Diesel-electric drive memories? thoughts? experiences?

Blocker in MS · Jan 28, 2020

Good evening all!

I was earlier this very evening talking with a visionary person and discussing the future of propulsion. After a time we started talking about diesel-electric propulsion. As I understand things, this is a fair bit more efficient way to transmit power as compared to mechanical or hydrostatically. So my curiosity has been peaked and I guess I need to add this to the list of things to use up my free time.

There is of course the prominence of this is the rail and mining industry and a few other notable examples such as the newer Cat D7E and Letourneau’s many fine examples.

Is there anyone with firsthand experience with any of these machines? Is there anyone who has any thoughts about the practical problems involved with diesel-electric drive propelling off highway equipment?

What is the main factor in the limited use or acceptance of this in midsized equipment (-1000HP) application? Weight? Initiatial cost? Is this going to be a viable option in the future. I understand technology has overcome some of the burdens of years ago, such as smoothly controlling DC drives.

Thanks for any thoughts on the matter.

John C. · Jan 29, 2020

I don't know much about the Cat D7Electric but was there for the rollout at the dealer level. Cat was claiming all the benefits, more efficient fuel use, cooler running components, longer service life, easier repair and so on and so forth. In my area of the country, I don't know of any of them being purchased and used. Initial cost I think was a big issue. They were about the same price as a D8T.

I have worked on old Letourneau scrapers where all the controls for the implements were electric. If I remember correctly, the generator was AC as were all the motors. Control of the motors was DC. A stack of rectifiers were used to change the type of current. The rectifiers were getting scarce when I worked on a couple of them and hugely expensive if you could find one. The motors had incredible power though. The ejector cables I think were 5/8 or 3/4 wire rope and when the limit switch failed, the motor would part that line like it was a piece of cheap cotton thread.

What I understand is that all the drives now days are AC. The initial issues with AC was that start up current is huge so they had problems on the big machines getting stuck in mud or trying to start moving on steep hills and burning out the motors. Apparently this issue was solved some years ago. What I have observed is that the components are very expensive. The run time is not much better if at all. The service ability is also no better. I know the dealer used mechanics to work on the dozers but some places require a licensed electrician. Now you have to have two highly trained and experienced people to take care of one machine. What might change the industry perceptions of diesel electric drives will be full integration of computer technology in driverless machinery. For the small stuff though, I believe the technology is just too expensive at this point.

excavator · Jan 29, 2020

Deere now has a couple of "hybrid" wheel loaders. The engine is running a 480V generator which in turn runs an electric motor mounted on a standard transmission. As far as I know the trans and drive axles are the same on the standard and the hybrid. They run a smaller engine in the hybrid therefore they are getting better fuel usage rates. I have a customer who just bought a 644K hybrid so I guess I will be finding out more about these.

Blocker in MS · Jan 29, 2020

I did not know Deere had a hybrid wheel loader! Wheel loaders are enough off the radar I have never looked at new I guess. This is all great information! Please keep it coming!

RZucker · Jan 29, 2020

John C. said:
I don't know much about the Cat D7Electric but was there for the rollout at the dealer level. Cat was claiming all the benefits, more efficient fuel use, cooler running components, longer service life, easier repair and so on and so forth. In my area of the country, I don't know of any of them being purchased and used. Initial cost I think was a big issue. They were about the same price as a D8T.

I have worked on old Letourneau scrapers where all the controls for the implements were electric. If I remember correctly, the generator was AC as were all the motors. Control of the motors was DC. A stack of rectifiers were used to change the type of current. The rectifiers were getting scarce when I worked on a couple of them and hugely expensive if you could find one. The motors had incredible power though. The ejector cables I think were 5/8 or 3/4 wire rope and when the limit switch failed, the motor would part that line like it was a piece of cheap cotton thread.

What I understand is that all the drives now days are AC. The initial issues with AC was that start up current is huge so they had problems on the big machines getting stuck in mud or trying to start moving on steep hills and burning out the motors. Apparently this issue was solved some years ago. What I have observed is that the components are very expensive. The run time is not much better if at all. The service ability is also no better. I know the dealer used mechanics to work on the dozers but some places require a licensed electrician. Now you have to have two highly trained and experienced people to take care of one machine. What might change the industry perceptions of diesel electric drives will be full integration of computer technology in driverless machinery. For the small stuff though, I believe the technology is just too expensive at this point.

