I know this might have been asked before, but I’m going to ask it again since I can’t find any evidence of it being asked. What ever happened to the “classic” EMD dynamic brake blister found on engines up to the SD40 and/or SD40-2? I’m going to guess that as the dynamic resistors got better, they probably got smaller, which meant that EMD could move the dynamics into an area forward of the air inlet and get rid of the blister found on earlier units. If anyone could help me out on this one, it would be great.
The blister went when the dynamic brake resistors and fan were moved to the end of the locomotive behind the radiators. It results in a longer locomotive, but the grids are no longer sitting right above a hot engine.
John
Or right behind the cab for SD50/60s. The grids actually got bigger not smaller, the blisters were due to the location above the diesel engines and their exhaust manifolds.
So for example on a SD50,
The three big fans on the far end are the Dynamic break fans, and the 2 up front are what, the air intake for the engine?
No, the three large fans at the rear of the SD50 long hood are the radiator fans. The dynamic brake resistor grids are located immediately behind the cab and in front of the central air intake.
On GP/SD50-up, the dynamic brake fan is hard to spot unless you’re higher than eye-level with the roof: It’s just behind the cab and somewhat recessed.
Well, it does make sense to move the grids, which get hot away from the extraneous (sp?) heat generated by the engine and its exhaust, but I guess I just figured that the grids would have been moved into the area ahead of the engine intake, if there was/is room as compared to tossing the dynamics all the way back out into the back behind the radiators.
Be careful. The positioning of the dynamic brake grids immediately behind the cab applied to the SD50/60/70M models. The current SD70ACe and SD70M-2 have them located at the rear of the long hood.
As an aside. the GP50/60’s dynamic brakes remained in blisters above the prime mover due to the shorter frame length.
One quick clarification - the SD50/60/70M/MAC/75I have the dynamics behind the cab and in front of the central air intake.
SD70M-2/ACe/80/90 series put the dynamics at the end of the long hood, behind the radiators.
The GP50/GP60 still retain the blisters above the prime mover, though on the 60 it looks more like an air conditioner than the classic ‘blister’. The GP60 is also the first, last and only 710-powered EMD to have the original location configuration for the dynamics. My avatar is a GP60, you can clearly see the blister over the engine.
Ok, so those “grills” right behind the cab (One’s higher than the other, and positioned diagonally across from the other,) are the dynamic break intakes? Where is the central air intake?
Justin
Yes, the grilles right behind the cab are the DB, the grill behind those and higher are the central air intakes.
I can apprecitate modern technology, but kinda miss the dynamic brake blisters. They gave the locomotive a little character. Don’t think it was mentioned, but GEs are in the radiator area I believe. I know that’s not the topic at hand but just wanted to add that.
On most GEs (well everyone of them that I’ve seen, up to and including the GEVO), the DYB is located behind the cab and ahead of the prime mover. One of the spotting features of the AC4400CW vs. a -9 is the location of the vents - the two square vents near the front - on the -9 they’re closer to the cab side of the top of the electrical cabinet, on the AC they’re closer to the prime mover side.`
The grids were moved from behind the cab to the end of the long hood to reduce noise levels inside the cab, when the dynamic brake fan spools up it makes a lot of noise. Moving it to the end of the long hood should help to save the crew’s hearing.
That also makes good sense. Kinda like sticking the trumpets (still can’t quite wrap myself into calling them horns) over the primer mover as compared to the top of the cab. And I thank you all for the information, it as just something that kinda made me scratch my chin and go “Hmmm?”
I wonder what those dynamic brake resistors are made of, and how hot they get. Also if a fan ever quit, and if so was there a cutout, or perhaps they melted…?
On this topic, before the Ski Train was sold to Algoma Central and left Denver, I noticed it had disk brakes on the cars (rode it several x). I wonder if it could get down the 2% from E. Portal to Arvada on the dynamics (it recently had 3 F-40s) or if they had to use the air too. What about freight trains on this long steep hill? I’m sure it has a low speed limit due to endless curves around the Front Range.–Roger Williams, Boulder.
From my experience running on 2.2% grades, On 2-2.2% the DB alone should be enough for a passenger train. A heavy freight needs both DB and air.
Thanks for the info. I was thinking of the original U-boats, weren’t they by the radiator area?
Dynamic brake grids on EMD and late model GE locomotives are made of strips of steel folded into an “accordian” shape. The grids are held in place in the grid “box” by round steel studs welded to the outer and inner folds of the “ribbons” that are inserted into ceramic supports that hold the “ribbons” into the “box”. The ceramic supports are not held rigid to the grid box but allow for ribbon expansion when they are hot, the supports must maintain ribbon separation to prevent shorting and burning a hole in the grids. A dynamic brake grid assembly consists of several grid “boxes” mounted in a frame. The grid boxes are connected together with buss bars or cables to provide the total grid resistance required. On a 4 axle locomotive one grid box is connected to the blower fan motor, on a 6 axle locomotive two grid boxes are fan boxes. Grid boxes that are not fan boxes all have the same resistance (0.43 ohm for standard capacity EMD dynamic brake). Grid boxes that are connected to the blower fan have a higher resistance, that with the blower motor in parallel result in the same total resistance of the other grid boxes,
All locomotives with dynamic brake have grid blower failure detection. The detection device varies by locomotive model and age. On an EMD Dash 2 locomotive it is the DG Module.
Dynamic brake grids are designed to be the “weak link” in the dynamic brake circuit. That is, the grids will fail before a fault in dynamic brake regulation or blower motor failure would result in serious damage to the traction motors, switch gear, or locomotive electrical cableing, in other words the grids act as the system “fuse”.
GE locomotives older than the very last of the Series 7 models placed the dynamic brake grids in back of the radiator air intakes at the long hood end of the locomotive.
I liked the big box blisters of the GP60 best. One reason I like the model as much as I do. How exactly did dynamic brakes work. The previous post makes it sound DB’s had there output control but from what has been described to me in the past the DB worked off current created from the main generator and there output was controled by throttle notch position, or so I understood.