PTO Generator

[mo1]

I might run the tractor for a generator too if our power outages were due to storms. But the last several have been due to forest fires and before that floods. So we need the big tractor free to be used. That's why we keep a hundred HP tractor fueled and ready to use.

On 510 vs 540 RPM question.... Voltage output goes down in proportional to the square of the decrease in RPM. That's reasonable for resistance heaters and not so good for computers, lights or TV.
The drop in frequency is less than the drop in voltage. Frequency is just a regular linear thing. i.e. drop the RPM in half and the frequency drops in half as well. But the problem is that it is the 60 cycle frequency is important to keep constant for some computer circuits. And nowadays even the coffee pot has a computer chip.

Best to just run it at the rated speed if you can.
rScotty

The things in your house that you run that particularly care about voltage and frequency being in a narrow tolerance range are induction motors, such as the motors in most air conditioners, blowers, refrigerators, and pumps. Too low of a voltage and they can't make rated power at rated amperage draw, so they draw more current and thus get hotter than they are supposed to. Too high of a voltage and there is flux saturation which also leads to excessive current draw and overheating. Operating speed is directly proportional to frequency, and if the frequency is too low, the motor runs too slowly, and if it's too high, the motor runs too fast. The major issues with this is a typical capacitor-start centrifugal-switch single-phase induction motor generally won't turn off its start circuit until 80-85% of rated speed, and keeping the start circuit energized for more than a few seconds can destroy it. Also, running certain motors too fast can lead to bearing failure, fan failure, or failure of whatever it is driving due to excessive speed. Resistance heaters and incandescent light bulbs can happily run on lower voltage, they simply make less heat/run at less brightness, and lights may flicker if the frequency gets way too out of spec. High voltage will cause premature failure though.

At least remotely modern computers (with an active power factor correction power supply) generally don't care too much about frequency or voltage as their power supplies rectify AC into DC, and this is not sensitive to input frequency, and the DC bus is voltage regulated with a wide regulation range. Look at the power supply on a computer and it will generally be marked for 100-240 volts, 50-60 Hz. Newer commercial lighting with an electronic driver or ballast (newer fluorescents, all LEDs, newer HID lights) have a driver or ballast that works very similarly to the computer power supply, so they are also insensitive to frequency and generally run on a wide voltage range as well (120-277 volts +/- 10%.)

Going back to why some PTO generators are rated for 510 input RPM rather than 540 has to deal with the gearbox used between the PTO input and the generator. Generators have to run at something just in excess of their synchronous speed which is (desired Hz * 60)/(number of pairs of poles in the generator). For a typical smaller two-pole generator, it must be driven at least 3600 RPM to make 60 Hz, and thus a gearbox is required to take a standard PTO speed of 540 or 1000 RPM and increase it to >3600 RPM. I suspect for the 510 RPM units, they took a 1:3.6 gearbox designed to run a two-pole generator on a 1000 RPM PTO and coupled it to a four-pole motor, which only has to be driven at half the speed of a two-pole motor, and thus you would need a touch over 500 RPM to run the motor. The slower-turning four-pole generators are quieter than the two-pole units and I suspect this is really why the 510 RPM units are out there.

 

[LouNY]

I have never put an accurate tach on my pto while it was running the generator.
I adjust the tractor rpm to get 60Hz and I'm also getting 120V/240V at that point. (1800rpm)
I have used standard 540 PTO's Economy 540's and 1000 rpm with adapters at half pto speed.
The Economy or 1000 rpm pto at half speed will depend upon the tractors capabilities and the loads.

Depending on the pto generator it can be a 2 pole (3600rpm) or a 4 pole (1800 rpm),
I have only seen the 2 pole on smaller units and they seem to be more sensitive to load changes
and seem to have less surge capabilities.

With the generator speed being responsible for the Hz the 4 pole design has a heavier rotating mass
to carry it through a surge situation. Also any fluctuations in tractor engine speed is seen as a change in
PTO speed which in turn is the generator rpm, a 2 pole unit is twice as sensitive to those rpm changes
as a 4pole is.

The better generators will have an adjustable Automatic Voltage Regulation (AVR) these will normally
have an adjustment for Voltage and Stability and sometimes a couple of other adjustments.

And as food for thought having a PTO generator is a good reason to have another tractor, a spare tractor
is always nice. It doesn't even have to be 4wd or have a loader to be a very usefull tractor. My IH 574 was less
then $5000 when I bought it and it is what is parked on the generator during the winter. It's chained up and what I
used to use for snow removal before I got my fancy cabbed 4wd tractor. At that time I had two older 2wd tractors
the 574 and an Oliver 1550 both of them could and did run the generator.

 

[mo1]

I have never put an accurate tach on my pto while it was running the generator.
I adjust the tractor rpm to get 60Hz and I'm also getting 120V/240V at that point. (1800rpm)
I have used standard 540 PTO's Economy 540's and 1000 rpm with adapters at half pto speed.
The Economy or 1000 rpm pto at half speed will depend upon the tractors capabilities and the loads.

