BX 25 specific PTO genny question

[ashdump]

I am looking at buying a 12kW genny head and stepping up the pto speed via twin v belt pulleys to 1800 RPM. According to my math, I'll need just about 16.1 HP @ the PTO. The PTO (according to Kubota) is rated @ 17.7 HP

I believe these numbers Kubota provides are respective to at or near WOT. Is it feasable or sensible to operate a PTO genny at less than WOT (perhaps 75% or a little more?) What I'm thinking is that fuel efficiency will be much greater at just less than WOT. The proper speed for the genny could be determined through pully ratios.

The genny will produce 50 amps @ 240 VAC at full load. I will probably never need the full potential, but would like to have it just in case. Does anyone have any experience or advice?

 

[PHILIP8N]

Your math is right, but your thought process is wrong. 12kw does equal 16.1hp, but your system is not 100% effiecient. Anytime there is heat, there is power lost. You will even have a small horsepower loss thru your belt reduciton. It takes approximately 1.75hp to get 1kw from a gen head this size, and this is only approximate. You need to get the specs from your gen head and see what it's effeciency is, and what hp is takes to get various kw. From your 17.7 hp you should be able to get around 10kw, which is about 40amps on a 240 volt circuit. I would run that engine full rated speed, that is what they are designed for. Will you get better fuel consumption at a lower rpm, yes, but it will not near as dramatic as you make it sound. The brake specific fuel consumption for a natually aspirated diesel engine is fairly flat. These figures are published on the Kubota engine (industrial) website. Personally, I would scrap the double belt drive speed increasing system, I think you will have lots of design and reliability problems with that. Go for a pto driveline system, they are simple and proven. Philip.

 

[ashdump]

Thanks. I do know there will be some sort of parasitic loss throught the final drive. I would like to go with the 12kW head though in case I upgrade tractors someday. My plan now is to just figure up how many amps the necessary circuits will draw and put an appropriate size breaker at the head of the backfeed. I have found a gearbox that steps up 540 to 1800 RPM on ebay. Maybe that's the route I need to go. I've also got plenty of scrap stock around to make a platform.

 

[keyman1808]

Please post your results and pics. I would like to get that kind of output for my BX24 as an emergency backup genny.

 

[ashdump]

Will do. May be a few months. I'm just trying to get my thoughts together now so when I do have the cash set back, I'll know just what to order.

 

[tommu56]

one thing to remember is the rated hp of the tractor is with the pto at 540 (engine at full speed or almost there) if you go below this it will be less.