The Davis blog lives!

Anyone -- particularly, any fan of GE locomotives -- who hasn't checked Will and David Davis's "Railroad Locomotives" blog recently should:
http://railroadlocomotives.blogspot.ca/ ... eries.html" onclick="window.open(this.href);return false;
There's a new (mid January 2014) post, devoted to the "Dash-7" line of locomotives and the ways in which they differed from the U-series.

(For those who don't know the blog: the Davis brothers have a collection of railroad and railroad supplier printed material, and have used it to provide information-- technically detailed information not to be found in the rail fan press-- on various points of locomotive history. Information derived from official sources. It's a resource anyone starved for technical content by the glossy picture books that seem to dominate the rail fan book market these days should know about.)

Great stuff from the Davis brothers!

Thanks for the link and info, Allen!

Thanks so much, Allen, and MEC407! I was spurred to post again after what felt like forever (and it's been well over a year) after a bit of searching on the internet for something turned up a bunch of clones of the same meager information at numerous sites. I'm reinvigorated, a bit, to make sure that knowledge and material I have gets passed on before (God forbid) something happens to me and my collection just gets dispersed to the winds. Not that something is going on - it's just that it's clear that this information - and lots more - just didn't get out there prior to now, and so I think I have a responsibility to get it out. After all - what good is it if I spend decades collecting, reading, interpreting all of this stuff if what I piece together as narratives and explanations goes with me? None.

There's more to come in the GE field too so keep an eye out. Not sure when I'll have time to post the various new things but I'm planning it.

-Will Davis

No mention of CHEC in the GE documentation.

You're right - there is no mention of CHEC excitation in any of the announcement of the 1977 Series Locomotives.

This tells me that it was either not important enough to trumpet as an improvement or that it wasn't cooked up along with these developments. Not sure which - but since we still cannot turn up any GE brochure that announces or advertises the CHEC excitation system, we have to run on assumptions for now.

-Will Davis

CHEC was applied to at least some units in the last CR U-23B order circa 1977.

Some units? Very interesting. Thanks for the tip!

From GEK-30130A these would be CR 2789-2798, serial numbers 41584-41593, GE Requisition Number 320-56769. Built May 1977 according to the Conrail historical society. Given the assumption that the CHEC excitation appeared more or less concurrently with the GE turbo (which itself appeared sometime in 1976) and also noting that these U23B units were built AFTER announcement of the "New Series Locomotives" this seems to fit well with my suppositions. The next higher requisition number for Conrail was that for its first B23-7 units, delivered beginning in September 1977.

-Will Davis

Some digging into notes that I have taken along the way reveals the following: CHEC was applied to all the units in the order, per the schematic diagram for that order. I saw ex CR2798 when it ran on the P&W...noting the presence of CHEC equipment (without the annunciator module). Additionally, the unit was equipped with an ELLIOT turbo.

By the way, CHEC was the first excitation system that was both conceived and designed in Erie. The earlier systems apparently came from other GE divisions.

Will, I am glad you are putting this material out there for the consideration of others. Too many folks are entranced by the external lumps and bumps on the locos, which more often than not do not reveal anything of substance.

Bright Star

Revised to remove incorrect citation pertaining to inventor of CHEC. USPO Database cites a different inventor.

Thanks so much, Bright Star! Very informative. And I'm glad you're along with me in believing that there's a whole lot more to be found inside than out.

Looking at the GE Unit Exchange manual, I see that the Elliott H581 was the turbo for the U23 model, and it's listed both with and without CHEC. There is also however listed the GE1412 which is only a CHEC turbo, at least in this listing of unit exchange turbos. This section was published 11/78.

A further look at the various turbocharger instructions in GEK-30130A shows for example that the included GEK-61249, published 3/77 makes no mention of CHEC excitation whatsoever (this instruction covers GE turbos of model numbers 7S1408A1, B1, B2 and 7S1412A1) but the previous GEK-61248A covering the same models (one is "instructions," the other "inspection and service") and which was published 5/78 does include CHEC excitation probe installation instructions. This is the first thing I've found, digging through looking for CHEC page by page, which shows GE turbochargers that do NOT have CHEC excitation. These turbos are for FDL8 and FDL12 engines. I had not looked specifically for anything CHEC ever until this whole topic of the U33B came up over at the TRAINS.COM forum, so I'm finding this ongoing thing (on two forums) very interesting.

