12-20kW PTO-driven 3 point generator for tractor

[Frank S]

Let's start off with your tractor is the 30 HP the stated engine HP the draw-bar HP or the tested PTO HP? For now we will go with the possibility of PTO HP @540 RPM which is pretty much standard What you would first need to do would be to locate a ST style generator head THis is a stand alone generator that has a keyed output shaft and and a bearing plate on the output end it will also have a built on connection box with built in AVR (Automatic voltage regulator). Then you will need agear box to step up the 540 PTO RPM to the required generator RPM usually around 1800 for a 4 pole generator 3600 RPM for a 2 pole generator to give you your 60HZ.
Next is your tractor is not diesel figure on a maximum of 35% of the PTO HP for the generator size at sustained loads this is to maintain voltage and HZ stability under changing loads if diesel then this can be more along the lines of 65%. This does not mean that you could not use a 25 to 40 KW generator head on your tractor you would only be able to use the amount of power that could be produced at the PTO. the over-sized unit would require more power to turn the rotating mass and larger gear box, the up side would be a more stable output for starting loads up to the max KW you r PTO was capable of.
So sticking with a 12 to 15 possibly a 20KW generator head would be a better choice.
Next another way to do this would be to locate an engine driven generator with a bad engine remove the engine and machine an end plate and bearing for the generator bolt that to the gear box make a 3 point frame and you would be good to go
l since there are several factory made PTO driven generators on the market already set up the one thing you mentioned that may be your deciding factor and that was the comment for not much money, you might be better off finding one on one of the for sale lists or watch the auctions.