Kub0ta for DC generator

Discussion in 'Diesel Engines' started by Timothy, May 30, 2010.

  1. Timothy
    Joined: Oct 2004
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    Timothy Senior Member

    I just bought a brand new Kubota deisel on ebay for $650.00. I already have an extra Balmar 210 amp alternator that according to specs operates at full capacity at 6000 rpm. The engine develops 13 hp at 3600 rpm. The power curve on both taper off slowly at higher rpm. The alternator should draw less than 8 hp. Should I run the engine at lower rpm and use a double pulley on the fly wheel with the ratio to the alternator pulley adjusted accordingly, or run the engine at full rpm with smaller pulleys. I am concerned with both fuel economy and noise, as well as loading the engine appropriately. Thanks in advance for any incite.
  2. capt littlelegs
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    capt littlelegs New Member

    I assume this is a 24 volt alternator. You should gear it to give the maximum rated output at the correct engine output/revs for the total load. The advantage with DC generators is you can reduce the speed as the load/charge drops off to keep the engine running at optimum output for fuel and noise and avoid light high speed running but you may have to do this manually. A 2:1 ratio would probably be ok.
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    FAST FRED Senior Member

    Some folks have find the throttle units used on welding machines to be excellent at controlling this style gen set.

    The unit will lower the RPM to as low as it can get , yet still produce the required voltage.

    This is greaT if YOU ATTEMPT TO 100% CHARGE A BATT SET , AS THAT LAST 10% OR 15% , goes in really slowly .

  4. marshmat
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    marshmat Senior Member

    I'd lean towards setting it up so that maximum alternator output comes with the engine fully loaded. If yours is a 24 V alternator, its peak output of 5 kW will probably come with around 8-9 hp on the input shaft, so about 3/4 of full power for the engine. Without knowing what engine you have and without being able to see its performance curves, a very rough guess would be around 3000 rpm for 3/4 power. Since you're home-brewing anyway, a diesel welder governor such as Fred describes would probably make sense, backing off the engine throttle when full output is not needed (ie. when the alternator's regulator eases off as the batteries approach full charge.)

  5. CDK
    Joined: Aug 2007
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    CDK retired engineer

    You probably bought a Balmar series 94 alternator, 210 Amps, 12V. That one will draw approx 6 hp at full output (including belt losses and fan), so you need an industrial belt, multi-V or even better a timing belt.

    The Kubota can supply the horses at less than 3000 rpm, so choose a ratio of 1:2.2, 2700 rpm for the diesel, 6000 for the alternator.
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