PTO generators

[Patrick NC]

I've recently been looking at buying a 15-25 kw pto generator for emergency power and for extra power at the sawmill. I've got a 25 hp Kubota and a 55hp ford tractor for options to power it. I would prefer to use the Kubota because it's easier on fuel, but it might not have enough power to run this size generator.  Max electrical load at the mill would be 50 amps. Has anyone used one of these for a similar application? Any input would be appreciated. 

[beenthere]

There is info on the web to size for what you want and what you will need. 

[FAQ]: What Will a 10000 Watt Generator Run? Tips & More [AUTUMN 2022]

Might help you decide. 

[scsmith42]

Patrick, I owned a PTO generator for a short while, and ended up getting rid of it.  It was fine for sawmill or barn use, but the problem with using it for the house was that it had no way of governing the engine when the electrical load changed.  Basically you set the tractor RPM, but as the generator loads down the RPM will drop and thus your voltage and 60HZ drops too.  This isn't good for some electronics.

Standalone generators have a governor that keep the voltage and hertz in the proper range.

The standard HP to KW ratio for generators is 1.8HP is required for every KW.  So a 10KW generator will require at least an 18hp engine. 

So your 25HP Kubota should be good for around 14KW and your 55hp Ford (assuming that's PTO HP) would be good for 30KW.

[Ianab]

The amount of Tractor you need depends mostly on the load, not the size of the generator.  Obviously a larger generator being fully loaded will need more grunt. So if you got a 25kw generator, but if you only need 10kw at the time, then the 25 hp tractor should be fine.  Hook up 25kw of load, and it will need the bigger tractor. 50 amps at 120V is 6 kw, so the 25hp tractor should deliver. There is some fiddle factors involving VA vs Kw and power factors etc, so allow for that, but if your power needs are only 1/2 what the tractor can provide, you should be fine. 

If you are wanting to power electronics, they you want an Inverter generator of some sort. The output is then produced by the electronics and stays stable, even if the engine revs fluctuate a bit. 

[chevytaHOE5674]

I have a 25kw pto generator. It takes a big hp tractor to run it and maintain rpms when starting loads. Your tractor has a governor and will try to maintain pto speed as load increases, but with a small HP tractor sometimes that's not fast enough. 

I run mine on a 125hp at the pto tractor and if you start high amp loads it will pull the tractor down for a few seconds as things recover. No big deal for motors, well pumps, stick welder, etc but not good for more sensitive electronics.

[Patrick NC]

I do have a 2000w honda inverter for sensitive electronics. It's just not big enough for any heavy loads. For the most part a bigger generator would be to power stuff at the mill and occasionally running the well, AC, and other big draw items at the house during power outages. A pto generator seems like the best way to get the most power for the least amount of money. 

[chevytaHOE5674]

A decent size gas generator will power most household appliance (ac, well, etc) on less expensive gas and save hours on the more expensive tractor.

A Honda gas engine for example is much cheaper to own, run, and maintain than any diesel tractor. 

When running your tractor is putting wear and tear on hydraulic pumps, valves, clutches, etc all of which likely cost more to replace than an entire self contained gas generator.

[Wlmedley]

I have a 10kw PTO generator that I run with a 20hp MF tractor and a Lincoln Ranger welder which puts out 10kw.Welder has a 24hp Kohler engine.When using to power house when electric is out tractor will use about 1 gallon of fuel every 2 hours and welder will use about 1 gallon of gas every hour. I rigged up a shut down solenoid on tractor to auto shut down with low oil pressure or high water temperature.Have used both quite a bit being outages around here are frequent and haven't had any trouble with electrical equipment.

[Greenie]

I've used a 15,000 watt Winpower PTO generator with no damage to electronics. When a heavy load comes on the governor on the tractor maintains RPMs - there might be a momentary drop in voltage - for a second, but it quickly recovers.

[GAB]

In this area to save fuel and some wear on the tractor, some owners run a 540 RPM generator with the 1000RPM pto shaft.  The tractor rpm's are lower, therefore less fuel consumption.
GAB

[chevytaHOE5674]

To run a 540 generator on the 1000rpm pto shaft at half tractor RPM you need a sizable tractor or a small load as a tractor doesn't have much torque at half RPM to do much meaningful work. 

