PTO Generator vs. Portable Generator

Head-to-Head Comparison

Prices and output are market-typical ranges that vary by brand, size, and region. Match any specific unit to its manufacturer spec sheet.

How a PTO Generator Works

A PTO generator connects to the tractor's rear PTO stub through a driveline, a shaft with universal joints, usually on the common 1-3/8 inch, 6-spline connection. Inside the generator, a gearbox steps the PTO speed up to the alternator's operating speed, and the alternator produces standard 120/240V single-phase power at 60 Hz.

• Most farm PTOs turn at 540 RPM; larger tractors and larger generators often use the faster 1000 RPM PTO. The generator is built to match one of these speeds, so order the right one.
• Frequency and voltage depend directly on holding PTO speed steady. Set the tractor to the RPM that produces rated PTO speed and watch the panel voltmeter; if engine RPM drifts, so does your 60 Hz.
• Mounting is typically a three-point-hitch deck or a wheeled trailer you can move barn to barn, well house to shop.
• Keep the driveline as straight as practical. Sharp U-joint angles cause bind and vibration.
• Units are drip-proof and ventilated, not weatherproof, so site them under a roof or cover and keep them out of standing water.

The appeal is durability and simplicity: there is no carburetor to gum up, no second battery to die, and no stale gasoline to drain. If your tractor starts, your generator runs. To understand the PTO itself in more depth, see our PTO attachments guide.

How to Size a PTO Generator

Sizing works backward from two numbers: the continuous kilowatts you need, and the PTO horsepower your tractor can deliver. A conservative rule of thumb is roughly 2 PTO horsepower for every 1 kW of continuous output. Smaller two-pole units are sometimes a little better than that, but the extra headroom helps the tractor hold RPM when a large motor starts and briefly pulls its surge load.

Figures above are representative of common single-phase, two-pole PTO generators (for example, the Baumalight TX line) and vary by brand. Note the surge column: motors draw two to three times their running watts for a fraction of a second at startup, so a unit's momentary rating, and your tractor's reserve power, matter as much as the continuous number.

To pin down the kilowatts side of the equation, use the sizing calculator on our best generators guide, which adds up your running and starting watts by appliance.

What a Portable Generator Brings

Portables are self-contained, affordable, and simple to store. They typically produce anywhere from about 2,000 watts (a small recreational inverter) up to 12,000 watts or more (a large open-frame unit). The two main types behave differently:

Many farm buyers land on a dual-fuel conventional unit in the 7,500 to 9,500 starting-watt class: it covers well-pump and freezer loads, runs on stored gasoline or clean-burning propane, and costs a fraction of a PTO or standby setup. Propane also sidesteps the stale-fuel, gummed-carburetor problem that kills so many generators left sitting between storms.

What It Costs

The math that makes PTO generators attractive is cost per kilowatt. A 25 to 40 kW PTO unit costs far less than an engine-driven standby of the same output because you are not buying a second engine, you already own it. The trade-off is that the tractor is a shared resource, and it is tied up for the duration of every outage.

Fuel & Runtime

• PTO generator: burns the tractor's diesel. A rough estimate is 0.05 to 0.08 gallons per hour per kW at moderate to heavy load, so a 20 kW load is roughly 1 to 1.6 gal/hr. A large tractor lightly loaded is less efficient per kW than a right-sized engine.
• Portable gasoline: commonly 0.5 to 1.0 gal/hr for mid-size units, giving about 8 to 12 hours on a tank at 25 to 50% load before refueling.
• Dual-fuel propane: a 20 lb (5 gal) cylinder lasts only a few hours at meaningful load, but propane stores for years without degrading, unlike gasoline.
• Diesel advantage: it is more energy-dense, stores better than gasoline, and most farms already keep bulk diesel on site, a real convenience during multi-day rural outages.

Whichever you choose, plan your on-site fuel to outlast a realistic outage. Our tractor diesel usage guide helps you estimate burn, and the farm fuel storage guide covers sizing tanks and keeping fuel fresh.

Connecting to Your House Safely

There are two code-compliant ways to feed your electrical panel:

• Manual transfer switch: a switch (or subpanel) that physically disconnects the house from the utility before connecting the generator, so there is no path back onto the grid.
• Interlock kit: a listed mechanical plate on your main panel that makes it impossible to have the main breaker and the generator back-feed breaker on at the same time. It is cheaper than a full transfer switch but must be listed for your specific panel.
• Power enters through a weatherproof inlet box and a proper generator cord, never an extension cord into an outlet.
• Transfer equipment ties into your service panel, so have a licensed electrician do the work and pull a permit. Grounding and neutral bonding rules (NEC Articles 445, 702, and 250) differ depending on the setup.

The good news is that the same transfer switch or interlock works for both a PTO and a portable generator, so if you install one now you keep your options open later.

Generator Safety (Read This First)

• Carbon monoxide is the number one killer. Run any generator outdoors only, at least 20 feet from windows, doors, and vents. Because a PTO setup also runs the tractor's diesel engine, keep that exhaust away from occupied and enclosed spaces too.
• Install battery-backup CO detectors on every level of the home.
• Keep the generator dry. Operate it on a dry surface under an open canopy; touching a wet generator or connected devices can cause electric shock.
• Never refuel a hot engine. Spilled fuel on hot parts can ignite, so shut down and let it cool first.
• Use heavy-duty, correctly rated extension cords in good condition, and use GFCI protection in wet conditions.
• Never back-feed through an outlet (see the hookup section above).

Which Should You Buy? Real Scenarios