Power Generation System

1.  Power Generation

2.  Engine Load System

3.  Alternator

4.  Battery and Inverter

5.  Electrical Load

      The power generation system was designed with the flexibility to eventually include a variable RPM component; the reason for the variable RPM is that the fuel economy could possibly increase as the engine RPM is tuned to the specific load.

      Alternating Current (AC) generators are tuned to run at specified RPM so that the power generated stays at 60Hz.   As a result, AC power generation is most efficient when the engine runs at full capacity all the time.  If only 1/3 of the engines power is needed, the engine wastes fuel maintaining a higher RPM. 

      Direct Current (DC) generators, or alternators, allow flexibility with RPM because they are designed to maintain a specific voltage with current generated changes over the RPM range.  If 1/3 the engine power is desired the engine can lower the RPM matching the current output to the load. Still, direct current carries many concerns including safety and transmission efficiency issues.  High currents can be dangerous and DC wires need to be very large in diameter to account for line loss which is expensive and cumbersome.

      The plan is to use modified sine wave inverters to create AC power from a DC generator.  These invertors have become much less expensive in the last 5 years.  Using the alternator/inverter method, the engine can be throttled to match the load while still maintaining the benefits of AC power.   For these reasons, we have used a DC alternator as our engine load.  

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      The Lister engine is throttled only with fuel; the air intake port remains constant.  Therefore, the engine cannot operate without a significant load nor can it idle like a car engine.   Additionally, for research purposes- to be able to perform efficiency and engine power experiments- the load must variable
      Without the use of an expensive dynamometer, we were forced to be more creative with analyzable loading methods.  When considering possible loads, we returned to the ultimate goal of the Lister Engine project: to create a sustainable power source for rural areas.  This particular power would be used either for electricity or for raw mechanical power such as pumping water or grinding grain.  For experimental reasons, an electrical load is the easiest type of power to measure and analyze. 

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      The alternator chosen is a 200 Ampere 13.8 Volt “Mean Green” aftermarket Ford Bronco DC alternator.  It is internally regulated and has an ideal RPM range of 6,000 to 9,000.  Two of these alternators were fitted with 2.0” diameter pulleys made of brass and machined to accept a 92” outer circle J-section 6 rib V-belt # 920J6.  The two belts slide over the outer face of the 23” diameter engine fly-wheel.   The pulley ratio of 23.5” to 2.0” at 600-650 engine RPM gives an alternator an RPM of 7,000-7,600.  The V-belt tension is critical because of the high ratio between the pulleys and the torque of the high output alternator. 
      A welded steel alternator stand was made with two levels of adjustment.  For the bulk alternator adjustment the stand slides between the two beams of the engine frame on steel angle iron.  This provides a sturdy base and torsional support; the stand can then be anchored in place with 3/8” set screws.  The alternator is also mounted so that it can pivot on the bottom bolt.  The top bolt then follows a groove in curved alternator bracket.  The arc of the alternator accounts for the last ~1” of tension and then can be bolted in place. 

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      Unlike AC generators, DC alternators need some current to operate.  The current traveling through the coils in the alternator, which creates the magnetic field, is controlled by the voltage regulator.   When the alternator output voltage is too high, the current in the coils is reduced thus reducing the magnetic field and finally reducing the output voltage. The same trend occurs if the alternator output voltage is too low.  A battery provides a current source.   This battery provides the small amount of current source for the alternator during start up and voltage regulation, but it is continuously being recharged in a “symbiotic” type relationship.
      The battery is a group 27, 105 Ampere-Hour reserve, deep discharge 12 Volt lead acid battery.   The alternator and battery are connected in parallel with a Whisper 3000 Inverter.  The inverter is capable of producing 3,000 Watts of modified sin wave AC power continuously with peak of 6,000 Watts.  Because of the high direct current being supplied to the Inverter, all of the DC power lines to the alternator, battery and inverter, both positive and negative, are 2-gauge wire.

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      Light bulbs provide the actual electrical load for the engine because they provide variable load flexibility with incremental reproducible units.  The light bulbs are arranged in a load board, which is mounted on the wall near the engine.  The load board contains six pairs of 200 Watt light bulbs, and two pairs of 100W bulbs for a total of 2,800 Watts.   Each pair is wired to a switch allowing for six levels of load.   The activation switch for the coils of the alternator is also located on the load board.    Because the alternator uses a small amount of current to power its coils, the alternator can drain the battery over time; an in-line switch stops the flow of current

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