PTO generator

alchemy · Jul 8, 2012

I'm strongly considering building a pto generator setup for my belarus 250AS since that tractor (31HP) seems to get unbelievable hours per gallon, something like 5-10hrs per gallon (diesel) it seems.
I want to make my own from one of the 3 generators I have. I would like to be able to run the tractor at slow speed maybe less than 1000 rpm. I also have several gear reductions or "gear ups" maybe, whatever they are called. Don't know if I can use a reduction type backwards or not. I'm not sure what speed generators need to be or what the PTO speed is at lower RPM. It would be nice to get close the first time since it would take some effort to rig everything. Part of the reason I want to go to PTO is because I hate the speed and loudness of those portable generators. Also, they are expensive on fuel and are pretty unreliable. Any ideas out there?

RoyJackson · Jul 8, 2012

First, you need to determine what RPM those generators require to produce the rated output. Then you can determine how you're going to increase the PTO RPM to the required RPM for the genny.

Running your tractor at the low RPM you suggested may not be good for the engine. Extended running at low RPM isn't good for the main bearings and can result in cold stacking. That is, unless your tractor's engine is designed to run at that low RPM (which I doubt).

JoelT · Jul 8, 2012

What are those "gear ups" you're talking about. I have a 12K pto designed to run at 540rpm which is 2600rpm engine speed for my tractor. I'd like to gear down through something to around 1800/2000rpm. I don't think the motor needs to scream along at 2600rpm to hold rpms for the genny.

alchemy · Jul 8, 2012

Thanks for the tips so far guys!
Roy, what do you think a good rpm is. My RPM gauge doesnt work btw so I assume about 3 K is max and maybe 500 kills it, don't remember. If higher rpm is most efficient then maybe it would only be good for a huge KW or to run something else worthwhile too. 4K is way more than I need during power outages and I imagine the engine power necessary would be small.
Joel, that seems real high to me too. I'd like to be around 750 actually, just a "quiet idle" The "gear ups" would be speed increasers, the opposite of gear reduction, but I forget what they are called. Essentially what you are looking for to slow your engine speed and maintain rpm for the generator.

Ductape · Jul 8, 2012

If your gen heads are off of cheap gasoline generators...... they are usually designed to run @ 3600rpms. Unfortunately..... these are usually one bearing generator heads, which use the engine crankshaft to keep the generator shaft centered. It won't be easy nor cheap to make them work being driven off your PTO (unless you are a machinist). I'm with Roy..... you don't want your tractor lugging @ 1000 rpms. I can see why you might not want it running at 2500, but you'll want to be closer to 2500 than 1000. Changing the gearing is reasonably easy with belts / pullery, or chains / sprockets.

SPYDERLK · Jul 8, 2012

What PTO speeds do you have available? As in Roys reply; Is your gen 1800 or 3600 rpm? I run a 12KW gen requireing 540 to its gearbox from a 25HP 2 speed pto. On the 540pto gear setting the tractor and gen are very happy together all the way to max gen output. Gen power is stable even with large changes in electrical load.

On the 1000rpm PTO gear setting the tractor runs at 1300 rpm to drive the gen at correct speed. RPM varys a lot with load. It works well at continuous light to heavy moderate electrical loads, but the tractor throttle must set for the load and it will bog or overspeed when the load changes significantly. -- A load change of 20% is quite significant. Normally, at full pto rpm a tractor governor holds the engine, and thus pto, rpm pretty stable with varying load. Its much less able to do this at lower tractor rpm.
larry

Dana Warner · Jul 8, 2012

I put this together just before the October New England storm. The tractor was run in high pto speed to cut down on the tractor rpm. When I built it I measured the circumference of the pulleys to calculate the needed diameters of the pulleys to get the correct 540 rpm to the generator speed of 1800 rpm. It is a 7kw onan generator. We did not use anywhere need full output and checked the voltage often. Once set the rpm/voltage was very constant. We ran it 16 hours a day for 7 days.

alchemy · Jul 8, 2012

Lots of great info guys !! Learned a ton already. I guess the clincher for me may be not wanting the tractor engine screaming. That's what I hate about the portable generators already. I cringe just running them an hour the way they sound. Thanks to the info, I need to find some specs on what speed they need to run. I also need to know a good rpm for the tractor. Then I probably need to fix my rpm gauge to see what my rpm is. 1800 may not be bad, don't know. I think I only have a one speed PTO.
My generators are a 2500 homelite with a 5hp B&S, 4000 coleman with an 11HP B&S, a 7-12K, probably onan, natural gas automatic, wisconsin motor. I'd like to use the 4000 because I always have trouble with that motor anyway. I'm not opposed to looking for another used generator to use.

RoyJackson · Jul 8, 2012

alchemy said:
I also need to know a good rpm for the tractor. Then I probably need to fix my rpm gauge to see what my rpm is. 1800 may not be bad, don't know. I think I only have a one speed PTO.

Your tractor is designed to run at what ever RPM is used to operate the PTO. For example, my Deere 4400 PTO speed is about 2600 RPM.
Granted, this seems like the engine would be screaming, but if you ever use off seat operation (tractor would be a stationary power source...such as I do when I'm running a chipper), you get used to the RPM pretty quickly.