What is a GE 785 traction motor?

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What is a GE 785 traction motor?

Postby Allen Hazen » Thu Aug 07, 2014 12:24 am

Trivia question: on what locomotive was the GE model 785 traction motor used? (785PA2, to be precise.) Does it help to be told that the traction generator (well, alternator) was a GTA-17 (GTA-17PF1 to be precise)?

These model designations are from the description of the locomotive at
http://www.viarail.ca/en/about-via-rail ... comotive-1
(apparently an ad trying to sell off retired units: I have no idea whether the locomotives are still available for sale, or whether VIS's webmaster just forgot to take the ad down.) Right: the MLW LRC passenger locomotive.

So, what are these bits of electrical equipment. The generator is probably a Canada-only variant (or maybe a designed-to-be- mated-with-a-251-engine-in-an-MLW-locomotive variant) of the GTA-11: the M-420 road switcher also (according to the technical details page at thedieselshop.us) also had a GTA-17 generator.

(I wondered if maybe it was a variant of the GTA-11 with a connection for an HEP generator, as on the U34CH, but no: the U34CH's generator was a GTA-16.)

But what is the 785 traction motor? First guess: basically a 752 with a non-standard gear ratio for a high-speed unit. Second guess: a seriously different, probably lighter weight, motor designed specially for the LRC project. (Note that GE has, on occasion, provided lighter motors than the 752 for units where weight was critical: the Australian NR class, a cousin of the
C40-8 built for use on Australia's more lightly built track, has a lighter, less powerful, motor than the 752.) Third guess:the Canadian branch of GE had a little bit of independence from the parent company when it came to assigning model designations.

But if anyone actually KNOWS, I'd be curious to hear just how different a 785 was from a 752. (Note that the E60 passenger electrics built for Amtrak also had traction motors that had some number other than 752. But I don't think it was 785.)
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Re: What is a GE 785 traction motor?

Postby NorthWest » Thu Aug 07, 2014 1:08 am

Allen Hazen wrote:So, what are these bits of electrical equipment. The generator is probably a Canada-only variant (or maybe a designed-to-be- mated-with-a-251-engine-in-an-MLW-locomotive variant) of the GTA-11: the M-420 road switcher also (according to the technical details page at thedieselshop.us) also had a GTA-17 generator.

(I wondered if maybe it was a variant of the GTA-11 with a connection for an HEP generator, as on the U34CH, but no: the U34CH's generator was a GTA-16.)

The GTA-11 was used for the concurrent HR616. Maybe Will Davis has something on this?

Allen Hazen wrote:But what is the 785 traction motor? First guess: basically a 752 with a non-standard gear ratio for a high-speed unit. Second guess: a seriously different, probably lighter weight, motor designed specially for the LRC project. (Note that GE has, on occasion, provided lighter motors than the 752 for units where weight was critical: the Australian NR class, a cousin of the
C40-8 built for use on Australia's more lightly built track, has a lighter, less powerful, motor than the 752.) Third guess:the Canadian branch of GE had a little bit of independence from the parent company when it came to assigning model designations.

But if anyone actually KNOWS, I'd be curious to hear just how different a 785 was from a 752. (Note that the E60 passenger electrics built for Amtrak also had traction motors that had some number other than 752. But I don't think it was 785.)

The E60s had the 780, a higher capacity traction motor (IIRC). I've seen them listed as having 752s, as well. This is going by memory, so I can't quote you any sources.
thedieselshop.us lists the LRC as having 752 traction motors, but also a GE 581 main generator. Therefore, I don't trust it.
I think your second guess is the most likely, as these used unique trucks designed to operate at 125MPH, unsprung weight becoming a serious concern. Frustratingly, I don't have any other information.
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Re: What is a GE 785 traction motor?

Postby Allen Hazen » Fri Aug 08, 2014 1:33 am

Northwest--
Thanks for reply!
Re: thedieselshop.us. They are not 100% reliable: I've found errors in some of their other specifications. … To complicate things, there were two kinds of LRC locomotives: the prototype (with a 12-251 engine) and the production version (with a 16-251). But it seems VERY unlikely that either version would have had a 581 generator! Even the prototype's engine was rated well over the 2400 hp of the highest-powered units (RS-27, C-424) that I know of as having that generator. And MLW's use of a traction alternator in the M-420 roadswitcher suggests a design philosophy that would have been against using a GT-581 in a new, high horsepower, type.

