# energy conversion efficiency question



## fishhead (Jul 19, 2006)

This is just an idle mind question that I'm wondering about.

I know that freight trains did or still do use combustion engines to create the electricity that really powers the wheels but would the same thing work for pumping water?

I know I can produce methane or possibly cattail ethanol to run a generator. Those energy sources could also directly power a water pump. 

Would there be any efficiency benefit to first converting the energy to electric through a generator to run the water pump?


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## mightybooboo (Feb 10, 2004)

Each conversion involves heat production (friction),hence lost power.


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## fishhead (Jul 19, 2006)

I'm assuming any conversion reduces the amount of energy but there must be a reason for diesel powered electric trains.

I know that when it comes to pumping water electric pumps have an advantage over combustion engines ie. a 10 hp electric will pump more water than a 14(?) hp combustion powered pump.

That's what got me wondering about converting methane or ethanol into electric rather than using it directly.


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## PastTense (Mar 22, 2010)

"Diesel-electric powerplants became popular because they greatly simplified the way motive power was transmitted to the wheels and because they were both more efficient and had greatly reduced maintenance requirements. Direct-drive transmissions can become very complex, considering that a typical locomotive has four or more axles. Additionally, a direct-drive diesel locomotive would require an impractical number of gears to keep the engine within its powerband; coupling the diesel to a generator eliminates this problem."

See:
http://en.wikipedia.org/wiki/Diesel_electric


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## 12vman (Feb 17, 2004)

Doesn't a 1 H.P. electric motor equal to a 2.5 H.P. gasoline internal combustion engine?

Ref: http://www.dieselenginemotor.com/engineering

Quote..
General Rule of Thumb for Motor Applications

1 HP Electric Motor equals 1Â½ HP Hydraulic Motor
1 HP Gasoline Engine equals 2/3 HP Hydraulic Motor
1 HP Hydraulic Motor equals 1 2/3 HP Gasoline Engine
1 HP Hydraulic Motor equals 2/3 HP Electric Motor
*1 HP Electric Motor equals 2Â½ HP Gasoline Engine*

Diesel engines are stronger than gasoline engines so the conversion could be a bit higher. I'll bet that covers some of the losses. 

This answers the question of why they didn't design using hydraulics.


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## ace admirer (Oct 5, 2005)

a hp is a hp (average) the above chart deals with with the application of the hp...for instance only 1/2 half of every second rotation of the flywheel of a 4 cycle single piston gas engine will produce the hp. thats why its called a 4 cycle engine.....only 1 power stroke per 4 cycles its a very inefficient way of delevering power compared to an electric motor that basically gives smooth power application. 
as Mighty Boo has pointed out (what ever happen to our science programs in middle school?) every transfer of power "waste" power in the form of heat. so direct conversion is higher efficiency......But would you want to be the guy that pushed in the clutch and messed gears on a train engine? or waste 25% energy of a hydraulic clutch and multiple gear box? so the smooth application of forward and reverse power of the eng-gen-motor of diesel electrics


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## 12vman (Feb 17, 2004)

Yea.. I wouldn't wanna be the clutch guy on a 164 speed tranny with 400k tons behind me.. LOL

The chart clearly shows the loss of efficiency between the two but the losses wouldn't be so great between a gasoline engine vs diesel being the nature of a diesel engine.

I guess I didn't state it correctly..


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## fishhead (Jul 19, 2006)

So a 2 1/2 hp gas engine is the equivalent of about 746 (theoretical 1 hp) watts.

How much is lost in running a generator to produce those watts?

I'm just wondering if it makes more sense to hook the engine up directly to the pump or to use the engine to run a generator that runs an electric motor.


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## ace admirer (Oct 5, 2005)

if you look at the internal 4 cycle engine (heat/air engine) the efficiency is horrible....probably down around 25% but what you gonna do? our whole country in based on fuel.....while every other modern nation zooms around on 200 mph electric trains.......

off the top of my head....and it depends on the pump model, head, volume, impeller diameter/trim/inlet/cutwater clearance, npsh, opp rpm of the pump (inother words, i'm making a wild a guess)...

you're stuck with the engine cause you're talking about making fuel.....so generator efficiency is around 75% the electric motor is probably around 85% a few points for electrical line losses...so you're only loosing (loose numbers mind you) around 45 % by doing engine-gen-motor. Its all relative since the pump efficiency is almost never over 70% and most likly down around 25% efficiency

what was the name of the antique engine/pump company that used the sterling cycle engine to pump water? erikson? anyway it had a fire box that you burnt,,whatever, and used the heat to run a sterling piston engine which directly ran a piston pump. 


i always wanted to try using a solar panel (or 8) to run a 12 volt motor running a derrick type piston water pump....not efficient but the speed and belting of a derrick pump was cheaper than the expensive 12 volt direct drive impeller pumps.


