# Generators

Discussion in 'Architecture & Engineering' started by one_raven, Jul 23, 2008.

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1. ### one_ravenGod is a Chinese WhisperValued Senior Member

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Can anyone point me to a decent resource for learning about generators?
How they are rated.
How to do the math to determine what your needs are.
What considerations need to be kept in mind.

Basiaclly, if I wanted to design a system, where should I start?

3. ### one_ravenGod is a Chinese WhisperValued Senior Member

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Let's say, for example, that I wanted to run a generator with a 100 HP motor and generate about 800 amps at 200 KW.

I need to know what I need to know to accomplish that.

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7. ### Echo3RomeoOne man wolfpackRegistered Senior Member

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First, know how to work between different units of energy. One horsepower is the equivalent of 746 watts. Thus, a 100bhp motor produces 74,600 watts at its output shaft. Maximum deliverable power across the output of a generator will always be less than that. So if you can do what you're asking, you'll have permanently solved the energy crisis.

Also, know the difference between watts and volt-amperes, because VA allow you to incorporate loads with different power factors. The average house has a power factor of 0.85 or so.

Last edited: Aug 4, 2008
8. ### ThoreauValued Senior Member

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If you need help, I'm a generator technician and have been working on them for 6 years now. I know you can get a lot of resources about them through major generator companies, such as mine (Cummins/Onan).

9. ### jpapplValued Senior Member

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The first thing to do is determine what you need or want to run with it.

For example, Furnace, stove, dishwasher, living room lighting, Fridge etc.

Then you need to know what the wattage run draw is and what the wattage start up draw of those devices are. For example, to turn on and start up a furnace or heat pump may have a high start up draw but a much lower run draw. If you get to small of a generator it may not be powerful enough to allow for the start up, or you will need to sacrifice some of the appliances from list.

Get the list of appliances you want to run and see what there start up and run draw is and a dealer should be able to figure it out for you.

Good luck.

10. ### jpapplValued Senior Member

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Raven,

Nevermind, I just realized your OP was 3 months ago.

I assume you already have the info you need.

11. ### one_ravenGod is a Chinese WhisperValued Senior Member

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I have not found the info, but I have not looked recently either.
Work got very busy and personal learning pursuits had to be put on hold.

Let's take the generator in the Prius as an example.
http://www.ornl.gov/~webworks/cppr/y2001/rpt/121813.pdf (page 11)

What factors would I need to know to understand what kind of power output this generator is capable of?
How could it be increased?
I have a vague memory of twenty years ago discussing the number of wire winds, strength of magnets, angle of wire bends in science class. That's about as much as I can recall.

As the Prius is running off the gas engine, the generator charges the battery, so the car can be run off the battery at take-off and low speeds, if I recall correctly.
So, what would be the math behind how much power the generator puts out at differing RPM values and how that translates into how much it can charge the battery?
How would you calcualte the efficeincy of such a feedback system and what effect changing components, like a different generator, will have?
Lets say you have a car like the Tesla, which runs off battery power...
What if you coupled a generator to a gas engine and used that to charge the batteries and you wanted to calculate how much more range you could expect - how would you go about doing that math?

I know that's a lot and I am not looking for a free lesson, I am just looking for advice on how and where I can find such information packaged for a newbie.

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13. ### one_ravenGod is a Chinese WhisperValued Senior Member

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Thanks.

I will check them out.
I am also very curious about wind turbine design.

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15. ### Fraggle RockerStaff Member

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That's a pretty big generator. It won't produce 200kw, but probably something like 50kw, which is still pretty big. Assuming it's a diesel engine it will probably burn about 2 gallons of fuel per hour. (This is way outside my field of expertise so my numbers aren't going to be terribly accurate, but still within maybe a factor of 2.)

We live in a fairly remote area where we have power outages that sometimes last for days, and I don't know anyone with a 100hp generator.

Ten-kilowatt generators are sold as "residential standby units," and one of those is going to cost you around three thousand bucks. I think ten kilowatts is enough power to run a modest-size house if you don't try to run the central air conditioning, the electric oven plus two burners, the water heater and the clothes dryer, all at the same time.
Internal combustion engines have a "torque peak" and a "power peak," each at a certain rotating speed. In a modern small overhead-cam gasoline automobile engine, power peak is around 6,000 rpm. Power can drop off dramatically at lower engine speeds, which is why those engines often have five- or six-speed transmissions, so you can stay near your power peak. An old-fashioned Detroit pushrod engine had a power peak closer to 4,000 rpm and the power range was so broad some of them had two-speed automatic transmissions.

There's no formula for what you're looking for, it depends on many different design factors in the engine, such as the shape of the cam, bore/stroke ratio, combustion chamber geometry, etc. You'll have to find the power chart for the individual engine you want to study. In general, higher-performance engines have much narrower bands of high power. Of course you'll be looking at very low-performance engines if you want to build a reliable generator to power your house. It might have a power peak at 2,500 rpm.

I'm not entirely sure what you want to do with this generator. But you'll do best if you keep it at a constant rpm. Check out the 10,000 hp diesel engines they use to power the electric motors on diesel-electric railway locomotives. Really, REALLY big stuff is always fascinating.