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36" Dynamic Brake fans on SD38

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Posted by Backshop on Thursday, September 7, 2023 4:12 PM

I wonder if it could have something to do with the later units having shorter radiator grilles.  They got rid of the middle partition and shortened it. That would allow room for the bigger fans.

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Posted by timz on Thursday, September 7, 2023 6:21 PM

Far as we can see, the two grid fans on B&LE 865 are the same diameter. But they're clearly smaller than the 48-inch? radiator fans.

Was there room for two 48-inch grid fans between the two engine exhausts of an SD38?.

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Posted by JayBee on Thursday, September 7, 2023 7:57 PM

Here is a link to a photo of B&LE 862, an early SD38 that predated the air filter box and never received one. It is also taken from a high enough elevation that you can clearly see that it has one older style fan and one newer style fan. Using 48" fans would bring the fan shroud 6" closer to the exhaust stacks.

B&LE 862

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Posted by M636C on Thursday, September 7, 2023 8:57 PM

The Victorian Railways purchased 24 locomotives that were basically SD38s.

The first four units were built with 16-567E engines, 645E engines fitted with 567 power assemblies and the next two were built with 16-567C engines recovered from wrecked cab units. These were model G16C. The next eighteen units were model G26C with 16-645E engines. All of these had SD38 radiators with two 48" cooling fans.

However, they all had export type dynamic brakes mounted forward of the engine, with a single 48" fan. These had shorter but deeper grids behind a basically square ventilation grille. I understand for radiator fans, two 36" fans are equivalent to a single 48" fan.

So these must have had similar limits on dynamic braking to an SD38 with two 36 DB fans.

Several of these locomotives were rebuilt with 16-645E3 engines and larger radiators, but retained the single 48" dynamic brake fan. Strangely, a number of new locomotives were built to this design with the 16-645E3 engine.

So clearly, even an SD40 could operate with the smaller dynamic brake capability.

Peter

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Posted by timz on Friday, September 8, 2023 10:56 AM

Looking at the drawing on the last page of the link below, I wonder if two 48-inch fans would fit between the SD38 exhausts

EMD Locomotive Specification Book SD38-SPEC8058-01JUN65.pdf (wildapricot.org)

If anyone has an SD38 service manual, it likely will show whether it can absorb 3800 horsepower in dynamic, like the SD40.

 

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Posted by bogie_engineer on Friday, September 8, 2023 1:51 PM

timz

Looking at the drawing on the last page of the link below, I wonder if two 48-inch fans would fit between the SD38 exhausts

I can confirm that two 48" fans will fit between the exhaust stacks on a 16-645E engine. In the 1970's, I had design responsibility for roots blown engine exhaust manifolds and designed the spark arrester-silencer exhaust manifolds that were required on locos built starting 1-1-1980 to meet EPA noise regs. Those manifolds had 10" round exhaust stacks rather than the oval stacks on prior manifolds and were designed to fit between two 48" fans on the SD38-2, even though no SD38-2's were built after 1979.

Dave

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Posted by YoHo1975 on Saturday, September 9, 2023 10:38 AM

The drawing clearly shows 36" fans.

And yeah, the SD38-2s had 48" fans so unless the 38-2 has a physically longer car body, it makes sense they would fit. 

 

I know the dash-2 was longer, but I don't personally know if the carbody is longer or if it was just the porches 

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Posted by Backshop on Saturday, September 9, 2023 12:36 PM

Whatever the size of their dynamic brake fans, the SD38-series have always been my favorite diesels.

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Posted by GWRR on Friday, September 15, 2023 9:29 AM

Dave, 

Can you send me a PM at Nicholas.longshore@gwrr.com

Nick

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Posted by cv_acr on Monday, September 18, 2023 2:02 PM

YoHo1975
The question I had was why they would build it this way. When the SD39, SD40, SD38-2, SD39-2 all have 2x48" As noted the smaller fans absolutely does change the capacity of the dynamics. 