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## 12vman (Feb 17, 2004)

I ran into this link somewhere around the web. These pumps are awesome! Seems they do a good job at low r.p.m.'s also.

http://www.dbestpump.com/index.html


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## fishhead (Jul 19, 2006)

It sounds like it may be a wash. In that case there's no point in adding another expensive component that will wear out and need replacing.

Thanks for the ideas.


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## ace admirer (Oct 5, 2005)

well it sounds like an interesting project,,,do you mind sharing more details of what you are trying to accomplish? water for house?


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## fishhead (Jul 19, 2006)

No I was thinking more along the lines of filling commercial fish ponds. One acre pond 6' deep takes 2,000,000 gallons. My 6" 5 hp well pump put out 200 gal/min so it took 10,000 minutes. I think it drew something like 25-30 amps but I could be way off on that number.

If I were to do it over I would sink ten 1 1/2" sand points and hook them to a single manifold. Then I could run it by a single above ground centrifical pump. I think that would be more efficient because the draw down would be much less. The draw down on the big pump was 40'. The static water level was 11'. By distributing the draw down between 10 wells I think I could reduce the draw down significantly. Plus the pump would be much cheaper and one that I could install and replace. It would also give me the option of reducing the flow without increasing the pressure.


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## Harry Chickpea (Dec 19, 2008)

There are a variety of reasons why diesel electric is used in trains. None of them really fit the situation of a stationary water pump.

Some of the reasons for diesel electric;

Probably the most critical advantage is the characteristic performance of an electric traction motor. As long as it is not run beyond the design limits and damaged by heat, it tailors output to the load requirement. Example: If the input from the generator is 600 volts and there is a light load of only a few cars, most of that voltage turns the motor at a a high "balancing speed" (where resistance of all forms of drag exactly balances the power supplied to the motor), and the motor runs fast and cool. Relatively low current (amperage) is needed in that case. Take those same cars and same train and put it on a 5% upward incline and the power requirements to move the cars increases. The electric motor "lugs down" and by slowing begins to draw more current and lower the input voltage. A different balancing point is reached and the speed of the train slows, but everything continues normally. The circuitry and feedback design will call for more diesel fuel to be consumed, but no major input is required from the engineer or driver. When descending a grade, the traction motor acts as a generator and the electricity supplied is funneled into huge resistor banks and safely dissipated as heat, reducing wear on braking components of the train.

The smooth action of the system prevents track and wheel damaging spinouts that were common with steam engines.

Hydraulic systems were tried at various times, but the DE combo was just too easy to work with and cost effective for hydraulics to make headway.

Using traction motors allowed trains entering cities or heavily populated areas or tunnels to cut the engines and use power fed from a third rail or overhead line.

Overall costs, even with fuel figured in, were enough lower that even the coal hauling lines were forced to abandon coal as a fuel in favor of the DEs.

Replacement of a traction motor truck is a matter of jacking up the engine or dropping the truck and disconnecting cables. Repair of steam engines was much more complex.

Boilers are expensive, dangerous, and have a short lifespan compared to a diesel engine.

As you can see, none of these factors is of any real importance when pumping water. A direct drive from engine to pump is simpler, more efficient, and reduces costs.


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## artificer (Feb 26, 2007)

Not to pick nits, but...

Hp is hp. Power doesn't depend on how it's produced. The "equivalent" numbers are typically the overload. A 6hp gas engine will put out a max of 6hp, since they put it on the dynomometer to see what it does. The electric motor, on the other hand, can produce several times its rated hp for a limited time. Run it too long at the high power level, and you smoke the motor.

As for pumping water with fuel... I would say the choices are using an engine, or find a fuel cell technology that works. I'd love to have a high temp, non poisoning methane fuel cell that makes electricity directly. Unfortunetly, you can't get them from the local store. Failing that, feed it to an engine, and either directly run a pump, or create the electricity. Electricity will be more controllable, but you have to live with the losses.

Thats quite a big pumping problem. Good luck.

Michael


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## fishhead (Jul 19, 2006)

A methane powered fuel cell would be great based on the little I know about them. Maybe they will be available in the near future.


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