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36" Dynamic Brake fans on SD38

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36" Dynamic Brake fans on SD38
Posted by YoHo1975 on Sunday, August 20, 2023 12:56 PM

Hi all, I had it pointed out to me that some (all?) SD38s had 36" Dynamic brake fans vs. the more common 48"

And these fans were "high shroud" but not the same fans as Say the F2/F3 nor the midddle fan on the 35 series.

I did a google search for more info on this, but it turned up empty. I don't have the physical books I'd need to learn more about this and was curious if anyone could provide details on this? Why the dual 36"? was it all units or just some? 

 

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Posted by Backshop on Monday, August 21, 2023 6:12 AM

As far as I know, all have 48" fans. Some have the shorter radiator section without the divider in the middle, but all have the full size fans. It makes sense...SD40 3000hp with 3 fans, SD38 2000hp with 2 fans.

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Posted by BigJim on Monday, August 21, 2023 10:58 AM

Backshop

As far as I know, all have 48" fans. Some have the shorter radiator section without the divider in the middle, but all have the full size fans. It makes sense...SD40 3000hp with 3 fans, SD38 2000hp with 2 fans.

 

I think that you will find that the three fans are radiator fans, not for the dynamic brake.

.

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Posted by YoHo1975 on Monday, August 21, 2023 11:57 AM

Yeah, this is specific to the Dynamic Brake fans.

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Posted by timz on Tuesday, August 22, 2023 11:12 AM

Seems unlikely EMD would give the SD38 punier dynamics. 4000 braking horsepower would be just as useful on an SD38 as on an SD40, so if the SD40 needs two 48-inch fans you'd think the SD38 would need them too.

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Posted by Overmod on Tuesday, August 22, 2023 11:33 AM

Didn't we have a prior thread where either Pneudyne or bogie_engineer discussed the history of fan types on these EMDs?

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Posted by Backshop on Tuesday, August 22, 2023 3:13 PM

timz

Seems unlikely EMD would give the SD38 punier dynamics. 4000 braking horsepower would be just as useful on an SD38 as on an SD40, so if the SD40 needs two 48-inch fans you'd think the SD38 would need them too.

 

I agree. I tried replying during the outage.  They both have the same traction motors, so should have the same amount of dynamic braking (and heat).  

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Posted by JayBee on Tuesday, August 22, 2023 6:05 PM

Here you can see two SD38AC locomotives on the Missabe. The smaller 36" dynamic brake fans are obvious.

Missabe 200

 

Every photo I can find showing DM&IR, EJ&E, B&LE or BNSF SD38-2s seem to show 48" dynamic brake fans. 

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Posted by YoHo1975 on Wednesday, August 23, 2023 10:58 AM

200 also has an older style 3" fan for the radiator. Which is very interesting.

The orange and black unit behind it also Shows the 36" fans.

It looks like the big 38 style access cabinet (never understood what that was) might be limiting the space for the fans.

 

 

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Posted by oltmannd on Wednesday, August 23, 2023 3:55 PM

YoHo1975
It looks like the big 38 style access cabinet (never understood what that was) might be limiting the space for the fans.

That's a housing for paper air filters.  (engine air intake)

-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/

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Posted by oltmannd on Wednesday, August 23, 2023 4:01 PM

JayBee

Here you can see two SD38AC locomotives on the Missabe. The smaller 36" dynamic brake fans are obvious.

Missabe 200

 

Every photo I can find showing DM&IR, EJ&E, B&LE or BNSF SD38-2s seem to show 48" dynamic brake fans. 

 

Here's a total SWAG...

The RR spec'd 36" fans to be compatible with the older locomotives in the fleet.  Perhaps they didn't use DB very often.  

RR:  "We want the same fans on our new locomotives as our current fleet"

EMD:  "No." (they always say "no" right away - to everything non-standard)

RR:  "okay.  Cancel the order."

EMD:  "Well....we can't do the engine cooling fans - air flow - housing design - new radiator core design - blah blah blah, but you can have 36" DB fans.  You just will be limited how much DB they have..."

RR:  "Okay then!  Deal!"

