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Dynamic Brake "Blisters"

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Posted by Erik_Mag on Wednesday, January 4, 2023 10:31 PM

bogie_engineer
If the fan pulled the air from the roof, it would blast the walkway on both sides with 900 degF air, to duct it to one side as GE does would be a significant flow restriction and bring back the problem of high temperature air on the fan blades and motor bearing.

900ºF is 1360ºR, which is more than double than the 570ºR that would be found on a very hot summer day in the southwestern deserts. The volume of air coming off the grids would be more than double the volume going into the grids. This would imply a doubling of power to move the air by pulling from the top, but as you pointed out, the temperature would be too mcuh for the motor and bearings.

With respect variable speed AC drives, power electronics has come a long way from when I took a course in it in 1976. At that time, the easiest way of making a variable speed drive was with cycloconverters, but those need a source frequency of at least 3X the desired output frequency.

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Posted by SD60MAC9500 on Wednesday, January 4, 2023 10:08 PM
 

When GE first introduced the DASH-8 series, early models had the DB heat exhausted through two horizontal vents on top of the long hood. IIRC there was an issue with moisture leaking into the hotside causing DB issues. Later DASH-8's had the hotside of the DB vent configured into a vertical configuration.

 
 
 
 
 
 
Rahhhhhhhhh!!!!
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Posted by Front Range Trains on Wednesday, January 4, 2023 11:56 AM

bogie_engineer

 Thanks Dave!  Very useful info.  

 
Front Range Trains

Interesting thread. Thank-you to those who have shared knowledge.

On the EMD SD50, is the dynamic brake fan visible from above or does the dynamic brake grid block the view of the fan?  Also, how many blades does the dynamic brake fan have? 

I haven't yet found any photos or videos of the EMD SD50 (or similar) which depict the fan itself.

 

 

 

The DB fans sits below the grids; the grids bolt to the fan frame. The grids are about 20 inches in height with a fairly dense ribbon array that you can't see through. On the roof, all you can see is the grille on top of the grids to prevent debris from falling into the grids. Air is pulled in the side grilles, then goes thru the fan where it's pushed upward thru the grids. IIRC, the fan, which was new with the radial grid development is 54" in diameter with space for 12 blades, which are all present. There is a mix of short and long blades done to get the airflow distributed evenly thru the grid ribbons. Looking up thru the intake air grilles on the sides of the carbody should let you see the fan blades.

Dave

 

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Posted by bogie_engineer on Wednesday, January 4, 2023 10:02 AM

Erik_Mag

"Air is pulled in the side grilles, then goes thru the fan where it's pushed upward thru the grids."

Does this have anything to do with pushing a given mass of cold air through the grids takes less energy than pulling the same mass of hot air from the grids? I'd also gues that from the tunnel motor experience, that the hot air needs to go up as opposed to going out the sides.

 

I think that's part of it. The development of the radial grids on top of the fan actually began with a "combined cooling system" concept started in the early 1970's as a way to get the grids off the engine and save the cost of the grid fans. In that system, the grids were much less in height and mounted on top of the 48" AC cooling fans for the engine cooling water radiators. It never left the drawing board because of the hit to fuel efficiency - the cooling fan speed was proportional to engine speed (this was long before cost-effective variable speed AC drives) so the engine would have to be run at a higher speed in dynamic braking to cool the grids. When the SD50 was being conceptualized the desire to get the grids out of the space above the engine led to the development of a bigger 54" fan with sufficient air mass flow to cool grids where the two 48" fans were previously used. It also puts the grid fan blades and motor in a nice cooler enviroment. 
 
If the fan pulled the air from the roof, it would blast the walkway on both sides with 900 degF air, to duct it to one side as GE does would be a significant flow restriction and bring back the problem of high temperature air on the fan blades and motor bearing.
 
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Posted by Erik_Mag on Wednesday, January 4, 2023 12:02 AM

"Air is pulled in the side grilles, then goes thru the fan where it's pushed upward thru the grids."

Does this have anything to do with pushing a given mass of cold air through the grids takes less energy than pulling the same mass of hot air from the grids? I'd also gues that from the tunnel motor experience, that the hot air needs to go up as opposed to going out the sides.

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Posted by bogie_engineer on Tuesday, January 3, 2023 12:39 PM

Front Range Trains

Interesting thread. Thank-you to those who have shared knowledge.

