Dynamic Brake Grids when they short out and ground in Tales of the Jointed Track

During the night, this is your own personal fireworks and light show. In the day maybe a flame, but the result a bell will ring. A ground relay condition will result.

For those that haven’t read some of my posts, I’ll give a quick overview. What is a locomotive Dynamic brake ? Well is is a retarding brake, not a stopping brake. The air brakes are the stopping brakes over-all. A Dynamic brake when equipped allows the traction motors to be reconnected as a generator. As electricity is generated, the armature slows in the rotation. The controller on the control stand is like a big variable rheostat, so you can vary the amperage produced, vs grade signal, and topography on the subdivision. It is mostly used in conjunction, with the train air brakes while descending the grade.

Where does all that electrical energy go. It is produced and has to go somewhere. It is channeled via circuitry to fan blown grids. The grid fans suck in the outside air and bring it over the grids. The grids themselves are like a toaster element. The electricity is introduced into the grids and it is dissipated at heat. The fans bring air-flow and dissipates the heat out and away from the grid elements. For a locomotive that draws current from a wire or third rail. That is placed back into the wire or current source. That is regenerative braking, the difference is that the electricity produced its recovered, instead of dissipated by heat.

Train 314 MP 45.1 reverse curves between Greenland and Larkspur Northbound:

We are dropping downgrade heading for Denver. It is a night run, and the sun will be rising in about an hour, hour and a half. The moon is somewhere in the night sky, but we are dropping down into the cuts along our descent. 314 is an origination out of Kansas City, KS. It is a drag, and receives a cut and fill at Pueblo. It is a standard Santa Fe train 3 units, and probably 5500 ton out of Pueblo, and a pick up and set out at Colorado Springs. Our lead was an old 4500 series SD-24. These were renumbered from the 900 series given when they were new.

A typical SD 24. It is the train to the right in the picture. The 932’s roofline, behind the four large looking tubes ( Main reservoirs) are two fans. Those are the dynamic brake cooling fans. The three fans behind that, are the diesel engine cooling fans. You can just make out dynamic brake blister, which houses the grids. The ATSF 1910 you can see its two dynamic brake fans housed in the cowling.

Air is set, to help bring down and maintain the speed through the 35 mph speed condition. The dynamics are full eight, but the consist itself is weak. A light wheel slip is coming into play, as we go over a curve greaser. A little lead axle sanding will usually correct, but it is not helping.

The SD-24’s are coming close to the end of their useful lifespan. They were sent to Cleburne, TX and the Topeka shops and were rebuilt into the SD-26 designation. They lasted about another 5 or six years. They spent most of their last days down in Texas and Oklahoma in drag service.

I just took the clear ABS signal at 44.7 and the sky lights up behind the cab. Looking out the window there is fire, smoke, and sparks coming from both sides of the grids. Shortly after, we lose the dynamic brake on that unit, and the bell rings. Ground relay and No Power is illuminated. A little more air to the train, and the locomotive is isolated. The ground is reset, the Dynamic brake is cut out. The other locomotives, will still aid in controlling our descent. This one can be used in power only.

The caboose is called, and the set will ride out to about 22 mph. The train is about a half a mile in length. I am nearing MP 43, and they’ll get around the 35 mph curves. We are in the lower Plum Creek part of Larkspur. We’ll head under I-25 in a mile and up the sag to the foot of the Buttes. Its an easy handler, just part of the trip.

Examples of Dynamic brake grids and fans, various models.

Rio GrandeSD-40T-2’s and SD 45’s out of Rocky, CO. You can see the dynamic brake blister, under the GRANDE logo.

Rear end of a U-28-CG, while still in passenger service. The rear black looking rectangle is the air intake. It has a dual purpose, the first and foremost, is to admit air into the radiators to cool the diesel. Look closer, the five squares, and there are five more on the opposite side. Those are the Dynamic brake grids.

OWY and KCS SD-60”s on Crawford hill in nebraska. They are getting close to the summit at Belmont. SD-40-2’s trail, you can see the car body blisters on the 40’s. Look behind the cab of the 9047 the small intake square is the air inlet to the grids and grid fan You can see it on the roof directly behind the cab. These screamed when in full 8 dynamic. No wonder I am deaf..lol.

The two “Squares” behind the cab on the fireman’s side. Oops “scuse” me Conductors side..This is the outlet where the fans blow the outside air through the grids.

A quick vignette. RCE consist Monument,CO :

We were called for an “extra”, well we were all extra’s per rule out here. We were dropped off at the town of Monument at the old siding, now called Wood Spur. There was a work train, in Wood Spur, a couple of ballast, a Burro crane car, a few gons, a Caboose, and two bad order cars. One was a air equipment problem, the other had a drawbar out on the north end. The bad orders were the last two cars. Eight cars, restricted to 40 mph, due to the Burro crane on the flat car. The conductor was told at call, that he should have a good fresh lantern battery,on hand, because that was going to be our “marker”, per rule for the rear end. The trainman’s lantern was illuminated, on bright, and hooked into the right hand side of the rear grab irons / steps. Plus being two cars ahead in the caboose, they can flag as needed.

We got dropped off, our van went to other requirements, and old “Uncle Fred”, Fred Sparks our road foreman took us to the train. He was two times of worthless.

We call the Santa Fe DS and get authority to occupy the mainline, after BN 5846 south passes. BN 5846 goes by, there are RCE swing helpers, controlled by the engineer on the head end. The swings had a U-28-C as part of the consist, the dynamics are in and helping the descent. The grids are a dull red, in color, due to the night time darkness.

A U-28-C

Fred says “I am gonna ream his ass for too many dynamic braking axles”. I say. “Really how can you? They are two separate consists, and who goes back to cut them out, if BN has that option?” Stammering, Fred says yep yer right”. “The time table Fred and Special Instructions, have the rules for handling”. “Yep”.
Nothing was reported…

Plasma Physics made me crazy.

Last updated May 18, 2015