PTO GENERATORS

[Soundguy]

NO

the rpm is tied to the CPS....

you need the rated input rpm to produce the correct frequency. from there as a rough hash.. figure ABOUT 2pto hp per KW generated. paper math says it's closer to near half that.. but real world proof shows otherwise once you get gears and thick oil and spinning shafts and smoke stacks involved.

fuel usage will be based on mechanical load. mechanical load will be based on electrical load.

2 identical tractors and those 15kw gennies running at rated speed, one with a 1kw load, and the other with a 12kw load.. the 12kw load will use more fuel as it is using more hp.

no magic involved..

I have a question about pto run generators. I understand they are made to run at the 540 that the rear pto produces, which on my tractor would be about 2500 rpm.
Lets use a 15kw generator for example. Running the tractor at 2500 rpm the pto at 540 produces 15kw so if i lower the rpm on the tractor i guess it would lower the speed of the pto accordingly correct producing less KW power? I have not contacted a generator supplier yet i figured i would ask you guys. Here is my thinking i don't need 15kw so is it safe to run the tractor at a lower rpm without damaging the generator or must they run at the 540? Thanks for the info yet again

 

[txhillcountry]

I've seen a couple of options to the "high-tractor-rpm" issue (meaning that you're burning more fuel) for running PTO attachments for long periods of time, like generators, pumps, even mowing very large areas.

One is that there are some PTO Generator vendors out there like Power Solutions : PTO Power who will change the gearing on the generator side to allow you to run slower RPMs on the tractor while maintaining the need RPM at the Gen head. Kind of "poor-man's" e-PTO. Somewhat more applicable to the medium to larger HP tractors (roughly speaking, where you have power to spare).

Or, your tractor may have e-PTO, which is an "economy" setting that still gets you 540 rpms out of the PTO while running lower tractor RPMs. My Zetor has this. There's a lever with two settings: Normal and E. On the Normal setting, you set the tractor at 2500 RPMs and you know your getting 540 out the PTO. On the E setting, you put the tractor at 1800 RPMs, and you'll still get 540 out of the PTO, thus saving fuel. Very handy for PTO drive implements that don't need that full "horsepower". My tractor is 65HP.

 

[Soundguy]

wow...

i gues you aren't thinking about the fact that in most cases.. fuel useage is based upon load.. not just rpm.

if your machine is making 10kw of electricity.. it will make little difference if it is doing it at higher or lower rpm.

you have a fuel efficiency and conversion to electricity cal to do.

fuel usage = load for the most part on a modern engine...

I've seen a couple of options to the "high-tractor-rpm" issue (meaning that you're burning more fuel) for running PTO attachments for long periods of time, like generators, pumps, even mowing very large areas.

One is that there are some PTO Generator vendors out there like Power Solutions : PTO Power who will change the gearing on the generator side to allow you to run slower RPMs on the tractor while maintaining the need RPM at the Gen head. Kind of "poor-man's" e-PTO. Somewhat more applicable to the medium to larger HP tractors (roughly speaking, where you have power to spare).

Or, your tractor may have e-PTO, which is an "economy" setting that still gets you 540 rpms out of the PTO while running lower tractor RPMs. My Zetor has this. There's a lever with two settings: Normal and E. On the Normal setting, you set the tractor at 2500 RPMs and you know your getting 540 out the PTO. On the E setting, you put the tractor at 1800 RPMs, and you'll still get 540 out of the PTO, thus saving fuel. Very handy for PTO drive implements that don't need that full "horsepower". My tractor is 65HP.

 

[5picker]

wow...

i gues you aren't thinking about the fact that in most cases.. fuel useage is based upon load.. not just rpm.

if your machine is making 10kw of electricity.. it will make little difference if it is doing it at higher or lower rpm.

you have a fuel efficiency and conversion to electricity cal to do.

fuel usage = load for the most part on a modern engine...

I don't completely agree...
I think what txhillcountry was referring to is if a LARGER HP tractor can sustain a PTO generator at 1800 RPM with an E-PTO (or some sort of gear reduction) to achieve the necessary 540 PTO-RPM's, then you would use less fuel than running that same tractor at 2500 RPM's to attain the same 540 PTO RPM. Again, that's based on the premise the tractor's HP can keep the generator output consistent without adding load.

It's the same as if you are able to run your vehicle down the highway and maintain 60 MPH in high gear at 1000 RPM's... why would you shift into the next lower gear and run it at 1800 RPM's if you didn't need to?

Of course we could get into the argument that a larger HP engine which is 'coasting' uses as much fuel as a smaller HP engine, running at higher RPM's under load, but that's another thread.

 

[Soundguy]

fuel usage is going to be based on load. hard to get around that.

don't matter much if you have a 50 hp tractor, and a 35 hp tractor.. and both are making 20hp worth of electrical load. the larger tractor might use just a hair mor efuel to get mass spun up.. after that.. it's load.. and load is what uses fuel.

as another poster pointed out.. many tractors are most efficient in their power band near normal pto operation speed.. derating to a lower rpm and using an epto may put them in a LESS fuel efficient mode. these things aren't linear.. half rpm is not half hp, and is not half fuel usage.

 

[5picker]

I don't recall anyone saying it was linear or claiming to cutting fuel usage in half. The statement was simply, running at a lower RPM could save fuel.

I've never done it with a PTO generator but I have with other applications.

Again, if you can sustain the generators load at 1500 engine RPM (using a gear reduction or e-PTO) you'll burn less fuel than you will sustaining the load at 2500 RPM.

 

[Soundguy]

fuel usage is based on load. if the load is the same.. your fuel usage is going to be just about the same...

for example.

I can mow my pasture with my 95hp tractor and 15' mower or my 70hp tractor and 10' mower.

takes less time with the 15 mower.. quite amazingly.. by about 30% less time.

also amazingly.. both machines seem to need about 5g to fill back up.

that tells me it takes 5g of fuel in usage to perform the work to cut that pasture.. speed irrelevant.

back before i had the 15' mower.. the largest i had was a 10' mower. at the time I didn't have the 70hp tractor.. but did have the 95 hp tractor. again.. quite amazingly.. it took about 5g of fuel for the 95 hp machine to mow the pasture with a 10' mower... which is what the 70hp tractor also uses.

again.. this tells me it's a load vs fuel usage issue.. other issues are much less of a factor.

less rpm might mean a bit less wear.. though.. my tractor is rated to run at pto rpm for extended periods.. as most are.. som i'm not concerned about using it.. that's what it was made for.

 

[Loadstar]

My Winpower will drop out below a fixed rpm (probably a centrifugal contactor). My guess its about 500 pto rpm. Running low frequency would work for a certain type of load (electric heat, laptop or phone DC power supply, for example). AC motors would overheat.

You can vary frequencies on an AC motor all day long. It is the volts and amps that are critical.

 

[5picker]

fuel usage is based on load. if the load is the same.. your fuel usage is going to be just about the same...

So you are saying if I drive my car down a 2 mile stretch of road at 60 MPH at 1500 RPM's in high gear and drive the same stretch of road in 2nd gear at 3500 RPM's, I'll use the same amount of gas?
Don't tell that to the EPA.

 

[Soundguy]

no.. i didn't say that.

i said equal loads will generally use about the same fuel. you may see some loss difference on a larger machine due to some friction and mass differences.. then again you may see differences the other way based on a machine running outside it's power band and being slightly less efficient.. etc.

we can assume in your 'car' example.. that at least one of the rpm ranges you specify are outside of it's power band ... among other things.. etc..