On the EMD SD50, is the dynamic brake fan visible from above or does the dynamic brake grid block the view of the fan?  Also, how many blades does the dynamic brake fan have? 

I haven't yet found any photos or videos of the EMD SD50 (or similar) which depict the fan itself.

 

The DB fans sits below the grids; the grids bolt to the fan frame. The grids are about 20 inches in height with a fairly dense ribbon array that you can't see through. On the roof, all you can see is the grille on top of the grids to prevent debris from falling into the grids. Air is pulled in the side grilles, then goes thru the fan where it's pushed upward thru the grids. IIRC, the fan, which was new with the radial grid development is 54" in diameter with space for 12 blades, which are all present. There is a mix of short and long blades done to get the airflow distributed evenly thru the grid ribbons. Looking up thru the intake air grilles on the sides of the carbody should let you see the fan blades.

Dave

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Posted by Front Range Trains on Monday, January 2, 2023 5:19 PM

Interesting thread. Thank-you to those who have shared knowledge.

On the EMD SD50, is the dynamic brake fan visible from above or does the dynamic brake grid block the view of the fan?  Also, how many blades does the dynamic brake fan have? 

I haven't yet found any photos or videos of the EMD SD50 (or similar) which depict the fan itself.

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Posted by M636C on Saturday, November 26, 2022 8:10 PM

The EMD radial dynamic brake unit is much louder from above then the older arrangement with two 48 inch fans. I was on an overline bridge in a location where loaded coal trains exit the mine branch on to a four track main line under dynamics, the branch connecting at the top of a grade. There was a grade on the branch as well, so once the train started moving, it was in dynamic brake for about two miles. The train had three JT26C-2SS and one JT42C (which had the radial dynamic brake). The JT42C was third unit and while I was ware of the dynamics working on the lead units, I was struck by the sound as the JT42C passed underneath. This noise was largely only noticeable immediately above, so might not have been a problem in the cab(s), the JT42C having two, both of which are fully isolated.

The JT42C, dating from 1994 was the first type to be subject to the current very stringent noise requirements, required by the Hunter Valley coal lines passing through residential areas. These started off with just a mesh grille over the side air intake but ended up with aluminium louvre grilles that cut down on horizontally transmitted noise.  The similar dynamic installation on Canadian built GT46CWMs were fitted with steel noise deflector plates, lined with acoustic material mounted on the side railings. Such plates have since appeared on most large GE locomotives in Australia, to reduce fan noise transmitted laterally out of air intakes. GE locomotives also have angled ducts on the exit grilles of the dynamic brakes. These serve the dual purpose of reducing horizonally transmitted noise but also direct the hot air away from the head of anyone on the walkway at the time...

Thinking about this, I thought about the concern that AC44C6m cabs being noisier than those of a C44-9... The AC units have three fan/grid units just behind the cab while the DC units have only two. I'm sure that would be heard when the loco was in dynamic brake...

Peter

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Posted by bogie_engineer on Wednesday, November 23, 2022 10:02 AM

The grids on the SD50 were moved away from over the engine to get the fan motor out of the hot environment over the engine while opening up the space above the engine to simplify power assembly changeout. We had lots of problems over the years with the lower DB fan bearing grease cooking even with the enclosure below the fan and the ducting of some traction motor air to the enclosure. The development of the larger capacity radial dynamic brake grids and 54" fan that went with them required finding space elsewhere, which could be accommodated by moving the cab forward and creating a space between the cab and clean air compartment. This space also was used for the electrical cabinet housing the alternator transition contactor introduced on the SD50. It was natural to place the DB system there to be in close proximity to the electrical cabinet and cabling. Of course, the downside was moving the noise source close to the cab. It turned out that on the sound level meter (I was the cab and wayside sound engineer at EMD at the time), it really didn't raise the measured sound level much, although the whine was very annoyingly audible, since the engine is not at full rpm and power when in DB. When I was tasked later in my career with developing the SD80MAC, one design requirement I insisted on was to move the DB away from the cab.

As I was told, GE's DB arrangement on the U series with the dynamic brake grids in the radiator cooling fan intake caused problems with the hot air pushed thru the radiators - the cooling water was diverted via a fluidic valve to keep from raising the cooling water temperature and the radiators had to be changed from the common soldered tubes into a header plate to a silicone-bonded joint that could deal with thermal shock from frequent diversion of the water flow thru them but it did not hold up well.

