PTO Generator Questions

[chamjoe]

Okay gents. I want a generator for hurricane season. For farm use and homestead from irrigation pump to home HVAC. I can do everything with 35kw and probably 25kw. Here is my Q. I have three tractors. Tractor HP is 28, 36, and 100 all of them have at least 540 and 1000. Can I get a 25kw and if I need to run a few things use my smaller tractor and if I want to run my air conditioners just hook it up to the 100hp tractor? Trying to find real world info. Thanks

 

[Popgadget]

Short answer is yes. You typically need 2hp per KW output, so your 28hp tractor would be good for about 14 kw before it’s starts to bog down. If you get a 540 rpm generator, you could use the 1000 rpm on the bigger tractor and run it at less than half speed to get 540 at the PTO shaft.

 

[Sawyer Rob]

Okay gents. I want a generator for hurricane season. For farm use and homestead from irrigation pump to home HVAC. I can do everything with 35kw and probably 25kw. Here is my Q. I have three tractors. Tractor HP is 28, 36, and 100 all of them have at least 540 and 1000. Can I get a 25kw and if I need to run a few things use my smaller tractor and if I want to run my air conditioners just hook it up to the 100hp tractor? Trying to find real world info. Thanks

I do it all the time... It works perfectly.

SR

 

[chamjoe]

I do it all the time... It works perfectly.

SR

Thanks for the response. What HP and KW you running? Does it really strain your lower HP tractors?

Short answer is yes. You typically need 2hp per KW output, so your 28hp tractor would be good for about 14 kw before it’s starts to bog down. If you get a 540 rpm generator, you could use the 1000 rpm on the bigger tractor and run it at less than half speed to get 540 at the PTO shaft.

I guess this is where I get confused. Set aside the 540vs1000 thing. The load is somewhat linear and based on pto RPM, right? So how do I produce 14kw on a 28hp and more on larger tractor? I guess what I’m worried about is that I can’t push a 25kw generator with the 28hp tractor at any RPM.

 

[ruffdog]

You can "push" a 25k gen with 28hp but you can't power 25k with 28hp. It takes about 2hp to power each kw.

 

[sea2summit]

Thanks for the response. What HP and KW you running? Does it really strain your lower HP tractors?

I guess this is where I get confused. Set aside the 540vs1000 thing. The load is somewhat linear and based on pto RPM, right? So how do I produce 14kw on a 28hp and more on larger tractor? I guess what I’m worried about is that I can’t push a 25kw generator with the 28hp tractor at any RPM.

The load is linear so you need ~2 HP for/KW, however to get the right frequency you need the tractor operating at ~540 PTO RPM which has most engines producing their max HP even if the load is 1KW on a 14KW generator so when the load surges to 14KW in theory the tractor wont notice (but it can/does). Ideally you'd want a fairly consistent load or a cruise control on the tractor to keep cleaner power going. The generator wont produce more power than it's rated for (for simplicity sake we'll assume that's true), so hooking up a 60PTO HP tractor to a 14KW gen set should only produce 14KW but hooking a 12 PTO HP tractor to the same gen set will only support a ~6KW load before it stalls out the engine.

Hope that makes sense.

 

[Doughknob]

OP, a generator turns easy when you have nothing that wants electricity from it. Once appliances start start drawing juice from it, that is when it gets harder and harder for the tractor to turn it.

 

[RickB]

I ended up with my dad's 25kw Winpower generator from the farm. I ran our whole house with it on a 42 PTO hp David Brown 885 with a 2 speed PTO which turned the output shaft at 540 at about 1200 erpm. I never measured the load but it ran everything on a half gallon of diesel per hour except the tractor would not make enough hp at that engine speed to run the central AC. It did that easily with the PTO set at the regular 540 at rated speed.

 

[CADplans]

As far as powering the heat pump,,
there are several factors that are involved in determining the power needed ,,
1) cooling capacity of the pump,, a 2 ton unit takes far less starting current than a 3 ton.
2) compressor type. My daughter has a heat pump with some sort of screw compressor,, I never see the lights dim when that thing starts,, it is like a variable speed start, showing no extra load due to starting. Heck, I have a little window unit in a small, remote office,, 6,000 BTUs, IIRC,, that thing will dim the lights when its piston pump tries to instantly come to full speed,,
3) the setting of the thermostat,, some new thermostats can be set for a longer delay prior to restart,, insuring the system pressure is low prior to restart.
4) I am sure there is other factors.

 

[chamjoe]

Thanks for the reply guys. I guess I wrongly assumed that the power produced was set and didn’t vary based upon demand draw. They’re *smarter* than I thought. I guess simply, it’s like any other implement like a bush hog where I can spin an 8’ mower with 28hp but sure can’t mow very fast without it bogging down.

okay. Now to go shopping! Any recommendations? Guess I’ll shoot for 25kw. I do have a 3-ph elec pump but everything else is single so will start the hunt for that.

to the commenter on running central HVAC, they make these soft start modules (I assume it works like a capacitor booster) to hook up. I don’t have one yet but know folks that do and swear by them.