[SawyerTed]

Running a tractor close to the house to power a generator would be too loud to suit me.  To maintain 540 rpm at the pto, my 52 hp Kubota has to run at 3/4 Wide Open Throttle.  It's pretty loud.  

Parking the tractor in the garage or carport presents its own set of issues for example, where do the exhaust fumes go?  And what about the hot exhaust?  Will it melt and/or blacken the carport ceiling?

My open frame 8,500kW generator with 10hp engine is pretty loud but a few strategically placed panels deflects the sound of the engine. 

When you look at standby generators from other manufacturers besides Generac, it isn't a big leap from a pto model to a standby self contained unit.   Check Cummins or Kohler brand standby generators.  

[scsmith42]

I've used a 15,000 watt Winpower PTO generator with no damage to electronics. When a heavy load comes on the governor on the tractor maintains RPMs - there might be a momentary drop in voltage - for a second, but it quickly recovers.

Wow - what kind of tractor do you have that governs the RPM output on the PTO?  All of mine are just a simple friction lock on a mechanical throttle - no governor at all.
I think that I'm about to get "tractor envy"  :D

[scsmith42]

The amount of Tractor you need depends mostly on the load, not the size of the generator.  Obviously a larger generator being fully loaded will need more grunt. So if you got a 25kw generator, but if you only need 10kw at the time, then the 25 hp tractor should be fine.  Hook up 25kw of load, and it will need the bigger tractor. 50 amps at 120V is 6 kw, so the 25hp tractor should deliver. There is some fiddle factors involving VA vs Kw and power factors etc, so allow for that, but if your power needs are only 1/2 what the tractor can provide, you should be fine.

If you are wanting to power electronics, they you want an Inverter generator of some sort. The output is then produced by the electronics and stays stable, even if the engine revs fluctuate a bit.

Ian, that's great advice.  I've never seen a PTO drive inverter generator, but if such a critter exists that would certainly be the way to go in order to avoid the voltage and cycle problems.

[scsmith42]

I have a 10kw PTO generator that I run with a 20hp MF tractor and a Lincoln Ranger welder which puts out 10kw.Welder has a 24hp Kohler engine.When using to power house when electric is out tractor will use about 1 gallon of fuel every 2 hours and welder will use about 1 gallon of gas every hour. I rigged up a shut down solenoid on tractor to auto shut down with low oil pressure or high water temperature.Have used both quite a bit being outages around here are frequent and haven't had any trouble with electrical equipment.

That's another great option.  An engine driven welder could serve as both a welding source and backup power supply around the sawmill. 

[moodnacreek]

Generating your own power for a small band sawmill will be expensive and a surprising amount of work plus with the cost of diesel fuel, it is hard to get excited about it.  You would want a high voltage [480] 3 phase gen, say 50 kw or smaller if you could find one. This would take care of the head saw, edger and most likely any other motors to be added over time. Next a transformer to get down to single phase and motor starter controls. Or you could use the power co. for single phase and small transformers for your motor controls. Thats what I do. Finding a used take out gen. is the easy part, after that it is all work and money. It is way cheaper to use engines. The big advantage to electric is convenience; push button and saw.

[chevytaHOE5674]

Wow - what kind of tractor do you have that governs the RPM output on the PTO?  All of mine are just a simple friction lock on a mechanical throttle - no governor at all.
I think that I'm about to get "tractor envy"  :D

Um every tractor I've ever seen has a governor in the injection pump (or externally on old gas tractors) to try and maintain engine RPM as load increases.
You set your throttle lever and the pump compensates for increased load/decreased RPM with more fuel.

[Tin Horse]

I currently running a 19 KW PTO that sits in a small shed about 50' from the house. My 7320 Kioti works well. Rated at about 65hp at PTO. It has the normal 540 @ 2500rpm and also an econ speed for light loads. 540 @ 1800 rpm which I always use with no issues. Set and leave it. Runs the whole house and electronics with no problems. Don't hear enough noise to bother us. The issue I have with it is like anything else that sits around for long periods of time is the mice. When you need to run it you'd better do a quick check for damage. I've fixed wiring in it twice so now leave some cover panels open for fast check. Even with traps set it's a losing battle.

