic brakes, I know the rule for going from power to dynamics in DC units is to wait 10 seconds for the circuits to set-up and all, but this person seems to think you can go directly from power to dynamics without waiting 10 seconds. They are totally convinced that they are right, just because they claim they saw someone do it. I've never seen what happens if you don't wait, I assume you fry the dynamics. Has anyone ever seen what happens?

NS212 wrote:Has anyone ever seen what happens?

Most of the time, absolutely nothing will happen.

Most later model diesel electrics are designed to automatically delay the setting up of dynamic brake circuits, thus making the action of waiting 10 seconds pretty much unnecessary these days (except, of course, unless you're concerned with rule compliance).

Just to clarify (because there's long been a lot of confusion about this) the proper time to wait 10 seconds is when the throttle is in idle, and before going to set-up on the dynamic. If you wait until the handle is in set-up, you've defeated the purpose of the waiting.

The reason for the delay is this: as the traction motors are being used for power (motoring), there is a certain amount of current flowing through the field windings of the motors. When the throttle is placed in idle, the current supply is shut off. However, for a few seconds, there may be some residual magnetic force remaining in the motor field windings. If the connections are made for dynamic braking (wherein the motors are to be used as generators to slow the movement of the train) while the residual magnetism is there, there may be a sudden jolt of braking force that was not anticipated or called for by the handle.

Waiting 10 seconds in idle allows enough time for any residual magnetic field to dissipate.

But as I said, this has been automatically taken care of by delay circuits on locomotives for many years now (I'm thinking the early 1970s).

Thanks for the info. Wasn't sure on what, if anything would happen. I've heard a lot of different things from people. Some said if you were to go from say run two or 3 directly into dynamics it would fry the traction motor, others say you could derail the train doing that. But thanks again for the info!

And many newer locomotives have instructions to wait the 10 seconds when transitioning from Dynamic to power as well.

As far as train handling goes, the sudden transition from "pulling" with the slack stretched to slowing a train with all the slack bunched could potentially cause a derailment, probably depending on how the loads and empties were set up in the train as well as the particular track layout was as far as hills and curves. If you had multiple units of power, any changes in power are multiplied by the number of units. Speed is also a factor.

I have seen a engineer go from #8 power to #8 dynamic in one solid motion (maybe I should say "throttle jockey" instead of "engineer".) with 125 cars. I thought the curve was going to set out half of the middle of our train.

Throttle stripping is not good train handling (or so the "experts" say) and now a lot of the newer engines send data to the the train ops center to the senior road foreman who calls your road foreman who calls you before you can get off work. Those GPS's and computers can work for you and against you.

Nowhere to hide these days, at least on the Class I roads.

I recall an instructor saying that you can change the slack in your train (bunched to stretched, stretched to bunched) either quickly or gently -- but never both at the same time.

Taking sufficient time between throttle positions -- allowing time for the effects of a single notch change to do its thing -- not only reduces in-train forces, but often saves fuel as well.

On the passenger ops. you'll find guys "stripping" and transitioning from power to dynamic to power without the 10 second wait as required on the freight jobs. On the P42's you'll find the computer provides much lag time between the transition from power to dynos and back. Even in power, the computer will not allow the amps to build up in any great hurry either. That is why many guys strip it back. With stripping, you'll find that some units take 20 seconds to fully load while others may take 30-40 seconds. Many of the older guys hate the P42's compared to the old F40's that came right to power when you wanted it.

It is always a blast to have a freight engineer pilot hop on board such as the case this past summer with the California Zephyr through Wyoming and they see us strip the throttle or transition as quickly as we do and cannot believe we operate that way. There is hardly any slack in the train, with most of it between the two units. It took me about 4 months to get the freight style out of my blood.

I have heard stories of guys operating back in the day on older Geeps and early SD40's who have burned up a few motors, but now with the amount of protection the computers provide, it is hard to do.

On some passenger locos with blended brakes, meaning the dynamics come on automatically with no input from the engineer, other than taking more than the miniumum BP reduction to get the dynamics/blended to kick on - usually about a 7-10PSI reduction at 110psi BP. It does everything on its own, and takes anywhere from about 5 to 10 seconds (on a GP40 or F40 that i run) for the dynamics to kick on. What I personally do (i think it maks for a smoother ride) is take a minimum reduction, first, then grab some more so the dyanmics kick on.

But when I on a loco with seperate DB control, I wait a few seconds and then go to set up, and basically just listen for the switch gear to change over and then go for the dynamics

I agree. A min. set before using blended does make for a nicer slow down when you do place the motors into blended mode. Coming out is a different story. The head end always feels the "letting go" of the leaders and the dynos.

Every trip is different depending upon what you do and how you do it. I try different ways of braking just to keep sharp and see what method works best.

LCJ wrote:
Most of the time, absolutely nothing will happen.

When I was a new engineer, there were times when things would be happening quickly, and I'd forgotten or cheated on the ten-second wait. With a few older models, SD-40s, I'd seen the ammeter jump quickly as soon as I'd put it into dynamic.

As noted, the electronics of units built in the last ten years or so prevents that...just as they prevent sudden loading and wheelslip when a careless engineer strips out the throttle.

LCJ wrote: Most later model diesel electrics are designed to automatically delay the setting up of dynamic brake circuits, thus making the action of waiting 10 seconds pretty much unnecessary these days (except, of course, unless you're concerned with rule compliance).

Yes, that seems to be the focus these days. Mindless adherence to the perscribed ritual. Funny thing, they pay us for our knowledge and judgment...and then won't allow us to use it, instead demanding compliance to ritual.

CSX Conductor wrote:And many newer locomotives have instructions to wait the 10 seconds when transitioning from Dynamic to power as well.

CSX Conductor,

Do any new Engines have the Regenerative braking as new subway cars?