Generator KW Rating Based Upon Engine Horsepower

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Ravenvalor said:
Is HP calculated based on the size of the engine block?
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No, there are ways to get more power out of same size package, all you need to do is increase fuel/air mixture introduced, then with modern controls they have ability for all sorts of fine tuning for different situations. Type of fuel used also can make a difference.

Along with that can lead to a necessity to remove more heat, have stronger load bearing materials, etc.

Diesel has more power in same volume as gasoline. That said diesel engines run at much higher compression than gasoline engines, so a same sized engine will be built to withstand those higher pressures, but based on same cubic inch displacement the diesel engine will have higher output rating before considering any other tweaking.
 
I think many of the previous responses show why engine HP isn't that relevant.

Too many different opinions on exactly what it means and how to define it, and how it affects the electric KW.

It becomes just like the cheap audio amplifier that says it has 200 watts output, but only takes 12 volts and 10 amps for the input. You know something doesn't add up.
 
Ravenvalor said:
Is HP calculated based on the size of the engine block?
Click to expand...
Some jurisdictions use/have used something called "taxable horsepower" which is calculated from the engine's dimensions. It's a work of fiction, often nonlinear and if there's any corelation to actual power developed, it's purely coincidental.

Tax horsepower - Wikipedia

en.wikipedia.org en.wikipedia.org


kwired said:
... Diesel [fuel] has more power in same volume as gasoline. That said Diesel engines run at much higher compression than gasoline engines, so a same sized ... Diesel engine will have higher output rating before considering any other tweaking.
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Um, no.
Diesel fuel contains more energy per liter (gallon, barrel, peck, et al) than gasoline. But there are many, many variables and it's impossible to make a (valid) blanket statement like that.
My all-time favorite Diesel engine, (yeah, I'm the sort of ubergeek who has an all-time favorite engine) the General Motors 567, developed 100 horsepower per 567 cubic inches.
Back in the 1970s-1980s, it was common for automobile manufacturers to offer both a gasoline and a naturally-aspirated Diesel engine based on the same block, bore & stroke. The Diesel versions ran much slower (typically 3500 rev/min v. 5500 rev/min) and developed 20-40% less power.


Usage note:
"Diesel" is Rudolph Diesel's family name. When referring to people, it's a proper noun and gets capitalized.
When referring to Diesel engines or Diesel fuel, it's a proper adjective, must be attached to a noun, (such as "engine" or "fuel") and gets capitalized.
 
200219-1616 EST

An internal combustion engine can be physically tested on a dynamometer for its speed torque curve for a given set of external conditions. Likely full throttle would be one condition.

This curve then defines the maximum capability of the engine. Knowing torque and RPM you can calculate power. Over much of the range power is lower at a lower RPM. In other words power increases with RPM.

If you overload the engine it stalls.

See https://x-engineer.org/automotive-e...mbustion-engines/performance/power-vs-torque/ for a useful discussion.

An electric motor or generator is quite different.

An internal combustion engine can be run at full power continuously, but if you overload it, then it goes plop, and quits.

An electric motor or generator has some continuous full power rating which is basically a thermal consideration. This full power rating can in some cases be exceeded by more than 10 times for short periods of time without harm.

,
 
drcampbell said:
Some jurisdictions use/have used something called "taxable horsepower" which is calculated from the engine's dimensions. It's a work of fiction, often nonlinear and if there's any corelation to actual power developed, it's purely coincidental.

Tax horsepower - Wikipedia

en.wikipedia.org en.wikipedia.org



Um, no.
Diesel fuel contains more energy per liter (gallon, barrel, peck, et al) than gasoline. But there are many, many variables and it's impossible to make a (valid) blanket statement like that.
My all-time favorite Diesel engine, (yeah, I'm the sort of ubergeek who has an all-time favorite engine) the General Motors 567, developed 100 horsepower per 567 cubic inches.
Back in the 1970s-1980s, it was common for automobile manufacturers to offer both a gasoline and a naturally-aspirated Diesel engine based on the same block, bore & stroke. The Diesel versions ran much slower (typically 3500 rev/min v. 5500 rev/min) and developed 20-40% less power.


Usage note:
"Diesel" is Rudolph Diesel's family name. When referring to people, it's a proper noun and gets capitalized.
When referring to Diesel engines or Diesel fuel, it's a proper adjective, must be attached to a noun, (such as "engine" or "fuel") and gets capitalized.
Click to expand...