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Posted by YoHo1975 on Thursday, August 24, 2023 1:33 AM

It really looks like it would be hard to fit 48" fans with the paper Air Filter in the way...on the other hand the 38-2 does so. 

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Posted by oltmannd on Thursday, August 24, 2023 3:17 PM

YoHo1975

It really looks like it would be hard to fit 48" fans with the paper Air Filter in the way...on the other hand the 38-2 does so. 

 

It does look tight. Although, I can't imagine they wouldn't fit...

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Posted by YoHo1975 on Thursday, August 24, 2023 6:32 PM

Which brings us back around to the question of why. Obviously prior to the 38/40 series, 36" dynamics were fairly typical on SD units. 

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Posted by wjstix on Friday, August 25, 2023 2:25 PM

What Backshop said got me thinking - the way regenerative / dynamic braking works on electric locomotives is that when doing downhill, the traction motors in the trucks can be adjusted to generate electricity, which can then be fed back into the overhead wire via the pantograph. With a diesel, there's no way to use the electricity generated, so it's used to create heat, which is then vented out of the loco body via a fan. 

It would make sense to me, since an SD-38 had much lower horsepower, it's motors would generate less heat, so would require smaller fans? At least to me, that makes more sense than suggesting some railroad forced EMD to build them that way against their better judgment.

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Posted by cv_acr on Friday, August 25, 2023 2:52 PM

wjstix
It would make sense to me, since an SD-38 had much lower horsepower, it's motors would generate less heat, so would require smaller fans?

The HP is of the diesel prime mover, not the electric traction motors, which are probably exactly the same as an SD40. So quite against what you're suggesting, it makes more sense that the DB capacity is the same, since it's the same set of traction motors, so that's based more on the number of axles/motors and irrelevent to the engine HP.

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Posted by Overmod on Friday, August 25, 2023 2:55 PM

I thought we established a few posts ago, from a good source, that the traction motors in the SD38-2 and SD40-2 were common, and the difference in power between the units was in the engine construction.  What might be likelier is that the amount of achievable dynamic braking current might be limited to match the capability of the prime mover: why pay for more braking power than for the load you could lift to the top of a particular grade?  So I think it's a cost thing, but an artificial economizing.

 

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Posted by Backshop on Friday, August 25, 2023 4:00 PM

I was under the impression that a 38 and a 40 could haul the same train but the 40 could do it faster. They do have the same/similar starting and continuous TE.

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Posted by Overmod on Friday, August 25, 2023 7:40 PM

Backshop
I was under the impression that a 38 and a 40 could haul the same train but the 40 could do it faster.

And burning much less fuel in the higher notches.

But of course if they have the same traction motors, you could expect both the characteristics up to where the TMs come out of low-speed limitation (in the 10 to 12mph range, iirc, but someone here will have a more exact figure) but down the rectangular hyperbola of engine power until the Roots engine starts to run out of efficient air to use for combustion...

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Posted by oltmannd on Wednesday, August 30, 2023 7:09 PM

Overmod

 

 
Backshop
I was under the impression that a 38 and a 40 could haul the same train but the 40 could do it faster.

 

And burning much less fuel in the higher notches.

 

But of course if they have the same traction motors, you could expect both the characteristics up to where the TMs come out of low-speed limitation (in the 10 to 12mph range, iirc, but someone here will have a more exact figure) but down the rectangular hyperbola of engine power until the Roots engine starts to run out of efficient air to use for combustion...

 

MCS for and SD40 is about 11 mph.  For an SD38, about 8 mph.  Both will have the same TE,  the 40 just gets you a bit more speed with that TE.

Yes, the roots blowers run out of breath after notch 6 or so, and fuel efficiency suffers.  My hazy memory thinks it's in the 15% range in notch 8.

But, same train, same route.  SD38 vs SD40, both will get you there.  SD38 will take longer and use a bit less fuel.  The going slower part outweighs the lower fuel efficiency part.

If you're running a drag RR and you can get your crews from A to B reliably with the 38s, they are a better choice.  

If you are running a train scheduled RR, you want the 40s for your road trains.

