PTO generator selection help

[tradosaurus]

I am looking at buying a PTO generator but all the information on youtube and post is confusing.
I need someone to explain the sizing, the operation, and hookup without using too many acronymns and as if they are teaching a 6th grade class.

I have a Kubota L3301 tractor with 28 PTO hp.
I'm thinking about using a 50 amp power outlet box and wiring that to a 50 amp breaker to my main feed panel so that if power ever goes out I flip the main power off, plug in the generator and then feed the house. RVGUARD 5 Amp 125/25 Volt RV/EV Power Outlet Box, Enclosed Lockable Weatherproof Outdoor Electrical NEMA 14-5R Receptacle Panel, ETL Listed - - Amazon.com

I've seen generators with AVR and without and don't understand the advantages.
It looks like a 15-16 kW PTO generator would work.

Once you hook the generator to your house and tractor do you just max out your tractor RPM, flip the generator to on, and start using powering anything you need in the house unless the breaker trips?

 

[LouNY]

Well you should shortly be hearing as to how your plan is unsafe and will kill someone.

How ever as far as your pto generator you can usually figure on needed close to 2 hp per kw of generated power.
That does not mean that you have to buy a generator of only 14KW for your 28HP tractor,
what is does mean is that no matter what size generator you buy your tractor will be limited to generating around 14KW,
you could be hooked up to a 30KW generator but you will be HP limited to around 14KW of production.
Generators sold for 540 rpm pto use will need your tractor to be turning whatever rpm it needs to provide 540 rpm on the pto,
The speed the generator is turning will determine the Hz of the power you produce with 60Hz being our standard.
The AVR is a means of maintaining a more stable voltage with load changes. The ultimate device that maintains your voltage and frequency
will be your tractors governor. And how stable it can maintain rpm with varying loads.

The normal acceptably method of powering your house with a pto generator generally would be as follows;
1) switch your transfer panel from utility to generator
2) connect your tractor to your generator
3) check that the generators main breaker is off
4) engage your pto and start rotating your generator
5) monitor the Hz reading and voltage reading from your generator, looking for 60Hz and close to 240Volts
6) while it stabilizes shut down all circuits in your main panel you don't want to energize, keeping in mind the max power you can generate
7) close your generator main breaker
8) you have now loaded your generator
9) you now need to verify your Hz and voltage adjusting your tractor throttle as necessary.
10) as your load changes you may see some variation in Hz or volts and it may require throttle changes depending on your tractor and the load.
11) if you overload your tractor you will see that the Hz and volts will be going lower and your tractor does not have the power to bring the rpm back up

There is no problem with buying a generator larger then your current tractor can handle,
you may end up with a larger tractor sometime so depending on your house and desired loads a 20 or 25Kw may work better for you.
I look for a 4 pole generator with copper windings and I went brushless,
there are advantages to brushes and advantages to brushless but unless you are willing and able to clean and replace brushes go brushless,
also check out if the manufacture specs a THD (Total Harmonic Distortion) it should be less then 5% and ideally under 3%

Then the decision to permanently mount it, trailer mount it or use the 3 point mounts,I prefer the trailer mounted units.

 

[workinonit]

Nice write up Lou. I have a 25 kW that I have had for years and I love it. I built a trailer and mounted mine on it. It's large enough that I can sit my welder on it if I have remote work I need to do. I tricked out the trailer with lights because you never ever lose power during the day. My tractors have always had economy PTO so they can sit and run around 1700 RPM for days if needed. Other than that, exactly what Lou said.

 

[RoyKing]

Don't buy a 3phase

 

[Sawyer Rob]

Good job Lou, you nailed it!

SR

 

[Popgadget]

Lou covered it very well. He might be able to get a mechanical interlock for his panel to only allow the main or the 50amp breaker from the inlet to be on. This would be the easiest and least expensive transfer device.
It depends on the brand panel and the ability to place the 50 amp breaker in the correct spot adjacent to the main.

 

[Larry Caldwell]

I bought a cheap transfer switch that only holds 8 full height or 16 half height breakers. It's rated for 60 amps@240v, or 14.4 kw. When I flip the switch it runs the well pump, the water heater, lights, refrigerator, freezer, microwave, satellite dish, computer, FIOS modem/router, ceiling fan next to the wood stove, and TV. The rest of the house is off, so load managing is pretty transparent.

Buying an oversize generator should depend on your habits. Any electrical equipment is only good for 80% of its rated load continuous, so a 14 kw generator should only be loaded to 11 kw for more than 15 minutes or so. The max rating on a generator is just surge, and should be ignored. A diesel engine will put out its rated hp forever. If you really want to suck 14 kw out of a genset, you should buy one rated for 18kw. Very few homes use that amount of power.

Starting current on well pumps and AC units can really stress smaller generators. A larger generator will give better starting surge, and the tractor engine will often have enough inertia to get the pump up to speed.

Speaking of pumps, there is this thing called power factor. A resistive load has a power factor of 1. 4400 watts of water heater load can be supplied by 4400 Volts times amps at the generator, or 44 KVA. The kw rating of a generator is KVA. The current and amperage of an electric motor are out of phase, which is measured by power factor (PF). The typical electric pump motor has a power factor of around 0.72 under full load, so a 4400 watt motor load will use 6.1 KW (KVA) of generator power. That's why it takes a bigger generator to run a pump than you might think. Any inductive load, like a power supply transformer, electric motor, etc. will need to have a PF correction for load calculations. Generally it's only a serious consideration when starting an electric motor, when the PF can drop as low as 0.2. A motor that runs fine on 6 amps may take 25 or 30 amps to start, way more than the rated surge of your genset. If you don't have enough surge power to start your well pump, you will let the smoke out.

If your tractor engine won't handle the surge, consider installing a flywheel off of a PTO powered baler on the PTO shaft to store some energy. If the generator slows enough to really drop the voltage, you have a serious problem. You also might speed up the tractor RPMs to start tough loads. A little over voltage won't hurt an electric motor, it's the under voltage that smokes it.

 

[ponytug]

FWIW: If you have the HP, and a two speed PTO, you can engage the 1000rpm setting, but then throttle down the tractor engine to get 540 at the PTO to save wear and tear on your tractor.

I would point out that if you plan to put lots of hours on your generator, your tractor hours tend to be expensive (cost of tractor, price of spares, etc.), and you may be better served by a generator, especially if you can find a low hour standby set that someone is upgrading.

Having used one for close to two weeks once, I would suggest figuring out how to have the tractor and genset a long way away from you, as tractors aren't very quiet...

YMMV....

All the best,

Peter

 

[LouNY]

It will take a tractor with excess power and a very good governor to run a 540 unit on the 1000 rpm shaft,
your engine rpms will be below your torque peak and many tractors will not be very stable at those rpm.
That said if equipped with the 540 economy mode which drops the rpm down to close to the torque peak
they will do very good. Mine turns around1750rpm in the economy mode for 540 out runningnice and quiet and steady.

 

[Sawyer Rob]

When I run my home off my PTO generator, if there's any noise in the house at all, I can't hear the tractor running it, and I park my tractor right by the house.

It's a great way to get a lot of generator for less money and a diesel powered generator at that, and I'm sure my tractor will last a LOT longer than it will ever be needed, to run my generator.

SR