Depending on the pto generator it can be a 2 pole (3600rpm) or a 4 pole (1800 rpm),
I have only seen the 2 pole on smaller units and they seem to be more sensitive to load changes
and seem to have less surge capabilities.

With the generator speed being responsible for the Hz the 4 pole design has a heavier rotating mass
to carry it through a surge situation. Also any fluctuations in tractor engine speed is seen as a change in
PTO speed which in turn is the generator rpm, a 2 pole unit is twice as sensitive to those rpm changes
as a 4pole is.

The better generators will have an adjustable Automatic Voltage Regulation (AVR) these will normally
have an adjustment for Voltage and Stability and sometimes a couple of other adjustments.

And as food for thought having a PTO generator is a good reason to have another tractor, a spare tractor
is always nice. It doesn't even have to be 4wd or have a loader to be a very usefull tractor. My IH 574 was less
then $5000 when I bought it and it is what is parked on the generator during the winter. It's chained up and what I
used to use for snow removal before I got my fancy cabbed 4wd tractor. At that time I had two older 2wd tractors
the 574 and an Oliver 1550 both of them could and did run the generator.

You can get a fairly good estimate of your PTO RPM by looking at your engine tach and comparing what your engine speed is compared to what it would be running when it's at full rated PTO speed and dividing.

I would be pretty leery of running a 1000 RPM PTO at half speed for a generator. The engine is being run well below its powerband, and on most of the tractors I've run that have had a 1000 RPM PTO, it would put the engine speed a couple hundred RPM above idle rather than 1200-1500 RPM above for full PTO speed and about 800-900 RPM above idle for economy PTO. An engine running at that low of a speed doesn't react very well to changes in load and with the multiplication of the 1000 RPM PTO gearing, it would lead to much wilder swings in generator speed with load changes than running the engine at a higher speed with the 540 RPM PTO gearing would.

A four-pole generator is going to have a slightly heavier rotor with slightly more magnetic flux than a two-pole generator of the same kVA rating, which would help a smidge with dealing with load. However, changes in engine speed are going to lead to the exact same changes in frequency as there are two multiplication factors used to get frequency and voltage- input gearing and then synchronous speed. Let's say you have a tractor with full 540 RPM PTO speed at 2000 engine RPM. For a four-pole generator, you will have a 3:10 gearset to yield 1800 RPM. For a two-pole generator, you will have a 3:20 gearset to yield 3600 RPM. So, let's say your engine sags 100 RPM to 1900 RPM in each case. Your PTO speed drops 54 RPM to 486 RPM. Your four-pole generator speed drops to 1620 RPM. Your two-pole generator drops to 3240 RPM. Both systems yield 54 Hz and assuming the V/Hz curve is the same shape, yield the same voltage loss.

 

[ROUSTABOUT]

Actually, at the advertised RPM it produces the correct frequency (60 cycle). The voltage is secondary.

That's what you run into with them old welding machines. 50 Hz instead of 60 Hz.

 

[LouNY]

You can get a fairly good estimate of your PTO RPM by looking at your engine tach and comparing what your engine speed is compared to what it would be running when it's at full rated PTO speed and dividing.

I would be pretty leery of running a 1000 RPM PTO at half speed for a generator. The engine is being run well below its powerband, and on most of the tractors I've run that have had a 1000 RPM PTO, it would put the engine speed a couple hundred RPM above idle rather than 1200-1500 RPM above for full PTO speed and about 800-900 RPM above idle for economy PTO. An engine running at that low of a speed doesn't react very well to changes in load and with the multiplication of the 1000 RPM PTO gearing, it would lead to much wilder swings in generator speed with load changes than running the engine at a higher speed with the 540 RPM PTO gearing would.

A four-pole generator is going to have a slightly heavier rotor with slightly more magnetic flux than a two-pole generator of the same kVA rating, which would help a smidge with dealing with load. However, changes in engine speed are going to lead to the exact same changes in frequency as there are two multiplication factors used to get frequency and voltage- input gearing and then synchronous speed. Let's say you have a tractor with full 540 RPM PTO speed at 2000 engine RPM. For a four-pole generator, you will have a 3:10 gearset to yield 1800 RPM. For a two-pole generator, you will have a 3:20 gearset to yield 3600 RPM. So, let's say your engine sags 100 RPM to 1900 RPM in each case. Your PTO speed drops 54 RPM to 486 RPM. Your four-pole generator speed drops to 1620 RPM. Your two-pole generator drops to 3240 RPM. Both systems yield 54 Hz and assuming the V/Hz curve is the same shape, yield the same voltage loss.

I have been around both 2 and 4 pole pto generators and the 4 pole all seemed to be steadier and smoother in operation.
Yes, when using a 1000 pto the tractor was much larger then needed (CIH 7220 with the 8.3 Cummins engine) it runs a 25-35 Kw
generators on the 1000 just above an idle very well.