[Patrick NC]

Thanks for all the opinions and information.  Really helps me weigh my options.  A generators biggest use for me would be for power tools at the mill and occasionally my lincoln buzz box welder. I was remembering when I was younger we ran a 120 cow dairy barn for 3 weeks on a pto generator hooked to a 75hp Allis Chalmers tractor after a major ice storm. I figured if one would work for that amount of power usage, it would certainly take care of my needs. I've looked into having a new power service installed where my mill is but the cost is more than I want to invest at this time.

[Dave Shepard]

I see pto generators as best for emergency or occasional remote use. I've run my house on one of ours, and with no safeties I don't like to do it. It is also hard to match the tractor to the load. The first time I ran this house on a generator, I had a 115 hp tractor on a 45kw generator for a 300 watt heating load. My 18kw is geared to run at less than 540 pto to make voltage and frequency. 
All tractor engines are governed. The Farmall H would run the dairy barn, but the bigger M wouldn't. The H governor was instantaneous, and the M was too slow to pick up the load.

[chevytaHOE5674]

I have my PTO generator packed in the shop. I keep it for the times when we lose power for an extended period of time and I want to run the entire farm at once.

I have a 10kw gas generator that gets used for running power tools, running the welder (before I bought an engine driven welder), or powering the house during shorter outages. Much more cost effective and user friendly to run for me. Runs on cheap gas, oil changes are cheap, is setup with low oil shut down, and even the wife can hook it up and start it when needed.

[scsmith42]

Wow - what kind of tractor do you have that governs the RPM output on the PTO?  All of mine are just a simple friction lock on a mechanical throttle - no governor at all.
I think that I'm about to get "tractor envy"  :D

Um every tractor I've ever seen has a governor in the injection pump (or externally on old gas tractors) to try and maintain engine RPM as load increases.
You set your throttle lever and the pump compensates for increased load/decreased RPM with more fuel.

Unfortunately mine don't work that way. When I set the throttle lever the engine rpm goes up or down depending on load. I'm dealing with tractors of less than 65 hp so perhaps the larger ones are different.

[Dave Shepard]

What tractor? Any tractor I've ever seen has a governor. From a 1923 Farmall regular to present day. You couldn't run any pto implement without one, or not very well.

[chevytaHOE5674]

Yep if its not adjusting fuel delivery based on load then you have a governor problem. The governor can only compensate for a certain percentage of load change though.

For instance a brush hog mower. If you lift it into clear air and set the throttle for 540rpm at the pto then lower it into thick dense grass then yes the rpms will drop down. But once in the thick grass if you increase throttle for 540rpm the governor should do its best to maintain that rpm in varying pto and engine load. If the engine pulls down and won't maintain rpm then you have too much load for the tractor.

[moodnacreek]

Thanks for all the opinions and information.  Really helps me weigh my options.  A generators biggest use for me would be for power tools at the mill and occasionally my lincoln buzz box welder. I was remembering when I was younger we ran a 120 cow dairy barn for 3 weeks on a pto generator hooked to a 75hp Allis Chalmers tractor after a major ice storm. I figured if one would work for that amount of power usage, it would certainly take care of my needs. I've looked into having a new power service installed where my mill is but the cost is more than I want to invest at this time.

So you where up there then. A customer of mine, a live stock trucker then] moved down here after that storm. They say that was a 500 year event.

[Patrick NC]

Yep. That was my last year up there. No power for 3 weeks,  some folks out for a month and a half. Not fun in January and February.  Don't miss those days at all.

[Greenie]

I've used a 15,000 watt Winpower PTO generator with no damage to electronics. When a heavy load comes on the governor on the tractor maintains RPMs - there might be a momentary drop in voltage - for a second, but it quickly recovers.