After reading what I wrote, it is maybe a little confusing, but bolded text of quote is pretty much what I was trying to say. I don't know about being impossible to make such blanket statement, there is more potential energy in Diesel than there is in the same volume of gasoline. The variables involve inefficiencies in the application and not in what energy potential is in the fuel.
 
drcampbell said:
.
Diesel fuel contains more energy per liter (gallon, barrel, peck, et al) than gasoline. But there are many, many variables and it's impossible to make a (valid) blanket statement like that.
My all-time favorite Diesel engine, (yeah, I'm the sort of ubergeek who has an all-time favorite engine) the General Motors 567, developed 100 horsepower per 567 cubic inches.
Back in the 1970s-1980s, it was common for automobile manufacturers to offer both a gasoline and a naturally-aspirated Diesel engine based on the same block, bore & stroke. The Diesel versions ran much slower (typically 3500 rev/min v. 5500 rev/min) and developed 20-40% less power.
Click to expand...

For the same geometry of the engine (i.e. stroke, bore, compression ratio, number of cylinders), a diesel engine will be less efficient than the Otto cycle engine (what you find in most automobiles) as its counterpart. The advantage to Diesel engines comes from the fact that it can be built with a higher compression ratio, which allows achieving a higher efficiency.
 
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Yes, this post is late. I've been called off to do work. I know, the shame of it.

Minor additions to previous posts:
A lot depends on what size generation is being discussed. For box store stuff, the engine horsepower is just an advertising number, similar to Sears 6HP compressor - and it has a 15A cord cap - yeah, ok, sure. The number is meaningless - a lie.

Once one gets above, maybe 50KW, and stays with 3ph, the generators are rated in KW, generally at .85pf, and may or may not have a KVA rating. The KVA rating doesn't matter too much, it is the KW/pf. But the KVA is needed.

The KW is a driver limitation. At rated RPM, that's all the torque the driver shaft will put on the alternator shaft. If one adds more load, the driver slows down.

The KVA is an alternator heat loading spec. As the KVA goes up, the stator current goes up, and the heat goes up. Driving into a highly reactive load, the current could be at nameplate, but the driver throttle is pulled clear back. KW is low, and the alternator current is high. And the stator gets hot.

Then there are a couple of more limiting issues:
  1. With high lagging loads (inductive) the rotor current is also high. The voltage tends to swag, and the regulator compensates by jacking up the rotor current. This adds significant heat to the stator. So, for lagging loads, the KVA rating is lower than nameplate.
  2. With high leading loads the voltage tends to climb. The VR reacts by lowering the rotor current. And that reduces the magnetic flux in the rotor/stator air gap. That magnetic field is what transmits the power from the driver shaft (rotor) to the stator. With less magnetic flux, less power can be transferred. So, for leading loads, the KVA rating is lower than nameplate.
  3. And sometimes, in the leading KVA, low KW quadrant, there will be a small quarter circle cutout. If this one shows up, it is from VR instability. This one is rarely a problem. The generators rarely operate in this area.
All this data will be on a Generator Capability Curve. See the attached sample.

The driver horsepower does not show up on this curve anywhere. The gen manufacturer rates the generator for a specified KW. And they will list all the limitations - ambient, altitude, power factor, duty cycle (prime, continuous, standby). And they will supply a driver that will do that. The driver has to supply the engine auxiliaries, coolers, alternator friction and windage, exciter, power loss to alternator impedance, and other stuff that eludes me. However they tend to not add even one extra mouse power - cause that costs money.

So, if the driver horsepower showed up on a generator spec, I would look for the context. If it were part of the MFG describing an industry standard engine they were buying as part of the spec, I would be okay with that.

But if it were a color glossy ad proclaiming, "We provide a FULL 100hp engine with all our 50KW gens!" I'd be thinking - Ah-ha they hired a Sears ad campaign writer. I wonder what else they are lying about.

Generator Specs - per the worm
 

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  • Gen capability curve.pdf
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Besoeker3 said:
Goodness...........
P=Tώ.
That's it.
Click to expand...

That's when you use a physicist's consistent set of units. Such as Watts, Newton-meters, and radians per second. Who's ever seen radians/second on a machine's datasheet? Usually you see RPM, which is why 2*pi/60 shows up.

No such system of units involves the horsepower, so you'll inevitably have unit translation factors when horsepower is involved. A unit invented to compare engine power to the performance of draft horses, at a time when most mechanical power came from muscles in some form or another.
 
Carultch said:
That's when you use a physicist's consistent set of units. Such as Watts, Newton-meters, and radians per second. Who's ever seen radians/second on a machine's datasheet? Usually you see RPM, which is why 2*pi/60 shows up.

