Is there a way to overdrive PTO speed?

[schmism]

I disagree... fuel usage will be based on load.. not max hp the tractor makes

IE.. My 95 hp tractor and my 70 hp tractor both pulling the same 10' mower to mow the same pasture.. By your logic, the larger tractor will use lots more diesel ( 25hp more! ) to do the same job.

Wonderfull reality is that both use right at 5g of diesel.. telling me the job is being done with much less than 70hp.. etc..

soundguy

is that the same as driveing at 4000 rpm in my truck in 3rd gear doing 55mph and going the same 55mph pulling 1500rpm in 5th gear. Are you saying both options use the same amount of fuel? because its only based on load? (psssttt in that example the load hasn't changed therefor the fuel usage has to be the same?)

 

[Shimon]

which I hate to do since the tractor is spinning the generator with little effort.

How many kW is the generator? I think your PTO is about 40HP. So you could effectively run a 20kW generator. But you are probably running an 8 or 12kW gen (I'm guessing) so the best thing you could do is load up the gen with lights and heaters or whatever loads you have to make your engine work a little harder and prevent light loading the engine. If you have a 20kW gen then load her up to the max.

If you don't have enough loads for the gen then this would be a good excuse to buy a 240VAC hot tub. Just call it a load bank for the tractor.

I know this doesn't answer your question of stepping down the engine speed, but it is a way to keep the engine loaded and prevent light loading the engine (carboned up exhaust). It will use a little more fuel, but at least you will have a warm place to soak your behind.

 

[Iplayfarmer]

is that the same as driveing at 4000 rpm in my truck in 3rd gear doing 55mph and going the same 55mph pulling 1500rpm in 5th gear. Are you saying both options use the same amount of fuel? because its only based on load? (psssttt in that example the load hasn't changed therefor the fuel usage has to be the same?)

Cars, trucks, and tractors are all going to behave differently. I know that in my truck I get a little better mileage pulling a load if I drop it out of overdrive. Lower RPM is not always going to give you the better economy.

It all comes down to what Ken's tractor does. Will his tractor burn more fuel with a light load at 2300 RPM or will it burn more fuel with the RPM lowered to match the load a little more?

 

[Soundguy]

is that the same as driveing at 4000 rpm in my truck in 3rd gear doing 55mph and going the same 55mph pulling 1500rpm in 5th gear. Are you saying both options use the same amount of fuel? because its only based on load? (psssttt in that example the load hasn't changed therefor the fuel usage has to be the same?)

No.. it's not the same. ( But i think you knew that! )

soundguy

 

[rbargeron]

No.. it's not the same. ( But i think you knew that! )

soundguy

It isn't quite the same but it is not far off. The engine wastes a little more friction energy at higher rpm, and it may develop the needed torque a little more efficiently at one rpm vs another, but the BSFC (brake-specific fuel consumption) should be similar - maybe only off 10% or 15%.

 

[Soundguy]

My example comparesa a driven load to a driven load...

not a speed issue...

IE.. tangible work done.

Everybody knows it takes more fuel to get their faster.. so compairing 2 machines with different gearing doing the same speed.. you know the tach'ed out one is gulping more fuel.


soundguy

 

[rbargeron]

.....Without digging into the gear box, which drives the generator, is there any other way, or attachment, I can use to overdrive my PTO so that I can use less RPM running the generator?

I don't know how a JD 3710 is built - so I didn't mention this above. But I have converted my pto so it has 2 speeds for just the reason you're talking about. I didn't dig into the implement gearbox - but I did dig into the tractor's.

If the JD 3710 is available anywhere in the world with a 2-speed pto, maybe you can buy the parts needed to convert yours.

 

[FLHayman]

I have read about, and experienced, better fuel efficiency (with a light load) at low rpms. For that reason, I select the 2 speed PTO on my Kioti DK65 to high and make sure to run just above idle. With a meter on the output of the generator, you could find the perfect rpm. Like soundguy says, this plan of mine wouldn't work in the event that the generator suddenly encountered a big electrical demand, because there would be more of a lag as the governor asked for more fuel, and some amount of diminished horsepower.....but nothing like a gas engine.

I even did some light (I did say 'light') duty mowing with the PTO at high, turning 540, and it worked fine. This is for cases where your tractor can make more power than you would need, but I was impressed with how much torque is available around 1200 rpm.

I think soundguy's experience of having 2 different hp tractors use the same fuel for the same field makes sense.... friction losses would be very nearly the same, since both would be working the same rpm.

 

[john_bud]

is that the same as driveing at 4000 rpm in my truck in 3rd gear doing 55mph and going the same 55mph pulling 1500rpm in 5th gear. Are you saying both options use the same amount of fuel? because its only based on load? (psssttt in that example the load hasn't changed therefor the fuel usage has to be the same?)

Let's say the torque peak (point of maximum mechanical efficiency) is at 2400 rpm. Then lets say that you are severely lugging it in 6th gear and 1000 rpm at 55 mph in one case and feather peddling it in 3rd gear 2400 rpm at 55 mph in the other. You would probably be getting better economy at 2400 rpm.

It's all in the details and assumptions.

But, in general, lower rpm result in lower frictional losses. For diesel engines, the fuel consumption tracks load VERY closely. That's why a 70 hp tractor mowing 10 acres and a 30 hp tractor mowing 10 acres will both use about the same amount of fuel.

 

[JB4310]

still it would be nice to have that high speed pto when you just wanted to have a few lights/TV on, drawing a small load off your genny.