Re: E-60. You have shamed me into looking up things I was too lazy to look up when I posted the other night! The GE entry (I assume the text was pretty much supplied by GE) in the Simmons-Boardman <i>Car and Locomotive Cyclopedia</i>, 1974 edition, says that the original freight E60C (the version used on the Black Mesa and Lake Powell) had 780 motors. It lists five optional gear ratios (85/21 for the highest continuous tractive effort, 80/26 for highest speed) all with a total of 106 teeth: the 752 supplied for GE's had either the 74/18 ratio (used on 752-equipped Alcos from the time of the FA-1/RS-2) or, for higher speeds (and high horsepower BB units) 81/22 or 77/26. Both of these higher-speed ratios for the 752 have a total of 103 teeth: so (assuming, as seems reasonable given the use of 40-inch wheels on the E60C, that the motors were of the same physical dimensions) the 780 used smaller gear teeth than the contemporary 752: something that makes sense for a higher power rating.
(F.w.i.w., GE's entry in this volume also says that the earlier E-50 (Muskingum Electric Railway) and E-44 (Pennsylvania) electrics had 752 motors.)
Amtrak's passenger E-60 types were still in the works when this volume came out: I thought that I'd seen a reference to their traction motor type here, but apparently not.
The GE entry in a slightly later reference <i>Jane's World Railways</i>, 1986-1987 edition, shows the E60C (apparently the freight version) as having 752 motors (page 87)! So… My guess here is that the 780 was just a (state of the art) 752 with special high-strength gears… and that after a while GE decided that the differences weren't enough to merit a new model number.
Note that the up-rated 752 motors used on late Dash-7 and Dash-8 units replaced the old 74/18 gear ratio (for 70mph) with 83/20: again, smaller teeth for higher power. But instead of going to the 106 tooth size used on the 780, they had 103 teeth, as in the ratios GE had used for higher speeds with 752 motors since Alco PA-1 days!

So. I hope that someone else who knows something will contribute, but my current GUESS is that a "785" was a 752 with a nonstandard gear ratio: my grounds for this guess being that the 780 story suggests that there was a period in the 1970s when GE was tempted to assign new model numbers to such modified motors, before deciding that "752" was valuable enough as a brand name to keep it for high-rated motors.
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Re: What is a GE 785 traction motor?

Postby Allen Hazen » Fri Aug 08, 2014 2:31 am

Hmmm…
According to this
http://en.wikipedia.org/wiki/CP_Class_1960
Wikipedia article, the same generator and traction motors (six of them this time) were used by MLW on a 1979 locomotive built for CP: not, as one might think from the red and white paint job on the unit portrayed, Canadian Pacific, but rather the Portuguese railways. Article doesn't say what size of 251 engine was used on this one, but with a raw horsepower a bit over 3000 and a final useful horsepower of 2200 or so, I'd guess a V-12. The locomotive was lighter in weight than North American units with six 752 motors, but probably not too light to use motors of that size: export diesels can be built a LOT lighter than North American ones with the same machinery.
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Re: What is a GE 785 traction motor?

Postby Allen Hazen » Fri Aug 08, 2014 2:48 am

Two posts up I said that GE had used the 103-tooth ratios for higher speed units since the Alco PA-1. WRONG!!! I had remembered that PA-1 gear ratios didn't have the same total number of teeth as the 74/18 freight gearing, but the ratios used involved LARGER rather than small er teeth: total of 83, not 103. 103 tooth ratios seem to have been introduced in the 1960s.
(For this, and other conceivably relevant data, see the strain "Traction motor gear ratio miscellanea," for the moment located about two dozen strings down on the index to this forum.)
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Re: What is a GE 785 traction motor?

Postby NorthWest » Mon Aug 25, 2014 5:43 pm

Sorry it has taken me so long to respond!
Interesting on the BBD CP units. They were designed to haul at least some passenger, but not at high speeds. (Usual uneasy trust of that website applies.)
Because of the light weight, I am wondering if this is a low weight motor, but your guess is as good as and probably better than mine.
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Re: What is a GE 785 traction motor?

Postby CREEPING DEATH » Mon Sep 15, 2014 11:55 pm

Many Canadian Alcos had 75 MPH gearing with a smaller 18-tooth pinion, instead of the American 65-MPH standard 74:18 gearing.

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