Wow - what kind of tractor do you have that governs the RPM output on the PTO?  All of mine are just a simple friction lock on a mechanical throttle - no governor at all.
I think that I'm about to get "tractor envy"  :D

Any tractor I connect the PTO generator to. I've used 3 different tractors - all maintain RPM with varying loads. Kubota L3400, Kubota L4600, John Deere 790. I set the throttle with the PTO generator attached and leave it run. The wife turns on the electric range or electric dryer and the tractor comes under load and continues to supply 120/240 VAC. When the wife turns off the appliances the tractor responds... 120/240.I'm not running outside to adjust the throttle each time a load comes on or goes off.

[Southside]

Yep. That was my last year up there. No power for 3 weeks,  some folks out for a month and a half. Not fun in January and February.  Don't miss those days at all.

Was that '98?  We got about a foot of snow in Aroostook, but the southern part of Maine was decimated.  

[Patrick NC]

Yep. 1998. Where I lived there was 9" of ice. Then more snow and the temperatures plunged to 20 below. We ran 3 farms on that generator. Finish milking at one and move it to the next. Everyone helped their neighbor back then. 

[newoodguy78]

I was milking cows out that way then and remember hearing about that storm but fortunately it wasn't in my area. That type of storm makes for some real long miserable days. 

[scsmith42]

What tractor? Any tractor I've ever seen has a governor. From a 1923 Farmall regular to present day. You couldn't run any pto implement without one, or not very well.

Kioti DK65, and a New Holland 3010.
Perhaps I'm mistaken, but I always interpreted mine as being a simple friction throttle and not a governor.  When I'm mowing, bush-hogging, going up a hill, etc, the RPM will drop depending upon load.  Going downhill the opposite occurs.

[chevytaHOE5674]

You have a governor. The load is just more than it can compensate for.

[DMcCoy]

I run a 15,000 watt Onan on my kubota 1750 (20 Hp)  I know it won't pull it at full load so I adjust.  My kubota has a 2 speed PTO and if my loads are light I use the 848 PTO rpm. 
This saves on fuel big time!  I might burn 5 gallons in 24 hrs and the tractor isn't screaming along while I'm trying to sleep
I use a bar clamp to hold the throttle is position, using the screw clamp allows for fine throttle adjustment.
The biggest thing I have learned is to adjust the PTO speed according to frequency and not voltage. I have a fluke meter with a frequency setting.  Getting the generator dialed in at 60 Hz has been a game changer.
I run electronics through a battery backup which has so far protected my stuff.
My biggest headache and largest automatic load is my submersible well pump.  When it kicks in it causes a lot of flickering. I keep my water heater off unless we are taking showers and then I run it separately.
I run our nursery at the same time as the house and having motor loads is beneficial in my opinion. In my case greenhouse fans. Someone smarter than me could perhaps explain why.  Heater loads don't seem to help as much with smoothing out the power as motor loads.
Lastly I try and keep my generator under constant and consistent load as much as I can.  Having the tractor pulling a little makes it settle down and run smoother.
My generator was cheap to buy and I have used it over 20 yrs without having an incident.  I feel like I still get the expected life out of fridges and freezers. 
The new inverter gen sets are incredibly cheap.  If I was buying today that is probably the direction I would go.
 

[Ianab]

I run our nursery at the same time as the house and having motor loads is beneficial in my opinion. In my case greenhouse fans. Someone smarter than me could perhaps explain why.  Heater loads don't seem to help as much with smoothing out the power as motor lo

Possibly because the spinning motors act like an additional flywheel in the system? If you suddenly dip the voltage to a running motor, it actually generates back EMF from it's momentum and it's power draw will drop off temporarily, much more than a resistive (heater load). That would make it easier for the governor on the tractor to boost the power to match the new load. As long as the dips aren't extreme you barely notice them.

There are also 2 types of computer backup. One simply runs the devices on mains, and if that fails switches over to battery, fast enough so the computer doesn't shut down. A full inverter setup puts all the power into DC (across the battery), and then creates clean power from that DC source. It costs more, but the power is much cleaner as it's fully isolated from any mains fluctuations. 

[Magicman]

There will also be a huge difference in fuel usage between a self-contained unit and the tractor/pto.