No such system of units involves the horsepower, so you'll inevitably have unit translation factors when horsepower is involved. A unit invented to compare engine power to the performance of draft horses, at a time when most mechanical power came from muscles in some form or another.
Click to expand...
I am not a physicist. As an electrical engineer, I use SI units. As does the rest of the world.
 
Besoeker3 said:
I am not a physicist. As an electrical engineer, I use SI units. As does the rest of the world.
Click to expand...
News Flash: All electrical engineers use SI units in electrical. That's the only electrical units there are.

Be that as it may, don't feel bad. You guys and girls will catch up one of these days. And hopefully you (as in "all y'all") don't screw up the Brit pint during your catchup

As for the physicists: NASA did figure out that rocket surgery and SI do go well together. Pounds (force), Pounds (mass), Slugs ... yuk
 
iceworm said:
News Flash: All electrical engineers use SI units in electrical. That's the only electrical units there are.
Click to expand...
We don't specify motors in horsepower, energy in BTU, area in acres, distance in feet and inches, conductors in AWG..........etc
 
Besoeker3 said:
We don't specify motors in horsepower, energy in BTU, area in acres, distance in feet and inches, conductors in AWG..........etc
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Ugh - you got me.
I agree, the next time I specify generator electrical area, I'll use 4047 X 10^20 angstroms^2 as opposed to acres

Curiosity Q: What do you use for metric seconds?

(edit to add) Arg - another question:
Would one think an excellent SI unit for automotive fuel economy would be "per meter^2" ?
 
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iceworm said:
Ugh - you got me.
I agree, the next time I specify generator electrical area, I'll use 4047 X 10^20 angstroms^2 as opposed to acres

Curiosity Q: What do you use for metric seconds?

(edit to add) Arg - another question:
Would one think an excellent SI unit for automotive fuel economy would be "per meter^2" ?
Click to expand...
AKAIK, Brits still use miles for distance and maybe inches for automobile wheel diameters.
 
drcampbell said:
... My all-time favorite Diesel engine, (yeah, I'm the sort of ubergeek who has an all-time favorite engine) the General Motors 567, developed 100 horsepower per 567 cubic inches. ...
Click to expand...
Ah - 567 in^3 per hole - an EMD. Nice choice, 900rpm, V6 to V16.

I'm at the other end. My all time favorite is a 6/1 LIsteroid, 82 in^3, 6 hp, thumping away at 5 hz (600rpm). Although as old as the design is, it probably should be "5 cycles".
 
iceworm said:
... Would one think an excellent SI unit for automotive fuel economy would be "per meter²" ?
Click to expand...
Fuel consumption is a better measure than fuel economy. Much less confusion and no need for harmonic averaging.
Fuel consumption on a mass basis equalizes different fuels.
My vote is for kg/m.

Most of the world -- other than the USA -- uses liters/hectokilometer.
 
iceworm said:
News Flash: All electrical engineers use SI units in electrical. That's the only electrical units there are.
Click to expand...

There are units in the no longer used CGS (centimeter-gram-second) metric system for electromagnetism concepts. This is the system with dynes and ergs, that are impractically small units of force and energy. The only one I know about that is still used today, is the Gauss. Tesla is its Si counterpart. Measuring magnetic field, or the quantity more precisely known as magnetic flux density.

The Franklin is the CGS unit for charge, like the SI System's Coulomb
The Biot is the CGS unit for current, like the SI System's Ampere
The statvolt is the CGS unit for electric potential, like the SI System's Volt
The Maxwell is the CGS unit for magnetic flux, like the SI System's Weber
 
Carultch said:
There are units in the no longer used CGS (centimeter-gram-second) metric system for electromagnetism concepts. This is the system with dynes and ergs, that are impractically small units of force and energy. The only one I know about that is still used today, is the Gauss. Tesla is its Si counterpart. Measuring magnetic field, or the quantity more precisely known as magnetic flux density.
Click to expand...
You can still get phonograph cartridges and their compliance (how much the needle moves vs. force) is still measured in cm/dyne like they have for many decades. But that's the only thing I know that still uses dynes exclusively.

By the way physicists often normalize certain physical constants to just the number 1 (unity) to simplify their equations, using so-called "natural units." There are various such systems of units depending on the sub-specialty in physics. This simplifies equations but you really have to know what you're doing because it's easy to lose track of things when the units seem to go away, and you can't rely on dimensional analysis to check your results.

Natural units - Wikipedia

en.wikipedia.org en.wikipedia.org
 
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