Hi-
Check out this little generator. Does it seem like it has more HP in electricity produced than the HP of the motor that drives it?

http://www.duropower.com/item.asp?PID=132&FID=1&level=0

Hi-

I've read in the available literature that a HP is the equivelant to 746 watts. So this little generator has an 9 HP diesel engine. At 100% efficiency it should only be able to put out 6714 watts. But the manufacture claims it can produce up to 7500 watts.
So just for fun thinking, I wonder if one replaced that desiel engine with a super efficient 9 hp electric motor?? If this theory could go this far even then one could plug your modified electric generator into the regular grid system and end up with excess electricity to use, store or sell back to the utility company. 
So I wonder how efficient they are making electric motors these days?

Best,

Reply for Legendre-

Hi-

Thanks once again for your information. Here's your reply from over at the moped thread-

pg46,

Ok, since you're obviously interested in this, here is the explanation for the 7500W rating on the 9HP generator (the key to this is the surge rating):

9HP is equal to about 6700W, which is in line with the continuous rated output of this generator - 6500W claimed. Ok, so far no overunity - average power output is rougly equal to average power input, with some losses.

What you aren't considering, is that most all devices which supply or consume power (in this case, engines and dynamos) have multiple ratings; continuous, surge, design maxiumum, do not exceed, etc. The fact is, both the engine and the dynamo in this generator have surge ratings that exceed the continuous rating. There is nothing special about this, just reasonable design. In fact, a 7500W surge from a 6500W rated generator is about right - 15% or so above continuous.

Also, since we were discussing flywheels, let's not forget to include them as well. The engine crankshaft and dynamo rotor work together as a large flywheel. Flywheels work like this: If 10HP can spin the flywheel to a given speed in 10 seconds, and you then put the flywheel to work so that it stops in 5 seconds, it will perform an average of 20HP of work over that 5 seconds - more at first, less at the end; twice the power over half the time. In the end, the same amount of work (minus losses)

Ok thats good then- for now at least Legendre and I agree and can go along with the manufactures claims about their stats. By the way, I wrote into the company the other day and asked how long the generator could run at 7500 watts but they were a bit vague by answering '30 to 60 minutes'. Still, it seems like a lot. Well the next question might be like "well OK then, how long a time is required before you could produce the 30 to 60 minutes of 7500 watts again?" It would be important to know the cycle times but never mind that detail for just now.
So then a HP can be equated to what about 746 watts of electricity?  This generator manufacturer claims that their 9HP engine runs the generator at 6500 watts continuously. If it were 100% efficient then it would produce a steady 6714 watts but it doesn't according to the stats but at this rate the generator is already 96.8% efficient. Hey that's not too bad already! but its as Legendre says it sn't overunity at these rates that's for sure.
The manufacture says it can run up to 7500 watts some of the time but not all of the time or as Legendre explained it can sometimes "surge". Legendre goes on to say that it is normal for a good generator to "surge" up to 15% above the normal continuous ratings.(I think the manufacturer mentioned 10% there somewhere in their stats) But 15% of 6500 is 950 so plus the 6500 continuous rating which is close enough to the declared 7500 surge rating.   
As one such as I who is not formally trained in these specific energy arts, I can only read what others are stating about various systems and products such as what this manufacturer and folks such as Legendre are saying and try to make common sense of it all. Lets have a look at it then from my simple perspective. If this generator was 100% efficient it would have to produce 6714 watts ( 9(engine hp) x 746(1hp =746watts) = 6714 ) is that right?
If for fun we tossed off that stinky desiel generator for ease of a test and in its place we put a nice 9 HP electric motor which was at least as efficient we'd be able to also run the 6500 watts continuously. The 9 HP motor would take 6714 watts to run it an hour.
At 6500 watts it's producing 108.33 watts/minute  Whenever it surges to 7500 watts it is producing 125 watts/min
If this generator ran 46 minutes out of an hour with a 6500 watt load and the remaining 14 minutes out of the hour at a 7500 watts load then the overall production would be 6731 watts ( 46 x 108.3 = 4981.8 plus 12 x 125 = 1750)....hmmmm?
Ok, so what gives here? a 100% efficient machine would produce 6714 watts and here this unit in this example produced 6731.8 watts ?? This is already over 100% efficient if the unit ran only 14 minutes out of any hour at 7500 watts where it's likely the manufacturer would claim it can run at those rates longer than 14 min/hr.
If you were to store this 6731 watts into batteries for example and then the next test ran the 9 hp electric motor from the batteries you might expect to run a closed loop with some energy to spare. So this generator can run 97% efficient most of the time and then 115% some of the time....is there not a unique energy opportunity here?
Well...likely I am missunderstanding or leaving out entirely something major here. Perhaps someone could point out just what that is exactly.

