What is the difference or reason to use dynamic brakes vs train brakes? Passenger or cargo train? The manual doesn't explain it. Thanks.
Incorrect I'm afraid, you are confusing Dynamic brakes with Independent brakes which is the locomotive only brakes as opposed to complete consist Train brakes. Dynamic braking is using the tractive (electric or diesel) power of the engine to slow the train typically on a decline (downhill stretch of track), it will not bring the train to a complete and holding stop because as the RPMs reduce as the tractive unit slows the less efficient therefore effective the braking force is that can be applied. Similar to Dynamic braking in road trucks are engine brakes and also exhaust (Jake) brakes in that they do the same sort of thing which is use the excess energy of the engine to slough off speed without having to apply the primary (wheel) brakes.
No I not confused. Both dynamic brake and independent brakes just brakes the locomotives. but I did not explain how dynamic brake worked. he never asked for it
Fair enough, but tbf your answer was a little vague therefore somewhat misleading, hopefully between us we've answered the OP's question clearly enough though.
The difference has been explained above, dynamic brakes use the motors of the train (could be just the loco, but also any "motored carriage" in an EMU) and the reason is that brake pads and shoes wear out, using the motor in reverse does put wear on the motor but a lot less than on the brake system There are also electric trains which can feed back the regained power from dynamic braking and retain or feed that power back into the system, in effect saving electricity (kind of like Kers in formula 1). In other words it's an energy retrieval or saving system If you think about it a generator is almost a motor in reverse, so they've just used this to their advantage
More reason beside wear and tear on brake stuff on wagons. Dynamic brakes responds directly you can increase and and decrease the braking force directly. Use Train brake in a train that is long (no dpu). It takes time for the brake to work and it takes time to release it. and once you've used the train brake, you have to fill up the cars air tanks before you can brake again. I take minutes You can loose braking ability in the train if you brake and release several times under short period. (American trains not Europe trains. Different types of brake systems) In Americans trains in heavy down slopes (Cajon pass) they use both dynamic brake and train brake Dynamic brake cant keep the speed down, so they must use train brake to. If they not have many locomotives in train then engine driver can only use Dynamic brakes. But not to stop. In the end they must use train brake
Its not similar to a jake brake actually. Dynamic braking has nothing to do with the diesel engine in a locomotive. It uses resistance through a bank of resistors and slows the trucks down. Where a jake brake uses back pressure from the exhaust against the pistons of the diesel to slow the crankshaft speed.
I said the dynamic braking principle was similar not the actual mechanics of the said systems, I think you may need to re-read what I wrote.
Nice article(s) on dynamic braking https://www.trains.com/trn/train-basics/abcs-of-railroading/dynamic-braking-101/ and https://trid.trb.org/View/732643. I guess its the same as Regenerative braking Class 76 Woodhead?
Mostly used to keep your speed downhill. Dynamic braking is wearless and applies/releases quicker than the train brakes (which you can only fully release, not partially on US freight trains). Depending on the grade, you're using "blended braking", means a light train brake application, bailed off indy and additionally dynamics for fine tuning. Jim Friedland has done a nice scenario on GN Cascadian, which punishes you if you're not using dynamics (brakes running hot). On german locos for example, you are using the electrical brakes to gently slow down the train for speed changes (don't let the AFB do it for you - your passengers may complain ), and generally only use the train brake for stopping or in an emergency. In the US, they say "Don't touch the big one!" meaning do not use the airbrakes unless necessary. They can take ages to fully release again on a long train, especially if there's no Distributed Power loco(s) that help charging the brake pipe. If you're new to US trains, you'll likely end up stopping very often due to overbraking.
Doesn’t running dynamics cancel out your air brakes if you have them on too? (Based on the famous cajon pass runaway that happened in the late 80s) train brake - self explanatory: applies brakes on the loco and carriages/wagons independent brake - applies in the loco only. dynamic brakes - reverses the electrical current of the traction motors on locks, used primarily to control speed on downhill runs on heavy freight trains. sub topic: what’s the difference between EP brakes and direct/auto brakes on British EMUs?
Yes, that's what the BailOff position on the Independent brake is for - it releases the brakes on the locos, so the Dynamics can come into effect. This happens on all MU'd locos in the consist that have their indy MU2A valve set to "Trail 6 or 26" and the dynamics cut in. So the way it works is apply trainbrake, bail off the indy until your BC pressure is 0, then apply dynamic brakes. Note that this is only simulated on "Pro Range" locos mostly. The Cajon Pass disaster was due to the train being massively overweight for the braking power supplied (the car loads were only guessed - a fatal mistake), and defect dynamic brakes on two locos iirc. And the emergency application by the DPU helpers (not knowing the exact train weight) which disabled the dynamic brakes completely and brakes starting to melt, making the train uncontrollable from this point onwards. The crew could do nothing but watch things unfold, running out of options, a real tragedy (plus resulting the gas pipe explosion) The best documentary on that one: That's what makes US railroading so different from all the rest (and rightfully deserved its own "Run8" sim) - it's a battle with physics.