We're zoning in on a date range for CHEC introduction during very late 1976 - early 1977 I'd say, bounded by the 12/76 date of the stand-alone supplementary instruction covering the CHEC probe installation and conversion shims, etc. and the 5/77 build date of the CR U23B order which we can now confirm from Bright Star's excellent notes to have had CHEC excitation. The fact that it's not mentioned at all in the "New Series Locomotive" material is quite interesting to me.

-Will Davis

The fact that GE would essentially hide a major product improvement is rather strange.The need to bias loading against turbo speed was recognized back in the days of the Alco-GE joint agreement. It took some thirty years and the introduction of digital electronics to bring the concept to fruition.

Bright Star

I don't know for sure yet if we could say they never mentioned it (CHEC excitation) in advertising, much less hid it; what's certain is that it's mentioned nowhere, directly or indirectly in the "1977 Series Locomotive" announcement brochure and not hinted at in the 1975 improvements list.

It's interesting what GE decided to advertise and decided not to, over the years. They played up the slip suppression system when they came out with the U25 and had that for a number of years. However, it's clear the railroads didn't all like it and many didn't want it. They did far, far less to advertise their wheel slip systems after this time. No big hoopla over making all-electric wheel slip control available; not much over the "power tie" or later ROC systems either, at least when compared with the radical SSBV system and how they trumpeted that. But they're rather idiosyncratic.

I'd have to say that the evidence is that, early, they were pushing in advertising the things that set the U25 apart in design from the other units available, and then when ALCO dropped off they were forced to focus on advertising the equipment changes that were made to improve reliability and reduce operating costs. If CHEC excitation really didn't make much difference in operating cost, then it's just an internal change.

I'm reminded of the video interview of ... was it Hockaday? ... an ALCO design engineer who said that they just applied transistorized excitation to the RS-11 as a matter of continued product improvement and didn't think it was a huge deal; he only found out years later that marketing had decided to change the locomotive's advertised model number because of that alteration. It's funny how the engineering department and the advertising department have different perceptions about the same things.

-Will Davis

I'm reminded of the video interview of ... was it Hockaday? ... an ALCO design engineer who said that they just applied transistorized excitation to the RS-11 as a matter of continued product improvement and didn't think it was a huge deal; he only found out years later that marketing had decided to change the locomotive's advertised model number because of that alteration. It's funny how the engineering department and the advertising department have different perceptions about the same things.

Yes, it was Hockaday. I suppose 'product improvements' can be viewed from at least two perspectives. Some may choose to view them as legitimate improvements-once they prove themselves in the field. Others may initially see them as a series of headaches...until the learning curves flattens out. Training needs to be done in the field, additional renewal parts need to be deployed...not withstanding the development of new performance/maintenance issues in the field that must be remedied.

I have experienced this scenario firsthand. When a new (to the property) group of AC drive locomotives was placed in service, some choose to dwell on the similarities between the new locos and the existing fleet of otherwise very similar DC drive locos. Others concentrated their attention on the differences between the the two groups of units. Same engine, same main alt, same LCC, etc. As fate would have it, the AC drive was mature and created little in the way of additional concerns. In my view, neither perspective was correct...or incorrect.

My theory about CHEC is this (having applied Occams' Razor)-They chose not to publicize it because at the onset, the downside potential was equal, if not greater, than the upside at the time of introduction.

I am going to check my GE files for maintenance and training materials that directly refer to CHEC...as to put some more dates in place.

Bright Star

Bright Star, Will Davis--
For the benefit of the ignorant among us, could one of you give a one-paragraph description of what CHEC is? I know it is the … system? … controlling generator excitation, I know it is involved in wheelslip control (I assume by automatically reducing excitation, and so power output, when incipient wheelslip is detected somehow). From what you say, it seems to also to have involved a sensor for ??speed of?? the turbocharger, so as to (I assume) match the generator excitation (and so the load on the engine) to the instantaneous power-output of the engine. I'd find bit more description very helpful, though.

Allan- your request has been noted.

Will-G E K-30150,First Edition,August, 1978 denotes the first Series-7 Running Maintenance Manual. I note that a deal of the GE materials that I have show no date.

Bright Star

Bright Star--
Googling, I have found the patent application for CHEC (Constant Horsepower Excitation Control). Skimmed (I don't know enough engineering to appreciate the details); I think I now understand things a bit better.
Quick question: does the sensor on the turbocharger monitor rotational speed or something else (temperature? pressure?)?