Diesel/Electric propulsion...What's up with that?

[12Footer]

Can somebody explain the concept of powering a locomotive or ship (many naval vessels used this propulsion system)....It just dawned on me how silly that is upon the face of it. What's the deal? Why not just that big honkin diesel? They had gobs of HP to turn those 10ft screws. And I can understand the principles of having electric backup on the old pre- WWII submarines. But I cannot grasp the concept of redundant propulsion in a surface vessel or a train puller. <br /><br />for why?

 

[mikecjn]

Re: Diesel/Electric propulsion...What's up with that?

I am familiar with Diesel/Electric in military submarine applications.<br /> The submarine would surface and run the diesels while charging the batteries. Once the batteries were charged the sub can submerge and will run on the batteries.<br /><br />Not sure of the surface ship or locomotive applications.

 

[SS MAYFLOAT]

Re: Diesel/Electric propulsion...What's up with that?

I think it has to do with the ability to vary the rpm to the prop or train wheels. Diesels are good at running at a constant rpm. Then the electric is able to have a higher rpm output than that of a diesel by itself. Thats my understanding of it.

 

[achris]

Re: Diesel/Electric propulsion...What's up with that?

The main reason for it is effiency. An engine has a most efficent speed range and running outside that range uses too much fuel. It's easier to have the engine set to run at best speed and then control the load on an electric motor. Most really big diesels don't like being throttled up and down. <br /><br />What Mike said about the subs is right too.<br /><br />Chris........<br /><br />Edit: You beat me to it SS.

 

[Bondo]

Re: Diesel/Electric propulsion...What's up with that?

But I cannot grasp the concept of redundant propulsion

Absolutely Nothing Redundant about it...........<br /><br />Imagine the size,+ complexity of a Transmission that you would need to power a train or ship..........<br /><br />The Diesel Engine spins nothing but an Altenator.......<br /><br />Varying or reversing the Electricity to the motor Moves the train or ship......<br /><br />Or another way to look at it........<br /><br />The actual propulsion is by Electric Motor...................<br />Now,<br />Where are you going to Plug it in ?????????<br /><br />Current technology is either Diesel or Nuclear.........

 

[12Footer]

Re: Diesel/Electric propulsion...What's up with that?

Thanks, Y'all . It makes more sense now. but--<br /><br />Would not the elctric motor burn-up from shear starting loads? <br />Heck, my house A/C unit had a starting cap' fail, and that puppy was huge, in a relative way. Do D/E pullers have these load limtting capacitors to keep the windings from smokin? If So, how big is it, and where do they hide it? It has to be bigger than a garbage can.<br />But the tranny requirments would be equally monsterous if they were to use them (I didn't even consider drive-to-load capacity to transfer all that HP)...

 

[achris]

Re: Diesel/Electric propulsion...What's up with that?

They don't use tranformers or starting caps, they use SCRs, very BIG SCR's. They're like electronic switches. The electricity is rectified (converted from AC to DC) then chopped up and feed to the motors, the duty cycle depending on the power output required.<br /><br />Chris..................

 

[JB]

Re: Diesel/Electric propulsion...What's up with that?

The electric motors do the pulling in the D/E locomotives, 12'er. (On the old subs it was either/or, but never both.)<br /><br />They function as a sort of infinitely variable transmission, allowing the Diesel to run constantly at optimum rpm.<br /><br />Sort of like my Diesel/hydraulic tractor. The Hydro-static drive (hydraulic motor) can apply full diesel engine power at anything from zero rpm to WOT.<br /><br />Both are very efficient packages. My tractor is a lot more useful than the Diesel/manual transmission tractor I had before.

 

[12Footer]

Re: Diesel/Electric propulsion...What's up with that?

ahHAA! SCR's.. Well if that aint a trip! I'd hate to have to herc the heatsink for that puppy!! <br />THat pretty-much filled-in the missing pieces. But don't the whole concept sound like a 'Rube Goldberg' (sp) to y'all?<br />And in the immortal words of Mr Goldberg, "It just goes to show , if you build a better mouse trap, the world will beat a path to your door (eventually,anyhow)". lol.

 

[briannh1234]

Re: Diesel/Electric propulsion...What's up with that?

It isn't just subs, loco's and big boats that use this. All the hybrid cars are using this technology too. Seems running the engine at it optimum speed to make electricity then run a electric motor is more efficient then the transmission/drivetrain setup on conventional cars. However some of the hybrids also sometimes run the wheels directly from the motor.<br /><br />Seems like a complicated mess for 5 more MPG.<br /><br />- Brian

 

[rolmops]

Re: Diesel/Electric propulsion...What's up with that?

A lot of the trains in Europe use this system too,but with a difference.The diesel engine supplies electricity to lots of small electric motors that are situated right on the wheels of different carriages.

 

[Peter J Fraser]

Re: Diesel/Electric propulsion...What's up with that?

We have got 8 new Komatsu Haulpak 730E Haul Trucks (built in Peoria) operating at a coal mine nearby that are Diesel Electric drive.<br />Cummins Diesels @ 1860 fwhp and 200 ton payload.<br />The engine drives a huge generator which provides the current for the traction motors in the rear hubs.<br />big boys toys to the max.<br />EDIT:<br />I forgot I had a day out on a Fisheries Training Vessel a few years back when in Launceston, Tasmania, Aust.<br />The vessel (300 ton approx)is powered by 3 Blackstone Diesels that ran a generator each and supplying the current to 1 electric motor for propulsion.<br />It could operate on 1, 2 or 3 engines depending how much speed was required.<br /> <br />Peter