Dave

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Posted by YoHo1975 on Monday, November 21, 2022 11:01 AM

silicon212

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.

 

 

Depending on how Pedantic you are being, the GP59/F59PH/F59PHI ALSO had dynamics over the engine. And are all EMD made 710 engined locomotives.

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Posted by SD70Dude on Thursday, November 10, 2022 9:48 AM

Ulrich
BigJim
beaulieu
Moving it to the end of the long hood should help to save the crew's hearing. 

And, not suck their brain out of their ears when having to go out the door to fix a dead unit!!!
Whoever decided that it was a good idea to move the DB to right outside the cab door never had crew safety in mind

Also, don't they get hot? 

The fans suck air in from the engineer's side on GEs, or both sides on EMDs.  If you stood on the conductor's side (also on top of an electrical cabinet on many units) on GEs you would get blasted with hot air, but the EMD fan exhausts upward.  

It's can get pretty darn hot in the cab during summer without A/C, but I can't say I've ever noticed prolonged use of DB making that worse.  And in winter you freeze no matter how long you're in DB for.  

Greetings from Alberta

-an Articulate Malcontent

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Posted by BigJim on Thursday, November 10, 2022 7:47 AM

Ulrich

 Also, don't they get hot? 

No, the grids are way inside and up. No heat whatsoever. Just a lot of sucking noise!

.

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Posted by Ulrich on Monday, November 7, 2022 3:55 PM

BigJim

 

 
beaulieu
Moving it to the end of the long hood should help to save the crew's hearing. 

 


And, not suck their brain out of their ears when having to go out the door to fix a dead unit!!!
Whoever decided that it was a good idea to move the DB to right outside the cab door never had crew safety in mind

 

 

 

Also, don't they get hot? 

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Posted by BigJim on Sunday, November 6, 2022 4:29 AM

beaulieu
Moving it to the end of the long hood should help to save the crew's hearing. 


And, not suck their brain out of their ears when having to go out the door to fix a dead unit!!!
Whoever decided that it was a good idea to move the DB to right outside the cab door never had crew safety in mind

.

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Posted by upgees on Friday, November 4, 2022 11:46 AM

Do you have picture of what these look like in the dynamic braking box? I've only been able to see the outside, but never inside.

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Posted by BerkshireSteam on Sunday, October 25, 2009 3:25 AM
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.
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Posted by tleary01 on Tuesday, October 13, 2009 7:54 PM

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.  The radiator fan acted as the grid blower during dynamic brake.  This did not always work very well, anything that would restrict airflow through the radiators would also reduce cooling air across the grids causing burn-ups.  To get sufficient cooling using the radiator fan, the diesl engine had to run at N8 speed during high levels of dynamic brake operation. And last, but not least, the radiatior fan was gear driven from the engine front end output shaft, the gear box that drove the radiator fan was prone to failure.      

        

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Posted by trainfan1221 on Tuesday, October 13, 2009 6:31 PM

silicon212

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.`

Thanks for the info.  I was thinking of the original U-boats, weren't they by the radiator area?
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Posted by enr2099 on Monday, October 12, 2009 11:10 PM

rogerac

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.

Tyler W. CN hog
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Posted by rogerac on Monday, October 12, 2009 8:26 PM

 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.

 

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Posted by BamaCSX83 on Monday, October 12, 2009 12:54 AM

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?"

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Posted by beaulieu on Sunday, October 11, 2009 10:01 AM

BamaCSX83

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. 

 

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. 

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Posted by silicon212 on Saturday, October 10, 2009 4:31 PM

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.`

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Posted by trainfan1221 on Saturday, October 10, 2009 3:46 PM

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.

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Posted by silicon212 on Saturday, October 10, 2009 10:35 AM
bubbajustin
MJChittick
bubbajustin

So for example on a SD50,

The three big fans on the far end are the Dynamic break fans

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.

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.

 

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Posted by bubbajustin on Saturday, October 10, 2009 8:42 AM
MJChittick
bubbajustin

So for example on a SD50,

The three big fans on the far end are the Dynamic break fans

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.

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

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Posted by silicon212 on Saturday, October 10, 2009 1:37 AM

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.

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Posted by MJChittick on Saturday, October 10, 2009 12:12 AM

The Railwolf

 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.

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.

Mike

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Posted by BamaCSX83 on Friday, October 9, 2009 10:43 PM

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. 

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