DC motor converted to DC generator?

[haypoint]

I've heard that you can use a DC motor to generate DC voltage, but I'm not clear on the process.

What I have in mind is a large DC motor, 20 horsepower that could drive a small vehicle. When the batteries run down, I want to power the DC motor with a diesel engine to generate electricity, while driving the vehicle on diesel power.

If I'm on the right track, the next step is locating a suitable DC motor/generator. Any ideas where to look?

[Michael Kawalek]

Haypoint, this sounds like an incredible waste of your time. Rather than trying to reinvent the wheel, why don't you just go buy a hybrid? Why start from scratch when teams of engineers have already worked out all the bugs of bringing a commercial product to market? I believe that VW has a diesel hybrid. It might be cheaper to fly to Germany, buy it there, and ship it back to the US in a container, then spend years perfecting something someone else has already done.

[Windy in Kansas]

You might see if this company has any or a call to them might tell you where to locate one. Burden Sales is out of Nebraska, Omaha if I remember correctly.

https://www.surpluscenter.com/home.asp

Whether you make a purchase or not their catalogs is beneficial for ideas. I'm hoping to drive to Omaha before the year is out in order to speak to them in person and make purchases and save shipping charges. Won't be too farm since I plan a run to Topeka, KS on the same trip.

[Ed Norman]

If you turn a DC motor, it generates DC current. Diesel locomotives use the diesel to turn the generator and the generator turns the motors on the wheels. You would never move a train with gears and a clutch. That's why they are either steam or electric drive.

I know the reefer units in semi trailers have a little 3 cylinder diesel.

Instead of going diesel to generator to motor, why not diesel to hydraulic motors on the wheels? But do what you want with your experiment, it's all fun.

[Windy in Kansas]

Originally Posted by Ed Norman

Instead of going diesel to generator to motor, why not diesel to hydraulic motors on the wheels?

Hm, because hydraulic conversion is so inefficient? Seems a local hydraulic specialty company told me 75% efficiency at best.

[Ed Norman]

I was thinking on the savings of a DC motor for the generator then the drive motor.

[haypoint]

Do all DC motors produce current or should I be looking for a specific type of DC motor?

Thanks for the encouragement, Michael Kawalek. Good thing Ford and Edison didn't wait for Corporations to perfect anything.

[roachhill]

All dc motors will but with varied degrees of efficiency. I know someone who converted a semi to run electric by installing a 600 hp train motor then connecting a refer motor to a generator head. It could run all day long on 1 little tank of fuel. This would probably be a good model for a car if you scale it down.

[Harry Chickpea]

Whenever you convert energy from one form to a different form you have conversion losses. This and the added weight penalty is why hybrids are only a good idea in certain situations. Diesel-electric locomotives are a rather unique situation where the conversion losses aren't as important.

There is a factor that most people have never learned about DC traction motors. As the load on the motor increases, the motor slows down and increases the amperage draw, while using a decreasing amount of voltage. As long as the motor can keep turning and cool itself, it will get the job done, just do it slower. Think of it as a horse that can go fast with a buggy on a flat road, but has to hunker down and work to get up a grade with the same buggy. The horse will get hot doing that harder work, and might even die if overstressed, yet can clip along at a good pace on level ground. That is the life of a traction motor in a locomotive or trolley.

Weight isn't a big issue in a locomotive, since it HAS to have enough weight to keep the steel on steel wheels from slipping. When you add the increased efficiency of an internal combustion engine, reduced maintenance, smaller crew, possibility of MU operation, increased safety, and the reduced fueling and water issues, diesel-electric hybrid locomotives were a vastly cheaper solution to train power, even though they were nowhere near as powerful.

Those special factors just don't exist in a car or truck. The rolling resistance of rubber on asphalt is much higher than steel on steel, and any flexation of the tires from increased weight reduces the efficiency, as does the greater percentage of aerodynamic drag in comparison to a streamlined train.

A hybrid car has greater overall efficiency in stop and go situations at low speed, but even an old Honda Civic will beat that MPG when doing extended driving at a steady 60 mph.

Not all DC motors make good traction motors anyway. (FWIW, traction motors ARE often geared to allow the motor to run at speed while the wheels barely turn.) Other motors can overheat or suffer damage in such heavy use, and when run as a generator they can fail rather quickly.

The technology of electric motors has been very well explored over more than 100 years. Before committing money and motors to any such project as a hybrid, it is better to do some serious reading.

[haypoint]

I understand the conversion losses in a hybrid. But if we consider the conversion losses from the coal fired power plant, the transmission losses, the losses converting that to DC and the losses from storing that electricity in a battery in an electric vehicle, is it anywhere near efficient? How can we justify charging our electric car from the grid and reject an onboard generation system on the basis of conversion inefficencies.

[wy_white_wolf]

Search though the parts suppliers for electric cars. They have double shafted motors capable of regenerative braking that would would for you. But they will cost quite a few bucks.