Not to hijack, but my tractor has 2 PTO settings one is the standard 540 and the other is 1080 (I think thats right). The dealership told me it was for over seas and not to use it. Could I set the PTO to this position and run at half the RPM to get the 540 RPM needed?
Tom
The answer to the question you asked is obviously, "Yes". To get a specific PTO speed in the "high range" would require only half the engine RPM it would take to get that same PTO speed using the "low range". However, I think your question is really whether or not you could run a generator using that technique.
The generator needs a certain amount of input power at a specific RPM to function properly. That power requirement is the same regardless of what PTO gearing is used. But whatever gearing is used, the PTO output shaft has to be turning at or near 540 RPM.
Your tractor has a "high range" gearing ratio that turns the the PTO output shaft at 1080 RPM at the tractor's engine "PTO Speed". I don't know what that throttle setting is for your tractor, but let's assume its somewhere around 2200-2400 engine RPM. So using the "High range" to get 540 RPM at the PTO to match the generator's requirements, your tractor engine RPM will have to be 540/1080 = 50% of the engine "PTO Speed", or using the example, 1100-1200 engine RPM.
Now, assume the generator operates at 100% efficiency (fat chance of that). In that case, for each KW produced by the generator, your tractor has to supply 1.34 HP at the PTO output shaft. But nothing works at 100% efficiency. Let's assume the generator runs at about 80% efficiency. That is, only 80% of each HP fed to the generator comes out the other side as electrical Kilowatts. That means, instead of 1.34 HP per KW required at the PTO output shaft, you'll need about 1.68 HP per KW. Now, that's not engine power, that's PTO power. If you further assume that the tractor is about 75% efficient in getting engine power out the PTO shaft, you'll need about 2.2 engine HP per generator KW. The rule of thumb is about 2 HP per KW. The above shows how that rule of thumb came about. The efficiency numbers I quoted are strictly off-the-wall estimates, but I don't think they are too far off.
So the real question is, "Will your tractor engine develop enough HP at 1100-1200 RPM to provide the input power required by the generator?" The more power you take out of the generator as electricity to run whatever it is you want to run, the more power you have to put in the generator from the tractor's PTO. As an example, to fully utilize a 10 KW generator, your tractor would have to supply 20 to 22 HP at the PTO. If you're only using 5 KW, even if it's a 10KW generator, you would have to supply only 10 to 11 HP at the PTO.
If your tractor can supply the required power at what is not too much more than idle RPM, you're good to go. If not, the generator will lug the engine down, possibly even to the point of stalling. In any case, the results will be highly unsatisfactory.
Without a set of HP vs RPM curves for your tractor and good efficiency numbers, there's no way your question can be answered "Yes" or "No" with any degree of confidence.