Uncle Bobs Tips: Generator Guide

PTO Generators

PTO generators use the vehicle engine for power and are driven directly off the transmission power takeoff with a driveshaft.

As modern vehicle power requirements continue to increase, the engine alternator often gets taxed to its limit. In some cases, it's taxed beyond its limit, and then an internal "electrical load manager" must selectively shut down circuits to prevent the batteries from being drained. One solution to this problem has been to shift some of the electrical load off of the vehicle's 12-volt system and onto a separate 120/240-volt system powered by a vehicle-mounted or PTO generator. The 120/240-volt power PTO generator also allows the use of more powerful lights and motors for improved effectiveness.

Here are some of the features, advantages, and disadvantages of PTO generators:
PTO generators use the vehicle engine for power and are driven directly off the transmission power takeoff with a driveshaft. PTO generators generate 120/240-volt, 60-cycle, single-phase AC and are available in models ranging in energy delivered from 7kw to 150kw.

Because they use the vehicle engine for power, PTO generators are relatively small and lightweight. For example, a 40kw PTO generator weighs only 500 pounds, compared to about 2,000 pounds for a diesel-powered, water-cooled mobile unit of the same electric rating. The PTO generator is usually mounted close to the transmission under the vehicle frame. The biggest advantage of PTO generators is that they don't need a separate engine, thus they take up less space, are lighter and less expensive, and require almost no maintenance. PTO generators are also quieter than other generators. On the basis of cost per kilowatt, PTO generators represent an excellent buy for higher power ratings.

The main disadvantage is that the power output is dependent on the vehicle engine speed. Thus, PTO generators are generally not suited for pumpers, where the engine speed varies depending on the required water flow rate. The mounting location of the PTO generator is also somewhat limited by the length and angle restrictions of the driveshaft.

PTO generators have many uses. Applications for PTO generators include aerials, rural and agricultural uses such as tractors, heavy-duty trailer homes, and some ambulances. Adding a PTO generator to your vehicle can thus improve its performance and give you added versatility at an incident scene. The additional electrical capacity can also help you and your employees work more efficiently and safely by providing better illumination and more powerful tools. PTO generators are also used as backup power during power outages and are attached to your vehicle using a manual transfer switch. Always ensure that your PTO generator is sized properly to prevent tip over.

Start-Up Procedure for PTO generators:

  • Check all fluid levels
  • Connect tractor to generator
  • Connect power cable
  • Start tractor and adjust PTO speed to proper RPM (either 540 or 1000)
  • Place transfer switch in emergency position
  • Add loads
  • Adjust tractor speed to maintain 60 Hertz
  • Monitor voltage and frequency
  • After utility power is restored, return transfer switch to normal
  • Allow 5 minutes for generator cool down
  • Disengage PTO lever
  • Remove connector power cable
  • Exercising the PTO-Driven Generator

  • Exercise the PTO generator every 90 days
  • Check all fluid levels
  • Following start-up procedure, start and run engine for 5 minutes with no load
  • Operate the generator under at least 50% load for 30 minutes
  • Check for any abnormalities and remedy as necessary
  • Remove load and run at rated speed and no load for a 5 minute cool down period

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