You'll also note that the GP38, GP40, etc. all have 1x48" fans. Almost like it has more to do with the number of axles or something........

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Posted by wjstix on Tuesday, September 19, 2023 2:37 PM

Since nothing definitive has turned up, it could be there really isn't an answer - at least not an answer beyond "because an EMD engineer in the 1970s did some calculations and determined that was the size it needed to work properly".

Stix
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Posted by YoHo1975 on Friday, September 22, 2023 3:30 PM

Well and given that our Resident former EMD engineer has not found any info on the subject. I'm content to leave it as unknown.

 

I didn't even know they were smaller until someone corrected me on it. I always find the engineering knowledge interesting.

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Posted by Backshop on Monday, September 25, 2023 8:45 AM

With some of the big terminal roads buying used SD40s and removing the turbos, there may be more "SD38s" out there now than were built new.

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Posted by Randy Stahl on Saturday, October 21, 2023 4:07 PM

cv_acr

 

 

 
YoHo1975
The question I had was why they would build it this way. When the SD39, SD40, SD38-2, SD39-2 all have 2x48" As noted the smaller fans absolutely does change the capacity of the dynamics. 

 

You'll also note that the GP38, GP40, etc. all have 1x48" fans. Almost like it has more to do with the number of axles or something........

 

Of course it does. It's one 700 amp grid per motor for 10K lbs of braking effort per axle. 

In dynamic brakes the control power comes from the AR10 alternator providing 975 motor field amps and 50(ish) motor field volts. Obviously the locomotive can create this low control power at idle, remember that the prime mover RPM increases only to provide traction motor cooling air. 

I do not believe the 48inch fans will  fit between the exhaust stacks on some stack arrangements. Obviously the smaller 36 inch fans are lower horsepower so I assume that there is at least two brake grids for the lower HP fans, different than the higher HP . I dont have my 190 book with me or I would look it up but I think this is the case .

Maximum braking effort occurs only when grid current is 700 amps and traction motor field amps is 975 amps period.

It is noteworthy that locomotives that have higher current grids have different braking characteristics.

 

R Stahl

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Posted by bogie_engineer on Sunday, October 22, 2023 11:49 AM

Randy Stahl

 

I do not believe the 48inch fans will  fit between the exhaust stacks on some stack arrangements. Obviously the smaller 36 inch fans are lower horsepower so I assume that there is at least two brake grids for the lower HP fans, different than the higher HP . I dont have my 190 book with me or I would look it up but I think this is the case .

R Stahl

 

SD38's and SD38-2's had a unique exhaust manifold system where the stack was moved to be over cylinders 1 and 8 rather than over 2 and 7 as on GP's. With the stacks moved, two 48" fans will fit between the stacks. EMD Master Parts Catalog 190 Volume 2, Parts list D3110, Pages 12 &13 confirm the SD38-2 uses the same 18HP 48" fans as all the SD-2 variants. Here's the parts list:

https://www.rr-fallenflags.org/manual/emd-mpc-3110.pdf

Interestingly, there is no parts list shown for SD38 dynamic brakes - does that mean none were built with DB, seems doubtful?

Dave

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Posted by JayBee on Saturday, October 28, 2023 3:03 PM

All the SD38, SD38AC, and SD38-2 locomotives built for US Steel railroads, DM&IR, EJ&E, B&LE, and Orinoco Mining. were built with dynamic brakes. Also the 3 SD38s built for McCloud Railroad (now McCloud River RR), have dynamic brakes.

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Posted by Backshop on Saturday, October 28, 2023 3:34 PM

JayBee--just a small correction.  It used to be the McCloud River, now it's just the McCloud.

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Posted by JayBee on Saturday, October 28, 2023 11:38 PM

You are correct, Backshop.

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Posted by YoHo1975 on Tuesday, November 28, 2023 12:26 AM

Pictures of SD38s with 36" dynamics fans exist. They don't appear to be retrofits. 

 

Perhaps the exhaust stack change was an enhancement to the 38 because of the fan size restriction. 

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