Posted 11/16/2023 15:22 (#10484557 - in reply to #10484475) Subject: RE: PTO generator sizing
Madison Co. Virginia
The more challenging part will be starting motors. The 76 pump likely has a 7.5-hp pump. The bulk tank compressors could be up to 5-hp.
I use a 25kw generator, and it really struggles to get 10-horse motors started. 5-horse motors are a nonissue. I would say that 25kw is the minimum that you want to consider, but 35-50 would be a lot better. The old rule of thumb is that you need two tractor HP for each generator KW, but that's not a hard and fast rule.
Another reason to go with a larger generator than you need, is because some electronics can be sensitive to the brown-out conditions when starting a motor on too small of a generator. I've learned that I have to kill my Delatron pulsation controller while starting the vacuum pump, and then restart it immediately after. Otherwise it trips out from the low voltage it experiences for that second or two. Many dairies have a lot more electronic stuff than I do, so the need for stable voltage is even more critical.
Is the house and dairy on the same electrical service? Can you install a single manual transfer switch that will power both on the generator?
Edit: depending on how handy you are with diesel engines, also consider the ubiquitous 60kw military units that were powered by 4-71 Detroit engines. Those show up at auctions from time to time, have been through several owners since the military discarded them, and they still have plenty of life left. That could be a cheaper option than a pto generator.
Make sure though, that any ex-military unit is 60-hertz. There were some really funky high-hertz generators used for specialty tasks, and those are completely incompatible with any task you want them for.