Model Train Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
881 Posts
Discussion Starter · #1 ·
Today I came across a loco that’s labeled a road slug. I worked along the csx today and kind of followed the local job as it was working. It almost looks like a gp-38 but without radiators. It’s got a dynamic brake fan in the center of the loco but nothing else. Anyone know what this thing would be a variant of?
 

·
Registered
Joined
·
2,523 Posts
Interesting, I guess it's purpose is for when you need more traction and not more locomotive power but why would that be necessary?.:dunno:
 

·
Registered
Joined
·
2,095 Posts
Later in the Wikipedia article...

A slug is used to increase adhesive weight, allowing full power to be applied at a lower speed, thus allowing a higher maximum tractive effort. They are often used in low-speed operations such as switching operations in yards. At low speeds, a diesel-electric locomotive prime mover is capable of producing more electricity than its traction motors can use effectively. Extra power would cause the wheels to slip and possibly overheat the traction motors. A slug increases the number of traction motors available to the locomotive, increasing both the pulling and braking power. In addition the load on each traction motor is reduced, which helps prevent overheating from excess current. Slugs typically carry ballast to increase their weight and improve traction. Large blocks of concrete are frequently used for this purpose, substituting for the weight of the now-absent prime mover.

Slugs can be built new or converted from existing locomotives. Conversion has enjoyed popularity as a way to reuse otherwise obsolete locomotives, especially those with worn-out diesel prime movers but having good traction motors.
 

·
Registered
Joined
·
1,459 Posts
Interesting, I guess it's purpose is for when you need more traction and not more locomotive power but why would that be necessary?.:dunno:
So here's the deal.
I saw this in MU operation, passenger traffic on SEPTA.
The motors in the trucks (of our MU's) took 200 amps each in the first throttle notch, we called it "switch" not "one"

After the train starts rolling, more power can be applied going to notch "one", 300 amps now.

Moving further up the throttle I think maxed out at 600 amps 89MPH (speed limited).

Now if the electronics fouled up which they did sometimes.
With train at a stop, the full 600 amps would be applied in the first notch. Wheels would slip violently and the truck would bounce around under the train car making lots of noise.

Same principle for locomotives.
The first diesel has e.g 600 AMPS available but cannot send more than 200 AMPS to it's own trucks. So, if you never need to go 89MPH, there is unused power which could be sent to a SLUG.
 

·
Registered
Joined
·
881 Posts
Discussion Starter · #7 ·
That is pretty interesting. Like I said it caught my eye yesterday and was nice to research something I see in my area. It was doing some switching in the Ottawa yard and did the local service in the area so I’m gonna guess maximum speed was around the 30mph mark due to it being in an area with a lot of crossings and working the different industries
 

·
Registered
Joined
·
4,912 Posts
Kind of interesting that one diesel can generate enough power to operate 2 locomotives
One of our volunteer firefighters is an electrical engineer. He told us one night in training that two locomotives could power our town of 35,000 people!! I asked him later if that was really true, and he said yes!! I still find it hard to believe, but he's one who ought to know.
 

·
Registered
Joined
·
4,912 Posts

·
Registered
Joined
·
31 Posts
A diesel electric locomotive can produce more power than it can use at low speeds. Usually, the slug mothers, the locomotive with the diesel engine, is a 4 axle locomotive. A four axle slug with a four axle mother is good for speeds up to about 30mph. After that the mother needs all the power it can make and none is left for the slug. This combination works well for heavy trains that are low speed and/or starting and stopping quite a bit. Here in Oregon, the PNWR uses old NS slug sets on the Toledo Hauler through the Coast Range from Albany, OR to Toledo, OR. The slugs are useful because of the grades and the slow speed due to the winding route. The slugs can be seen as the third and fourth units on this train, https://www.railpictures.net/photo/611810/

Burlington Northern used SD35 mothers and rebuilt SD9s as slug sets in their hump yards. With 12 motors total, the mother could not supply power for itself and the slug at speeds as high as a four axle set but when humping cars usually only moved about walking speed so it wasn't a problem.

The mother is mostly a normal locomotive but with extra electrical connections to the slug. The slug can vary quite a bit, from complete purpose built to varying degrees of modification to an existing locomotive. All that is used are the electric traction motors and control circuitry but some have dynamic brakes, some have a cab, some a fuel tank that can supply the mother, and so on. Usually the prime mover has been replaced with a block of concrete for weight.

Here's a photo of one of the BN sets, http://archive.trainpix.com/BN/EMDRBLD/TEBUC6/6291.HTM

BN also had some cabless locomotives that were often referred to as slugs but were not because they had their own power plant. They were numbered 4000 to 4119. http://archive.trainpix.com/BN/GE/B30-7A/4077.HTM

Paul
 
1 - 13 of 13 Posts
Top