I've worked on the old LeTourneau and Wabco stuff, the control circuits for the contactors were AC from 2 legs of the 3phase system, the rectifiers were only for the battery charging system and boosting the generator (alternator) rotor field when the load increased, I have replaced many of those old selenium plate rectifiers with full wave bridges using 6 diodes. In fact for the battery charging rectifier I've used a bridge from a big Delco alternator to simplify things. Even though the best charging fix was to add an alternator to the engine to feed batteries.

ianjoub · Jan 29, 2020

I still want to know why most cars aren't diesel electric hybrids.

John C. · Jan 29, 2020

I wasn't smart enough to come up with a fix like that. Still not now either. Nice work. I knew it was something about those monsters. The owners had no stomach for buying parts so as soon as the spares they had were gone, that was the end of the scrapers. That was OK to me. Changing stranded wire rope and pulling engines to put new used clutches in them got old real fast.

Sounds like Deere is trading in torque converters and hydraulic pumps for gen sets. I wonder what the weight difference is between the two? I don't see that being a big difference in fuel used though. Moving X amount of weight takes X amount of power which eats X amount of fuel. Generators create heat, wiring is heavy and copper is a lot more expensive than oil. It will be interesting to watch from the side lines this time.

Diesel cars are a dirty word in this country.

excavator · Jan 29, 2020

John C. said:
I wasn't smart enough to come up with a fix like that. Still not now either. Nice work. I knew it was something about those monsters. The owners had no stomach for buying parts so as soon as the spares they had were gone, that was the end of the scrapers. That was OK to me. Changing stranded wire rope and pulling engines to put new used clutches in them got old real fast.

Sounds like Deere is trading in torque converters and hydraulic pumps for gen sets. I wonder what the weight difference is between the two? I don't see that being a big difference in fuel used though. Moving X amount of weight takes X amount of power which eats X amount of fuel. Generators create heat, wiring is heavy and copper is a lot more expensive than oil. It will be interesting to watch from the side lines this time.

Diesel cars are a dirty word in this country.

I haven't looked into it to much yet but like I said it looks like I will be.

RZucker · Jan 29, 2020

John C. said:
I wasn't smart enough to come up with a fix like that. Still not now either. Nice work. I knew it was something about those monsters. The owners had no stomach for buying parts so as soon as the spares they had were gone, that was the end of the scrapers. That was OK to me. Changing stranded wire rope and pulling engines to put new used clutches in them got old real fast.

Sounds like Deere is trading in torque converters and hydraulic pumps for gen sets. I wonder what the weight difference is between the two? I don't see that being a big difference in fuel used though. Moving X amount of weight takes X amount of power which eats X amount of fuel. Generators create heat, wiring is heavy and copper is a lot more expensive than oil. It will be interesting to watch from the side lines this time.

Diesel cars are a dirty word in this country.

What I've been hearing about the new AC powered locomotives, is that they are using an AC generator with diodes to feed DC to an invertor that makes AC with a controllable frequency at full voltage to run the traction motors. The full voltage keeps the heat down and the variable frequency controls the speed output of the motor. even at full stall you cant burn up the motors unlike the old DC motors that went up in smoke at the least amount of low speed abuse. I think Deere is working along the same lines.
So I think the trade to an electric "torque convertor" might be pretty accurate.

Blocker in MS · Jan 29, 2020

Do you know what sort of voltage the locomotives currently use?

RZucker · Jan 29, 2020

Blocker in MS said:
Do you know what sort of voltage the locomotives currently use?

The DC models I worked on were 600V, the AC models, I'm not sure. I think 480V would be a fair guess.
I should quantify this statement by saying the DC models were 600V at full engine RPM, at lower throttle settings, voltages were lower.

