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Building a PTO Generator - Questions
I'm looking to build a PTO electrical generator. I have a generator motor that requires 3500 RPM at least 16hp that I would like to hook up to a 540 RPM PTO ( about a 6.48:1 ratio). Obviously I need either gearing or pulleys to increase the PTO RPM to the speed needed for the generator. All of the commercial PTO generators I've seen use gears to do this.Northern Tool sells a 6:1 gear box, but I'm not sure if it could handle the 16 hp the generator would take. Also, is it possible to use pulleys and belts to do the same thing or is this not advisable? I would also prefer to have about a 7:1 ratio so I can run the RPMs lower on the tractor.Does anyone else know of a source for gear boxes for such applications?And other advise/commentary/warnings? TIA!
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Building a PTO Generator - Questions
I'd go with the belt approach, is cheaper and less complicated. That is and serves as a slip clutch when heavy surges are required. Sounds like a cool project. I may now be on the lookout for a worn out generator!
big ed
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Building a PTO Generator - Questions
You are going to have to step up the rpm's in several stages. I think you will find that it is not very practical to try to transfer 16hp with a belt between pulleys in a ratio of 7:1. The amount of surface on the small pulley engaged by the belt will not be enough to provide the power transmission that you are looking for. My two cents - looking forward to others' views.
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Building a PTO Generator - Questions
I remember seeing OEM catalogues for computer stuff. Clone manufacturers would pick and choose the basic components to put together their particular boxes. I assume OEM catalogues also exist for mechanical components, and that's what a PTO generator manufacturer would use. Exactly the gearbox needed probably could be found. Of course, finding a catalogue and an OEM manufacturer that would deal with individuals is another question. It may be easier to think of the gearbox as matched to the generator rather than the tractor. If the peak load of the generator used doesn't require 16hp, than a smaller gearbox would work. A shear pin suitable for the gearbox could be used in the PTO shaft. What ever sized generator is used, I think that it's important to use a generator whose peak load rating (or the main circuit breaker rating) is not capable of lugging the engine. If the engine lugs, then the AC frequency falls off and there's a risk of burning out electric motors. If you're considering running the engine at something other than the PTO RPM, the exact ratio of a gearbox probably isn't too important. An rpm that produces 60 cycle AC could be found, however a good rpm would be near the max torque/hp point (the two points are close on many diesels). Many high-end PTO generators have frequency meters to help set the AC frequency. A trick I heard is to compare a clock with a sweep second hand that is plugged into the generator with a battery operated digital clock for a minute or so.
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Building a PTO Generator - Questions
I didn't remember seeing the output of the generator that you are looking at, that is critical as it normally takes two horsepower for each kilowatt.
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Building a PTO Generator - Questions
The output of the generator is 9500 watts. Another option is a homemade chain drive reduction system I guess. Dual/triple pulleys would probably be needed for belt drive setup. I'd be inclined to think that the chain drive would be able to handle more HP: is that a fair assumption?
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Building a PTO Generator - Questions
I would believe you would want a belt drive for the noise that the chains as well as the maintence. You also should have a 20 pto horsepower tractor for it.
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Building a PTO Generator - Questions
The drives on 4" chippers I've seen are triple belts, so a belt drive could handle the HP. The risk of a belt drive is that it could start slipping, and slippage would lower the AC frequency. The engine on my Honda 6500, which is more realistically a 5,500 ‘watter’, is rated at 12HP, but I don't know how the hp is rated or how much gets to the generator. However, depending on the generator's duty cycle, 16 HP does sound a bit light for 9,500 W. Running a generator that is capable of lugging an engine really should be avoided. An alternative to a bigger tractor is a smaller main breaker on the generator.
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Building a PTO Generator - Questions
The belt drive system should work, you might have to look at two shafts to make the gearing change right. Belts have codes on them to tell of manufacturer plants, often dates and other codes. Make sure the codes match if doubling them up in matching runs. This will lower the risk of having the length be different.
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Building a PTO Generator - Questions
Here we go again Peters with some wild idea.
My suggestion is to salvage the components from a car with a new serpentine belt. This belts will handled the load as they are designed to power all the equipment on the car. eq. 10hp, air conditioner, 5hp for the alternator etc. They run quiet, they components required may be off one car. I would think the drive and the air conditioner or alternator may be near 7:1.
Some of the drives have more than one belt possibility, so you could double up if needed.
You could use the tensioner off the system also to help keep proper tension.
Where do I get the old generator?
Peters
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10-29-2001, 14:14 
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