# PTO RPM Question for JD 990



## IdahoShepard (Mar 15, 2008)

Howdy all. New to the forum and have a question. Maybe this just shows my ignorance, but here goes. 

I have a JD 990 with rear 540 rpm PTO. I know that I get the max horsepower out of the PTO at 2600 rpm on the tractor. My question is what is the ratio of tractor engine speed to PTO? I don't need max horsepower to drive a PTO driven power generator but I do need the rpms to be 540 to get the proper voltage level. I need power for extended periods of time (4 to 5 hours at a time) but I do not want to run the tractor engine at this speed for that long. Is it possible to get 540 rpm pto shaft speed at say 1800 rpm tractor engine speed?

Also, as a corollary question, does anyone have experience with PTO driver generators for AC power?


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## Simpleprestige (Apr 20, 2007)

No, you will not get 540 RPM out of the pto at 1800 rpm engine speed simply because it is a direct ratio to the engine speed, and I'll have to check the tach on mine, but it will not hit 540 until probably 2600.


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## jd2355 (Mar 9, 2008)

Hi there. I was just looking through my jd tech manual for the 2355 tractors to see what the engine rpm it would take to run the pto at 540 rpm (your tractor is smaller and could be different)but it gives two different specs depending on what transmission is in the tractor. syncronized trans: engine rpm is 2070 for 540 pto rpm. and for collar shift trans: engine rpm is 2075 for 540 pto.not a huge difference. Anyhow on the 2355 there is a pto symbol right on the tachometer guage it self that tells you. I don't know if your tractor has the same thing or not, but it could be real handy for you if it did. maybe someone out there has a tech manual for your tractor and can tell you for sure.


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## Simpleprestige (Apr 20, 2007)

On my 3520, the tach has a little PTO symbol next to the 2650 rpms marker. The 990 is similar to the 3520 size wise, but it packs about three more horsepower.


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## Live Oak (Dec 22, 2003)

Welcome to Tractor Forum Idahoshepard! 

I am thinking you are wanting to find the most ecomonical point to run a pto generator for extended periods. With any engine a given amount of fuel is consumed to maintain a specified rpm. As the load is increased on the generator to provide more current, so the load is increased on the tractors engine. 

A diesel being much more efficient than a gas engine does not expend nearly as much fuel to maintain no load rpm. As the load increases on a diesel engine the governor portion of the injector pump will increase fuel delivery for each fuel injection event upto a predetermined max. With a turbo charged diesel this fuel governing has an even wider range of load due to the turbo providing more air to efficiently burn more fuel. 

In the case of your 990, you have no secondary pto range in which to operate like the larger farm tractors do with the 1000 rpm pto so unless you put a secondary gearbox on the 990's pto or arrange a set of pulleys and belts to provide 540 rpm at a much lower tractor speed, you will have to run the 990 at the specified pto rpm which is approx. 2,600 rpm. Some generators are geared to run at the correct speed with lower pto rpm. 

As rule of thumb, it requires approx. 2 hp for each kilowatt to run a pto driven generator. If you drop below this ratio with too large of a generator, when the load becomes heavy enough, it will bog the engine down and rpms will fall off wreaking havoc with frequency sensitive equipment. If the load is too great for the engine, it can be damaged by lugging it. 

What size generator are you wanting to run? With the 35 pto hp your 990 has, it can run a 17.5 KW generator at full load. You can run a larger generator but at some point the load will pull the rpms down and over load the tractor engine.


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## alhorne2 (Feb 17, 2013)

I have a 3600 Ford diesal tractor and i want to operate a New Holland Disc mower at 540 pto rpm. At what speed is the tractor motor turning to obtain this PTO speed


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## Hoodoo Valley (Nov 14, 2006)

alhorne2 said:


> I have a 3600 Ford diesal tractor and i want to operate a New Holland Disc mower at 540 pto rpm. At what speed is the tractor motor turning to obtain this PTO speed


First, welcome to the forum! If it's anything like my Kubota or Deere, it's going to be full throttle.


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## Mickey (Aug 14, 2010)

IdahoShepard said:


> Howdy all. New to the forum and have a question. Maybe this just shows my ignorance, but here goes.
> 
> I have a JD 990 with rear 540 rpm PTO. I know that I get the max horsepower out of the PTO at 2600 rpm on the tractor. My question is what is the ratio of tractor engine speed to PTO? I don't need max horsepower to drive a PTO driven power generator but I do need the rpms to be 540 to get the proper voltage level. I need power for extended periods of time (4 to 5 hours at a time) but I do not want to run the tractor engine at this speed for that long. Is it possible to get 540 rpm pto shaft speed at say 1800 rpm tractor engine speed?
> 
> Also, as a corollary question, does anyone have experience with PTO driver generators for AC power?


First off, welcome to the forum. 

A little food for thought. *DO NOT* use engine rpm to set generator voltage. Engine rpm is used to set the A.C. frequence, i.e. 60 Hz. Voltage will take care of itself. Some A.C. motors are not happy being run off frequency.


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