Oil & Fuel Kohler 30KW standby generator

[5030]

A little clarification....

Chances are, if the power unit is diesel, the alternator head will be 4 pole simply because most diesels, with the exception of small, single cylinder ones like Hatz are designed to turn an optimum rpm of 1800 for fuel efficiency, torque rise and longevity....

Whereas, gasoline engines because of their design, are more efficient at a higher rpm, thus a 2 pole head and 3600 rpm.

Understand, an alternator (in a standby unit) don't need to turn 1800 or 3600 rpm to produce power. On the contrary. The alternator will produce useable power at a lower or higher RPM, it's just that the Hz (hertz) won't be 60 cycles.

...and it's not about horsepower when driving an alternator head, it's about torque because as the load increases, so does the resistance to rotation of the armature. Torque is the force necessary to overcome that resistance, not horsepower, which is why companies that build standby units dont blow about horsepower because horsepower means very little,

The exception would be a coupled alternator like a Winco where a gearbox increases the PTO speed from 540 to the required alternator armature speed, 1800 or 3600 as the case may be.

I won't get into inverter units because it will just muddy the water, suffice to say that an inverter unit capable of providing standby power in sufficient quantity to power a whole house or farm operation is out of the reach of most folks, me included.

 

[JB4310]

A little clarification....

Chances are, if the power unit is diesel, the alternator head will be 4 pole simply because most diesels, with the exception of small, single cylinder ones like Hatz are designed to turn an optimum rpm of 1800 for fuel efficiency, torque rise and longevity....
That's right, only if it's a multi cylinder diesel, have yet to see a single cyl diesel 4 pole genset. You mention hatz, that may of been one of the first diesel whiz bangers, but now there are countless 1 cyl diesel, air cooled 3600 rpm units out, almost exclusively from china.
Seems multi cylinder is needed to to hold hz in spec at lower rpms regardless of hp, which I believe is due to the greater spinning mass of the heavier engine (flywheel effect)

Whereas, gasoline engines because of their design, are more efficient at a higher rpm, thus a 2 pole head and 3600 rpm.
No argument here, except the effieciency part, especially when compared to diesel. They just don't make their HP till they get into the higher rpms


Understand, an alternator (in a standby unit) don't need to turn 1800 or 3600 rpm to produce power. On the contrary. The alternator will produce useable power at a lower or higher RPM, it's just that the Hz (hertz) won't be 60 cycles.
Mute point cause you have to maintain hz within ~5% I believe ?

...and it's not about horsepower when driving an alternator head, it's about torque because as the load increases, so does the resistance to rotation of the armature. Torque is the force necessary to overcome that resistance, not horsepower, which is why companies that build standby units dont blow about horsepower because horsepower means very little,
This is an area I'm not well versed in, but from my observation every generator that I have read the specs on holds to that 2 hp per kw rule.
From little 3kw disposables to large 30-50 kw units. I don't completely understand all the forces going on but it's obvious hp does play a critical and predictable role.

The exception would be a coupled alternator like a Winco where a gearbox increases the PTO speed from 540 to the required alternator armature speed, 1800 or 3600 as the case may be.

I won't get into inverter units because it will just muddy the water, suffice to say that an inverter unit capable of providing standby power in sufficient quantity to power a whole house or farm operation is out of the reach of most folks, me included.

I know by reading some of your other posts you have way more mechanical knowledge than I'll ever have. But I don't think anything I mentioned contradicts anything that you have clarified. Just put in a different way.

I'll address some things in different colored text above.

I have been interested in home generators for a few years now, trying to understand all I can, so I don't mind be corrected.

Really all I'm trying to understand and point out is the obvious, A gas engine is far cheaper than a diesel, that's why gas gen set, even a 30 kw is going to be a 2 pole, to utilize it's max hp range, no doubt it would use a little oil. It's the most economical way to produce a generator, but depending on how much that gen will get used will ultimately determine if it's the most economical to own and operate.

And BTW this subject is even closer to my heart this past week being in a state that had nearly a million people out of power, with some still in the dark/cold.
People are literally dieing in their houses from this disruption.
I did not lose power, but I'm always thinking about the doomsday scenario.

JB

 

[wrede]

The conversion from kw to hp is 1.341, and so a 30 kw rating means about 40 hp. The ratings are true, but the code requires one to look at connected load, and so the actual average running load is probably 30-50% in the worst case. The motor is running at 3600 rpm to assure the frequency, but the load is only a fraction of maximum. These generators are rather low priced, and so they have to be designed for the least cost, and a two pole alternator is definitely simpler than a four pole. It's quite normal for a gas engine, especially one designed for cars, to achieve its maximum horsepower in the range of over 3000 rpm.

 

[JimP]

"Why change the oil viscosity? is it still within the manufactures recommendation?"

Hi JB. For expected temperatures Onan listed a number of possible oils from 5w30 to 15w40. The generator goes back well before 5w40 synthetics existed but I felt comfortable making the change. It also allows me to use one oil for all of the 4 stroke equipment.

10-12 kw would be ideal but I can't complain as the 7.5 ran everything we needed at about 0.5 gallons/hour average. Given the last couple of months I want to tie the rest of the house into the generator supply.

Wrede - since both choices have a hot viscosity of 30 would there be an improvement in usage? Was the oil in the Kohler generator mineral oil based or synthetic based?

 

[Gale Hawkins]

Well that's it, that engine would never make enough HP at 1800 rpm for 30 KW. And if you were really taking 30 KW off the generator that would be every ounce of reserve that engine could produce. so basically it would be flat out and would help explain the oil consumption.

The engine would have to be direct coupled to the gen head, so it would be turning 3600 as well. Typically the rule is 2 hp per KW, but it must be something a little less than 2hp/kw for 52 horse to make 30kw. Unless that 30 kw is it's surge rating and it's continuous is more like 25KW???