If you are running a yard, you want the 38s.  They don't burn enough fuel in that service for fuel economy to matter.

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Posted by oltmannd on Wednesday, August 30, 2023 7:11 PM

Hazy memory...  SD40 in N8 160 gal/hr.  SD38 in N8 120 gal/hr perhaps?  (I should look it up.)

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Posted by YoHo1975 on Thursday, August 31, 2023 3:47 PM

Looking at pictures,

SD39 appears to universally have 48" Dynamics fans. I would expect SD38 and SD39 to match on this.

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Posted by wjstix on Tuesday, September 5, 2023 2:31 PM

cv_acr

 wjstix

It would make sense to me, since an SD-38 had much lower horsepower, it's motors would generate less heat, so would require smaller fans?

 

The HP is of the diesel prime mover, not the electric traction motors, which are probably exactly the same as an SD40. So quite against what you're suggesting, it makes more sense that the DB capacity is the same, since it's the same set of traction motors, so that's based more on the number of axles/motors and irrelevent to the engine HP.

 

Both used a V16, but the SD40 was turbocharged, as was the SD39 and SD45. Wonder if that has anything to do with the different fans? 

I think the bottom line is that EMD knew what they were doing, that they determined the SD38 would work fine with the fans they used. Since the SD38s have worked for decades without any problems relating to the dynamic brakes, I'd have to assume EMD was correct.

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Posted by oltmannd on Wednesday, September 6, 2023 12:06 PM

YoHo1975

Looking at pictures,

SD39 appears to universally have 48" Dynamics fans. I would expect SD38 and SD39 to match on this.

 

Yes.  Six D77 traction motors should need 2 48" fans on the DB hatch to provide standard amperage for DB.  If you plop 36" fans up there, your max amperage for full DB would be reduced.

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Posted by Backshop on Wednesday, September 6, 2023 12:39 PM

I don't think the majority of SD38-series locomotives had dynamic brakes anyways. Many were bought for hump and transfer service.

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Posted by oltmannd on Wednesday, September 6, 2023 3:03 PM

Backshop

I don't think the majority of SD38-series locomotives had dynamic brakes anyways. Many were bought for hump and transfer service.

 

Yes.  PC bought U23Cs and SD38s for yard service w/o DB.  The SD38s got six axle slugs in their Conrail years.

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Posted by SD70Dude on Wednesday, September 6, 2023 3:54 PM

On the other hand, some railroads would have sought a lower HP six axle unit (same high tractive effort at low speeds) for service on steep grades.  Northern Alberta's four SD38-2s are an example, they were purchased specifically for heavy trains between CN's Great Slave Lake Railway and the NAR terminal at McLennan, this run involved descending and then climbing out of the Peace River valley, with long 2% grades in both directions.  Dynamic braking was definitely a bonus here. 

Greetings from Alberta

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Posted by YoHo1975 on Thursday, September 7, 2023 8:33 AM

wjstix

 

 
cv_acr

 wjstix

 

 

I think the bottom line is that EMD knew what they were doing, that they determined the SD38 would work fine with the fans they used. Since the SD38s have worked for decades without any problems relating to the dynamic brakes, I'd have to assume EMD was correct.

 

 

No need to defend EMD's honor here. Nobody is questioning whether this would work. 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. 

 

No doubt EMD had a reason. What was it?

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Posted by bogie_engineer on Thursday, September 7, 2023 1:59 PM

YoHo1975

No need to defend EMD's honor here. Nobody is questioning whether this would work. 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. 

 

No doubt EMD had a reason. What was it?

 

I have no answer for why if EMD built them this way. I checked the parts catalog and there is no listing for SD38 with 36" fans. Could it be these were delivered without dynamic brake and the RR added it later with parts from an earlier model?

Dave

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Posted by SD70Dude on Thursday, September 7, 2023 2:37 PM

Here is DMIR 200 during its earlier life as Bessemer & Lake Erie 865.  Look at the DB grid, the two fans are different. 

http://www.rrpicturearchives.net/showPicture.aspx?id=4177352

Greetings from Alberta

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