John C. · Jan 29, 2020

I don't know about locos but what I was referring to were the big electric drive haul trucks. For years the big dogs were DC but didn't catch on well because of the start ups. Cat came on with the big mechanicals and about the same time the AC drives seemed to come on line. I didn't work on any of the big Haulpaks at the time but they were brought in for the Centralia coal mine. I got sent to school for the smaller mechanical drive units and saw a bunch of the training cells put together for the two hundred ton trucks. I was happy to dodge that bullet.

HardRockNM · Jan 31, 2021

Blocker in MS said:
I did not know Deere had a hybrid wheel loader! Wheel loaders are enough off the radar I have never looked at new I guess. This is all great information! Please keep it coming!

I worked at a sand mine that has a CAT 988K XE hybrid-electric wheel loader. I never ran it, was just on the various 980s at that site. While it seemed to work well enough aside from minor teething trouble, it didn't accrue enough hours to be significant before I moved on to greener pastures. They demoed a Deere 944K for about a month before going with the CAT machine - guessing it was due to dealer support since they didn't have any other Deere equipment in the state. That same company had another Deere 944K at a mine in Arizona - don't remember if it was purchased, leased, or on demo.

old-iron-habit · Jan 31, 2021

A couple of years ago I read an article about the future of AG tractors. In it was a fairly detailed report of John Deere's prototype diesel electric, 200 HP equivalent row crop tractors that were then being tested on European farms. They had all electric implements to use with them. Switching implements included switching the computer program to enable the controls to operate the different attachments. It also had a welding outlet built in to the tractor generator. They touted the advantage of no more blown hydraulic hoses and no oil spills. I have occasionally wondered when we were going to here more about how they were turning out but have not seen anything more on them. In fairness, I have not searched for info either.

Coaldust · Feb 2, 2021

Letourneau log stackers were fairly popular in the PNW. Not sure how many are still operating. There were still some working in Longview in 2007.

The Alaska Railroad just retired a couple of them in Anchorage. To expensive to operate and downtime for parts was crazy. They were used for unloading intermodal. AllPro Alaska delivered a giant Toyota lift truck as a replacement.

Tones · Feb 2, 2021

In my lifetime things have done a 180. Early on Cat couldn't say enough bad things about diesel electric drive and now have reversed their position which IMHO makes them total hypocrites.
Le Tourneau has always been ahead in this field not only scrapers but also dump trucks and wheel loaders and are still the leaders in diesel electric drive today under the Komatsu brand. Stuff that Le TourneU designed 50 years ago has still not been matched in size by Caterpillar which makes Johnny come latelys.
I won't deny there weren't problems with WABCO scrapers, most were minor but with serious consequences but on the whole it ran rings around Caterpillar equipment and still does

lantraxco · Feb 3, 2021

Tones said:
In my lifetime things have done a 180. Early on Cat couldn't say enough bad things about diesel electric drive and now have reversed their position which IMHO makes them total hypocrites.
Le Tourneau has always been ahead in this field not only scrapers but also dump trucks and wheel loaders and are still the leaders in diesel electric drive today under the Komatsu brand. Stuff that Le TourneU designed 50 years ago has still not been matched in size by Caterpillar which makes Johnny come latelys.
I won't deny there weren't problems with WABCO scrapers, most were minor but with serious consequences but on the whole it ran rings around Caterpillar equipment and still does

CAT bought out Terex/Bucyrus so now they have both mechanical and electric haul trucks. Go figure.

Tones · Feb 3, 2021

lantraxco said:
CAT bought out Terex/Bucyrus so now they have both mechanical and electric haul trucks. Go figure.

And I bet they'll butcher that by adding computers and electronic gizmos.

lantraxco · Feb 3, 2021

Tones said:
And I bet they'll butcher that by adding computers and electronic gizmos.

LMAO! No doubt!

Nige · Feb 3, 2021

lantraxco said:
CAT bought out Terex/Bucyrus so now they have both mechanical and electric haul trucks. Go figure.

Support for the forner Unit-Rig electric drive trucks continues. I don't think they're actively pushing sales of new units at this time. The newest Specalog I can find online is 7 years old.

Diesel-electric drive memories? thoughts? experiences?

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