I think, actually I'm pretty sure it's not that a 2 pole gen head is cheaper to make (can't be a big difference in price) it's that a disposable gm 4 banger is far cheaper than comparable diesel power would cost, it would likely double the cost of the gen-set.

JB

Good points.

That small of a gas engine then factor in the lower power from propane means a serious under powered generator if trying to run it fully loaded but this is typical for back up generators based on three that we own.

TWO real world HP per KW out output is required as noted. Rated HP and real world HP can be two different animals. :laughing:

 

[wrede]

According to the Kohler spex, the 30 KW generator is rated at 120/240 V at 70 degrees F. The engine is rated at 52 hp at 3600 rpm when running on LP gas. This equates to 38.8 KW, and so the engine has lots of reserve. These ratings are from established technical standards, and so they are comparable. At higher temperatures and high altitude the ratings are lower.

This unit is running synthetic oil. The question about 5W-30 and 10W-30 both having a hot viscosity rating of 30 is an interesting one. I've seen articles claiming that with the 5W-30, oil consumption will be higher, but it does seem to make sense that if the hot viscosity is the same, why would the consumption not be the same.

For continuous use, there would be no question that a diesel motor would last longer.

 

[5030]

I know by reading some of your other posts you have way more mechanical knowledge than I'll ever have. But I don't think anything I mentioned contradicts anything that you have clarified. Just put in a different way.

I'll address some things in different colored text above.

I have been interested in home generators for a few years now, trying to understand all I can, so I don't mind be corrected.

Really all I'm trying to understand and point out is the obvious, A gas engine is far cheaper than a diesel, that's why gas gen set, even a 30 kw is going to be a 2 pole, to utilize it's max hp range, no doubt it would use a little oil. It's the most economical way to produce a generator, but depending on how much that gen will get used will ultimately determine if it's the most economical to own and operate.

And BTW this subject is even closer to my heart this past week being in a state that had nearly a million people out of power, with some still in the dark/cold.
People are literally dieing in their houses from this disruption.
I did not lose power, but I'm always thinking about the doomsday scenario.

JB

JB...

Actually, rated power (as it pertains to horsepower or realized torque) plays no role in sizing a standby. All standby gensets are rated by output power, usually in KW (1,000 watts). As long as one purchases a genset with adequate output, realized horsepower/torque is not important. Manufacturers have already load tested their products so they know full well, what the output is.

The other factor is the diesel factor. A deisel genset in comparison to a gasoline or vapor (NG-LPG) genset will cost more so you have to look at the payback versus the cost plus, standing diesel fuel in the genset's fuel tank, infrequently used, can go bad and grow algae much like the new gas we have gums fuel systems (something I deal with with my motorcycle collection).

A vapor powered genset (LP-LPG) will never have fueling problems.

In my instance, I knew going in that a 17KW genset would not cover all my power needs but would supply enough power during an outage to run important items like the stove, washer/dryer, well pump, some lights and the furnace.

 

[wrede]

At my place, I have a 12 KW Kohler, and it is hooked up to a bunch of lights and outlets, the alarm/telephone/wifi/TV circuits, electric garage doors, well pump, 2 refrigerators, and oil fired furnace and three air handlers. Based on last week's 6 day outage, and a 3 day outage in September, and the known LP usage, I guesstimated the average load at maybe 15-20%, using the manual's expected fuel consumption.

 

[Gale Hawkins]

According to the Kohler spex, the 30 KW generator is rated at 120/240 V at 70 degrees F. The engine is rated at 52 hp at 3600 rpm when running on LP gas. This equates to 38.8 KW, and so the engine has lots of reserve. These ratings are from established technical standards, and so they are comparable. At higher temperatures and high altitude the ratings are lower.

This unit is running synthetic oil. The question about 5W-30 and 10W-30 both having a hot viscosity rating of 30 is an interesting one. I've seen articles claiming that with the 5W-30, oil consumption will be higher, but it does seem to make sense that if the hot viscosity is the same, why would the consumption not be the same.

For continuous use, there would be no question that a diesel motor would last longer.

wrede 52HP only equates to 26 KW and not the 38.8 KW you posted.

While the 2 HP requirement is a solid number to use the wild card is the who/how of the HP rating. :B

When a marketing department is involved there may be some creative math involve.

Derate the rated HP by 20% if you seriously want to know the max long term output in a life or death usage case.

In this case for 24/7 use weeks at a time the Kohler 30KW stand by generator in question would be able to do about 20 KW of continued output.

A 6000 watt rated cheap gas generater may be good for around 4000 watt continued loads.

Now I just derate the engine HP by 20% and divide that number by 2 to get the expect KW output of a basic generator.

In the case you mentioned then that would be 52HPx.8/2 or 41.6/2 for an expected 20.8 KW output from this Kohler 30KW stand by generator.

What was the load it was running when it was using engine oil?

 

[5030]

We use the 20% benchmark everyday in our business to calculate parasitic losses due to friction and rotational masses as well as lubrication drag.

My thought is I'd never spec a genset taking into account maximum output, nor do I want to explore the upper limit of my 17KW unit. Running any equipment at maximum rated output for hours on end is detrimental to not only the mechanical end of the equipment but the overall life expectancy as well.

I would assume that parasitic loss from a direct coupled genset would be quite a bit less than say a gearbox driven unit but there will still be measurable loss because it's a rotational mass.

On the subject of lube oil, any engine that's running at rated output is playing internal blender with oil, whipping it around with lots of fast moving internal parts so I expect some oil consumption. All internal combustion engines consume oil by their design. Some more and some less.

However, any engine operated close to it's designed maximum output, for a prolonged time will consume more oil than a similar engine operated below it's maximum designed output.