It seems like I remember that someone here was looking for a PTO-Driven Generator recently (?) ... so I thought I would pass on this link to Harbor Freight that I came across.

I wonder if there is a significant Fuel Efficiency trade-off between running a generator with it's own engine, and running a generator with a tractor PTO?

Depends on the tractor, but in general, PTO generators are not as efficient with regards to fuel as a stand alone genny. This is pretty obvious when you consider that the tractor engine involved may be 25-70 HP, while a typical genny is less than 25 HP (often a lot less).

The PTO genny gives you easy portability and they tend to crank out a larger amount of power than the smaller units, so they do have some uses. Just make sure you have lots of fuel.

Greg

The thing about tractor implements is you need to be able to dedicate a tractor to them.
However if you already have a tractor you save the cost of buying a separate motor and paying to maintain it.
That does not sound like much if you are only thinking of one generator.
If you are thinking of several implements then the costs start to add up. They soon add up to where it is cheaper to keep two or more tractors than buy a bunch of different motors.
So with one tractor your PTO can run a mower, a bailer, a snow blower, a grain auger, a generator, a bail elevator, a water pump and a host of other items. The only restriction is you can't run more of them at one time than your tractors will power.

A short note about PTO.
You can run shaft, belt, air or hydraulic PTO on most tractors now. Some tractors are equipped with fairly large onboard generators to power electrically driven implements.

If the amount of electrical power you need is limited, in most cases it is easy to manage to keep it small, it is often easier to run loads off an inverter that feeds of a motor vehicles electrical system than an actual generator. On remote sites I have often used an inverter running off the battery in the truck, with the engine running if there is any significant load, to run a few lights and a power tool off and on.

The inverter is lighter, smaller, and a lot easier to set up than any generator. It is also pretty much silent.

When the lights went out after a storm a year ago I ran my computer, a small light and a small fan for a few hours on the inverter. Then changing over I ran the refrigerator. The fridge had to be run on its own because starting dropped the voltage quite a bit but I got by running it roughly twenty minutes every hour on average and had no losses as long as I ran it at least once every two hours in round figures.

The inverter I used that time was a small 750 watt unit that produces a stepped sine wave so a fluorescent light I tried didn't like it but the computer, running a fairly sophisticated and over-sized power supply, didn't so much as blink. Then again it isn't the most power hungry computer made.

I have a generator but the inverter was easier and juggling the power wasn't that hard. I have been thinking of setting up a system of the generator, and inverter, and a couple of deep cycle batteries.

Adding an inverter and batteries I should be able to get by with a tiny generator barely capable of handling the biggest loads. Smaller generators use less fuel in standby, about 70% of run time typically, so efficiency should be much greater. During periods of low use, when there is just a tiny light and a radio perhaps, the generator can be recharging the batteries. Once the batteries are topped up the inverter can run on them and the generator can be off.

The PTO generators I have seen need to run at a minimum RPM, usually a pretty high one.

So, as others have suggested, it depends on whether your load matches the generator, and whether the generator matches the engine that's driving it.

If you're running a much larger engine at a high RPM without needing the torque/horsepower it can provide, you're wasting fuel.

But there are other considerations -- larger, commercial-grade engines that are run and maintained regularly tend to be far more reliable than small, consumer-grade engines that are only run occasionally. And, despite potential fuel waste, the "care and feeding" of one engine is simpler and more efficient.

If you could put some sort of transmission between the PTO and generator, and find the sweet spot between RPM and torque, you would do much better fuel-wise. Wonder if that exists?

There is an interesting thought. I'm assuming we are talking about a diesel engine.

Jeanette Isabelle

BTW, larger tractors have a dual speed PTO -- 540 RPM and 1000 RPM. If your tractor is significantly larger than what the generator requires, you could conceivably change the drive shaft to accept the 1000 RPM spline and throttle down 50%.

A lot of the commercial/farm PTO generators have gearing built in. Some are made with belt transmissions so the rpm from the PTO could be matched easier than with a direct gear drive. they change the size of the pulleys.
You should still be matching the RPM to get the frequency right on most of them. Voltage and current are usually handled electronically now with the tractor governor just handling the RPM and the fuel to keep it steady under different loads.
Some gennies use an electronic signal from the generator to control the motor speed.
You might find some other information about them on this page.
http://www.omafra.gov.on.ca/english/engineer/farm_mech.htm