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SD70MAC

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  • Member since
    February 2009
  • From: South Central Virginia
  • 179 posts
SD70MAC
Posted by VGN Jess on Saturday, May 8, 2021 10:53 PM

Location: Large roof top fan behind cab

Question?: What was the purpose of this fan? Exhaust air up for dynamic brakes?  Blow air down to cool traction motors?
Cool the electrical panels (how)? All three? None of these and something else?

Thanks.

 

 

  • Member since
    December 2017
  • From: I've been everywhere, man
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Posted by SD70Dude on Sunday, May 9, 2021 4:14 AM

It is indeed the cooling fan for the DB grid. 

EMD placed the DB grid behind the cab on six axle units starting with the SD50.  It was moved to the far rear of the unit (behind the radiator) on the SD70ACe and SD70M-2.

Greetings from Alberta

-an Articulate Malcontent

  • Member since
    February 2009
  • From: South Central Virginia
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Posted by VGN Jess on Sunday, May 9, 2021 5:59 AM

Thanks. Where are the fans for the traction motor blowers and for the electrical panel cooling located?

  • Member since
    April 2007
  • From: Palos Park, IL
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Posted by bogie_engineer on Sunday, May 9, 2021 12:52 PM

VGN Jess

Thanks. Where are the fans for the traction motor blowers and for the electrical panel cooling located?

 

The SD70MAC has an engine driven traction motor/alternator blower on the loco left side behind the bulge to the rear of the DB inlet screen and below the inertial air filter screens. All six motors are cooled by this dual wheel blower, the rear truck air going down the loco left side in the duct on top of the underframe below the walkway. Some air is diverted from the traction motor blower thru paper filters to ventilate the electrical control cabinet, about 600 cfm. The traction motors each get about 2800 cfm. The alternator gets about 8000 cfm which is exhausted into the engine room to pressurize it to keep dirt out and ventilate it. 

This is the same basic arrangement introduced on the GP30 and used on all successive models. The SD70 and SD70M were the first units since to incorporate electrically driven traction motor blowers, with separate blowers for each truck. The SD70MAC, however, did not have that arrangement as it was an update of the SD60MAC design, pre-dating the SD70.

Dave

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Posted by daveklepper on Sunday, May 9, 2021 1:12 PM

Thanks for a cpomplete explanaition.

  • Member since
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  • From: South Central Virginia
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Posted by VGN Jess on Monday, May 10, 2021 6:44 AM

Dave: Thanks!!  What a great response, my questions are answered!!!!

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Posted by YoHo1975 on Monday, May 10, 2021 11:27 AM

bogie_engineer
oduced on the GP30 and used on all successive models. The SD70 and SD70M were the first units since to incorporate electrically driven traction motor blowers, with separate blowers for each truck. The SD70MAC, however, did not have that arrangement as it was an update of the SD60MAC design, pre-dating the SD70.

Dave

 

 

This explains the flatter and wider bulge on the 70/70M compared to the angled blower duct on the 70MAC and previous units.

I'd never known what that change signified.

What did the SD90 use? I know it looks like there's a standard older rounded blower duct laid flat underneath the raised walkway on the SD90. 

  • Member since
    April 2007
  • From: Palos Park, IL
  • 173 posts
Posted by bogie_engineer on Monday, May 10, 2021 12:50 PM

YoHo1975

What did the SD90 use? I know it looks like there's a standard older rounded blower duct laid flat underneath the raised walkway on the SD90. 

 

The SD80/90MAC had similar electric blowers to the SD70 for the traction motor cooling as well as an electric alternator blower. They also had electric driven water cooled air compressors; EMD wasn't a fan of the air cooled compressor used by GE.

The H engine, which those locos were designed to use eventually, short-sightedly had no provision on the engine rear (alternator end) to drive a mechanical blower and aux gen. IIRC, they drove the aux gen at the engine front end. Although I did the original locomotive design/equipment layouts for the SD80MAC, I moved on to other projects before they were built so don't recall all the final details. I do remember that the 20-710 in the SD80's had a high pressure external oil system unlike all other EMD 2-stroke engines which had a scavenging oil pump with low pressure external plumbing for the oil cooler and filter loop.

Dave

  • Member since
    January 2021
  • 24 posts
Posted by Max Karl on Tuesday, June 8, 2021 8:40 PM

Considering talking about equipment locations on the MACs, I'm linking the maintenance access diagram and equipment location diagram for anyone who could find it useful in the future.

 

  Max Karl, MRL and BNSF

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