Hi everybody. I found this website while hunting some info. I know very little about hydraulics. I am building a 10000 watt generator and was wondering about driving it with a tractors hydraulics system. The generator head that I purchased needs a 20hp engine and needs to spin at 3600 rpm. What hydraulic motor would this need. Any tips would be great. We have some new john deere tractors with some amazing hydraulic capabilities.

Thanks

Turning the generator is easy but maintaining the exact speed will be more difficult than you think. This is essential for maintaining the output electrical frequency, usually 50hz or 60hz. Electrical appliances designed to run at 60hz for instance usually need 60hz ± .5hz. To accomplish this with the hydraulic system will require some type of closed loop control system for the pump stroke driven by a speed sensor in the hydraulic motor. It would be my guess that the existing pump in the tractor's hydraulic system does not have such a feature.

I can offer a few details of one system I developed as an add-on to an existing machine design.

• Power came from a diesel engine with a gear pump that had already been specified for other functions on the machine.
  
• Generator was driven by a gear-type motor.
  
• The motor was sized (a) small enough for speed well in excess of 1500rpm (for 50Hz, 4 pole generator) with the engine idling and (b) large enough for about 75% of system pressure at full electrical output.
  
• The motor speed was set using a priority flow regulator. This is the preferable type of regulator because it diverts excess flow to tank at load pressure plus a small differential.
  
• Engine speed was interlocked to be only in idle when the generator was operating. High revs would cause overheating and noise.
  
• Flow to the motor was controlled by a solenoid diverter valve on the gear pump output.
  

This is an open-loop system as opposed to the feedback system that Clay proposed. I would rate it as a low-budget approach - it was adequate for this application, which was mainly to power floodlights.

The shortcoming in open-loop performance in this case is basically the poor speed regulation of the generator. The generator was an induction machine and both its voltage and frequency are determined by shaft speed. Shaft speed regulation is therefore critical and in the system described would vary due to:

• Pull-down of the engine (if pump flow cuts below flow regulator setting)
  
• Volumetric efficiency of the pump (as above)
  
• Droop in the flow regulator as load pressure varies
  
• Volumetric efficiency of the hydraulic motor as generator torque varies
  

All of these variables can be obtained at the design stage from spec sheets. Some droop is inevitable and will require the voltage/frequency to be set at a nominal electrical load.

Another key point is the electrical efficiency of the generator. I used an over-rated generator because it had an attractive low price but it still required generous louvres for airflow due to internal losses.

For a high-performance system, provided the electrical load is "kind" i.e. small appliances not welding kit, solid-state inverters are available. One example is made by Electrolux and called "Travel Power" (I think). These systems regulate final voltage and frequency by synthesising the waveform from DC derived from the raw generator output. This would enable an ultra-simple system on the hydraulic side so might be ideal for a retrofit, but at a high price.

Please be aware of safety requirements for mains voltage.

Hope this helps.

Take a look at this thread on another forum:

http://www.ifps.org/phpBB2/viewtopic.php?t=81

Also go to Google search and type in "Hydraulic Motor Driven Generator" and see a long list of hits.

quote:

This is an open-loop system as opposed to the feedback system that Clay proposed. I would rate it as a low-budget approach - it was adequate for this application, which was mainly to power floodlights.

And this would be OK with most resistive loads like lighting and heating. Inductive loads, particularly motors, are sensitive to frequency. Geodisc's suggestion to use a rectifier and an inverter will help with these.

Hey Duster, first of all, you need to see what kind of hydraulic pump your John Deere has, as far as GPM (gallons per minute)output. I'm assuming it has some quick connect attachments on it, correct? So hooking up an external device should not be a problem.

quote:

hydraulic generator

Ford made a big mistake this time and screwed all of us prospective customers as well as themselves this time. The new Ford F550 4X4 has the transmission PTO yoke facing forward instead of to the rear. They also didn't leave adaquate room for larger hydralic pumps or other connections. It will permit a wrecker or dump truck hydraulic pump but not a hydraulic pump big enough to drive a hydralic generator or a water pump. I even heard that a company was playing around with a system to drive a water pump with a hydraulic system like a generator just to have somthing to offer on these Ford chassis. This was a mojorly overlooked mistake on Fords part and I heard a rumor that they are now looking at future changes due to complaints from most of the fire appataratus manufactors.

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