Best Regards,

pg46,

Yes, you are misunderstanding a couple of things, and also failing to correctly consider what 'surge' ratings mean.

First - your statement "The 9 HP motor would take 6714 watts to run it an hour." shows that you don't understand what a Watt is. A Watt is a unit of power at work, and 1 Watt = 1 Joule per second. So, you see that you cannot say "The 9 HP motor would take 6714 Joules per second to run it an hour." - the time factor is already accounted for, in seconds. If the motor is being delivered 6714 Joules every second (6714 Watts) it will run continuously at 9HP of output. Likewise, the statement "At 6500 watts it's producing 108.33 watts/minute" is also misconstrued.

The problem here, is the typical use of the kW/h (kilowatt hour) metric to describe electrical power consumption; this is simply a matter of convenience, as you will soon see.  Trouble is, people get confused, and think that the unit of power (Watt) is somehow related to the Hours rating - it is not. When you say "1 kW/h", what you mean is: "1000 Joules per second was consumed for one hour" (3600000 Joules).

As you can see, it's a lot easier to understand an electrical bill when it states that you consumed 500kW/h of power this month, as opposed to  1800000000 Joules. Not only are there too many zeroes in that figure (most people cannot comprehend or work with numbers that large, in their heads), but all of their appliances are rated in Watts. So, we use the kW/h to get rid of a lot of zeroes. And even if we used a metric like kJ (kilojoules) or MJ (megajoules), it would still be confusing.. again, everything is rated in Watts.

Now, about surge ratings. By definition, "surge" has no limit on time, other than what the manufacturer decides is correct for their equipment. In this case, the manufacturer has set their surge rating at 7500W for 30-60 minutes. During this time, the equipment strains beyond its intended continuous rating, creating more heat than is desired, and potentially fatiguing the components. Understand that for a reciprocating engine like a diesel or gasoline motor, it's best to operate at not above 75% of maximum, to ensure long life for the engine (general rule of thumb).

So, you can see that if this product is designed intelligently, there is a potential for as much as 25% additional reserve power, in excess of its continuous rating. The surge rating limits this to around 15% over rated continuous, which again, is just typical good design. Try to pull much more power, and the circuit breaker(s) on the generator are very likely to trip, and cut off the power output. Obviously, they wouldn't let you draw continuous power at a level that would damage the equipment - they have warranty obligations, you know

Hopefully this makes sense to you, as I've taken a bit of time to compose it. Thankfully, you seem to be the type of person who doesn't think they know it all - but are wise enough to realize what they *do not know*. There is a particular type of intelligence (and humility) in that, and it will serve you very well as you continue to learn.

Best,
Murder Legendre

 Hi All-

For Legendre-
Yeah, I took the chance that someone might thrash me because of my likely misuse of the terminology  thats OK. I must make a note to quit writing so late at night!
Just because I am not trained in these 'particular' arts doesn't mean I don't know what a watt is at least in a practical sense. After all it is part of our everyday lives with all our electrical appliances, heaters, lights and such that have their electrical ratings in watts. For the work I've done in the past I needed to know that volts x amps = watts. This small formula allowed me to rig up extensive systems for DC lighting and control systems on mobile heavy equipment. This of course included upgrading alternator and battery systems to match the new demands.
Yeah, I do know what is meant by the 'surge' but I like your description - thanks. I also owned portable welding equipment and knew too the continuous power ratings of the units and what that all meant.

Ok so back to our example generator here. I will try to place a more direct question where one won't get lost in the verbiage. This of one of course is open to anyone out there as I am not trying to convince anyone but only ask the question and get an answer.
So again its a commercially available 9HP diesel motor rated to run at a continuous 6500 watts with a surge capacity of up to 7500 watts. Let's say then for example that we are using our little generator with its 9 HP diesel motor and we've hooked up all sorts of appliances and tools etc. so that the output is now cruising along at 6500 watts. Then we plug in yet even one more appliance that draws an additional 1000 watts so that now our generator is putting out 7500 watts to keep up to the demand.
Now the question is - while this generator is putting out the 7500 watts be that for 1 second, 1 minute, 10 minutes or how ever long it does, is it producing more HP in electricity than the HP it takes to run it?

The Answer is simply a Yes or a No

Best Regards,