Now these numbers you have for a gears, how did you come up with them?
A 540 rpm output to a 2 pole 3600 rpm generator will need a 6.666 to 1 gear box,
a 540 rpm output to a 4 pole 1800 rpm generator will need a 3.3333 to 1 gear box.

At 2000 (engine rpm) to 540 needs a 1 to 3.7 ratio in the pto then the 3.3333 to 1 in the generators gear box to get back to 1800 generator rpm.
So lots of gearing to get back to almost the same rpm 2000 to 1800 rpm.

And again at 2000 (engine rpm) to 540 pto rpm 1 to 3.7 in the pto then to 6.666 to 1 in the generators gearing to get to 3600 rpm.
So again lots of gearing but now it has to do 2000 engine rpm to 3600 generator rpm the generator has to turn 1.8 times faster then the engine.


Then 1900 engine rpm would be 513.5 pto rpm so the 4 pole generator would be 1711.5 rpm.
1800-1711.5= 88.5 rpm loss or about 57 Hz.

!900 engine rpm to 513.5 pto rpm to the 2 poles 6.6666 would be 3423 generator rpm
3600-3423= 177 rpm loss or also about 57 Hz.

So yes the change in Hz would be the same but from observation of both it has always seemed like the 4 pole has been much more stable.

 

[newbury]

For the frequency if you search my name I have a post on adding a good digital meter that will give voltage, current and frequency self powered by the generator. I have all of the details of the meter and how I wired it in with pictures.

PTO generator volt meter upgrade.

I recently got a good deal on a Voltmaster PTO 15/12 generator on craigslist. While it ran great the volt meter is hard to see from the tractor seat and while I could have marked the gauge so I could just rev the tractor until the needle is in the green I thought I would try and add a better...

www.tractorbynet.com

 

[newbury]

One thing to remember is that a PTO generator may need to be "flashed" if left unused.
linky

I bought a lightly used Winco 12KW about a decade ago, and have only tested it twice. I'm expecting I may need to "flash" it this summer

 

[mo1]

I have been around both 2 and 4 pole pto generators and the 4 pole all seemed to be steadier and smoother in operation.
Yes, when using a 1000 pto the tractor was much larger then needed (CIH 7220 with the 8.3 Cummins engine) it runs a 25-35 Kw
generators on the 1000 just above an idle very well.

Now these numbers you have for a gears, how did you come up with them?
A 540 rpm output to a 2 pole 3600 rpm generator will need a 6.666 to 1 gear box,
a 540 rpm output to a 4 pole 1800 rpm generator will need a 3.3333 to 1 gear box.

At 2000 (engine rpm) to 540 needs a 1 to 3.7 ratio in the pto then the 3.3333 to 1 in the generators gear box to get back to 1800 generator rpm.
So lots of gearing to get back to almost the same rpm 2000 to 1800 rpm.

And again at 2000 (engine rpm) to 540 pto rpm 1 to 3.7 in the pto then to 6.666 to 1 in the generators gearing to get to 3600 rpm.
So again lots of gearing but now it has to do 2000 engine rpm to 3600 generator rpm the generator has to turn 1.8 times faster then the engine.


Then 1900 engine rpm would be 513.5 pto rpm so the 4 pole generator would be 1711.5 rpm.
1800-1711.5= 88.5 rpm loss or about 57 Hz.

!900 engine rpm to 513.5 pto rpm to the 2 poles 6.6666 would be 3423 generator rpm
3600-3423= 177 rpm loss or also about 57 Hz.

So yes the change in Hz would be the same but from observation of both it has always seemed like the 4 pole has been much more stable.

The gear ratios are what will turn 540 PTO RPM to either 1800 or 3600 RPM at the gearbox output shaft, which is directly coupled to the generator rotor shaft. 3:10 will turn 3 input rotations into 10 output rotations (1:3 1/3) for a four-pole generator and 3:20 will turn 3 input rotations into 20 output rotations (1:6 2/3) for a two-pole generator. I just used proper fractions rather than 1: a rounded decimal as it is easy to do that with ratios and gives an exact answer. You also have the ratios backwards as ratios are expressed as input : output and you need to increase the output speed relative to the input speed as the generator must be spun faster than the PTO spins.

EDIT: edited to remove the silly auto-inserted smiley face icon, apparently the Facebook generation designing web forums assumes everything is a text message and doesn't think anybody will ever do any math...

 

[Rod in Forfar]

If you use a Killawatt and set the tractor's throttle to deliver 60 hz, the specs won't matter. I run a 7.5 Baumalight on an 18 hp diesel turning the pto at 740. It requires 7 hp worth of fuel and wastes little.

 

[Like Tractors]

Using a tractor with an electronic governor, once you set the throttle to 60 Hz it doesn't matter what load you put on the generator up to the input Horsepower capacity. That is with a good quality PTO generator like a Winco 27PTOC4 that uses Automatic Voltage Regulation. With a light load fuel consumption is low.