In the 26-L (the most common modern brake schedule), the locomotive brakes will be bailed-off (without the handle actually moving) automatically when the dynamic brakes are used. It doesn't affect the train brakes (on the train cars). This is simulated in the more recent Pro-range locos (including those from HIS and DTM that I've worked on). In some variants, this interlocking can be disabled, such that the independent brakes can be held on even while performing dynamic braking.
Interesting. That's for the modern electronically controlled 26L I take it, not for the old versions where the handle directly controls the valve. Very handy especially if you need to apply more autobrakes, as it needs you to hold the Indy handle in BailOff until BP matches EQ. Classic 26L vs Electronic ("fly-by-wire") Controls
Electro-Pnuematic (EP) Brakes use an electrical signal to signal to each unit on the consist the required brake application - Results in faster application and release than traditional auto brakes, Direct Brakes are what is typically used for Loco brakes where it directly applies the main res air into the brake cylinders, Auto Brakes is the use of a charged brake pipe and triple valve where a reduction in pressure applies the brakes, The auto name coming from if there is a break of continuity in the BP then the pressure drops and the brakes "automatically" apply. This website has some good info and diagrams. Brakes | The Railway Technical Website | PRC Rail Consulting Ltd (railway-technical.com)
That is not true, Mike. There is no auto-bail except in trains equipped with blended braking (passenger locos), or remote consists in DP service. You must manually actuate upon any reduction in brake pipe pressure to keep the BC pressure off. The interlock you refer to is inverse in operation. It will knock out dynamic braking when BC pressure is above ~10psi. Responding to earlier reference to the Duffy St. Runaway, many locomotives (except Southern which had the "Saluda Key") did not initially have a DB Holding feature, which allowed for continued Dynamic Braking effort when the PCS was open. After Duffy St. and a couple other notable incidents, DB holding became a standard feature. Do note, however, that the engineer would have to bail off to keep the dynamics working.
Is that perhaps the case in modern locos? What I've described is stated in the operating manuals for older diesels with dynamic braking. For example (this is the first one I came across just now when I looked for an an example), the GE U25B OM has this: See "Dynamic-Braking Operation". The way it's implemented in the braking scripts is as follows: --The dynamic brake interlock feature functions during dynamic braking to -- release or prevent an automatic service brake application on the locomotive. -- In other words, any locomotive brake cylinder pressure that has been set up -- as a result of applying the automatic train brakes will be released. The -- independent brake handle can still be used to apply the engine brakes at the -- same time as the dynamic brakes are applied.
I've run every brake schedule under the sun in North America at this point and have never once encountered anything with an auto-bail off that isn't some blended braking equipment. U boats, Dash 7s, FP7s, and worked with guys with way more experience than I. I can wholeheartedly assure you my statement is true and factual. Any locomotive so-equipped with dynamic braking will knock out the dynamics when you apply any brake cylinder pressure over ~10PSI.
I was wondering why this was not implemented in Run 8, which does have the most realistic brake simulation, or any modern US loco. Seems it existed on paper but was dropped for technical, reliability or safety reasons. On a modern electronically controlled loco this would've been easy to implement, but a mechanically controlled brake valve would have to be completely reengineered. Of course that's only speculation from my side, what do I know
Did a bit of reading on these forums and elsewhere. First of all it's puzzling because virtually all European trains use blended brakes in the last 30 years, and I keep hearing traction sounds as air brakes are added. Particularly in Germany, where Pzb braking distances often require hyper-aggressive applications. That said, I get that I may be hearing train brakes which are not applied on the loco (directly). There seem to be many systems, some explicitly say that the handle defines a brake effort request and each unit decides how to achieve it with a mix of dynamic and air. Sounds like EP. One big pressure point is the 10psi. Some describe it as applied to the brakes, but others as reduction (that 90 going to 80, or forgivingly 75). For comparison, the "minimum application" is 6psi reduction (in the brake pipe), 15psi applied (in the brake cylinder). If we're talking BP reduction, it sort of makes sense - running a train down Donner Pass with 10+ BP, 20-30 BC for hours on end doesn't sound healthy (quite possibly the reason of the staircase design of the route, to allow stopping). It's one of the risks of stuck brakes actually, heating the wheels which eventually detaches from the rod, which in the absence of further locks, means a derail soon (rod is held by the truck / bearings but the wheel can shift to the middle). Distributed power is also an interesting point - I'd love to know how dynamic tractive effort compares to pulling tractive effort, in other words, can a train that can climb also descend with electric only.
Play Run8 and you can experiment with all that. Control the DPU dynamics separately based on the current situation (rear of train climbing while front is descending etc . Or on long trains doing a hill start having the DPU running in a higher notch to push and lessen force on the couplers.
Dynamic Braking has improved over the years with AC traction and high-capacity grids. Some locomotives, notably EMDs, will actually switch to plug loading (reversing direction of traction input) at very slow speeds down to 0.1 MPH
