The dynamic brake

[dave]

Hi guys,

This more out of interest then needed, but can somebody briefly explain the principle behind the dynamic brake system please. I'm not sure about how it works.

I gather that it is just applied to the locomotives rather then the whole train and that (I think) it uses the braking effect that is refered to in the phrase 'brake horse power' when measuring an engines power. But other then that I don't understand how it works.

I understand that it's main roll is to help control speed on long and/or steep downhill sections where prolonged use of the main brakes might lead to excess wear and possible eventual failure or even fire through overheating, and is not for general slowing and stopping. But other then that I am blank (grins)

So if anybody could enlighten me I'd be greatful, even if it is only for some more background knowledge that underpins the game

[Captainbob]

Google the topic. Here is one http://trn.trains.com/railroads/abcs-of-railroading/2006/05/dynamic-braking

[simonmd]

In a nutshell, it is using the engine to brake instead of the brakes themselves. If you've ever driven a car downhill and kept it in a low gear to help control the speed, you'll know what I mean. In a loco, instead of a low gear, you're basically puting it into reverse a bit, the more throttle you give it in reverse, the more resistance at the wheels and the greater the braking effect. This is not only more controllable but in real life, helps reduce physical wear on the brakes themselves.

[dave]

Right, thanks Captainbob. I have never driven a train, but have driven heavy goods vehicles in the past. I had sort of pictured dynamic braking as like with a heavy truck negotiating a steap hill, where you basically knock down into a low gear and use the engine 'tick over' to keep your speed down. But this is a system where the train driver/engineer needs to 'charge up' the system before hitting the downhill section.

I would like to see some more realism in the Sim, so here's hoping that when TS UR4 comes in we might have the option of having to remember to charge up the dynamic brake system and, I suppose, then manage it on a long decent as it should not be an infinite resource as it currently appears to be under the current model.

[mvsmith]

Hi Dave: Most modern locos in TS do emulate what you called "charge up". You will notice that there is a delay when you first apply dynamic braking. That is the time when tthe loco is switching over from driving to braking. Older locomotives (and older train simulators) required closing the throttle completely and manually switching over.
Dynamic braking is an "infinite resourrce" in that it is availlable as long as the loco is moving, and does not "run out of air" as repeatedly re-applied air brakes do.

[GeneralGeldenhuys]

On an techical aspect, dynamic brakes is a method used to prevent the use of shoe brakes.

On diesel electric locomotives, dynamic brake use its own electric motors on the wheels to change itself into generators. These motor generators create electricity which then taken to a heat element or resistor bank which generates heat. The heat generated is blow away with air and thats why you hear fans screaming when turning the dynamic brakes on. The more dynamic brake you apply, the faster these fans spin, because the more current is sent to the resistor bank which makes more heat.

Diesel hydraulic locomotive doesn't have dynamic brake, because of the design of the engine and hydraulic pump and gears.

Electric locomotives sent their electricity generated into the overhead wires, which is regenerative braking, and other use rheostatic brake, which use the concept of the diesel electric locomotive.

Metro trains use regenerative braking, but long distance electric locomotives usually have rheostatic braking.

Let me know if you want to know more about the technical aspects of these features.

In a nutshell, it is used to prevent wear and tear on brake shoes and also spare air in the brake system.