KyleIt sounds like most road slugs are old locomotives, do they just remove the engine (prime moved) when it would need to be replaced? Also, are they mostly used in yards?
Slugs are for the most part built from retired locomotives but some have been built new (see above) and Southern had a batch of yard slugs built on steam locomotive tender frames.
There is more to a slug conversion than replacing the prime mover and main generator with a block of concrete ballast. A lot of electrical work and re-wiring is also involved. Slugs tend to be more common in yard service since they are essentially low-speed units.
Seems like the BA&P "tractor" was the first slug. But I would say the GE "MATE" is the ultimate "road" slug, which need not go off line above a specific speed but transition just like the motors under the prime movers.
erikem Probably the first "slugs" were the singe truck "tractors" built for the BA&P ca 1913-14. The motors on these slugs were wired in series with the motors in the main cab, resulting in two groups of three motors in series as opposed to two groups of two motors in series. Note that the motors were rated at 1200V, the cat on the BA&P was energized at 2400V, so at least two motors would need to be in series to handle the voltage.
Probably the first "slugs" were the singe truck "tractors" built for the BA&P ca 1913-14. The motors on these slugs were wired in series with the motors in the main cab, resulting in two groups of three motors in series as opposed to two groups of two motors in series. Note that the motors were rated at 1200V, the cat on the BA&P was energized at 2400V, so at least two motors would need to be in series to handle the voltage.
BAampPtractortruck_zps86b7151d by Donald Schmitt, on Flickr
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
GE's MATEs are slightly different from road slugs in that they have motor transition, and so don't cut out at any speed. Seaboard bought them in order to have two U36Bs when they were needed, and then attached them to a MATE, so they became in effect two U36Cs.
EMD built GH-00a and GH-00b yard slugs for CN.
And at least some of them have been built new. Seaboard's MATE's from GE that were paired with U36B's are the most famous examples. Here's a picture of a set.
http://www.rrpicturearchives.net/showPicture.aspx?id=2393256
And I've heard at least 1 mention of EMD having built them new but have never seen any evidence of a EMD factory constructed slug of any sort.
Thanks, Dave, for the additions. Road Slugs have a higher cut-out speed than yard slugs. CSX's are made from EMD Geeps with the prime mover and radiators removed.
A slug is any of what was described in the previous post. A road slug is intended for line-haul use, rather than being restricted to transfer-train (most frequent application for slugs) and/or switcher use. A road slug and locomotive lashup will probably have mu capability with other locomotives while a slug and switcher pair might not. There are probably other differences, like a john in the locomotive.
A road slug is a car (or locomotive frame) that has traction motors but no prime mover. At slower speeds, a locomotive produces more power than the motors can use. A slug uses this power to help pull the train. Road slugs typically cut out at about 30MPH and are pulled along as just another car, when the locomotive no longer has excess power. They also may have dynamic brakes, and might be used as a fuel tender. Some also have cabs that can be used to control locomotives. This allows a mother-slug set to be bidirectional, while only having one prime mover.
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