Tractor PTO Generators

[LowGear]

I want to keep my factory 240 volt single phase generator on my Witte.  It turns over pretty smooth that about 750 RPM.  I'm thinking that a side mounted tractor PTO might be the way to go.  How much power do the step up gear boxes on these units eat?  Does this sound feasible? 

I'm over really complicated projects like building a PM low speed PM generator unit to mount on the flywheel.  (It's drilled and tapped for four 1/2 (? guessing from my chair at this moment) inch bolts.  The older I get the more I want KISS built into my projects.

Casey

[LowGear]

I forgot to mention this second generator would be rectified to about 350 volts DC for the Windy Boy I got excited and bought last month. 

I gave up on the mythical induction motor over-spin when I simply couldn't find anyone producing actual in the pocket electricity with one.

Casey

[XYZER]

Most modern tractors have the pto in the rear......some of the smaller have a midmounted pto for a mower deck. Some of the older and smaller tractors have a 2 speed pto....540 and 1080(I think). If you have one on the side it would probably be an older tractor(real old) and have a flat pulley. Not sure of the rpm. I understand the simplify! I rationalized a welder/10kw for my big power needs....turn key .

[Tom T]

Casey what kind and size tractor do you have. Like said most newer one's have a rear shaft pto  some are just 640 rpm and some also have 1000 rpm on a shifter. some lawn tractors had a belt drive for a pto on the front and rear of the tractor.Tom  T

[Thob]

Casey,

Are you asking about using a tractor to power a generator, or connecting a second generator to your Witte using a PTO gearbox to step up the RPM?

I've always assumed that gear drives were fairly efficient.  According to the following link, a simple spur gear runs 98-99% efficient; but I believe that may be the gears only (not including the bearings and seals).

http://www.roymech.co.uk/Useful_Tables/Drive/Gears_Gearboxes.html

Any loss in the gear box is going to show up as heat, which must be dissipated or the gear box will overheat and destroy itself.  If it doesn't have cooling fins, then it probably doesn't dissipate much heat.

I think the PTO gear boxes are setup to step 540 RPM to 1800 RPM, or 3.33:1 ratio.  That gives 2500 RPM on the generator if you operate the input of the gear box from the Witte at 750 RPM.  That would be bit too fast, I would think (lots of power lost in the fan).

[XYZER]

Throb,
I had to re read......yep it could be for the Witte

[LowGear]

Are you asking about using a tractor to power a generator, or connecting a second generator to your Witte using a PTO gearbox to step up the RPM?

Second generator off the side of the Witte via the flywheel direct drive.

I think the PTO gear boxes are setup to step 540 RPM to 1800 RPM, or 3.33:1 ratio.  That gives 2500 RPM on the generator if you operate the input of the gear box from the Witte at 750 RPM.

Hmmmmm.  That is a game changer.  I have a dead Yanmar with three speeds on the PTO.  Beside 540 I can't remember the other two.  Obviously this brainstorm requires more fundamental thought. 

Hey, I could get a 3600 RPM three phase and run it at 2/3s speed.  I'm pretty impressed with these units because the generator cradle is built and the drive shaft is a double universal joint unit.

Casey

[billswan]

Guys all modern farm tractor PTO's run at either 540 rpm at full load or 1000 RPM at full load. Of course with no load the speeds are slightly higher. I will admit there are a few odd cases where this does not hold true.

I do own a tractor that was built from about 1969 to about 1977 that at full load the pto runs 1100 RPM. If you need the pto powered machine to run rated speed you must manually just not fully open the throttle. Tachometer's on most older tractors are usually marked at the point the pto is at the proper speed. Newer larger tractors usually have a separate PTO digital speed readout.

But most pto powered generators would be either 540 or 1000 rpm now days.

Billswan

[Thob]

Running at 2/3 speed probably won't develop full voltage.  The equation for voltage is basically the magnetic field strength multiplied by the RPM (times a factor that depends on the design of the alternator).  The magnetic field strength can be varied by changing the the current in the main rotor (field), which is what the voltage regulator attempts to do.  But if you slow it down too much the voltage regulator and the field may not be able to make up for the RPM loss by supplying more current.  Plus you risk burning something up.  In addition, modern regulators have a speed sensor in them to keep problems at bay, most turn off below something like 55 Hz.

But if you do go that route, here's a guy that has a large quantity of single bearing 3600 RPM units on ebay.  I don't know anything about him or what he's selling, but the pictures look good, and it's a known brand:

http://www.ebay.com/itm/230557910201?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Why not just setup a serpentine belt around one of those big flywheels, and drive a proper sized pulley on the alternator?  Similar to what the lister guys do, but I assume you have bigger flywheels and would need a pretty good size pulley on the alternator (requires a two bearing unit).  What's the diameter of your flywheels?

[LowGear]

Hi,

Thanks for doing the research. 

I'm attracted to the PTO system because they have the framework already built and ready to go.  They also direct drive with a very flexible coupling device.  The third reason is that I could leave the Witte standard 240 volt generator in place which is run by a couple of V belts off the 25" flywheel.  That's the next question as well.  If a generator is just riding the engine but not providing any power to anything does it put much of a load on the engine once it's up to speed?

Casey